Beolab 50


TheBeoLab50isaloudspeaker conceptfromBang&Olufsenthat givesthecustomeranunprecedented levelofcontrolofitsacoustic behaviourandperformance. Likethe flagshipBeoLab90,theBeoLab50can bealteredbytheusertobehaveasifit werecompletelydifferentloudspeakers fordifferentlisteningsituations. ImaginethatyouhaveapairofBeoLab 50loudspeakers,perfectlypositioned inyourlisteningroom,withasingle chairinthecorrectlocation,asis showninFigure1.1. Yousitinthischair tolistentoarecording–tohear sparklinghighfrequenciesandatight, punchybassthatextendstothelowest audiblefrequencybandsalongwith theaccurateandpreciseplacementof theinstrumentswithinthespacein frontofyou(betterknownas“stereo imaging”).
Speaker Distance Compensation
Perceived location of left loudspeaker
Figure 1.1: The sound stage presented byBeoLab50’sforactivelisteningwhen sitting in the sweet spot with properly placedloudspeakers.
Now,imaginethatyouhavethesame loudspeakersinthesamepositionsin thesameroom,butyou’vemovedto thesofaasinFigure1.3(orperhaps you’restillinthesamechairasbefore asinFigure1.2)andyouprefertohear musicinthebackgroundwhileyou readabook. Inthiscase,thebass precisionandtheimagingofthe recordingisnotimportant–youjust wantacloudofsoundthatdoesnot distractyouwhileyouread. Usingyour controlleryousimplyswitchthe behaviouroftheBeoLab50’stodeliver
thisexperienceinstead.
Speaker Distance Compensation
Perceived location of left loudspeaker
Figure 1.2: The sound stage presented by BeoLab 50’s for passive listening whensittinginthesweetspot.
Thesetwoscenariosillustratethe primarylisteningmodesthatthe BeoLab50candeliver. We’llcallthe firstoneactivelistening–sinceyour primaryactivityistolistentothe recording. We’llcallthesecondone passivelistening,since,inthiscase, listeningtomusicissecondaryto anotheractivity(inourexample, reading)inastationarylistening positionorarea. Inordertobeableto dothis,therearemanydifferent adjustableparametersinsidethe BeoLab50. Youcanchoosetoalter eachoftheseparametersindividually accordingtoyourpreferencesand listeningpositions–andthensavethe settingstoapresetforfutureuse.
1.1 Features
BeoLab50givesyouthepowerto makethesechangesusingalarge numberof“handles”–controllersthat letyouchangetheacoustical behaviouroftheloudspeaker. Among thesefeatures,therearetwothat standout:
• BeamWidthControl • ActiveRoomCompensation
Inadditiontothese,theBeoLab50has amanyotherparametersthatgiveyou awiderangeofcustomisation possibilitiessuchas:
• SpeakerDistance(for time-alignmentatthelistening position) • SpeakerLevel • BasicToneControls (Bass,Treble,FrequencyTilt, SoundEnhance) • SelectableSoundDesigns • 10-bandParametricEqualiser
Speaker Distance Compensation
Perceived location of left loudspeaker
Figure 1.3: The sound stage presented by BeoLab 50’s for passive listening whennotsittinginthesweetspot.
1.1.1 BeamWidthControl
Whenarecordingengineermakesa recordinginawell-designedstudio,he orsheissittingnotonlyina carefully-designedacousticalspace, butaveryspecialareawithinthat space. Inmanyrecordingstudios, thereisanareabehindthemixing consolewheretherearenoreflections fromthesidewallsarrivingjustafter thedirectsoundfromthe loudspeakers. Thisisaccomplished eitherbyputtingacoustically absorptivematerialsonthewallsto soakupthesoundsoitcannotreflect (asshowninFigure1.4),ortoangle thewallssothatthereflectionsare directedawayfromthelistening position(asshowninFigure1.5).
7
"Reflection-free Zone"
Figure1.4:Onewaytoreducetheproblemofsidewallreflectionsistoabsorb thematthewallssothatthereisnoreflection. Thisisasolutionoftenusedin recording studios, however, it also results in an unnatural-sounding “dead” room.
"Reflection-free Zone"
Figure1.5: Analternativemethodtoreducetheproblemofsidewallreflections is to re-direct them away from the listeningposition,producinga“reflectionfree zone”. This method is often used inrecordingstudiosthatareinitiallydesigned with the help of an experienced acousticalconsultant.
Thisisdifferentfromyourlivingroom whichhasnotbedesignedprimarilyas anacousticalspace. Ithassidewalls thatreflecttheenergyfromyour loudspeakersandsendthatsoundto youatthelisteningposition–a situationthatismorelikethatwhichis showninFigure1.6.
"Reflection-free Zone"
Figure 1.6: The direct sound (in red) from the loudspeakers is influenced by the reflections off the side walls (in grey).
Inordertogetthesameacoustical behaviourinyourlivingroomthatthe recordingengineerhad,wehaveto reducetheamountofenergythatis reflectedoffthesidewalls. Ifwedonot wanttochangetheroom,onewayto dothisistochangethebehaviourof theloudspeakerbyfocusingthebeam ofsoundsothatitstaysdirectedatthe listeningposition,butitsendsless energytothesides,towardsthewalls. ThisisoneoftheoptionsthatBeoLab 50givesyou–tomakethebeamof sounddirectedoutthefrontofthe loudspeakernarrowertoreducethe levelofsidewallreflections,sothatyou getamoreaccuraterepresentationof thesoundtherecordingengineer heardwhentherecordingwasmade. "Reflection-free Zone"
Figure 1.7: BeoLab 50 solves the problem of side wall reflections by reducingtheamountofacousticenergythat is radiated towards the side walls – so thereislessenergytoreflect.
However,ifyou’resharingyourmusic withfriendsorfamily,dependingon wherepeoplearesitting,thebeam maybetoonarrowtoensurethat everyonehasthesameexperience. In thiscase,itmaybedesirabletomake BeoLab50’ssoundbeamwider. Thisoptiontochangethepatternof theradiationofsoundfromtheBeoLab 50iscalledBeam Width Control.
1.1.2 ARC:ActiveRoom Compensation
In2002,Bang&Olufsenintroduced theBeoLab5whichincludedABC – Automatic Bass Calibration. Thiswasa systemthatusedamicrophoneto measuretheeffectsofthelistening room’sacousticalbehaviouronthe soundoftheloudspeaker,andthen
createdafilterthatcompensatedfor thoseeffectsinthelowfrequency band. Asasimpleexample,ifyour roomtendedtoincreasetheapparent basslevel,thentheBeoLab5’swould reducetheirbasslevelbythesame amount. BeoLab90tookthisconcepttoanew levelwithitsActive Room CompensationorARC,andthatsystem isalsoavailableintheBeoLab50. Usinganexternalmicrophone (suppliedwiththeloudspeaker),you canmeasuretheeffectsofyourroom’s acousticalbehaviourindifferentzones intheroomandsubsequentlyselect optimisedcompensationfiltersfor differentsituations. Forexample,you cancustomiseafilterforthesofa,and anotherforyourdiningarea. Incases whereyouaremovingbetweenthese locations,youcansimplyselecta combinationofbothfilterstocreatea singlecompensationfilterthat improvesthesoundexperienceinboth locations. TheBeoLab50alsooffersanother developmentinacousticalroom compensation: multichannel processing. Thismeansthatthe loudspeakersnotonly“see”eachother ashavinganeffectontheroom–but theyhelpeachothertocontrolthe room’sacousticalinfluence.
8
ApplicationInformation
2.1 MenuNavigation
Figure2.1:Presstheleft-pointingarrowheadatthetopleftofthescreentoreturntothepreviousmenu.
Presets
Easy Chair
Party
Sofa Left
...Presets
Easy Chair
Party
Sofa Left
...
Figure2.2:Pressthe“...” iconinthetop righttoswitchtotheeditmodeforthe currentscreen.
Presets
Easy Chair
Party
Sofa Left
...Presets
Easy Chair
Party
Sofa Left
...
Figure2.3:Circularselectionbuttonsallowforoneitemfromthelisttobechosen.
Room Compensation
Sweet Spot
Sofas
Entire Room
...
Dining Table
Room Compensation
Sweet Spot
Sofas
Entire Room
...
Dining Table
Room Compensation
Sweet Spot
Sofas
Entire Room
Dining Table
+
Figure 2.4: Rounded square selection buttonsaretogglesthatallowformore thanitemfromthelisttobechosen.
9
2.2 MenuMap
Beolab 50 Presets ... PRESETNAME PRESETNAME Volume / Mute
Beam Control Beam Width
Latency Mode Parametric EQ Loudness Frequency Tilt Sound Enhance Sound Designs Preset Number
ZONENAME ZONENAME +
Speaker Role Speaker Distance Speaker Level
Room Compensation Advanced RenameTone Controls +
PRESETNAME
Wireless PowerLink Automatic Power Link RCA S/P-DIF Optical USB Audio Inputs ...
Bass Treble Tone Controls
Beam Control
Room Compensation ...
Gain Offset
Listening Preset Detect Threshold
Max Input Voltage Control Volume Input Impedance Time-Out
INPUTNAME
About
Guide Network
Reset
Power Enhance Max Volume Default Volume
System
Automatic Update UTC Time Search for Update Submit Log Product information About
Speaker SPEAKERNAME Preset Input System SPEAKERNAME etc.
Advanced
Figure 2.5: Simplified and generalised navigational map for the BeoLab 50 interface when completed. Some items shown above are only visible when the menu is in edit mode which is entered by pressing the “...” icon at the top right of some menus. Also, not all parametersareavailableforallitems(e.g. differentinputshavedifferentoptions).
10
Presets
3.1 WhatisaPreset?
Almostallparametersthatcanaffect theaudiocharacteristicsoftheBeoLab 50canbepre-programmedandsaved asapreset thatiseasilyandquickly selectablebytheenduser. Apreset containsawiderangeofcontrolsthat canbecustomisedtosuitboththe listener’spersonalpreferencesandhis orherlocationinthelisteningroom. Presetscaneitherbeselected manuallyusingtheBeoLab50 interfaceortheycanbeselected automaticallyasisexplainedin AutomatingPresetSelection.
3.2 Presetmanagement
3.2.1 SelectingaPreset
Thelistofcurrently-availablepresets areshowninthePresetSelectmenu, anexampleofwhichisshowninFigure 3.1. Fromthismenu,youcanmanually selectapresetbyclickingonitsicon asshown,oryoucanmovedeeperinto theEditPresetmenuasshownin Figure3.2.
Presets
Easy Chair
Party
Sofa Left
Presets
Easy Chair
Party
Sofa Left
Presets
Easy Chair
Party
Sofa Left
Presets
Easy Chair
Party
Sofa Left
+
Presets
Easy Chair
Party
Sofa Left
...
Presets
Easy Chair
Party
Sofa Left
...Presets
Easy Chair
Party
Sofa Left
...
Figure 3.1: Select a Preset by pressing its icon on the right of the screen as shown. Thecurrently-selectedPresetis indicatedwithacheckmark.
Presets
Easy Chair
Party
Sofa Left
...Presets
Easy Chair
Party
Sofa Left
...
Figure 3.2: Press the three dots at the toprightofthescreentoentertheedit mode.
3.2.2 CreatingaPreset
Inordertocreateanewpreset,enter theeditmode(asshowninFigure3.2) andpressthe“+”iconinthePreset menu. Thiswillstartaprocesswhere youcannamethepresetandeditits parameters.
Easy Chair
Party
Sofa Left
Easy Chair
Party
Sofa Left
Presets
Easy Chair
Party
Sofa Left
Presets
Easy Chair
Party
Sofa Left
+
Presets
Easy Chair
Party
Sofa Left
...
Presets
Easy Chair
Party
Sofa Left
...Presets
Easy Chair
Party
Sofa Left
...
Figure3.3: Pressthe“+”icontocreate a new preset. Note the check mark on the top right of the screen which indicates that we have entered the “edit” mode.
3.2.3 EditingaPreset
Toedittheparametersofanexisting preset,pressitsassociatediconafter youhaveenteredthepresetmenu’s editmode(bypressingthe‘...’ iconon thetoprightofthescreen).
Easy Chair
Party
Sofa Left
Easy Chair
Party
Sofa Left
Presets
Easy Chair
Party
Sofa Left
Presets
Easy Chair
Party
Sofa Left
+
Presets
Easy Chair
Party
Sofa Left
...
Presets
Easy Chair
Party
Sofa Left
...Presets
Easy Chair
Party
Sofa Left
...
Figure3.4:Pressanywhereonapreset’s linetobegintoedititsparameters.
3.2.4 DeletingaPreset
Inordertodeleteapreset,enterthe presetmenu’seditmodeandswipeto theleftatanypositionintherow. This willrevealan“x”ontherightsideof thescreen. Pressingthe“x”willdelete thepreset.
Presets
Easy Chair
Party
Sofa Left
Presets
Easy Chair
Party
Sofa Left
Presets
Easy Chair
Party
Sofa Left
Presets
Easy Chair
Party
Sofa Left
+
Presets ...
Presets
Easy Chair
Party
Sofa Left
...Presets ... Figure 3.5: An example of deleting a preset. To delete the “Party” preset, swipetotheleftonitsrow. Thiswillreveal the “x” on the right of the screen. Pressthe“x”todeletethepreset.
11
ControlParameters
4.1 BeamWidthControl
Thebeamofsoundthatisradiated fromtheBeoLab50canbeadjustedby selectingfromtwooptions:
• Narrow • Wide
Beam Control
Master
Distance
Level
Left
3.5 m
5.0 dB
Master
Distance
Level
Left
3.5 m
5.0 dB
Master Left
3.5 m
5.0 dB
Wide sound
... Beam Control
Wide sound
... Beam Control
Level
Wide sound
Figure 4.1: The Beam Control menu for the Master loudspeaker. To switch between the Master and the Slave loudspeaker, swipe the upper area of the screenleftandright.
Notethat,ifanActiveRoom Compensationzonehasbeencreated, andisappliedtothepresetyouare currentlyediting,thenanappropriate filtersettingwillbecalculatedeach timeyouchangeBeamWidth. This calculationtakesapproximately20 secondstoperform,andisindicatedby aprogresswheel. Ifyouwishto auditiondifferencesinBeamWidth morequickly,thiscanbedoneby disablingtheARCfilterforthepresetin theRoomCompensationmenu.
4.1.1 Narrow
Sitinthe“sweetspot”–alocationin yourlisteningroomthatisexactlythe
samedistancefromeachofyour BeoLab50’s,andwherethetwo loudspeakersarefacing(shownin Figure4.2). UsingyourBeoLab50 interface,settheBeamWidthControl to“Narrow”.
Figure4.2:A“perfect”loudspeakerconfigurationwithBeoLab50’s. Bothloudspeakersareaimedatthelisteningposition. The distance from the listening position to each loudspeaker is the same as the distance between the two loudspeakers. For more detailed information on loudspeaker configuration, see Appendix 1: Recommendations for CriticalListening
Whilefacingapointlocatedatthe centrebetweenthetwoloudspeakers, play“Tom’sDiner”(recordedby SuzanneVegain1987forheralbum “SolitudeStanding”). Vega’svoice shouldappeartofloatataposition betweenthetwoloudspeakers. Ifher voicedoesnotappeartobelocated exactlymid-waybetweenthetwo loudspeakers,itislikelythatyouare sittingslightlyclosertoone loudspeakerthantheother–inother words,toonesideofthesweetspot. Trymovingslightlyside-to-sideand payattentiontothelateralmovement ofVega’svoiceinspace. Thisabilityforapairofloudspeakersto delivertheillusionofasoundcoming fromalocationinspacebetweenthem iscalledphantom imagingorstereo imagingorsimplyimaging. Nowpayattentiontotheapparent distancetothevoice. IftheBeam WidthControloftheloudspeakersis setto“Narrow”mode,thevoicewill appeartofloatingatadistance somewherebetweenyouandthe loudspeakers. Thisisillustratedin
Figure4.3.
tri
tri
tom
tom
tom
hh
voice
bongos
bk
bk bass
bass
gtr
synth pad at end
sax
snare
"choir""choir"
cow
synth fx around 2:20
shake
tri
tri
Figure 4.3: A map of the phantom imagelocationofthevoice(showninred) in Suzanne Vega’s recording of Tom’s Diner. BeamWidth: Narrow
ChangethetracktoJenniferWarnes’s recordingof“BirdonaWire”fromthe Album“FamousBlueRaincoat: The SongsofLeonardCohen”. Inthis recording,therearemanymore instrumentsandvoices,however,it shouldbeveryeasytolocatethe positionofeachofthosesourcesas comingfromsomewherebetweenthe twoloudspeakers. Apartialmapof theselocationsisshowninFigure4.4.
tri
tri
tom
tom
tom
hh
voice
bongos
bk
bk bass
bass
gtr
synth pad at end
sax
snare
"choir""choir"
cow
synth fx around 2:20
shake
tri
tri
Figure 4.4: A map of the phantom imagelocationsofinstrumentsandvoices inJenniferWarnes’srecordingofBirdon aWire. BeamWidth: Narrow.
BeoLab50isabletodeliversucha precisestereoimagingforactive listeningbecauseitisabletoreduce theamountofenergyinthereflections offthesidewallsofyourlistening room. Thisgivesthesameresultatthe listeningpositionasifyouused acousticallyabsorptivematerialson
12
yourwalls,orchangedthegeometryof yourlisteningroomtoavoidhaving firstreflectionsinthelisteningposition.
Figure4.5:Conceptualdrawingshowing thebeamwidthoftheNarrowBeam.
Youshouldnote,however,thatthere areside-effectstousinganarrow beamwidth. Themostobviousmaybe inthelowfrequencybehaviourofyour BeoLab50’s. Generally,theoverall impressionwillbethatthebass contentis“tighter”orhasmore “punch”whentheBeoLab50isin narrowmode. However,thiseffectis alsodependentonthesettingof anotherparameterdescribedin LatencyMode.
Figure 4.6: Press the sector (or “pizza slice”) on the BeoLab 50 interface to changetheBeamWidthtoNarrow.
Asecondpotentialsideeffectisthe sensitivityofthesystemtoanincorrect listeningposition. Youmaynoticethat, innarrowmode,itiscriticalthatyou areseatedatexactlythecorrect listeningpositioninordertoachieve bothpreciseandaccuratestereo imaging. Smalldeviationsinlistening positionmayresultinnoticeable detrimentsinthespatial representationofyourrecordings.
4.1.2 Wide
Asmentionedabove,whentheBeoLab 50’saresettoanarrowbeamwidth, theyaresomewhatunforgivingofa mis-placementofthelistening position. Thisisparticularlynoticeable whenyouarelisteningtorecordingsor movieswithfriendsandfamily. Consequently,inmoresocialor passivelisteningsituations,itislikely preferablethattheBeoLab50’shavea widerbeamwidth,moresimilarto BeoLab5loudspeakers. Althoughthis willlikelyresultinmoreenergyinthe sidewallreflections,italsoensuresthat thereisamoreequaldistributionof thedirectsoundacrossawider listeningareaintheroom.
Figure4.7:Conceptualdrawingshowing thebeamwidthoftheWideBeam.
Figure4.8: Pressthecurvedlineshown above to change the Beam Width to Wide(Front).
ThesideeffectsoftheWidebeam widtharedependentonthestrengthof thesidewallreflections,however,in manysituations,fourdifferenteffects maybeaudible. Thefirstisthattheapparentdistance tothevarioussourcesinthestereo mixwillcollapseslightly,resultingin theperceptionthatthesourcesinthe recordingareroughlythesame distancefromthelisteningpositionas
theloudspeakersthemselves. This meansthat(relativetothenarrow mode)veryclosesourceswillmove furtherawayandveryfarsourceswill moveclosertothelisteningposition. Secondly,theapparentwidthofthe sourceswillbecomeslightlylargerwith lesspreciseleft-rightlocations. Youwill nothavepinpointlocationsasin narrowmode–imagingbecomes slightlymore“cloudy”or“fuzzy”. This isduetotheextraenergyreflectedoff thesidewalls.
tri
tri
tom
tom
tom
hh
voice
bongos
bk
bk bass
bass
gtr
synth pad at end
sax
snare
"choir""choir"
cow
synth fx around 2:20
shake
tri
tri
Figure 4.9: A map of the phantom imagelocationofthevoice(showninred) in Suzanne Vega’s recording of Tom’s Diner. Beam Width: Wide. Compare to Figure4.3
tri
tri
tom
tom
tom
hh
voice
bongos
bk
bk bass
bass
gtr
synth pad at end
sax
snare
"choir""choir"
cow
synth fx around 2:20
shake
tri
tri
Figure4.10: Amapofthephantomimagelocationsofinstrumentsandvoices inJenniferWarnes’srecordingofBirdon aWire. BeamWidth: Wide. Compareto Figure4.4
Thirdly,theoveralltimbreortone colourofthesoundmaychangeasa resultofincreaseinfluenceofthe sidewallreflectionsatthelistening position.
13
Finally,asmentionedabove,the overall“punch”ofthebasswillchange whencomparedtothenarrowmode.
4.1.3 Comment
Notethattheaboveillustrations connectingBeamWidthstolistener positionaremerelythat–illustrations. Itshouldalsobesaidthatchangingthe BeamWidthoftheBeoLab50has non-intuitiveconsequencesonthe perceivedsoundoftheloudspeakers. Forexample,theoverallsensationof “punch”inthebassmaybedifferent forthethreeBeamWidths,regardless ofyourlocationinthelisteningroom. Consequently,itmaybethatyou prefertheoverallsoundofaparticular BeamWidth,evenifyouarenotsitting “inthebeam”.
4.2 SpeakerDistance
TheSpeakerDistancecontrolisusedto ensurethatthetimesofarrivalofthe loudspeakers’signalsatthelistening positionarematched,despitetheir beingplacedatdifferentdistances fromthelisteningposition. Thevalue displayedonthemenushouldbethe distancefromthelisteningpositionto eachloudspeaker. Theresultofthis alignmentisthatthecloser loudspeaker’ssignalisdelayedto matchthetimeofarrivalofthesound fromthemoredistantloudspeaker.
Notethat,sincetheListeningPosition canbedifferentfordifferentPresets, thesedistancesmaynotnecessarilybe thesamefromPresettoPreset. Units Metres,Feet Range(m) 0.0–10.0 Range(ft) 0.0–30.0 Resolution 0.1 FactoryDefault 1.0m
4.2.1 AdjustingSpeaker Distancesformorethan onelisteningposition
Incaseswherethereismorethanone listenerpresent,theSpeakerDistances canbeoptimisedbymeasuringeach loudspeaker’spositionrelativetothe closestlisteningposition,asisshown inFigure4.12.
Figure 4.12: The Speaker Distance for each loudspeaker should be measured fromtherelevanttweeterforthegiven BeamDirectionstotheclosestlistening position.
AutomatedMeasurementof SpeakerDistance Thedistancefromthelisteningposition toeachBeoLab50canbemeasured automaticallyusingthemicrophone includedwiththeloudspeakers. Thisis donebypressingthemicrophoneicon atthebottomoftheBeamControl menu(showninFigure4.13)and followingtheinstructions. Beam Control
Master
Distance
Level
Left 3.5m
dB5.0
180  directional sound
... Beam Control
Master
Distance
Level
Left 3.5m
dB5.0
180  directional sound
... Beam Control
Master
Level
180  directional sound
Figure 4.13: Pressing the microphone icon in the Beam Control menu starts the Speaker Distance measurement procedure.
4.3 SpeakerLevel
ThesensitivityofanytwoBeoLab50’s hasbeencalibratedduringtheir creationtobewithin1dBofeachother atanythird-octavefrequencyband withintheirfrequencyrange.1 However,therearecaseswhere,due toplacementinthelisteningroom, roomacoustics,orthelistening positionrelativetotheloudspeakers, youmaywishtofine-tunetherelative levelsofthetwoloudspeakers. This canbedonewiththeSpeakerLevel adjustment. ItisrecommendedthattheSpeaker Levelsshouldbeadjustedatthe listeningposition. Notethatthiscanbe performedeitherbeforeorafteran ActiveRoomCompensationprofilehas beencreated–theARCcompensates foranyadjustmentsautomatically. TheSpeakerLevelforeachBeoLab50 inthepairisadjustedfromtheBeam Controlmenu,showninFigure4.1.
4.4 SpeakerRole
TheBeoLab50iscreatedasapairof loudspeakers–one“master” loudspeakerwhichhastheconnection panelfortheinputsignalsandone “slave”loudspeaker. Sinceboththeleftandrightaudio channelsareinputtoyourmaster loudspeaker,thereisnophysicalway ofknowingwhichloudspeakerisonthe leftandwhichisontheright(compare Figures4.14and4.15asanexample). Asaresult,theinterfaceallowsyouto swaptheSpeakerRole,toensurethat thecorrectaudiochannelis reproducedbythecorrectloudspeaker. TheselectionofLeftorRightforthe MasterandSlaveloudspeakersisdone intheBeamControlmenu,shownin Figure4.1.
1Preliminaryspecification. Subjecttochange.
14
Slave (Left)
Master (Right)
Slave (Right)
Master (Left)
Figure 4.14: An example of a loudspeaker configuration where the Masterloudspeakershouldbeassignedthe SpeakerRoleof“right”.
Master (Left)
Slave (Right)
Slave (Left)
Master (Right)
Master (Right)
Slave (Left)
Slave (Right)
Master (Left)
Figure 4.15: An example of a loudspeaker configuration where the Masterloudspeakershouldbeassignedthe SpeakerRoleof“left”.
NotethataMaster/Slavepairof BeoLab50’scannotsharethesame SpeakerRole. Ifyouwishtosendthe sameaudiosignaloutofboth loudspeakers,thiswillhavetobe arrangedusingthesourcedevice.
4.5 ActiveRoom Compensation
Forageneralintroductiontothe effectsofroomacousticsonthesound ofaloudspeaker,pleasereadAppendix 3: TheInfluenceofListeningRoom AcousticsonLoudspeakers Itshouldbenotedthattheacoustical behaviourofaroomcanchange considerablywhenwindowsordoors areopenedandclosed. Consequently, foroptimaltuning,itisrecommended thatARCprofilesbemadeforthese cases,particularlyifthischangeis madeoften(e.g. patiodoors).
4.5.1 CreatinganewARC Zone
AnewActiveRoomCompensation zonecanbecreatedbypressingthe “+”iconintheRoomCompensation Editmenu. (EntertheRoom CompensationEditmenubypressing thethreedotsatthetoprightofthe RoomCompensationSelectmenu.)
Room Compensation
Sweet Spot
Sofas
Entire Room
...
Dining Table
Room Compensation
Sweet Spot
Sofas
Entire Room
...
Dining Table
Room Compensation
Sweet Spot
Sofas
Entire Room
Dining Table
+
Figure 4.16: Press the “+” icon in the Room Compensation Edit menu to createanewARCzone.
Thiswillstartaprocedurewhereyou willbeguidedthroughtheprocessof positioningthemicrophoneindifferent locationstooptimisedtheARCfilters. EachARCiscreatedusing measurementsmadeinthree microphonelocations,andamaximum of5differentARCZonescanbe created. Foradditionalguidance,pleasesee Appendix5: Microphoneplacement strategywhencreatingARCZones.
4.5.2 SelectinganARCZone
Itispossibletocreateupto5different ActiveRoomCompensationZonesthat canberecalledeithermanually,or automaticallyaspartofaPreset. Inordertodisabletheactiveroom compensationfilters,simplyde-select theminthemenu.
Figure 4.17: An example of a listening space showing four different overlappingARCzonesinred,blue,green,and yellow.
Room Compensation
Sweet Spot
Sofas
Entire Room
...
Dining Table
Room Compensation
Sweet Spot
Sofas
Entire Room
...
Dining Table
Room Compensation
Sweet Spot
Sofas
Entire Room
Dining Table
+
Figure 4.18: Selecting one or more ActiveRoomCompensationzonesaccordingtoyourlisteningarea(s)intheroom. Note that it is possible to select more thanonezonesimultaneously.
4.5.3 CombiningARCZones
UptothreeARCZonescanbeselected simultaneouslytocreateafilterthat incorporatesthemeasurementsfrom theapplicableareasofthelistening room. Note,however,thataddinganextra zonetoacurrentonemaycompromise thequalityoftheaudiosignalinthe originalzone. Forexample,ifyouhave twoARCZones,oneforthe“Sweet Spot”andtheotherforthe“Dining Table”,addingtheDiningTablezoneto theSweetSpotzonewillreducethe qualityoftheARCfilteringinthesweet spotlocation. Thisisduetothefact thatsomeofthefilteringrequiredto compensatefortheroom’sacoustical
15
effectsinthediningareamaynotbe requiredinthesweetspot. AlsonotethatchangingRoom Compensationzoneswillcausean approximately20-secondbreakinthe audiosignalastheBeoLab50 calculatesandupdatestheappropriate filters. Thisisnormal.
4.6 Volume
ThevolumeoftheBeoLab50is controllablefrom0to90instepsof1 dB.NotethatVolumeStep0isafull mute. Initsdefaultsettings,BeoLab50has beencalibratedtomatchthelevelof otherBang&Olufsenloudspeakersfor itsPowerLinkandWirelessPowerLink inputs. Tables7.1and7.3showthe outputleveloftheloudspeakerfor variousinputsandparameters. Notethat,althoughtheVolumecontrol oftheBeoLab50isdisabledforPower LinkandWirelessPowerLinksources,2 thevolumeofthesourceisduplicated ontheBeoLab50app. Thisisto ensurethatchangestoadifferent sourcearematched. Forexample,sayyouhaveaBeoVision AvantconnectedtoPowerLinkinput andaCDplayerconnectedtothe S/P-DIFinputoftheBeoLab50. You startbylisteningtoaCDatahigh volumelevel,thenswitchtowatching thetelevisionnewsatalowlevel(set onthetelevision). Whenyouswitch backtolisteningtoCD,thevolumeof theBeoLab50willautomaticallyhave beenchangedtothelowsettingofthe television.
4.7 Mute
Pressingthemutebuttoninthecentre ofthevolumewheelreducesthe volumetoafixedvalueof0.
Figure4.19:TheVolumecontrol(theexterior circle) and the Mute control (the iconinthecentreofthecircle).
Inordertounmutethesound,either pressthemutebuttonagain,oradjust thevolume. Notethat,ifthevolumesettingofthe BeoLab50washigherthanthestartup volumewhenmuted,thenthevolume settingafterunmutingwillbethesame asthestartupvolume.
4.8 ToneControls
TheToneControlsontheBeoLab50 consistoftraditionalBassandTreble controls. Theseareglobaladjustments thatareappliedtoallPresetsandto bothloudspeakerssimultaneously.
4.8.1 Treble
TheTrebleadjustmentallowsyouto changetherelativeamountof high-frequencysoundgloballyusinga high-shelvingfilterwithafixed turnoverfrequencyof8kHzandaQof 0.707. Notethatthegainatthe turnoverfrequencyisonehalfthe maximumgainappliedbythefilterin decibels. Forexample,whenthegain ofthecontrolleris-4dB,thegainat8 kHzis-2dB. TheTreblecontrolisappliedtoaglobal filterandthereforeisappliedtoall Presets. Itisalsoisindependentofthe settingsofotherequalisation controllersinthesystemsuchasthe FrequencyTilt,SoundEnhanceand ParametricEqualisercontrols. The rangeofthecontrollerisfrom-6.0dB to+6.0dBinstepsof0.5dB.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure4.20: MagnitudeResponses,Treblecontroller. Notethatthisfilterisapplied to both loudspeakers simultaneously.
4.8.2 Bass
TheBassadjustmentallowsyouto changetherelativeamountof low-frequencysoundgloballyusinga low-shelvingfilterwithafixedturnover frequencyof120HzandaQof0.707. Thegainattheturnoverfrequencyis onehalfthemaximumchangeingain appliedbythefilterindecibels. For example,whenthegainofthe controlleris+6dB,thegainat120Hz is+3dB. TheBasscontrolisaglobalfilterand thereforeisappliedtoallPresets. Itis alsoisindependentofthesettingsof otherequalisationcontrollersinthe systemsuchastheFrequencyTilt, SoundEnhanceandParametric Equalisercontrols. Therangeofthe controllerisfrom-6.0dBto+6.0dBin stepsof0.5dB.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 4.21: Magnitude Responses: Bass controller. Note that this filter is appliedtobothloudspeakerssimultaneously.
2Thisrestrictionismadetopreventincorrectcalibrationoflevelsinsurroundsoundconfigurations.
16
4.9 AdvancedControls
TheAdvancedControlssectiongives theuseranalmost-surgicalcontrol overthetimbralcharacteristicsofthe BeoLab50usingacombinationof legacyBang&Olufsenaudio processing,standardequalisationtools foundinprofessionalstudio equipment,andproprietaryprocessing availableonlyinthisloudspeaker. TheAdvancedControlsoftheBeoLab 50are
• LatencyMode • Loudness • FrequencyTilt • SoundEnhance • SoundDesign • ParametricEqualiser
Advanced
Latency Mode High
Flat
0
0
Parametric EQ
Loudness
Frequency Tilt
Sound Enhance
Sound Design
Default
Flat on-axis
Trigger
Preset#
Figure 4.22: The Advanced Controls menu.
4.9.1 LatencyMode
InordertocontroltheBeamWidthof thesoundradiatingfromtheBeoLab
50,acustomisedFiniteImpulse Response(FIR)audiofilterisselected foreachwooferandmidrangeto accompanythechangesresultingfrom themovingAcousticLensabovethe tweeter. Thesefiltersareappliedto eachoftheDSP’s6audiooutput channelsforthosedrivers. However,in ordertocontroltheverylowfrequency bands,itisnecessaryforthewoofers’ FIRfilterstobeverylong. One implicationofthisisthatittakessome timebetweenthemomentanaudio signalenterstheinputofthe loudspeakerandthemomentitexits theloudspeakerassound. Thelowerin frequencytheBeamWidthControlis extended,thelongerthelatency(or delay)oftheloudspeaker. Thisultimatelymeansthatthereisa directrelationshipbetweentheoverall latencyoftheloudspeakerandits soundcharacteristics–especiallyin thelowfrequencybands. Oneexample ofthiseffectis: thelongerthelatency, the“tighter”thebass. However,thismaymeanthat,for somesourcesandprogrammaterials, thereisalossofsynchronisation. For example,initslongestlatencysetting, theloudspeakermaybetoolateto maintainlipsynchwithsome televisionsorsomemultiroom systems. Thisiswhythelatencyofthe loudspeakerisuser-selectablebetween twodifferentsettings.
Auto IfyouareusingBeoLab50’switha currentBeoVisiontelevision3,thenthe LatencyModeshouldbesetto“Auto”. Thiswillallowthetelevisiontomanage thelatencymodeoftheloudspeakers automatically. Notethat,iftheLatencyModeissetto “Auto”andtheinputisneitherPower LinknorWirelessPowerLink,thenthe BeoLab50willdefaulttoaHigh LatencyModeof100ms.
High Toachievethehighestpossiblelevelof audioqualityfromtheBeoLab50,the internaldigitalprocessingmusttake 1/10thofasecondinordertocontrol thelow-frequencybehaviourofthe system. Thisisselectedbysettingthe LatencyModeto“High”,thus deliveringtheultimatepossiblesound qualityfromtheloudspeaker. However,therearecaseswheresucha longdelayintheloudspeakerwill resultinlossofsynchronisationwith otherdevicesinthesystemsuchas thevideo(lipsynch)orother loudspeakersinasurroundsystem. If youareexperiencingsuchproblems, thenthelowerlatencymodeshouldbe selected. ThelatencyoftheBeoLab50in“High” latencymodemeasuredusingan analogueinputis100ms.
Low Insomecases,aBeoLab50is connectedtoasystemthatrequiresa lowerlatency. Oneexampleofthisisa casewheretheloudspeakeris connectedtoanon-B&Otelevisionor surroundprocessor. Asecondexample isanon-B&Omultiroomsystemthat lackstheabilitytoadapttodifferent loudspeakerlatenciesthroughoutthe network. Anotherexamplewouldbea multichannelloudspeakersetupwitha non-B&Osurroundprocessoranda mixtureofdifferentloudspeakersinthe configuration. Inthiscase,theoveralldelayofthe BeoLab50shouldbesetto“Low”to ensuresynchronisationwithother loudspeakersinthesystem. ThelatencyoftheBeoLab50in“Low” latencymodemeasuredusingan analogueinputis25ms.
3BeoPlayV1,BeoVision11,Avant,AvantNG,14,Horizon,Eclipse–orlater
17
EffectsofLatencyModeon BeamWidth
Frequency
Beam Width
Front SideSideBack Back
Figure 4.23: Conceptual plot showing therelationshipbetweenLatencyMode and a Narrow Beam Width over frequency. The black curve shows a High latency mode. The red curve shows a low latency mode. Note that the high frequency beam width is the same for both latency modes. Only the beam widthofthelowfrequencybandswiden forlowerlatencies.
4.9.2 Loudness
Sadly,humanhearingisimperfect. Oneoftheissuesthatweallsuffer fromisthatourperceptionofthe timbreor“tonecolour”ofasoundis notconstantwithlisteninglevel. We arelesssensitivetolowfrequencies whentheyareplayedatlowlistening levels. Inotherwords,ifyouare listeningtomusicatahighleveland youturndownthevolume,youwill noticethat,thelowerthevolume,the lessbassyoucanhear. Thisisalsotrue ofhighfrequencies,albeittoalesser extent. TheLoudnesssettinginyourBeoLab 50’scounteractsthiseffect. Asyou reducethevolume,thebassandtreble levelsareautomaticallyincreasedto compensateforyourreduced perceptionintheouterfrequency bands. Ifyoudonotwishthissettingenabled, LoudnessshouldbesettoOFF. NotethattheLoudnesstoggle (whetheritisonoroff)isstoredwith thePreset,sodifferentmodescan havedifferentsettings. Options On/Off Default On
10 100 1,000 10,000
0
2
4
6
8
10
12
Frequency (Hz)
Gain (dB)
Figure4.24:Magnituderesponsesofthe loudnessfunctionatvarioussettingsof thevolumecontrol.
Notethat,whenconnectedtomost Bang&Olufsensources,theLoudness functionintheBeoLab50willbe disabledforthePowerLinkand WirelessPowerLinkinputs. Thisis becauseinthesecases,theLoudness functionisperformedbythesource ratherthantheloudspeaker.
4.9.3 FrequencyTilt
FrequencyTiltcanbeconsideredtobe acombinationofBassandTreble settingsinasingleparameter. When FrequencyTiltissettoalowvalue,the lowfrequencycontentofyouraudio signalisincreasedandthelevelofthe highfrequencycontentisreduced. IftheFrequencyTiltissettoahigh value,thentheoppositewillbetrue. TheFrequencyTiltfunctionwillhave noeffectontheaudiosignalatits middlesetting. NotethatFrequencyTiltcanhave differentsettingsfordifferentPresets. Therangeofthecontrollerisfrom-6.0 dBto+6.0dBinstepsof0.5dB.As canbeseeninFigure4.25,acontroller settingof+6.0willresultina peak-to-peakmagnituderesponse deviationofapproximately6dB, howeverthemaximumdeviationfrom aflatresponseisonly3dB.
10 100 1,000 10,000 −4
−3
−2
−1
0
1
2
3
4
Frequency (Hz)
Gain (dB)
Figure4.25: MagnitudeResponses,FrequencyTiltcontroller. Notethatthisfilter is applied to both loudspeakers simultaneously.Blackcurvesshowtheresultforpositiveslidervalues,redcurves shownegativeslidervalues.
4.9.4 SoundEnhance
TheSoundEnhancesettingissimilarto theFrequencyTiltsettinginthatit affectsthelowandhighfrequency bandswithasingleslider. Increasing theSoundEnhancevaluewillincrease thelevelofthebassandtreblebands whilereducingthemidrange. DecreasingtheSoundEnhancevalue willhavetheoppositeeffectandwill enhancethemidrange. TheSoundEnhancesettingwillhave noeffectonthisaudiosignalatits middlesetting. NotethatSoundEnhancecanhave differentsettingsfordifferentPresets. Therangeofthecontrollerisfrom-6.0 dBto+6.0dBinstepsof0.5dB.As canbeseeninFigure4.26,acontroller settingof+6.0willresultina peak-to-peakmagnituderesponse deviationofapproximately6dB, howeverthemaximumdeviationfrom aflatresponseisonly3dB.
18
10 100 1,000 10,000 −4
−3
−2
−1
0
1
2
3
4
Frequency (Hz)
Gain (dB)
Figure 4.26: Magnitude Responses, Sound Enhance controller. Note that this filter is applied to both loudspeakers simultaneously. Black curves show theresultforpositiveslidervalues,red curvesshownegativeslidervalues.
4.9.5 SoundDesign
Attheendofthedevelopmentprocess, allBang&Olufsenloudspeakersgo throughafinaltuningprocesswhere theloudspeaker’stimbreisevaluated indifferentlisteningenvironments. In ordertoachieveanoptimisedbalance betweentheon-axisfrequency responseandthethree-dimensional “powerresponse”,filtersareincluded inthesignalpathtogivethe loudspeakerafinalsound design. TheBeoLab50isnoexceptiontothis– asaresult,ithasacustom-tuned, factory-defaultsounddesignforevery combinationofbeamwidths,beam directions,andlatencymodes. However,theremaybesomespecific caseswherethistuningisnot applicable. Oneexampleofthisisa casewheretheBeoLab50isusedina listeningroomsuchasarecording studiowhereacousticalabsorptionhas beenappliedtothevarioussurfaces. Inthiscase,itmaybepreferableto usetheBeoLab50asa“studio monitor”styleofloudspeaker,where theoveralltuningisdesignedto deliveraflatmagnituderesponse whenmeasuredon-axistothe loudspeakerinafreefield. TheSoundDesigncontrolallowsyouto switchbetweenthesetwotunings. Itis currentlyplannedthatadditionalsound designswillbemadeavailablein futuresoftwarereleases.
4.9.6 ParametricEqualiser
For a general introduction to equalisation, please see Appendix 2: Introduction to Parametric Equalisers. Incaseswhereamoredetailedcontrol ofthefrequencyresponseofthe loudspeakerisneeded,a10-band parametricequaliserisavailable. This allowsyoutosculptthetimbral balanceoftheloudspeakerwithahigh degreeofprecision. Whenthegainsofalltenfiltersinthe ParametricEqualiseraresetto0dB, theprocessingblockisautomatically disabled. Figure4.27isgivenasarough“map” offrequencyasreferencewhenusing theParametricEqualiser.
440.0 Hz
660.0 Hz
880.0 Hz
1320.0 Hz
220.0 Hz 261.6 Hz 330.0 Hz
110.0 Hz
165.0 Hz
55.0 Hz
55.0 Hz
Figure 4.27: Pitch vs. Fundamental frequencyforreferencepurposeswhen equalising.
BeoLab50’sParametricEQconsistsof onelow-shelvingfilter,one high-shelvingfilter,and8reciprocal peak-dip(orpeaking)filterswith differentfrequencyrangesaslistedin Table7.4. Eachfilterhasavariable Frequency,Gain,andQ. Thecentrefrequenciesofallfilters haverangeslimitedto5octavesin ordertooptimisetheirsignal-to-noise ratioswhileprovidingawiderangeof control. FrequenciesarelimitedtoISO 1/6thoctavecentresaslistedinTable 7.5. TheavailableQ’softhefiltersare limitedtothevalueslistedinTable7.6.
Notethatallfiltersareimplementedin series,andthatfrequenciesmay
overlapeachotherincaseswhere additionalgainisdesired. AllfiltersintheParametricEQsection areimplementedasminimumphase filters. Inordertoensurephasematchingof thetwoloudspeakersandthereforeto maintainphantomimaging characteristics,identicalParametric Equaliserparametersareappliedto bothloudspeakerssimultaneously.
MagnitudeResponsePlots Low-ShelvingFilter TheBeoLab50ParametricEqualiser hasonelow-shelvingfilteravailable withafrequencyrangeof16.0Hzto 500.0HzandaQrangeof0.35to1. Thegainrangesfrom-6.0dBto+6.0 dBinstepsof0.5dB.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 4.28: Magnitude Responses, AdvancedEQ,low-shelvingfilter:Fc=100 Hz,Gainvariedfrom-6.0to+6.0dB,Q =1.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 4.29: Magnitude Responses, AdvancedEQ,low-shelvingfilter:Fcvaried from16to500Hz.,Gain=±6dB,Q= 1.
19
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 4.30: Magnitude Responses, AdvancedEQ,low-shelvingfilter:Fc=100 Hz,Gain=±6dB,Qvariedfrom0.35to 1.
PeakingFilters TheBeoLab50ParametricEqualiser haseightreciprocalpeak-dipor peakingfiltersavailable. Allpeaking filtershaveaQvaluethatrangesfrom 0.35to8.0wheretheQisbasedona bandwidthdefinedbythehalf-gain points4. Thegainrangesfrom-6.0dB to+6.0dBinstepsof0.5dB.The peakingfiltershavearangeof5 octaveswithdifferinglimitsasfollows:
• Fourlow-frequencyfilterswitha rangeof16.0Hzto500.0Hz. • Threemid-frequencyfilterswith arangeof250.0Hzto8.0kHz. • Onehigh-frequencyfilterwitha rangeof2.0kHzto63.0kHz.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 4.31: Magnitude Responses, AdvancedEQ,Peakingfilter: Fc=100Hz, Gainvariedfrom-6.0to+6.0dB,Q=1.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 4.32: Magnitude Responses, Advanced EQ, Peaking filter: Examples of Fcvariedfrom16Hzto32kHzononeoctave centres, Gain = ±6 dB, Q = 1.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 4.33: Magnitude Responses, AdvancedEQ,Peakingfilters:Fc=100Hz, Gain=±6dB,Qvariedfrom0.35to8.
high-shelvingFilter TheBeoLab50ParametricEqualiser hasonehigh-shelvingfilteravailable withafrequencyrangeof500.0Hzto 16.0kHzandaQrangeof0.35to1. Thegainrangesfrom-6.0dBto+6.0 dBinstepsof0.5dB.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 4.34: Magnitude Responses, Advanced EQ, high-shelving filter: Fc = 1000 Hz, Gain varied from -6.0 to +6.0 dB,Q=1. Notethatthisfilterisapplied tobothloudspeakerssimultaneously.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 4.35: Magnitude Responses, Advanced EQ, high-shelving filter: Fc varied from 500Hz to 16 kHz, Gain = ±6 dB,Q=1.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 4.36: Magnitude Responses, Advanced EQ, high-shelving filter: Fc = 100 Hz, Gain = ±6 dB, Q varied from 0.35to1.
4.10 AutomatingPreset Selection
Itisnotnecessarytomanuallyselect PresetsusingtheBeoLab50app. Itis possible,instead,tohavePresets triggeredtobeselectedautomatically usingoneoftwopossibleexternal controls: BySpeakerGroup(ifyou haveaBang&Olufsentelevisionsuch asaBeoVision11orBeoVisionAvant) orBySource.
BySpeakerGroup IfyouhaveapairofBeoLab50’s connectedtoaBang&Olufsen televisionsuchasaBeoVision11or BeoVisionAvantasshowninFigure 4.37,thenitispossibleto automaticallytriggerpresetsin tandemwiththetelevision’sSpeaker Group. Thisselectionisdoneinthe SpeakerGroupmenusonthe television,whereyoucanselectthe 4For more information on this, please see “The Equivalence of Various Methods of Computing Biquad Coefficients for Audio Parametric Equalizers” Robert Bristow-Johnson, Preprint3906,97thInternationalConventionoftheAudioEngineeringSociety,November1994
20
“SpeakerPreset”numberforthe BeoLab50asoneoftheparametersin theSpeakerGroup. SeetheBeoVision TechnicalAudioGuideformore informationaboutthis. Notethat,incaseswherea multichannelloudspeaker configurationincludesmorethanone pairofBeoLab50’sorBeoLab90’s connectedtoaBeoVisiontelevision,it willbenecessarytoensurethatthe Presetnumbersarethesameforall pairsofloudspeakersinthesystem, sincethetelevisionsendsoutonlyone SpeakerPresetnumberforall loudspeakersconnectedtoit.
BySource ImagineyouhaveapairofBeoLab 50’sconnectedtotwonon-B&O
sourcesasshowninFigure4.38.
• anAVSurroundProcessor connectedtotheRCALine inputs. Thedeviceisalso connectedtootherloudspeakers toformamultichannel (surround)configurationfor watchingmovies. • ahigh-resolutionaudioplayer connectedtotheS/P-DIFinput.
Inaddition,youhaveconfiguredtwo PresetsinyourBeoLab50’s:
1. Optimisedformultichannel listeningwithalisteningzone thatencompassesmorethanone listeningposition(e.g. thewhole sofa). 2. Optimisedfor2.0Stereolistening
withonlyone“sweetspot”inthe centreofthesofa.
Inthissituation,youwanttheAV Surroundprocessortoautomatically selectPreset1andthehigh-resolution audioplayertoautomaticallyselect Preset2. Inthisway,thereisnoneed tomanuallychangeBeoLab50presets.
Mixedsystems Notethatispossibletotriggerbothby sourceandbySpeakerGroupinmixed systemssuchasthatshowninFigure 4.39. Inthiscase,theBeoVision televisioniscontrollingtheBeoLab50 presetwithinitsSpeakerGroup parameters. However,theBeoLab50 canalsohaveapresetthatis automaticallytriggeredbytheaudio playerconnectedviaS/P-DIF.
21
 Audio Player
AV Surround Processor
Power Amplifier
XLR
S/P-DIF
Audio Player S/P-DIF
Digital Power Link
Digital Power Link
Power Link
Digital Power Link
Power Link
Figure4.37: AnexampleofapairofBeoLab50’sconnectedtoaBeoVision11usingPowerLink.
 Audio Player
AV Surround Processor
Power Amplifier
RCA
S/P-DIF
Audio Player S/P-DIF
Digital Power Link
Digital Power Link
Power Link
Digital Power Link
Power Link
Figure 4.38: An example of a pair of BeoLab 50’s connected to two third-party sources: an AV Surround Processor using RCA and a separateaudioplayerusingS/P-DIF.Notethat,inthiscase,thelatencyoftheBeoLab50’smustbecarefullymanagedinthesetupof theloudspeakersandtheAVSurroundProcessorinordertoensurethatthemultichannelsystemisbehavingcorrectly.
 Audio Player
AV Surround Processor
Power Amplifier
XLR
S/P-DIF
Audio Player S/P-DIF
Digital Power Link
Digital Power Link
Power Link
Digital Power Link
Power Link
Figure4.39: AnexampleofapairofBeoLab50’sconnectedtooneB&OsourceusingPowerLinkandathird-partyaudioplayerusing S/P-DIF.
22
Inputs
Ascanbeseenontheconnectorpanel showninFigure5.5,theBeoLab50has atotalofsevendifferentaudioinputs asfollows: Bang&OlufsenProprietary
• PowerLink(analogue) • WirelessPowerLink(digital) Digitalinputs
• S/P-DIF(or“coaxial”) • Optical • USBAudio Analogueinputs
• RCAPhono(or“unbalancedline”) Wirelessinputs
• WiSA Thetechnicalspecificationsforthese canbefoundinInputs. Itispossibletoenableanaudiosource connectedtoaninputeithermanually (viatheBeoLab50interface)or automatically,asdescribedbelow.
5.1 InputsSelection
5.1.1 AutomaticSelection
Inputs
Power Link S/P-DIF
RCA
Optical
USB-Audio
WPL / WiSA
Automatic
AUTOMATIC SENSE
MANUAL SENSE
... Inputs
Power Link S/P-DIF
RCA
Optical
USB-Audio
WPL / WiSA
Automatic
AUTOMATIC SENSE
MANUAL SENSE
...
Gain Offset
Detection threshold
Max input voltage
Input impedance
Time-out
Figure5.1: TheInputSelectmenu.
SelectionPriority IftheBeoLab50issettoautomatically detectaninputsignal,thenitmaybe necessarytocustomisethe prioritisationofthesources. For example,ifyouhaveaCDplayer connectedtotheS/P-DIFinputanda turntableconnectedtotheRCAinput, andbothsourcesareplaying,this parameterallowsyoutodetermine whichsourceshould“win”andbe playedbytheBeoLab50. Thisprioritisationcanbepersonalised bychangingtheverticalorderofthe inputsonBeoLab50interfaceinthe InputSelectmenu(pressthe“...” icon atthetoprighttoentertheeditmode).
Inputs
Power Link S/P-DIF
RCA
Optical
USB-Audio
WPL / WiSA
Automatic
AUTOMATIC SENSE
MANUAL SENSE
... Inputs
Power Link S/P-DIF
RCA
Optical
USB-Audio
WPL / WiSA
Automatic
AUTOMATIC SENSE
MANUAL SENSE
...
Gain Offset
Detection threshold
Max input voltage
Input impedance
Time-out
Figure5.2:Thepriorityofautomaticallyselectedsourcescanbechangedbyrearrangingtheirorder.
5.1.2 ManualSelection
Theremaybecaseswhereyouprefer tomanuallyselectaninput. Inthis case,youcandragtheinputintothe “ManualSense”listatthebottomof theInputsmenuscreen. Inthiscase,a signalononeoftheseinputswillnot beautomaticallydetectedbythe BeoLab50andmustthereforebe switchedonandoffmanually. Notethatitispossibletomanually selectinputswithouttheinterface usingtheBeoRemote1remotecontrol. Foradescriptionofhowtodothis, includinginstructionsonsettingupthe BeoRemote1,pleaseseeSection20.
5.2 IndividualInput Parameters
Notethatnotallcontrolsareavailable forallinputs.
5.2.1 Re-naming
Itispossibletore-nametheinputs labelsintheBeoLab50interfaceby enteringtheeditmodeoftheInputs menu,selectinganinput,andthen press-and-holdthenameoftheinput atthetopofthescreen. Thispersonalisedname(i.e. “CD Player”or“Turntable”,forexample) willbedisplayedthroughoutthe
23
BeoLab50interface.
... RCA
Gain Offset 5 dB
-76 dBV
5 min.
50 kΩ
2.0 V
Detection threshold
Max input voltage
Input impedance
Time-out
Figure5.3:Renameaninputbypressing andholdingitsnameintheInputmenu
5.2.2 GainOffset
Youcanchangetherelativelevelsof theindividualinputsusingtheGain Offset parameter. Forexample,ifyou haveaparticularsourcethathasa loweroutputlevelthantheothers,its GainOffsetcanbeincreaseto compensate,makingitappeartohave thesamelevelasyourotheraudio sources. Range -12to12dB Resolution 1dB FactoryDefault 0dB NotethattheGainOffsetparameteris notavailableforthePowerLinkand WirelessPowerLinkinputs.
5.2.3 DetectionThreshold
TheBeoLab50canbesetto automaticallyturnitselfonby detectingthepresenceofasignalon theRCAlineinput. However, dependingonyoursourceand/orthe styleofmusicyoutypicallylistento,it maybenecessarytomakethe detectionmoreorlesssensitive. This canbedoneusingtheDetection Thresholdcontrol. Forexample,ifyoulistentomusicwith alargedynamicrange,itmaybe necessarytolowertheDetection ThresholdtomaketheBeoLab50more sensitivetothepresenceofquiet signals. Conversely,ifyouhavean
audiosourcethathasahighernoise floor,itmaybenecessarytoincrease theDetectionThresholdinorderto maketheBeoLab50lesssensitive. Range -76to-46dBV Resolution 3dB FactoryDefault -76dBV SeeFigure5.4foragraphic representationofthethedetection thresholdrelativetothesignal strength. NotethattheDetectionThreshold parameterisnotavailableforthe PowerLinkinput,sincethe loudspeakerisautomaticallyturnedon andoffbythePowerLinksource. Notethat,fortheUSBAudio,S/P-DIF andOpticaldigitalinputs,the Auto-detectioncontrolisusedinstead oftheDetection Threshold.
5.2.4 Auto-detection
TheBeoLab50canbesetto automaticallyturnitselfonby detectingthepresenceofasignalon itsdigitalinputsbysettingthe Auto-detectiontoON.However,thisis slightlydifferentfromthedetectionof analoguesignals,sincethedigital inputsaretriggeredbythepresenceof aanynon-zerosignalonthedigital audiostreamratherthanasignal aboveauser-definedlevel. Options On/Off FactoryDefault On NotethattheAuto-detection parameterisonlyavailablefortheUSB Audio,S/P-DIFandOpticalinputs. Notethat,fortheRCAanalogueinput, theDetection Thresholdcontrolisused insteadoftheAuto-detection.
5.2.5 MaximumInputVoltage
Differentaudiosourceshavedifferent maximumanalogueoutputlevels. Typically,amaximumlevelfroma line-levelRCAoutputis2.0VRMS, however,differentmanufacturers occasionallychoosetodeliverahigher outputlevelonsomemodels.
Inordertomaximisethe signal-to-noiseratioofyouraudio system,theBeoLab50givesyouthe optiontochangetheMaximumInput VoltageforthetheRCAlineinput. The datasheetforyouraudiosourceshould indicateitsmaximumoutputlevel. The valueintheBeoLab50interface shouldbesettomatchthisvalue. Ifthesourcehasahighermaximum outputlevelthanthatwhichissetin theBeoLab50interface,thismay causedistortionduetoclippingofthe signalattheloudspeaker’sinputs. Ifthesourcehasalowermaximum outputlevelthanthatwhichissetin theBeoLab50interface,thiswillcause yourmaximumoutputofthe loudspeakertobelower,andthe outputnoisefloortobeincreased. Options 2.0,4.0,6.5VRMS FactoryDefault 2.0VRMS NotethattheMaximumInputVoltage parameterisonlyavailablefortheRCA lineinput.
5.2.6 Time-out
Incaseswheretheautomaticsignal detectionisusedtoturntheonBeoLab 50,theTime Out controlcanbeused todeterminethelengthoftimethe loudspeakercontinuestobepowered upaftertheaudiosignalhasstopped. Itmaybenecessarytoincreasethe lengthofthistimeifyoulistento musicwithanextremedynamicrange. Forexample,aquietpassageina pieceofmusicmaybebelowthe detectionthreshold. Ifthedurationof thatpassageislongerthantheTime Out value,thentheloudspeakerwillgo intostandbymodewhilethepieceis playing. Options 2,5,10,15,20Minutes FactoryDefault 15Minutes NotethattheTime-outfunctionisnot availableforthePowerLink,Wireless PowerLinkandWiSAinputs.
24
Detection Threshold
BeoLab 90 turns ON
BeoLab 90 turns OFF
Time Out
Audio level  at input
Time
Audio Signal
Figure5.4: The“DetectionThreshold”and“TimeOut”parameters
5.2.7 InputImpedance
IftheBeoLab50’sRCALineinputis connectedtoadevice’sheadphone outputthatusesaClass-Damplifier, theremaybeinstanceswherethis causesthenoisefloortoriseaudibly. Thisiscausedbytheinputimpedance oftheBeoLab50beingmuchhigher thanthatwhichisexpectedbythe headphoneamplifier’sdesigner. In ordertocorrectthisproblem,theinput impedanceoftheRCAinputcanbeset toalowvalueof50 Ω. However,iftheinputimpedanceofthe RCAinputissetto50 Ω anditis connectedtoadevice’sstandard low-impedancelineoutput,thismay haveadetrimentaleffectonthesignal. Forexample,themaximumpossible outputlevelwillbereduced. Insome cases,incorrectlysettingtheinput impedanceto50 Ω mayalsocause distortionoftheaudiosignal. Options 50 Ω,50kΩ FactoryDefault 50kΩ NotethattheInputImpedancecontrol isonlyavailablefortheRCAlineinput.
5.2.8 ControlVolumeof S/P-DIF(orOptical) inputusingPowerLink
Bang&Olufsenaudioproductsthatare abletosendtheaudiosignalonan S/P-DIFoutputadditionallysendthe volumesettingonthedataconnection includedinthePowerLinkcable. Thisis usedforvariousreasons. Oneprimary exampleofthisiscurrentcustomers whoconnectaBeoSound9000toa
pairofloudspeakerssuchasBeoLab 5’sorBeoLab50’sviaaS/P-DIFdigital connection. SincetheBeoSound9000 doesnotapplyvolumeregulationto theS/P-DIFoutput,thevolumesetting mustbesentseparatelyonthePower Linkcableandappliedtotheaudio signalinsidetheloudspeakerinstead. ThisparameterontheBeoLab50 allowscustomerstousethevolume controlofaBang&Olufsensource (sentviaaPowerLinkconnection)and applyittoanaudiosignalcominginto theBeoLab50viaitsS/P-DIFinput. Notethat,inorderforthisoptionto functionproperly,theS/P-DIFinput mustbeassignedahigherprioritythan thePowerLinkinputintheSelection Priority. Thisfunctionisalsoindependently availableforsignalsontheOptical input. WhenthevolumeoftheBeoLab50is controlledbyanexternalPowerLink source,thevolumewheelinthe BeoLab50interfaceisgreyedoutand willnotrespondtotouchcommands. It does,however,displaythevolume settingassignedtotheBeoLab50by thePowerLinkdatasignal. Options Enabled/Disabled FactoryDefault Disabled
5.2.9 USBVolumeenabled
WhentheBeoLab50isconnected usingUSBAudiotoanaudiosource, youhavetheoptionofusingthe source’svolumeasanexternalcontrol forthegainoftheloudspeaker. This
alsomeansthatthevolumeofthe BeoLab50(setbyitsremotecontrol) wouldbereflectedontheuser interfaceoftheaudiosourceor softwareplayer. However,thisexternalcontrolofthe BeoLab50maynotbedesirableinall situations. Forexample,itisveryeasy toinstantlychangethevolumeofa softwareaudioplayertomaximum, whichwillbesurprisinglyloudwitha BeoLab50ifthechangewas accidental. Italsomaybepreferableto settheBeoLab50toastatic(e.g. low) volumesettingandtohavean independentadjustmentonthesource device. Inthesecases,theUSBVolume EnabledshouldbesettoDisable. Options Enabled/Disabled FactoryDefault Disabled NotethattheUSBVolumecontrolis onlyavailablefortheUSBAudioinput.
5.3 ConnectionPanels
TheconnectionpanelsontheMaster andSlaveBeoLab50’sareslightly differentinthataudiosignalscanonly beconnectedtotheMaster loudspeaker. Theaudiosignal connectionsfromyoursourcedevices shouldbeconnectedtotheMaster loudspeaker. Theonlyaudioinputon theSlaveloudspeakeristheDPLor DigitalPowerLinkinput.
25
OPTICAL
S/P-DIF
MIC / IR POWER LINK
LEFT RCA RIGHT
USB 5V    0.5 A
USB AUDIO
DPL DPL DPL / ETHERNET
USB 5V    0.5 A
DPL / ETHERNET
DPL DPL
Figure 5.5: Audio connection panel – Master loudspeaker. Analogue inputs are shown in blue. Digital audio connections are shown in red. Utility connectionsareshowninblack.
OPTICALLEFT XLR RIGHTMIC / IR POWER LINK
USB 5V    0.5 A
USB AUDIO
DPL DPL DPL / ETHERNET
USB 5V    0.5 A
DPL / ETHERNET
DPL DPL
Figure 5.6: Audio connection panel – Slave loudspeaker. Note that the only audio connectors on this loudspeaker arefortheDigitalPowerLinkconnection totheMasterloudspeaker.
Forspecificinformationregardingthe variousinputs,pleaseseeInputs.
26
System
6.0.1 About
The“About”menuallowsaccessto informationregardingtheloudspeaker aswellastheaudiosignalitis currentlyplaying. Selectthe“Speaker Info”,andtheneitherthe“Input Signal”todisplaydetailedinformation abouttheinputaudiosignalor “Temperatures”todisplaythecurrent temperaturesoftheloudspeaker drivers.
6.0.2 MaxVolume
TheMax Volumecontrolallowsyouto determinethelimitofthevolume control. Range 0–90 Resolution 1dB FactoryDefault 90 NotethattheMaxVolumeparameteris notavailableforthePowerLinkand WirelessPowerLinkinputs.
6.0.3 StartupVolume
TheStartup Volumecontrolallowsyou todeterminethevolumelevelwhen
theBeoLab50wakesasaresultofa detectedsignal,orismanuallyturned on. Range 0–90 Resolution 1dB FactoryDefault 42 NotethattheStartup Volume parameterisnotavailableforthe PowerLinkandWirelessPowerLink inputs. AlsonotethattheStartup Volumemaybeoverriddenbythe volumecontrolfromPowerLink(if enabledforS/P-DIForOptical)oraUSB Audiovolumecontrol(ifenabled).
27
Tables
7.1 LoudspeakerSensitivity
Input dBSPL “MaxInput”LevelSetting PowerLink 88.0 6.5Vrms(Fixed) RCA 88.0 6.5Vrms RCA 92.2 4.0Vrms RCA 98.2 2.0Vrms Table 7.1: Unweighted Sound Pressure Level (SPL) of the BeoLab 50 at 1 m in a free field (200 Hz – 2 kHz). Input signal strength: 125 mV rms. Volume Step: 90. All other parameters settoFactoryDefaults.
Input Output USBAudio,S/P-DIF,Optical 92.3dBSPL WirelessPowerLink 92.3dBSPL WiSA TBD Table 7.2: Unweighted Sound Pressure Level (SPL) of the BeoLab50at1minafreefield(200Hz–2kHz). Inputsignal:-30.0 dB FS. Volume Step: 90. All other parameters set to Factory Defaults.
7.2 VolumeControl
VolumeStep Output 90 92.3dBSPL 89 91.3dBSPL 88 90.3dBSPL . . 51 53.3dBSPL 50 52.3dBSPL 49 51.3dBSPL . . 2 4.3dBSPL 1 3.3dBSPL 0 -∞dBSPL Table7.3: UnweightedSoundPressureLevel(SPL)oftheaudio signalfromaBeoLab50at1minafreefield(200Hz–2kHz). Inputsignal: -30.0dBFS.Notethatthesevaluesconsideronly the output level of the audio signal and assume that thermal protectionhasnotbeenengaged.
7.3 ParametricEqualiser
Type Range(Hz) Filters low-shelving 16.0–500.0 1 Peaking(LF) 16.0–500.0 4 Peaking(MF) 250.0–8.0 3 Peaking(HF) 2.0k–63.0k 1 high-shelving 500.0–16.0k 1 Table7.4: FrequencyrangesofParametricEQfilters.
Band Frequency(Hz) Ultrasonic 31.5k35.5k40k45k50k56k63k Treble 16k18k20k22.4k25k28k 8k9k10k11.2k12.5k14k 4k4.5k5k5.6k6.3k7.1k Midrange 2k2.24k2.5k2.8k3.15k3.55k 1k1.12k1.25k1.4k1.6k1.8k 500560630710800900 250280315355400450 125140160180200224 Bass 63.071.080.090.0100112 31.535.540.045.050.056.0 Infrasound 16.018.020.022.425.028.0 Table 7.5: ISO 1/6th octave-spaced centre frequencies (in Hz) ofParametricEQfilters. FrequencyBandsaregivenforapproximateinformationonly.
FilterType Qvalues low-shelving 0.35,0.5,0.7,1.0 Peaking 0.35,0.5,0.7,1.0,1.4, 2.0,2.8,4.0,5.6,8.0 high-shelving 0.35,0.5,0.7,1.0 Table7.6: AvailableQvaluesofParametricEQfilters.
28
Features
8.1 Resonance-basedSound Design
Averylargepartofthesoundtuningof theBeoLab50,likemanyotherBang& Olufsenloudspeakers,isbasedon acousticalmeasurementsperformedat manylocationsaround,aboveand belowtheloudspeaker. Oneoftheimportantaspectsofthese measurementsistofindthebehaviour oftheloudspeakerintime. For example,ifasoundissenttothe loudspeaker,andthenstopped suddenly,doestheloudspeakeralso stop,ordoesit“ring”atsome frequencies(inexactlythesameway thatabellringswhenstruck). Ringing inthetimeresponseofaloudspeaker isanindicationthatithasaresonance –afrequencyatwhichit“wants”to move. Thisresonancehasa detrimentaleffectontheoverallsound oftheloudspeaker,sinceit“smears” soundsintime. Forexample,ifyouhavealoudspeaker thathasanaturalresonanceat110Hz (twooctavesbelowa“ConcertA”,to musicians)thenitwillnaturallyringat thatnotewhenitis“hit”withan impulsivesignalsuchasakickdrum. If thesongthatthebandisplayingisnot inA(majororminor),butinB-Flat instead,thentherewillbea dissonancebetweenthenotesplayed mostofteninthesong,andthenote thatis“singingalong”withthekick drum. Thiscancontributetothe loudspeakersounding“muddy”(touse onlyoneword...). Thisiswhythemeasurement-based portionofthefilteringofallcurrent Bang&Olufsenloudspeakersis primarilydesignedtocounteractthe naturalresonancesinthesystem. So, forexample,ifoneofthewoofersin theBeoLab50hasanaturalresonance at110Hz,thenthatresonanceis mirroredwithanequal,butopposite phasebehaviourintheDigitalSignal Processingengine. Thetotalresultof
thefilterintheDSPandthebehaviour ofthewooferisthatthereisno unwantedringingintheentiresystem. This,inturn,meansthatthe loudspeaker’sresponseiscontrolled notonlyinthefrequencydomainbutin thetimedomainaswell. Thisisonlypossiblewithanextensive setofmeasurementsofeach loudspeakerdriver’smechanicaland acousticalbehaviouranda custom-createdsetoffiltersforit.
8.2 Phase-OptimisedFiltering
Likeallaudiodevices,inorderforthe BeoLab50todeliveritslevelofsound performance,filtersareusedinthe DigitalSignalProcessing(DSP). Generally,anaudiofilterisadevice thatchangestheoverallresponseof thetheaudiosignal. Inthecaseof BeoLab50,theseareusedforvarious reasonssuchascontrollingthe relationshipbetweenthedifferent loudspeakerdrivers,actingas crossoverstodistributethecorrect signalstothetweeters,midrangesand woofers,andoptimisingtheoverall magnituderesponseofthetotal system. Anaudiofilterhasaneffectonthe behaviourofthesignal’smagnitude (howlouditisatagivenfrequency) and/oritsphase(atypeofmeasureof theamountoftimeittakesagiven frequencytogetthroughthefilter). SincetheBeoLab50usesdigital insteadofanaloguefilters,weareable tochoosethecharacteristicsofeach filter’sphaseresponseindependently ofitsmagnituderesponse. For example,afiltercanbeimplemented tohavea“minimumphase”ora “linearphase”(thetwomostcommon responses)characteristic,regardlessof themagnituderesponseitisrequired todeliver. Thephaseresponseofeachfilterin BeoLab50’sprocessingchainhave beenindividuallytailoredaccordingto
itsparticularfunction. Forexample, someofthecrossoverfiltershavebeen implementedaslinearphasefilters. MostfiltersintheActiveRoom Compensationalgorithmare implementedasminimumphasefilters (sinceroomresonanceshavea minimumphasecharacteristic). The BeamWidthControlfiltershave customisedphaseresponsesthatare dependentontheparticular frequency-dependendent characteristicsoftheindividual loudspeakerdriversthattheycontrol andarethereforeneitherminimum phasenorlinearphase.
8.3 AutomaticBass Linearisation(ABL)and ThermalProtection
AlmostallloudspeakersintheBang& Olufsenportfolio(includingBeoLab50) featureAutomaticBassLinearisationor “ABL”.Thisisanalgorithmthatwas patentedbyB&Oin1991andis custom-tunedforeachofourproducts. Itspurposeistoensurethat,whenthe physicallimitsofacomponentofthe loudspeakerarereached(forexample, awooferisapproachingitsmaximum excursion,orapoweramplifierisclose toclipping)theloudspeakereither preventsthatlimitfrombeingreached, orthetransitiontothatlimitis “softened”(dependingonthe componentinquestion). Inaddition,BeoLab50’sprocessing continuallymonitorstheindividual temperaturesofmanyinternal componentsincluding:
• Individualloudspeakerdriver magnets • PowerAmplifiermodules • DSPcircuitboards • PowerSupplycircuitboards Usingthisinformation,combinedwith thepowerthattheamplifiersdeliverto theloudspeaker temperaturesofmanymore componentswithinBeoLab50are calculatedusingcustomisedthermal modelsoftheloudspeaker. Ifthetemperatureofacomponent insidetheloudspeakerapproachesits “thermallimit”(thetemperatureat whichitstopsworkingdueto overheating)thesignalprocessingof theBeoLab50adjuststhesignalsto protectthecomponent. Theexacttype ofadjustmentdependsonthe particularcomponentthatis approachingitslimits. Asasimple example,ifatweetervoicecoilis calculatedtobeapproachingitslimit, thenitsgainisreducedtoattemptto protectitfromdestruction. Itisimportanttostatethatthisdoes
not meanthattheBeoLab50is indestructible–butitdoesmakeit verydifficulttodestroy. Moreinformationcanbefoundin Appendix6: ABL-AdaptiveBass Linearisation.
8.4 ThermalCompression Compensation
BeoLab50’sprocessingincludes automaticcompensationforchangesin loudspeakerdriverresponseasaresult ofinternalchangesintemperature. Formoreanin-depthdiscussionofthis feature,pleasereadAppendix7: ThermalCompressionCompensation.
8.5 Production“Cloning”
EveryBeoLab50thatleavesthe productionlineismeasuredina custom-builtanechoicchamberto ensurethatitsperformancematches themasterreferenceloudspeaker. This automatedmeasurementisperformed usinganumberofmicrophoneswhere smalldifferencesintheresponsesare foundandcustomcorrectionfiltersare createdandloadedintotheDigital SignalProcessing. Thisensuresthat eachloudspeaker’sthird-octave smoothedresponsematchesthatof themasterreferenceloudspeaker within1dBbetween20Hzand20 kHz.1
1Notethatthesevalueshavenotyetbeenfinalised.
30
TechnicalSpecifications
9.1 TotalSystem
Note: Total System measurements performed with Sound Design set to “Flat on-axis” and Active Room Compensation disabled. FrequencyResponse XXHztoXXkHz(±1dB,1/3octavesmoothed) FrequencyRange XXHztoXXkHz(-10dB,ref. 200Hz-2kHz,unsmoothed) Sensitivity seeSection7.1 MaximumSPL XXdBSPL(C)@1m,on-axis SelfNoise(Digitalinput) XXdBSPL(C)@1m,on-axis SelfNoise(Analogueinput) XXdBSPL(C)@1m,on-axis
9.2 PreamplifierandProcessorSection
InordertosimplifycomparisonofBeoLab50’stechnicaldatatootherproducts,theinformationinthischapterhasbeendividedinto threesections:
• Preamplifier and Processor,equivalenttoasurroundprocessor,preamporreceiver • Power Amplifiers • Loudspeaker Drivers
Stereo Preamp
BeoLab 90
Power Amps Loudspeakers
Figure9.1: AblockdiagramoftheBeoLab50showingthecomparativesectionsintermsofcompetingdevices.
9.2.1 OverallSpecifications
Note: Hardware-only measurement. All filters and equalisation bypassed or removed from signal processing for measurements.
DigitalinputtoDACoutputs FrequencyResponse 0Hzto40kHz(+0dB,-1dB) FrequencyRange 0Hzto75kHz(+0dB,-3dB) THD+N 0.004%(997Hz,-1dBFS,22Hz–20kHz) DynamicRange 122dB(A)(997Hz,-60dBFS,20Hz–20kHz,AES17)
AnalogueinputtoDACoutputs FrequencyResponse TBD(+0dB,-1dB) FrequencyRange TBD(+0dB,-3dB) THD+N TBD(997Hz,-1dBFS,22Hz–20kHz) DynamicRange TBD(A)(997Hz,-60dBFS,20Hz–20kHz,AES17)
31
9.2.2 Inputs AnalogueInputs Analogue-to-DigitalConverter NotethatthesameADCmodelisusedforallanalogueinputs. Model TexasInstrumentsPCM4220 SamplingRate 192kHz(fixed) Resolution 24bits FrequencyResponse 10Hz–80kHz(+0dB,-0.2dB) FrequencyRange < 2Hz–85kHz(-3dB) DynamicRange(Typical) 122dB(A)(997Hz,-60dBFS) DynamicRange(Worst-case) 117dB(A)(997Hz,-60dBFS) THD+N 0.001%(997Hz,-1dBFS,22Hz–20kHz) ChannelSeparation 100dB(20Hzto20kHz) PassbandRipple ±0.001dB PowerLink Connector RJ45 InputImpedance 100kΩ AudioChannels 2 MaximumInputVoltage 6.5VRMS Features 5VcontrolvoltageforOn/Standby PowerLinkDatasupport Sensitivity 125mVRMSproduces88dBSPL(1m,on-axis,free-field) RCALine InputImpedance 50 Ω ,50kΩ (Selectable) MaximumInputVoltage 2.0,4.0,6.5VRMS(Selectable)
DigitalInputs SamplingRateConverter NotethattheSRCisappliedtoalldigitalinputs. Model TexasInstrumentsSRC4392 Outputsamplingrate 192kHz(fixed) Outputwordlength 24bits THD+N 0.000014%(f=997Hz,0dBFS,22Hz–40kHz,unweighted) DynamicRange 138dB(f=997Hz,-60dBFS,22Hz–40kHz,unweighted) PassbandRipple ±0.008dB
32
S/P-DIF SupportedFormat LinearPCM Samplingrate Standardsamplingratesupto192kHz Wordlength 24bits OpticalConnector SupportedFormat LinearPCM Samplingrate Standardsamplingratesuptoandincluding96kHz Wordlength 24bits USBAudioConnector SupportedFormat LinearPCM Samplingrate Standardsamplingratesuptoandincluding192kHz Wordlength 24bits WirelessPowerLink SupportedFormat LinearPCM Samplingrate StandardWiSAsamplingratesuptoandincluding96kHz(48kHzstandard) Wordlength 24bits WiSA SupportedFormat LinearPCM Samplingrate StandardWiSAsamplingratesuptoandincluding96kHz Wordlength 24bits
9.2.3 DigitalSignalProcessor
Model AnalogDevicesADSP-21489 Number 2 InstructionRate 400MHz Samplingrate 192kHz(fixed) Notes 32-bitfloatingpoint
9.2.4 DigitaltoAnalogueConverters
NotethatthesespecificationsincludetheanaloguestagesthatfollowtheDACoutputs. Model TexasInstruments/Burr-BrownPCM1798 AudioChannels 18 Samplingrate 192kHz(fixed) Wordlength 24bits FrequencyResponse 0Hzto40kHz(+0dB,-1dB) FrequencyRange 0Hzto75kHz(+0dB,-3dB) THD+N 0.004%(997Hz,-1dBFS,22Hz–20kHz) DynamicRange 122dB(A)(997Hz,-60dBFS,20Hz–20kHz,AES17) ChannelSeparation 110dB(20Hz–20kHz,AES17) LevelLinearity ±1dB(at-120dBFS)
33
9.3 PowerAmplifiers
Oneamplifierperloudspeakerdriver Model Bang&OlufsenICEpowerAM300-X PeakVoltage 50V PeakCurrent 20A PeakPower 780W(into3.2 Ω) FrequencyRange < 2Hz– > 100kHz(+0dB,-3dB) THD+N 0.02%(20Hz–20kHz,100mW-300W,4 Ω,AES17) Features DualLoop3-ICEpower’sthird-generationClass-Dtopology
9.4 LoudspeakerDrivers
9.4.1 Tweeter
Model TymphanyDX19TD07-08 Number 1 NominalImpedance 8 Ω EffectiveDiameter 19mm Features KFUmembrane Magneticfluid
9.4.2 Midranges
Model TymphanyT04-2C0041001 Number 3 NominalImpedance 4 Ω EffectiveDiameter 87mm Features Kevlarreinforcedpapermembrane
9.4.3 Woofers
Model TymphanyT04-2B0101001 Number 3 NominalImpedance 3 Ω EffectiveDiameter 211mm Features EICAWvoicecoilwire Rubbersurround
9.5 DigitalPowerLink
Technology AudioVideoBridge(AVB) SamplingRate 192kHz(fixed) Bitdepth 24 Features IncludesproprietaryB&Odatachannelsforinter-loudspeakercommunication
34
FAQ
10.1 Multichannelsystem setup
Incaseswhereyouusemorethanone pairofBeoLab50’sinaconfiguration, therearesomerecommendationsthat shouldbefollowedinordertofacilitate dailyuse.
10.1.1 Bang&Olufsen televisionassource
AsdescribedinSection4.10.0.1,a currentBang&Olufsentelevisioncan automaticallyswitchBeoLab50 PresetsaspartoftheSpeakerGroup function. However,itshouldbenoted thatagivenSpeakerGroupinthe televisionsendsonlyoneSpeaker PresetvalueonitsPowerLinkoutputs toallloudspeakersconnectedtothe television. Thismeansthatthepreset identificationnumbersinallBeoLab 50’smustmatchforagiven configurationcorrespondingtoa SpeakerGroupinthetelevision.
10.1.2 Third-partydeviceas source
Whenusingathird-partymultichannel deviceasasourceformorethanone pairofBeoLab50’s,eachMaster-Slave pairofloudspeakersshouldbe configuredcorrectlyforagivensource. Theresultingparametersshouldbe savedtoaPresetthatisthentriggered bytheappropriateinput. SeeSection AutomatingPresetSelectionformore information.
10.2 DoesBeoLab50support DSD?
DSDandDSDoverPCM(DoP)arenot currentlysupportedbyBeoLab50. In ordertoplayDSDaudiofiles,itis thereforenecessarytoconverttoPCM intheaudioplayerbeforesendingthe signaltotheloudspeakers.
Notethat,sincetheBeoLab50audio signalpathcontainsasignificant amountofdigitalsignalprocessing (DSP)whichisperformedonlinearPCM signals,aconversionofDSDtoPCMis requiredsomewhereintheaudio chain. Placingthisconversionprocess aheadoftheloudspeakers’inputs givestheusertheoptiontochoosehis orherpreferredfilterfortheprocess.
10.3 DoesBeoLab50support DXD?
DXDisnotcurrentlysupportedby BeoLab50,sinceitsdigitalinputswill notoperateatsamplingratesabove 216kHz. InordertoplayDXDfilesonthe BeoLab50,theaudiosignalwilleither havetobedownsampledto192kHz (maximum)orconvertedtoanalogue inadvanceofsendingthesignalsto theloudspeakers’inputs.
10.4 WhydoestheBeoLab50 sound“different”whenI switchtowatching television?
SomefeaturesoftheBeoLab50are disabledwhentheyareconnectedto currentBang&Olufsensources. Thisis toensurethatsimilaraudioprocessing isnotperformedtwice. Thereare cases,however,wherealthoughtwo processesaresimilar,theyarenot identical. Forexample,itmaybethe casethatthebassortreble adjustmentsintheBeoLab50donot havethesamefrequencyresponsesas thoseintheaudiosource. Formore informationaboutthis,pleasesee Section12.1. Itmayalsobethecasethatthe adjustmentofsomeofthese processorsaredifferentinthe loudspeakersandthesource. For example,ifthebassisincreasedinthe loudspeakers,andthendisabled
becausethePowerLinkinputis chosen,therewillbearesultant changeintimbreoftheloudspeakers. Theremayalsobeinstanceswherea Bang&Olufsensourceautomatically changesthelatencymodeofthe BeoLab50’sinordertopreservelip syncorsynchronisationwithmultiroom systems. Thiswillalsohavea potentiallyaudibleeffectontheaudio qualityoftheloudspeakers.
35
Setup“TipsandTricks”
SettingSpeakerLevels AlthoughitispossibletosetSpeaker LevelsusinganSPLmeter,thiscan,in somecases,beimprovedbymaking smallfinaladjustments“byear”while listeningtomusicinstead. Whilesitting inthepreferredlocation,playatrack withasolidcentrephantomimage (“Tom’sDiner”bySuzanneVegaisa goodchoice)andadjustoneofthe SpeakerLevelvaluestoplacethe centreimageinthecorrectlocation. Thisshouldbedoneafter theSpeaker Distanceshavebeenadjusted. ARCvs. BeamWidthandBeam Direction TheActiveRoomCompensation algorithmcalculatesacustomfilterfor theBeamWidth,BeamDirection,and LatencyModeofthepreset. When editingapreset,itiswisetoturnoff theARCfilterswhileswitchingbetween differentBeamWidths,Beam Directions,andLatencyModesinorder toavoidwaitingforthiscalculationto beperformed. Whentheappropriate settingshavebeenchosen,thengo backtoyourARCsetupandenablethe filters. iOSsettingsduringsetup Insomecases,particularlywhen makingARCmeasurements,itmaybe helpfultochangetheSettingsofyour iOSdevicetoensurethatitdoesnot “sleep”,sincethiscancauseittolose communicationwiththeBeoLab50’s SpeakerDistancesforlarger listeningareas WhenmeasuringtheSpeaker Distancesforlargerlisteningareas (withmorethanoneperson),itis sometimesbettertomeasurethe distancefromagivenloudspeakerto theclosestlistener. Thisisparticularly trueinmultichannelsystems. Fora“PartyMode”wherethereisno singlelisteningposition(eitherdueto thesizeofthecrowd,orthefactthat thelistenersaremovingthroughout
thespace),itisusuallybettertoset theSpeakerDistancesandSpeaker Levelstothematchingvalue(e.g. 1.0 mand0.0dB). Multichannelsystemswithmore than2BeoLab50’s Incaseswheretwoormorepairsof BeoLab50’sareusedinamultichannel system,thencareshouldbetakento ensurethatthePresetnumbersforthe differentpairsofloudspeakersmatch appropriately. Thisisbecausethe BeoVisiontelevisionsendsonlyone SpeakerPresetvaluetoallPowerLink andWirelessPowerLinkoutputs. BackgroundnoiseduringARC measurements Itisimportanttoensurethatthereis aslittleextraneousnoiseaspossible duringtheARCmeasurement procedure. Thisincludesturningoffair conditioningsystemsorperformingthe measurementsduringlow-traffichours, wherepossible. ARCfiltercalculationtime WhencreatinganARCfilterthatuses themeasurementsfrommorethan ARCZone,itisadvisabletowaituntil thefirstcalculationisdonebefore includingthesecondZone.
36
Troubleshooting
12.1 Somefeaturesinthe BeoLab50interfaceare disabled
WhenconnectedtomanyBang& OlufsensourcesviaPowerLinkor WirelessPowerLink,somefeaturesin theBeoLab50maybedisabled. Thisis toavoiderrorssuchasmis-calibration ofthevolumesettingwithother loudspeakersinasurround configurationorduplicationof processing(e.g. turninguptheBass controllertwice: onceinthesource andonceintheloudspeaker).
12.2 LipSyncproblems
WhenusedwithanolderBang& Olufsentelevision(BeoSystem3-based orearlier)orathird-partytelevision, theLatencyModeoftheBeoLab50is notautomaticallycontrolledbythe source. Consequently,theLatency Modeshouldbesetto“Low”toensure synchronisationwiththevideosignal. Thiscanbedonemanuallyusingthe interface(seesection4.9.1),orsetas thedefaultforthepresettriggeredby theaudioinputconnectedtothe television.
12.3 Echoproblems
12.3.1 Multiroomaudio systems
WhenaBeoLab50isusedwitha third-partymultiroomsystem,the loudspeaker’sLatencyModeshouldbe setto“Low”inordertoreducethe delaytimeoftheBeoLab50toa minimum. IftheLatencyModeissetto “High”andifitisimpossibletoadjust theexpectedloudspeakerlatencyin themultiroomsystem,thenthe BeoLab50’slatencywillbehigh enoughthattheyappeartoproducean audibleechorelativetoother loudspeakersinthesystem.
12.3.2 SurroundProcessors
WhenaBeoLab50isusedwithan olderBang&Olufsensurround processor(suchastheBeoSystem3or earlierdevices)orathird-party surroundprocessor,theloudspeaker’s LatencyModeshouldbesetto“Low”in ordertoreducethedelaytimeofthe BeoLab50toaminimum. Ifthe LatencyModeissetto“High”andifit isimpossibletoadjusttheexpected loudspeakerlatencyinthesurround processor,thentheBeoLab50’s latencywillbehighenoughthatthey appeartoproduceanaudibleecho relativetootherloudspeakersinthe system. Itmaybepossibleto“trick”some surroundprocessorsintocompensating forBeoLab50’slatencyinHigh LatencyModebyadding34.3m(112.5 feet)totheiractualdistancefromthe listeningposition. Thisvalue correspondstoa100mslatency. WhenusedinLowLatencyMode,8.6 m(28.1feet)shouldbeaddedtothe actualdistancefromthelistening position. Thisvaluecorrespondstoan 25mslatency.
12.4 Loudspeakersdon’tturn onautomatically
IftheBeoLab50’saresettorecognise theWirelessPowerLink/WiSAinput, thenallcabledinputsaredisabled. Ifacabledsourceisnotinthelistof signalssetforauto-detectionas describedinAuto-detection,thenitwill notautomaticallyturnonthe loudspeakers. ItispossiblethattheDetection Threshold,describedinDetection Threshold,issettotoohighavalueto detectthesignal.
12.5 Loudspeakersnever shutoff
12.5.1 Analoguesources
AdjusttheDetectionThresholdhigher asdescribedinDetectionThresholdto ahighervaluetopreventitfrom detectingnoiseontheinputcable.
12.5.2 Digitalsources S/P-DIFandOptical Ensurethatthesignalonthedigital connectioneithershutsdown,or transmitsa“digitalblack”signal. The BeoLab50detectsanynon-zerosignal onthesedigitalinputsandwillturnon automaticallyasaresult.
12.6 TheBeoLab50interface doesn’twork
EnsurethattheDigitalPowerLink cablebetweentheMasterandSlave loudspeakersisconnected. Ensurethattheloudspeakersandthe deviceareconnectedtothesame network.
12.7 Loudspeakersare distorting
TheMaximumInputLevelasdescribed inMaximumInputVoltagemaybeset totoolowavaluetobecompatible withtheaudiosource.
12.8 Loudspeakersarenoisy/ tooquiet
Ifthesourcehasavariableoutput level,thenthebeststrategyforgain managementistoincreasethe source’soutputleveltomaximumand usethevolumecontroloftheBeoLab 50’s. Thiswillensurethelowest possiblenoiseflooroftheoverall system. Itisalsoimportanttoensurethatthe
37
MaximumInputLevelasdescribedin MaximumInputVoltageissettothe correctvalueforthesourcedevice. Usingtoohighasettingwillresultinan elevatednoisefloor. SeeInputImpedanceonInput Impedance
12.9 USBAudionotworking
TheUSBAudioinputwillonlyaccept PCMsignalsupto192kHz. IfyoursourceisoutputtingDoP(also knownasDSDoverPCM)orPCM signalsathighersamplingrates(e.g. DXDat384kHz)therewillbenoaudio outputfromtheloudspeaker.
12.10 S/P-DIFinputnot working
TheS/P-DIFinputwillonlyacceptPCM signalsupto192kHz. IfyoursourceisoutputtingDoP(also knownasDSDoverPCM)orPCM signalsathighersamplingrates(e.g. DXDat384kHz)therewillbenoaudio outputfromtheloudspeaker. IfthevolumecontroloftheS/P-DIF
inputusingPowerLinkhasbeen enabled,thenitisimportanttosetthe priorityoftheS/P-DIFinputhigherthan thatofthePowerLink. Ifthisisnot done,thenthePowerLinksignalwill overridetheS/P-DIFinputandthe latterwillnotbeheard.
12.11 Opticalinputnot working
NotethattheOpticalinputwillnot acceptsamplingratesabove96kHz duetounreliabilityofanopticaldigital audioconnectionathighersampling rates. IfthevolumecontroloftheOptical inputusingPowerLinkhasbeen enabled,thenitisimportanttosetthe priorityoftheOpticalinputhigherthan thatofthePowerLink. Ifthisisnot done,thenthePowerLinksignalwill overridetheOpticalinputandthe latterwillnotbeheard.
12.12 Automaticswitchingof inputsnotbehavingas expected
IfyouareusingtheAutomaticinput selection,theremaybecaseswhere
theloudspeakerdoesnotbehaveas youwouldintuitivelyexpectduetothe Timeoutparameterofthecurrently selectedsource. Thisisbestexplained bygivingexamples. Takethecasewhereyouareplaying audiofromtwosources,aCDplayer connectedtotheS/P-DIFinputanda turntableconnectedtotheRCAinput (viaanRIAApreamplifier),andletus assumethattheS/P-DIFinputhasa higherselectionprioritythantheRCA input. Inthiscase,theloudspeakers willplaytheCDsignal. Ifyouthen pressSTOPontheCDplayer,the loudspeakerswillnotswitchtothe signalontheRCAinput(theturntable) untiltheS/P-DIFinput’stimeout durationhaspassed. (SeeSection 5.2.6foradetaileddescriptionofthe Time-outparameter.) Thisbehaviourwouldalsobetrueif youwerefirstplayingasignalonthe CDplayer,youpressSTOP,andthen youstartplayingasignalonthe turntable. Again,untiltheS/P-DIF input’stime-outdurationhaspassed, thesignalontheRCAinput(fromthe turntable)willnotbeautomatically selectedbytheBeoLab50.
38
Appendix1: RecommendationsforCriticalListening
13.1 Loudspeaker Configuration
TheBeoLab50providesyouwithan extremelywiderangeofparameters thatcanbeusedtoadjustthetimbral andspatialpresentationofyour recordingsforvariouslisteningrooms, loudspeakerplacementsandlistening positions. However,itisalwaysbestto startwithanoptimalconfigurationin yourlisteningroom. Firstconsidertherelationshipbetween theloudspeakersandthelistening positionitself. Thetwoloudspeakers andthelisteningpositionshouldbethe threecornersofanequilateraltriangle. Thismeansthatthedistancefrom eachloudspeakertothelistening positionshouldbethesameasthe distancebetweeneachloudspeaker. Thisalsomeansthattheloudspeakers willbe30◦ awayfromthefront,centre location,directlyinfrontofthe listeningposition. Secondly,thetwoloudspeakersshould be“toed-in”by30◦. Thismeansthat theyshouldbeslightlyrotatedsothat theyarebothfacingthelistening position. ThisisshowninFigure13.1. "Reflection-free Zone"
Figure 13.1: A “perfect” loudspeaker configuration with BeoLab 50’s. Both loudspeakersareaimedatthelistening position. The distance from the listening position to each loudspeaker is the same as the distance between the two loudspeakers.
Ifpossible,theheightofthelistening chairshouldbesetsothatthe
listener’searsarelevelwiththecentre oftheverticalbeam,showninFigure ??. Thispointis108.6cmabovethe floor. Thenextconsiderationissymmetry withinyourlisteningroom. Itis commonlyrecognisedthatthebest stereoimagingwillbeachievedifthe listeningconfiguration(thetriangle formedwiththelistenerandthetwo loudspeakers)isplacedinleft–right centreoftheroom. Therefore,theside wallswillbothbethesamedistance fromthelisteningposition,andthe loudspeakerswillhavethesame distancetoitsadjacentwalls. Thisisto saythatthedistancefromtheleft loudspeakertotheleftwallisthesame asthedistancebetweentheright loudspeakerandtherightwall. The distancetothefrontwall(behindthe loudspeakers)shouldbethesamefor bothloudspeakers,butcertainlydoes nothavetobethesameasthe distancetothesidewalls.
Figure 13.2: An optimal placement for the loudspeakers with respect to adjacent walls. Note that the distance between each loudspeaker and its closestsidewallareidentical, andthatthe distances from the loudspeakers to the frontwallarealsomatched.
Figure13.3: Anless-optimalplacement fortheloudspeakerswithrespecttoadjacent walls. Note that the distances from the loudspeakers to the front wall arematched,however,thedistancebetweeneachloudspeakeranditsclosest sidewallarenotidentical.
Figure13.4: Anotherexampleofalessoptimal placement for the loudspeakers with respect to adjacent walls. The distances from the loudspeakers to the front wall are matched, however, the right loudspeaker and lacks a side wall nearby.
Figure13.5:Anexampleofaworst-case placementofloudspeakerswithrespect tothelisteningroom. Notwodistances betweenaloudspeakerandanadjacent wallmatcheachother.
Itshouldbenotedthattheprimary
39
casualtyofpoorloudspeaker placementinalisteningroomwillbe thespatialrepresentationofyour recordings. Theprecisionandaccuracy ofthestereoimaging,aswellasthe sensationofenvelopmentfromthe recordingwillbeadverselyaffectedby earlyreflectionpatternsthatarenot matchedforthetwoloudspeakers. Thisproblemisminimisedbyusing BeoLab50’snarrowbeamwidth, however,eventhismodecanbenefit fromcorrectloudspeakerplacementin theroom. Finally,itisrecommendable(but certainlynotrequired)thatthe loudspeakersbepositionedaminimum of1mfromtheclosestwalls. The ActiveRoomCompensationalgorithm willcompensateforchangesinthe BeoLab50’stimbralresponsecaused byadjacentboundaries. However, placingtheloudspeakersslightly distantfromreflectivesurfaceswill reducetheseboundaryeffects,and thereforealsoreducetheamountof compensationthatisrequiredbythe ARCfilters.
13.2 ListeningRoom Acoustics
TheBeoLab50hastwofeaturesthat canovercomesomedetrimental effectsofthelisteningroom’s acousticalbehaviour(BeamWidth ControlandActiveRoom Compensation). However,thesoundof anyloudspeakercanbeoptimisedby improvingtheroom’sacoustics. Oneofthemainacousticalproblemsin listeningroomsisthatofroommodes orresonances. Theseoccurbecause theroombehavesverymuchlikean organpipe,naturally“singing”at specificfrequenciesthatare determinedbythedimensionsofthe room. Withoutcorrectacoustical treatment,theseresonancesare almostunavoidable. Itispreferredto ensurethattheresonancesinthe room’sthreedimensions(length, width,andheight)donotoverlapeach
other. Thismeansthatthebetter listeningroomshavecomplex relationshipsbetweenthesethree dimensions. Forexample,a“worst case”foralisteningroomwouldbea cube,whereallthreedimensionsare identical,thusallresonanceshavethe samefrequencies. Anext-worstcaseis onewhereadimensionisamultipleof another,forexample,aroomthatis 9mx6mx3m. Inabestcase,the ratiosoftheroom’sdimensionswould havenon-simplevalues(e.g. 1: 2.16: 2.96–so,asanexample,3mx6.48m x8.88m).1 Asecondissueinmanylisteningrooms isthatofhard,reflectivesurfaces– particularlyinlocationswherethe soundfromtheloudspeakerisdirectly reflectedtothelisteningposition. Therearetwowaystoalleviatethis problem: absorptionanddiffusion. In ordertoabsorbasoundwavesothatit doesnotreflectoffasurface,an absorptivematerialsuchasfibreglass insulationoracousticalfoammustbe placedonthesurface,orinthepath takenbythereflection. Areflectioncan bediffusedbymakingthereflective surfaceirregular. Forexample,placing abookcaseatthepointofreflection willhelpasadiffusorifthebooksare arrangedinrandomheightsand depths. Finally,itiswisetoabsorbthesound wavesthatwouldbereflectedoffthe floor(e.g. withcarpetorarug)and ceiling(usingabsorptiveceilingtiles). Thiswillalsohelptoreducetheoverall reverberationtimeoftheroom.
13.3 SourceDevices
Whenconnectinganaudiosourceto theBeoLab50,therearesomebasic, generalrulesthatshouldbefollowedin ordertogettheoptimalperformance fromyoursystem. Notethattheseare generalrules–sothereareexceptions.
• Ifpossible,thesourceshouldbe connectedtotheBeoLab50 usingadigitalaudioconnection.
• Ifthesourcedevicehasavolume controlitshouldbedisabledand theBeoLab50’svolumecontrol shouldbeusedinstead • Ifthesourcehastwoanalogue outputs: onevolume-regulated andtheotheratafixedlevel,the fixed-leveloutputshouldbeused • Ifyouareconnectingasource usingaline-levelanalogueinput, checkthesourcedevice’s datasheettofinditsmaximum outputlevelandsetthevalue appropriatelyontheBeoLab50 (SeeMaximumInputVoltage). If themaximumoutputofyour deviceisgreaterthanthe BeoLab50’smaximumpossible setting(6.5VRMS)thenitis recommendablethatthesource device’soutputlevelisreducedif possible,eitherwithinitsown settingsorusinganexternal attenuator. Table13.1andFigure 13.6showthenecessary attenuationtoreducevarious voltagelevelsto6.5VRMS.
MaxOutput Attenuation 7.0VRMS -0.64dB 9.0VRMS -2.83dB 11.0VRMS -4.57dB 13.0VRMS -6.02dB Table 13.1: Examples of minimum attenuation required to externally converttheMaximumOutputLevelsfroma sourcedeviceto6.5VRMSattheinput oftheBeoLab50.
6 8 10 12 14 16 18 20 22 24 −12
−11
−10
−9
−8
−7
−6
−5
−4
−3
−2
−1
0
Maximum Output Voltage (V rms)
Attenuation (dB)
Figure 13.6: The minimum attenuation required to apply to a source with a given Maximum Output level to reduce it to 6.5 V rms in order to prevent clippingtheBeoLab50analogueinputs.
1See“Roomdimensionsforsmalllisteningrooms”byDr. TrevorCoxforagoodintroductiontothistopic.
40
13.4 Cablerecommendations
Thereareinnumerablebeliefsand opinions,bothfoundedandunfounded, regardingcablesusedforconnecting audiodevices. Thefollowingisasmall setofrecommendationsthatarebased oncommonpracticesforwiring professionalaudiosystemssuchasare foundinrecordingandmastering studios. Decisionsregardingthe specificthebrandorconstructionof thecablesusedforconnectingBeoLab 50arelefttothereader’spreferences.
13.4.1 Analoguecables
Inordertoensurethatthenoisefloor ofanaloguesourcesisaslowas possible,thefollowingguidelinesare recommended: Usecableswithgoodshielding(or screening)toreduceRF(Radio Frequency)interferenceontheaudio signalsfromexternalsources. Avoidgroundloopswhenconnecting audiodevicestoeachother. Inordertoreducemagneticinductance ofinterference(typically50Hzor60 Hz“hum”)frompowercablesonthe audioinputs,itisalsogoodpracticeto physicallyseparatesignalcablesand mainscablesasmuchaspossible. In caseswherethesecablesmustcross eachother,itisrecommendedthat theycrossata90◦ angle. Forathoroughguidetoinstallationof high-endaudioequipment,“Audio SystemsDesignandInstallation”by PhilipGiddingsishighlyrecommended. Althoughthisisbookintendedfor installationofaudiodevicesin recordingandmasteringstudios,the practicesandrecommendations detailedthereinarealsoapplicableto consumer-levelaudioequipment.
13.4.2 Opticalcables
Itisrecommendedthathigh-quality opticalcablesareusedfortheBeoLab 50,particularlyforlongercableruns.
Thisisduetothefactthatthereis attenuation(dimmingorlossoflight intensity)oftheopticalsignalonthe plasticorglassfibreinthecable. This attenuationisproportional(indB)to thelengthofthecable. Therefore,in ordertoensurethattheoptical receiverontheBeoLab50hasan adequatesignalatitsinput,thelight attenuationonthecableshouldbe minimisedeitherbyusingshortcables orhigh-qualityopticalfibre. Traditionally,manypeoplehave claimedthatopticaldigitalsignalsare lessreliablethanelectricalconnections (suchastheAES/EBUandS/P-DIF protocols)duetohigherlevelsofjitter causedbythelimitationsoftherise andfalltimeoftheLEDinthe transmitter. TheBeoLab50usesa very-high-qualitysamplingrate converteratitsinputforalldigital signalswhichattenuatesthejitterof incomingsources,therebyreducing thisconcernconsiderably.
13.4.3 S/P-DIFcables
WhenconnectingasourcetoBeoLab 50’sS/P-DIFinput,itisrecommended thatacablewitha75 Ω impedanceis used. Thiswillensurethatthereareno reflectionsofthesignalonthecable whichmayincreasethelevelofjitterat theinputoftheBeoLab50. Notethat thisrecommendationisparticularly trueforlongercableruns. Itshould, however,bestatedthatthesampling rateconverteratthedigitalinputsof theBeoLab50isveryeffectiveat attenuatingjitterartefactscaused eitherbythesignalsourceorproblems inthecabling.
13.5 ACmainscables
Itishighlyrecommendedthatan additionaldeviceusedtofiltertheAC powerfromthemains(sometimes calledan“audiophilemainsfilter”or “powerpurifier”,forexample)not be usedwiththeBeoLab50. Thisis becausetheinternalpowersupplyof theBeoLab50hasacustom-designed
filterthatreducesnoiseonitsAC mainsinput. Thisfilterhasbeen optimisedforthetime-variantcurrent demandsoftheBeoLab50,makinga genericexternalfilterredundant(at best)ordetrimental(atworst)tothe performanceoftheloudspeaker. Similarly,itisunnecessarytousea so-called“exotic”or“audiophile” mainscablefortheBeoLab50.
41
Appendix2: IntroductiontoParametricEqualisers
Almostallsoundsystemsofferbass andtrebleadjustmentsforthesound– thesearebasicallycoarseversionsofa moregeneraltoolcalledanequaliser thatisoftenusedinrecordingstudios. Onceuponatime,ifyoumadea long-distancephonecall,therewasan actualphysicalconnectionmade betweenthewirerunningoutofyour telephoneandthetelephoneatthe otherendoftheline. Thiscausedabig probleminsignalqualitybecausealot ofhigh-frequencycomponentsofthe signalwouldgetattenuatedalongthe wayduetolossesinthewiring. Consequently,boostercircuitswere madetohelpmaketherelativelevels ofthevariousfrequenciesmoreequal. Asaresult,thesecircuitsbecame knownasequalisers. Nowadays,of course,wedon’tneedtouse equaliserstofixthequalityof long-distancephonecalls(mostly becausethecommunicationpathsuse digitalencodinginsteadofanalogue transmission),butwedousethemto customisetherelativebalanceof variousfrequenciesinanaudiosignal. Thishappensmostofteninarecording studio,butequaliserscanbeagreat personalisationtoolinaplayback systeminthehome. Thetwomainreasonsforusing equalisationinaplaybacksystemsuch astheBeoLab50’sarepersonal preferenceandcompensationforthe effectsofthelisteningroom’s acousticalbehaviour. Equalisersaretypicallycomprisedofa collectionoffilters,eachofwhichhas upto4“handles”or“parameters”that canbemanipulatedbytheuser. These parametersare
• FilterType • Gain • CentreFrequency • Q
14.1 FilterType
TheFilter Typewillletyoudecidethe relativelevelsofsignalsatfrequencies withinthebandthatyou’reaffecting. Althoughthereareupto7different typesoffiltersthatcanbefoundin professionalparametricequalisers,the BeoLab50containsthethree most-usedofthese:
• low-shelvingFilter • high-shelvingFilter • PeakingFilter
14.1.1 low-shelvingFilter
Intheory,alow-shelving Filter affects gainofallfrequenciesbelowthecentre frequencybythesameamount. In reality,thereisabandaroundthe centrefrequencywherethefilter transitionsbetweenagainof0dB(no changeinthesignal)andthegainof theaffectedfrequencyband.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 14.1: Example of a low-shelving filter with a positive gain. Frequencies below approximately 80 Hz have been affected.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 14.2: Example of a low-shelving filterwithanegativegain. Frequencies below approximately 80 Hz have been affected.
Notethatthelow-shelvingfiltersused intheBeoLab50definethecentre frequencyasbeingthefrequency wherethegainisonehalfthe maximum(orminimum)gainofthe filter. Forexample,inFigure14.1,the gainofthefilteris6dB.Thecentre frequencyisthefrequencywherethe gainisone-halfthisvalueor3dB, whichcanbefoundat80Hz. Somecareshouldbetakenwhenusing low-shelvingfilterssincetheiraffected frequencybandsextendto0HzorDC. Thiscancauseasystemtobepushed beyonditslimitsinextremelylow frequencybandsthatareoflittle-to-no consequencetotheaudiosignal. Note, however,thatthisislessofaconcern fortheBeoLab50,sinceitisprotected againstsuchabuse.
14.1.2 high-shelvingFilter
Intheory,ahigh-shelving Filter affects gainofallfrequenciesabovethe centrefrequencybythesameamount. Inreality,thereisabandaroundthe centrefrequencywherethefilter transitionsbetweenagainof0dB(no changeinthesignal)andthegainof theaffectedfrequencyband.
42
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure14.3: Exampleofahigh-shelving filter with a positive gain. Frequencies above approximately 8 kHz have been affected.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure14.4: Exampleofahigh-shelving filterwithanegativegain. Frequencies above approximately 8 kHz have been affected.
Notethatthehigh-shelvingfiltersused intheBeoLab50definethecentre frequencyasbeingthefrequency wherethegainisonehalfthe maximum(orminimum)gainofthe filter. Forexample,inFigure14.4,the gainofthefilteris-6dB.Thecentre frequencyisthefrequencywherethe gainisone-halfthisvalueor-3dB, whichcanbefoundat8kHz. Somecareshouldbetakenwhenusing high-shelvingfilterssincetheir affectedfrequencybandscanextend beyondtheaudiblefrequencyrange. Thiscancauseasystemtobepushed beyonditslimitsinextremelyhigh frequencybandsthatareoflittle-to-no consequencetotheaudiosignal.
14.1.3 PeakingFilter
Apeaking filter isusedforamorelocal adjustmentofafrequencyband. Inthis case,thecentrefrequencyofthefilter
isaffectedmost(itwillhavetheGain ofthefilterappliedtoit)andadjacent frequenciesoneithersideareaffected lessandlessasyoumovefurther away. Forexample,Figure14.5shows theresponseofapeakingfilterwitha centrefrequencyof1kHzandgainsof 6dB(theblackcurve)and-6dB(the redcurve). Ascanbeseenthere,the maximumeffecthappensat1kHzand frequencybandstoeithersideare affectedless.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure14.5: Exampleoftwopeakingfilters. Theblackcurveshowsafilterwith apositivegain,theredcurveshowsthe reciprocal with a negative gain. The centrefrequencyofthisfilteris1kHz.
YoumaynoticeinFigure14.5thatthe blackandredcurvesaresymmetrical– inotherwords,theyareidentical exceptinpolarityofthegain. Thisisa particulartypeofpeakingfiltercalleda reciprocal peak/dip filter –so-called becausethesetwofilters,placedin series,canbeusedtocanceleach other’seffectsonthesignal. NotethatBeoLab50usesreciprocal peak/dipfilters.
14.2 Gain
Ifyouneedtomakeallfrequenciesin youraudiosignallouder,thenyoujust needtoincreasethevolume. However, ifyouwanttobealittlemoreselective andmakesomefrequencybands louder(orquieter)andleaveother bandsunchanged,thenyou’llneedan equaliser. So,oneoftheimportant questionstoaskis“howmuchlouder?” or“howmuchquieter?” Theanswerto
thisquestionisthegainofthefilter– thisistheamountbywhichissignalis increasedordecreasedinlevel. Thegainofanequaliserfilterisalmost alwaysgivenindecibelsordB1.Thisis ascalebasedonlogarithmicchanges inlevel. Luckily,it’snotnecessaryto understandlogarithmsinordertohave anintuitivefeelfordecibels. Thereare reallyjustthreethingstoremember:
• againof0dBisthesameas saying“nochange” • positivedecibelvaluesare louder,negativedecibelvalues arequieter • Addingapproximately6dBtothe gainisthesameassaying“two timesthelevel”. (Therefore, subtracting6dBishalfthelevel.)
14.3 CentreFrequency
So,thenextquestiontoansweris “whichfrequencybandsdoyouwant toaffect?” Thisispartiallydefinedby thecentre frequencyorFcofthefilter. Thisisavaluethatismeasuredinthe numberofcyclespersecond2,labelled Hertz orHz. Generally,ifyouwanttoincrease(or reduce)thelevelofthebass,thenyou shouldsetthecentrefrequencytoa lowvalue(roughlyspeaking,below 125Hz). Ifyouwanttochangethe levelofthehighfrequencies,thenyou shouldsetthecentrefrequencytoa highvalue(say,above8kHz).
14.4 Q
Inalloftheabovefiltertypes,there aretransitionbands–frequencyareas wherethefilter’sgainischangingfrom 0dBtothedesiredgain. Changingthe filter’sQ3 allowsyoutoaltertheshape ofthistransition. ThelowertheQ,the smootherthetransition. Inboththe caseoftheshelvingfiltersandthe peakingfilter,thismeansthatawider
1The“B”isacapitalbecauseit’snamedafterAlexanderGrahamBell. 2Thisisliterallythenumberoftimesaloudspeakerdriverwillmoveinandoutoftheloudspeakercabinetpersecond. 3Notethat,althoughtheterm“Q”isusedthroughoutthismanualandtheBeoLab50interfaceforbothpeakingandshelvingfilters,thisisincorrect. Tobetechnicallycorrect, theterm“S”(orshelfslope)shouldbeusedforshelvingfilters.
43
bandoffrequencieswillbeaffected. Thiscanbeseenintheexamplesin Figures14.6and14.7.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure 14.6: Example of two lowshelving filters. The black curve shows a filter with a Q of 0.35, the red curve showstheafilterwithaQof1. Forboth filters,thecentrefrequencyis1kHzand thegainis+6dB.
10 100 1,000 10,000
−6
−4
−2
0
2
4
6
Frequency (Hz)
Gain (dB)
Figure14.7: Exampleoftwopeakingfilters. Theblackcurveshowsafilterwith a Q of 0.35, the red curve shows the a filter with a Q of 8. For both filters, the centre frequency is 1 kHz and the gain is+6dB.
ItshouldbeexplainedthattheQ parametercancauseashelvingfilter toslightlydifferentlythanapeaking filter. WhentheQofashelvingfilter exceedsavalueof1,thegainofthe filterwill“overshoot”itslimits. For example,ascanbeseeninFigure14.8, afilterwithagainof6dBandaQof8 willactuallyhaveagainofover10dB andwillattenuatebymorethan4dB. Thisover-andundershootingofthe filter’smagnituderesponseisthe reasontheQofthehigh-shelvingand low-shelvingfiltersintheBeoLab50’s parametricequaliserhavebeenlimited toamaximumvalueof1.
10 100 1,000 10,000
−10
−5
0
5
10
Frequency (Hz)
Gain (dB)
Figure14.8:Exampleoflow-shelvingfilterswithaQofmorethan1. Theblack curveshowsafilterwithaQof1forreference,theredcurvesshowstheafilter with Q’s of 2, 4, and 8. The centre frequencyofthisfilteris1kHzandthegain is+6dB.
44
Appendix3: TheInfluenceofListeningRoomAcousticsonLoudspeakers
Aroomcomprisedoflargeflat reflectivesurfaceswithlittleacoustical absorptionhasaverydifferent acousticalbehaviourfromarecording ormasteringstudiowherethefinal decisionsaboutvariousaspectsofa recordingaremade. Consequently, thismusthaveaneffectonalistener’s perceptionofarecordingplayed throughapair(assumingstereo reproduction)ofloudspeakersinthat room. Theinitialquestiontobeasked is“what,exactly,aretheexpected effectsoftheroom’sacoustical behaviourinsuchacase?” Thesecond is“iftheroomhastoomuchofan effect,howcanIimprovethesituation (e.g. byaddingabsorptionorchanging thephysicalconfigurationofthe systemintheroom)?” Thethird,and possiblyfinalquestionis“howcana loudspeakercompensate(oratleast account)fortheseeffects?” Theeffectaroom’sacoustical behaviourhasonaloudspeaker’s soundcan,atasimplelevel,be consideredunderthreegeneral headings:
• EarlyReflections • RoomModes • Reverberation
15.1 EarlyReflections
Earlyreflections,fromsidewallsand thefloorandceiling,haveaninfluence onboththetimbre(tonecolour)and thespatialcharacteristicsofastereo reproductionsystem. Wewillonly discussthetimbraleffectsinthis article.
Figure15.1: Thesoundarrivingatalistenerfromaloudspeakerinaroomwith only one wall. Note that the sound arrives from two directions – the first is directly from the loudspeaker (in red). Thesecondisa“firstreflection”offthe wall(inblue).
Let’sstartbyassumingthatyouhave aloudspeakerthathasamagnitude responsethatisperfectlyflat–atleast from20Hzto20kHz. Wewillalso assumethatithasthatresponse regardlessofwhichdirectionyou measureitin–inotherwords,it’sa perfectlyomnidirectionalloudspeaker. Thequestionis,“whateffectdoesthe wallreflectionhaveonthemeasured responseoftheloudspeaker?” Verygenerallyspeaking,theansweris thatyouwillgetahigherlevelatsome frequencies(becausethedirectsound andthereflectionaddconstructively andreinforceeachother)andyouwill getalowerlevelatotherfrequencies (becausethedirectsoundandthe reflectionworkagainsteachotherand “canceleachotherout”). Whatis potentiallyinterestingisthatthe frequenciesthataddandthe frequenciesthatcancelalternateas yougoupthefrequencyrange. Sothe totalresultlookslikeacomb(asina combthatyouusetocombyourhair, if,unlikeme,youhavehairtocomb). Forexample,takealookatFigure15.2.
10 100 1,000 10,000 −20
−15
−10
−5
0
Frequency (Hz)
Gain (dB)
Figure15.2: Distancetoloudspeaker= 2m. Distancetowall=1m. Wallisperfectly reflective and the loudspeaker is perfectly omnidirectional. The red line isthemagnituderesponseofthedirect sound. The blue line is the magnitude response of the reflected sound. The blacklineisthemagnituderesponseof thecombination.
Youcanseethat,attheverylowend, thereflectionbooststhelevelofthe loudspeakerbyaapproximately5dB (oralmosttwotimesthelevel)atthe listeningposition. However,asyougo upinfrequency,thetotalleveldropsto about15dBlessbeforeitstartsrising again. Asyougoupinfrequency,the levelgoesupanddown. This alternationactuallyhappensata regularfrequencyspacing(e.g. anotch atmultiplesof200Hz)butitdoesn’t lookregularbecausetheX-axisofthe plotislogarithmic(whichbetter representshowweheardifferencesin frequency). Whathappensifwemovethewall furtheraway? Well,twothingswill happen. Thefirstisthatthereflection willbequieter,sothepeaksand notcheswon’tbeaspronounced. The secondisthatthespacingofthepeaks andnotchesinfrequencywillget closertogether. Inotherwords,the effectstartsatalowerfrequency. Forexample,takealookatFigure15.3.
45
10 100 1,000 10,000 −20
−15
−10
−5
0
Frequency (Hz)
Gain (dB)
Figure15.3: Distancetoloudspeaker= 2m. Distancetowall=3m. Wallisperfectly reflective and the loudspeaker is perfectly omnidirectional. The red line isthemagnituderesponseofthedirect sound. The blue line is the magnitude response of the reflected sound. The blacklineisthemagnituderesponseof thecombination.
Conversely,ifwemovethewallcloser, wedotheopposite(theproblemgets worse,butatahigherfrequency),as canbeseeninFigure15.4.
10 100 1,000 10,000 −20
−15
−10
−5
0
Frequency (Hz)
Gain (dB)
Figure15.4: Distancetoloudspeaker= 2m. Distancetowall=0.25m. Wallis perfectlyreflectiveandtheloudspeaker is perfectly omnidirectional. The red line is the magnitude response of the direct sound. The blue line is the magnituderesponseofthereflectedsound. The black line is the magnitude responseofthecombination.
So,ifyouhavearoomwithonlyone wallwhichisperfectlyreflective,and youhaveaperfectlyomnidirectional loudspeaker,thenyoucanseethat yourbestoptionistoeitherputthe loudspeaker(andyourself)veryfaror veryclosetothewall. Thatwaythe artefactscausedbythereflectionare eithertooquiettodoanydamage,or haveaneffectthatstartsattoohigha frequencyforyoutocare. Thenagain, mostroomhavemorethanonewall, thewallsarenotperfectlyreflective, andtheloudspeakerisnotperfectly omnidirectional.
So,whathappensinthecasewhere theloudspeakerismoredirectionalor youhavesomeabsorption(better knownas“fuzzystuff”)onyourwalls? Well,eitherofthesecaseswillhave basicallythesameeffectinmostcases sinceloudspeakersaretypicallymore directionalathighfrequencies–soyou getlesshighenddirectedtowardsthe wall. Alternatively,fuzzystufftendsto soakuphighfrequencies. So,ineither ofthesetwocases,you’llgetlesshigh endinthereflection. Let’ssimulate thisbyputtingalowpassfilteronthe reflection,asshowninFigure15.5, 15.6and15.7whichhaveidentical distancesasthesimulationsinFigures 15.2,15.3,and15.4–forcomparison.
10 100 1,000 10,000 −20
−15
−10
−5
0
Frequency (Hz)
Gain (dB)
Figure15.5: Distancetoloudspeaker= 2m. Distancetowall=1m. Wallisabsorptiveand/ortheloudspeakerisdirectional at high frequencies. The red line isthemagnituderesponseofthedirect sound. The blue line is the magnitude response of the reflected sound. The blacklineisthemagnituderesponseof thecombination.
10 100 1,000 10,000 −20
−15
−10
−5
0
Frequency (Hz)
Gain (dB)
Figure15.6: Distancetoloudspeaker= 2 m. Distance to wall = 3 m. Wall is absorptive and/or the loudspeakers is directional at high frequencies. The red line is the magnitude response of the direct sound. The blue line is the magnitude response of the reflected sound. The black line is the magnitude responseofthecombination.
10 100 1,000 10,000 −20
−15
−10
−5
0
Frequency (Hz)
Gain (dB)
Figure15.7: Distancetoloudspeaker= 2 m. Distance to wall = 0.25 m. Wall is absorptive and/or the loudspeaker is directionalathighfrequencies. Thered lineisthemagnituderesponseofthedirect sound. The blue line is the magnituderesponseofthereflectedsound. The black line is the magnitude responseofthecombination.
Whatyoucanseeinallthreeofthe previousplotsisthat,asthehigh frequencycontentofthereflection disappears,thereislessandlesseffect onthetotal. Thebottomplotis basicallyaproofoftheage-oldruleof thumbthatsaysthat,ifyouputa loudspeakernexttoawall,you’llget morebassthanifit’sfartherfromthe wall. Sincethereisnotmuchhigh frequencyenergyradiatedfromthe rearofmostloudspeakers,Figure15.7 isaprettygoodgeneralrepresentation ofwhathappenswhenaloudspeakeris placedclosetoawall. Ofcourse,the exactbehaviourofthedirectivityofthe loudspeakerwillbedifferent–butthe generalshapeofthetotalcurvewillbe prettysimilartowhatyouseethere. So,theendconclusionofallofthisis that,inordertoreduceundesirable artefactscausedbyawallreflection, youcandoanycombinationofthe following:
• movetheloudspeakerveryclose tothewall • movetheloudspeakerfarther frontthewall • sitveryclosetothewall • sitfartherawayfromthewall • putabsorptiononthewall
However,thereisoneinteresting effectthatsitsontopofallofthis– thatisthefactthatwhatyou’llseeina
46
measurementwithamicrophoneisnot necessarilyrepresentativeofwhat you’llhear. Thisisbecausea microphonedoesnothavetwoears. Also,thedirectionthereflectioncomes fromwillchangehowyouperceiveit. A sidewallreflectionsoundsdifferent fromafloorreflection. Thisisbecause youhavetwoears–oneoneachside ofyourhead. Yourbrainusesthe sidewallreflections(or,moreprecisely, howtheyrelatetothedirectsound)to determine,inpart,howfarawaya soundsourceis. Also,since,inthe caseofsidewallreflections,yourtwo earsgettwodifferentdelaytimeson thereflection(usually),yougettwo differentcomb-filterpatterns,where thepeaksinoneearcanbeusedtofill inthenotchesintheotherearandvice versa. Whenthereflectioncomesfrom thefloororceiling,yourtwoearsget thesameartefacts(sinceyourtwo earsarethesamedistancetothefloor, probably). Consequently,it’seasily noticeable(andit’sbeenprovenusing science!) thatafloororceiling reflectionhasabiggertimbraleffect onaloudspeakerthanalateral(or sideways)reflection.
15.2 RoomModes
Roommodesareacompletelydifferent beast–althoughtheyexistbecauseof reflections. Ifyoupluckaguitarstring, youmakeadeflectioninthestringthat movesoutwardsuntilithitstheendsof thestring. Itthenbouncesbackdown thestring,bouncesagain,etc. etc. As thewavebouncesbackandforth,it settlesintoatotalresultwhereitlooks likethestringisjustbouncingupand downlikeaskippingrope. Thelonger thestring,thelowerthenote,because ittakeslongerforthewavetobounce backandforthonthestring. Youcan alsolowerthenotebyloweringthe tensionofthestring,sincethiswillslow downthespeedofthewavemoving backandforthonit. Thelastwayto lowerthenoteistomakethestring heavier(e.g. bymakingitthicker)– sinceaheavierstringisharderto
move,thewavemovessloweronit. Theairinapipebehavesexactlythe sameway. Ifyou“pluck”theairinthe middleofapipe(say,byclappingour hands,orcoughing,ormakingany noiseatall)thenthesoundwave travelsalongthepipeuntilithitsthe end. Whethertheendofthepipeis cappedornot,thewavewillbounce backandtravelbackthroughthepipe intheoppositedirectionfromwhence itcame.1 Asthewavebouncesback andforthoffhetwoendsofthepipe,it alsosettlesdown(justliketheguitar string)intosomethingcalleda “standingwave”. Thisisthepipe’s equivalentoftheskippingrope behaviourinthestring. Theresultis thatthepipewill“resonate”orringat anote. Thelongerthepipe,thelower thenotebecausethespeedofthe soundwavemovinginairinthepipe staysthesame,butthelongerthe pipe,thelongerittakesforthewaveto bouncebackandforth. Thisisbasically howallwoodwindinstrumentswork. What’sinterestingisthat,intermsof resonance,aroomisbasicallyabig pipe. Ifyou“pluck”theairintheroom (say,bymakingsoundwitha loudspeaker)thesoundwavewillmove downtheroom,bounceoffthewall,go backthroughtheroom,bounceofthe oppositewall,etc. etc. (Ofcourse, otherthingsarehappening,butwe’ll ignorethose.) Thiseffectismost obviousonagraphbyputtingsome soundinaroomandstopping suddenly. Insteadofactuallystopping, youcanseetheroom“ringing” (exactlyinthesamewaythatabell ringswhenit’sbeenhit)atafrequency thatgraduallydecaysastimegoesby. However,it’simportanttoremember thatthisringingisalwayshappening– evenwhilethesoundisplaying. So,for example,akickdrum“thump”comes outofthespeakerwhich“plucks”the roommodeanditrings,whilethe musiccontinueson.
Time (sec)
Figure 15.8: The concept of the effect ofaroommodeandActiveRoomCompensation. See the associated text for anexplanation.
Figure15.8showstheconceptofthe effectofaroommodeandhowit’s dealtwithbyActiveRoom Compensation. Thesoundcomingout oftheloudspeakerisshownonthetop plot,inblack. Theresponseofthe loudspeakerandasingleroommodeis shownbelow,inred. Youcanseethere thattheroommodekeeps“ringing”at onefrequencyafterthesoundfromthe loudspeakerstops. Therearetwoaudibleeffectsofthis. Thefirstisthat,ifyourmusiccontains thefrequencythattheroomwantsto resonateat,thenthatnotewillsound louder. Whenyouhearpeopletalkof “unevenbass”ora“one-note-bass” effect,oneofthefirstsuspectsto blameisaprominentroommode. Thesecondisthat,sincethemodeis ringingalongwiththemusic,the overalleffectwillbemuddiness. Thisis particularlytruewhenonebassnote causestheroommodetostartringing, andthiscontinueswhenthenextbass noteisplaying. Forexample,ifyour roomroomringsonaC#,andthebass playsaC#followedbyaD–thenthe roomwillcontinuetoatC#,conflicting withtheDandresultingin“mud”. This isalsotrueifthekickdrumtriggersthe roommode,soyouhaveakickdrum “plucking”theroomringingonaC#all throughthetrack. Ifthetuneisinthe keyofF,thenthiswillnotbepretty.2 Inorderfortheloudspeakerto compensatefortheeffectoftheroom mode,ithastonotonlyproducethe 1Whetherthepipeisclosed(capped)oropenonlydeterminesthecharacteristicofthereflection–therewillbeareflectioneitherway. 2Doasearchfor“tritone”or“diabolusinmusica”.
47
signalitshould(showninblack)butit mustalsoproduceasignalthat counter-actstheringingintheroom mode. Thisisshowninthelowerplot inblue. Ascanbeseenthere(most easilyintheringingafterthesignal hasstopped),theloudspeaker’s compensationsignal(thebluecurve)is themirrorimageoftheroom’s “misbehaviour”(inred). Ifyouadd thesetwocurvestogether,theresultis thattheycanceleachotherout,and theresultistheblackcurve. Ifyouwouldliketocalculatea predictionofwhereyou’llhavea problemwitharoommode,youcan usethefollowingequation:
• metricversion: frequency=172/(lengthinm) • imperialversion: frequency=558/(lengthinfeet)
Thiscalculationwillproducethe fundamentalfrequencyoftheroom modeinHzforthedimensionofthe roomrepresentedby“length”. Your mostaudiblemodalproblemswillbeat thefrequenciescalculatedusingeither oftheequationsabove,andmultiples ofthem(e.g. 2timestheresult,3 timestheresult,andsoon). So,forexample,ifyourroomis5m wide,yourworst-casemodes(forthe room’swidth)willbeat172/5=34.4 Hz,aswellas68.8Hz,103.2Hzandso on. Rememberthatthesearejust predictions–butthey’llcomepretty close. Youshouldalsorememberthat thisassumesthatyouhavecompletely immovablewallsandnoabsorption–if thisisnottrue,thentheseverityofthe actualproblemwillvaryaccordingly. Sadly,thereisnotmuchyoucando aboutroommodes. Therearewaysto managethem,including,butnot exclusivetothefollowingstrategies:
• makesurethatthethree dimensionsofyourlistening roomarenotrelatedtoeach otherwithsimpleratios • putupmembraneabsorbersor slotabsorbersthataretunedto
themodalfrequencies • placeyourloudspeakerinanode –alocationinaroomwhereit doesnotcoupletoaproblematic mode(however,notethatone mode’snodeisanothermode’s antinode) • sitinanode–alocationina roomwhereyoudonotcoupleto aproblematicmode(seewarning above) • useroomcorrectionDSPsoftware suchasARCintheBeoLab50
15.3 Reverberation
Reverberationiswhatyouhearwhen youclapyourhandsinabigcathedral. It’sthecollectionofalotofreflections bouncingfromeverywhereasyougo throughtime. Whenyoufirstclapyour hands,yougetacoupleofreflections thatcomeinseparatedenoughintime thattheygettheirownlabel–“early reflections”. Afterthat,thereareso manyreflectionscomingfromsomany directions,andsodenselypacked togetherintime,thatwecan’t separatethem,sowejustcallthem “reverberation”or“reverb”(although you’lloftenhearpeoplecallit“echo” whichisthewrongwordtouseforthis. Reverbiswhatyougetwhenyouhave alotofreflectivesurfacesinyourroom –butsinceit’ssoirregularintimeand space,itjustmakesawashofsound ratherthanaweirdcomb-filtereffect likewesawwithasinglereflection. So, althoughitmakesthings“cloudy”–it’s morelikehavingafogonyourglasses insteadofascratch,orasoft-focus effectonakitschyphotographofa fieldofflowers.
15.4 Solutions
Aswe’veseen,ifyourlisteningroomis normal,youhaveatleastthesethree basicacousticproblemstodealwith. Eachproblemhasadifferentsolution... Thefirstsolutionhasalreadybeen startedforyou. Asisexplainedinthe
sectiononSoundDesign,thefinal tuningofeveryBang&Olufsen loudspeaker(includingtheBeoLab50) isvoicedinatleastfourroomswith verydifferentacousticalbehaviours rangingfromavery“dead”livingroom withlotsofabsorptiveanddiffusive surfacestoalargerandvery“live” spacewithaminimalisticdecorating, andlargeflatsurfaces. Oncewehave asinglesounddesignthatisbasedon thecommonelementsthoserooms, wetesttheloudspeakersinmore roomstoensurethatthey’llbehave wellunderallconditions. ThesecondsolutionisBeoLab50’s ActiveRoomCompensationwhichwill correcttheeffectsofboundaries (walls)androommodesonthetimbre oftheloudspeakeratthelistening position(s). Usingmeasurementsofthe characteristicsoftheloudspeakerat thelisteningpositions,theARC algorithmthencreatesafilterthatis usedto“undo”theseeffects. For example,iftheloudspeakeriscloseto awall(whichwillgenerallyresultina boostedbass)thenthefilterwill reducethebasssymmetrically. Similarly,ringingcausedbyroom modeswillbeactivelycancelledby bothBeoLab50’s. Thatway,thelossin thefilterandthegainduetotheroom willcanceleachother. Thethirdsolutionisuniquetothe BeoLab50–BeamWidthControl. This allowsyoutocustomisetherelative levelsofthedirectsoundandthe reflectedsoundatthelistening position. Theresultofthisisthat,even ifyouhaveacousticallyreflectiveside walls,theBeoLab50canstilldeliver anaccurateandpreciserepresentation ofthespatialpresentationofyour stereorecordings.
15.5 Conclusions
Ofcourse,thissectiondoesnotcover everythingthereistoknowaboutroom acoustics. And,ofcourse,youcan’t expectaloudspeakertosoundexactly thesameineveryroom. Ifthatwere true,therewouldbenosuchthingasa
48
“good”concerthall. Aroom’s acousticalbehaviouraffectsthesound ofallsoundsourcesintheroom. On theotherhand,humansalsohavean amazingabilitytoadapt–inother wordsyou“getusedto”the characteristicsofyourlisteningroom. However,thereisnodebatethat,due tomanyissues(thefirsttwothatcome tomindarefrequencyrangeand directivity)twodifferentloudspeakers willbehavedifferentlyfromeachother intwodifferentrooms. Inotherwords, ifyoulistentoloudspeaker“A”and loudspeaker“B”inashowroomofa shop,youmightpreferloudspeaker“A” –butifyoutookthemhome,youmight preferloudspeaker“B”.Thiswouldnot besurprising,sincewhatyouhearis notonlytheloudspeakerbutthe loudspeaker“filtered”bythelistening room. Thisisexactlywhy,evenwith automatedroomcompensation algorithms,somefinetuningmaybe necessarytoachieveasoundthatbest