HOME THEATER ACOUSTICSWord文件下载.docx

HOME THEATER ACOUSTICSWord文件下载.docx

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reathome,it'

snotquitethesame.--

--AndsobeginsthechallengeforthoseAVspecialistswhoworkinhometheater.--

Playwrights,actors,anddirectorshavelongknownthattoentertain,theymustcapturetheimaginationoftheaudience.Composers,musicians,andconductorsalsoknowthattobringsatisfactionintotheperformance,theymustenrapturetheaudience.Toachievesuchabandoninvolvement,theaudiencemustbecultivatedintoamentalstatesuchthattheyforgetthemselvesandwheretheyare,beingconscioussolelyoftheshow,and,thus,becomingpartoftheshowthemselves.

Inthemoviesorliveperformances,thisaudienceinvolvementeffectisdevelopedbytwomeans.First,goodmaterialandagoodperformanceisnecessary.Thesefactorslieinthehandsofthosewhoproducetheshow.Secondly,agoodsettingmustbeprovidedforexperiencingtheshowandthisliesinthehandsofthosewhoputontheshow.Therearenumerouselementsthatgointoandcomposeagoodsettingforashow.Alightdimmermightbeone.Apullcordforthecurtainisanother.Comfortableseatsinaneventemperatureanddraft-freeroomareneeded.Airconditioningnoiseneedstobereducedjustastheexcesslightfromwindows.Andthelistgoeson.

TheA/Vspecialistinhometheateristhepersoninchargeofputtingontheshow.Partofthisresponsibilityistogettheequipmentoperatingproperly,andtheotherpartistocreateapropersettingsothatdistractingeffectsareeliminated.Forthemostpart,theprogrammaterialavailablethesedaysforhometheaterisprettygood,andsoistheequipmentusedtoprocessit.Whatseparatesthegoodfromthebadanduglyinhometheateris,inmostcases,thedistractionfactoroftheroom.Bycontrollingdistractions,theA/Vspecialistcanbringintoplaythatfinaltouchandenduppresentingareallygoodshowwithoutbreakingaleg.

Thecustomerdoesgotothestoretobuybothprogrammaterialandtheequipment.Thethirdelementis,however,a"

customerservice"

commodity.It'

sthepersonaltouchpartofthesalethatonlytheA/Vspecialistcanimplement.Notunlikehighendaudio,thehometheatersalegoesbeyondtheequipment-in-a-boxmentalitytoincludethesetup.Tomaximizecustomersatisfactionandloyalty,goodequipmentmustbesetupinaroomthathasbeenorganizedforminimaldistractioneffects.Wenowturnourattentioninsomedetailtodescribingvariousdistractioneffectsthatexistinhometheater.

A/VDISTRACTIONS

Thehometheateraudiencegenerallyhasaccesstoallfivesenses:

sight,sound,smell,touch,andtaste.Beingatthedowntownmoviescankeepallfivesensesprettybusy,especiallyifwelikepopcorn.Wecanbeeasilydistractedfromthemoviebyoursenses.Let'

ssaywetakeaseat--onlytodiscoverthatthepersonnexttousisdevouringhotpopcornbythehandful.Ifwedon'

tcareaboutpopcorn,onlythenoiseisdistracting.Butifwelovepopcorn,thesmelldrivesuscrazyandwe'

llprobablygetupandgobuysomepopcorn.Thepointbeingthatsensorydistractioncankeepusfrombeinginvolvedinthemovie.

Therearetwokindsofdistraction:

primaryandsecondary.Forthemovies,themediumofcommunicationinvolvessightandsound.Primarydistractionswouldbethingsweseeorhearthatarenotthesightandsoundofthemovie.Secondary,butnotlightlydismissed,distractionsarethecomfortofchairs,temperaturesettings,anddraftsintheroom.Primarydistractionsfromthemovieprogrammaterialinvolveauditoryandvisualdistractions.TheA/VspecialistwillworktominimizeA/VdistractionfromtheA/Vprogrammaterial.

Hometheaterisamixofsightandsound.Twooutofourfivebasicsensesarefedcoordinatedsignalsthatresultintheaudio/visualmessageexperience.Imagineforamomentavideoprojectionscreendisplayedinsidearoom,whoseentiresurfaceiscoveredwithmirrors.Thefloor,ceiling,andwallswouldallbemirrors.Considerthevisualconfusionyouwouldexperienceinsuchahouseofmirrorswhenthevideoscreenlightsup,Whichimagewouldbetherealimage?

Theoneahead?

Maybeit'

stotheleftoragaintotheright?

Isitaboveontheceilingorbehindyou?

Tosomedegree,itmaynotmatterwhichimageisrealandwhichonevirtual,aseachlooksliketheother.Onapracticalbasis,itistheconfusionanddistractionthatcomesfromhavingsomanyimagespresentedatonetime.Someoftheimagesmaybesimple,clearvisions,oftherealscreen,butlookinginanotherdirection,we'

llseethestacked,multipleimageeffectofparallelmirrorsthatfadesawayfromusintovirtualinfinity.

Noonewouldreallyproposea"

houseofmirrors"

settingforhometheater.Fortunately,thepaintedsurfacesofmostroomsarefarfromamirrorsurface;

theyarepartiallylightabsorbing,andduetotheirroughsurface,theyarepartiallylightdiffusing.Whateverlightreflectsoffthewallisdiffuselyscatteredinpracticallyalldirectionswithnearlyequalintensity.Abluewallstaysabluewallnomatterwhereyouarelocatedintheroom.Blueisthecolorreflected,butthereflectingsurfaceofthewallissoroughthatbluelightisscatteredeverywhere.

Weareluckythatlightisprettywellbehavedinrooms,butwe'

renotsoluckywithsound.Theroomdoesbecomeahouseofmirrorsasfarasthespeakersareconcerned.Forsound,thewallsare"

acoustically"

flatlikeapolishedmirror.IfwecouldvisuallySeethespeakerimages,theywouldbefoundalloverthewalls.Unfortunately,withsound,theroomreallydoesbecomeahouseofmirrors.

Agoodroomforhometheaterwillbesetuptocontrolbothvisualandsonicdistractioneffects.Beforewecangoveryfarwithguidingthehometheaterroomawayfrombehavinglikeahouseofmirrors,weneedtounderstandtheprincipleofsensoryfusion.Sensoryfusionispartofournaturalconditionandcomesasamixedblessing.Withoutthisfusionprocess,moviesasweknowthemtodaywouldbeimpossible.Yet,becauseofit,webecomesusceptibletosensoryinputoverload.Butfirst,let'

sreviewsomeaspectsofsensoryfusion.Therearetwokindsofsensoryfusion;

oneinvolvestimeandtheotherinvolvesspace.Thereisalwaysalimitastohowcloseeventscanoccurandstillbedistinguishedasindividualevents.

TEMPORALFUSION

Considervideo.Itisactuallyarapidlyflashedsequenceofstillimageslikemovieframes.Thesestillsareflippeduptousataratejustalittlefasterthanourabilitytoperceiveseparatevisualeventsintime.Hence,thisstaccatoofstillsseemstotheviewertocreateacontinuousmotion.Thevisualimagesareflashedatarateof60times/second（every1sec/60or17ms）andatthatratewecannotseparateoneimagefromthenext.Thesewell-definedstillframesarebeingflashedtousataratefasterthanourvisualreactiontimefordiscriminationofseparateeventsintime.Thisiscalledtemporalfusion,thetimeperiodofsensoryfusion.

Thereasonweareslowtoperceivetherapidlyflashingvisualimagesisbecauseweemployaslowspeedbiochemicalsensor（notaspeedoflightelectronicphotocellsensor）inoureye/brainsystem.Therelativeslownessofourelectro/chemicalvisualsensorsresultsinthe"

visualfusion"

ofactuallyseparate-in-timeevents.Itisnotaweakness,butitisthenatureofourbiochemicalbeingthatmultipleeventsareperceivedasseparateevents,onlyiftheyoccursufficientlyseparatedoutintime.Ifseparateeventsarrivetooquickly,theyareperceivedasonecontinuousevent.Withoutthis"

visionfusion"

process,videoasweknowittodaywouldbelikewatchingastrobelightshow--anovelty--butnotanentertainmentmedium.

Let'

sutilizethiscardflippingprocesstointroducethesenseofsoundintotemporalfusion.Mostofushavedonesomethinglikethiswhenwewereyoung.Weusedaclotheslinecliptopositionacardintothespokesofthebikewheelandwegotthesoundofamotorcycle.Tryanexperiment.Takeadeckofcardsinyourhands,archthembackandthenwiththethumb,releasetheentiredeckinonesecond.Whatdowehear?

Abreathy,flutteringtypeofsound,butatonenonetheless.Ifweflipthrough50cardsinonesecond,weget50separatepositivepulsesofairpersecond.Butwehearthisprocessasifitwasabreathy50Hztone,whichisabassnotewhoselocationisaboutfourkeysupfromthebottomendofthepianokeyboard.

Ifwefliponecardpersecond,weheardistinctsnaps.Ifweflip50cardspersecond,wedonothear50snapspersecond,butperceiveacontinuoustoneof50cyclespersecond.Becausewearehuman,andourdetectionsystemsarebiochemical,ourexperienceswithsightandsoundarequitesimilar.Rapidlyflippedcartooncardscreatetheimpressionofcontinuousmotionandrapidlysnappedplayingcardscreatetheimpressionofcontinuoussound.Botheffectsoccurbecauseofthetemporalfusionthreshold（time）inourabilitytodetectseparateevents.Separateeventsthatoccurwithin1/20secondareperceivedasoneevent.Multipleeventsthatarespacedcloserthan1/20secondapartareperceivedasacontinuousevent.

SPATIALFUSION

Again,weconsidervideoandfindthespatial（location）versionoffusiononthevideoscreenitself.Atthemovies,theimageispracticallyacontinuousdistributionofcolorsandshadingsbecauseitisaprojectedphotograph（slideshot）ofrealobjects.Thesmoothnessoftheimageiscontrolledbythegraininessofthefilm,whichlongagowasreducedtothelevels.Notsowithvideo.Wehavepixels,dots,orblocksofcolorsonthescreen.The