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Soundabsorp-onistheprocessbywhichsoundwavesaretakeninorsoakedupbyso7surfaces.Soundabsorp-onproductsareintendedtoabsorbunwantednoise,likeecho,withinaspace.*Thepropertyofsurfacebywhichsoundenergy(kine-cenergy)isconvertedintootherformofenergy,generallyheatenergy(duetofric-on)andgetabsorbed.Ifwehavetoomuchsound,weuseabsorp-ontoreduceit.Mostcommonwayofcontrollingsound.Usedtomanagelow,medium,andhighfrequencies.Intelligentuseofacous-cabsorp-onishowwekeepconcerthallsfromturningintoechochambersorensurethatspeechinofficesandclassroomsisintelligible.*Reflec-onoffofahardsurfacecanbealmostasloudastheoriginalsound.*Diffusiondoesn’tdirectlyreflectorabsorbsound,insteaditscaLersitinmanydirec-ons.Soundproofingisnotsoundabsorbing.

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*Pressureac4vatedisthe‘base’lowfrequencypressurethatpeoplefeelinsmallroomenvironments.Couldevensitinadistor-onandnothearcertainfrequencies,orsitinamodeandheartoomuch.Absorp-onperformancevariesalotbasedonthefrequencyofsoundandtheabsorp-vecapabili-esofthematerial.àDiaphragma4c:Aboxorpanelthathasafacethatisdesignedtovibrateormovewiththesoundpressurethatisexerteduponit.àDiaphragma-cabsorbershaveamembraneorsomematerialtypethatisstretchedacrossthefaceofacabinetwhichisbuilttoaspecificdepth.àHighratesandlevelsforsmalleramountsofspacetakenbythecabinet.ààDiaphragma-cabsorp-onisaboutthe3D's:Density,Depth(determinesresonancefreq),Dimension(sq7requirement).ààCabinetdensity,cabinetdepth,anddimensionorsurfacearearequiredwithinyourroom,allcontributetotheabsorp-onratesandlevelsthatcanbeachieved.

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*NRC:250,500,1000,2000Hz.Scalarrepresenta-onoftheamountofsoundenergyabsorbeduponstrikingapar-cularsurfaceAnindustrystandard,butnotenforced&becauseit’saverages,twomaterialswithsamera-ngmaynotperformthesame.AnNRCof0indicatesperfectreflec-on;anNRCof1indicatesperfectabsorp-on.Duetotheformulasused,thecoefficientisnotapercentageandvalueslargerthanonearepossible(andcommon).Beingreplacedbythesoundabsorp-onaverage.SoundproofingproductsdonothaveNRCs.NRCsapplytoabsorp-onproducts,whileSTCra-ngsapplytosoundproofingproducts.Thethicknessanddensityofaproductaretwofactorsincalcula-ngaNoiseReduc-onCoefficient.Anacous-cproductwitha.95NRCra-ngmeansthat95%ofsoundinthespaceisabsorbed,whiletheother5%isreflected.*AbsCoeff:same4+125Hzand4000Hzaswell

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Echo:Soundorseriesofsoundscausedbyreflectedenergyboomingbackandforthbetweensurfacesandlistener.Becomesapparenttothelisteneronlywhenthedistancefromthesourceandthereflec-ngmediumisgreatandthedifferencebetweentheoriginalandreflectedsoundisgreaterorequalto1/17ofasecond.FluLer:Higherfrequency(>800Hz)SisterofReverbera-on.Broughtaboutbyaseriesofreflec-onsbetweentwoparallelsurfacesresul-ngtoprolonga-onofsound,createslisteningfa-gueInterference:Reflec-oncausedbytwoparallelsurfaces,producingstandingwavesReverbera-on:AmountofSoundintheroom,amountthatdecaysover-me

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Reverbera4on:AmountofSoundintheroom,amountthatdecaysover-meLotsofreverb=loud=>hardtohearsomeone10feetawayfromyouatconversa-onlevel~60dBataHuskiesgameisn’tit?Withonlysolidwallsandairforabsorp-on,soundcanreverberateforastartlinglylong-me.RT:Theamountof-meittakesforsoundenergytobouncearoundtheroombeforebeingabsorbedbythematerialsandair.Themorereflec-vearoom,thelongeritwilltakeforthesoundtodieawayandtheroomissaidtobe'live’.Inveryabsorbentrooms,sounddiesawayquickly,thustheroomisdescribedasacous-cally'dead’.Vienna,Musikvereinsaal:2.05secondsBoston,SymphonyHall:1.8secondsNewYork,CarnegieHall:1.7secondsRT-60:-meittakesfortheenergytodecay60dB.Kindofarbitrary,butthereisagoodra-onaleforusing60dB:

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Theymaylookliketorturechambers,butthey’renot.Unlessyoucan’tstandsilence.*Theanechoicchambersareconstructedasaroomwithinaroom.Theouterwallsarethick,andtheinnerroomismadeupofmetallicpanelsmountedonafloa-ngfloorà preventsthereflec-onofbothsoundandelectromagne-cwavesAnechoicchamberscomeinallshapesandsizes.-Fromsmallcubiclesthesizeofamicrowavetoonesaslargeasaircra7hangars.Thesizeofthechamberisdependentonthesizeoftheitemsbeingtestedandthefrequencyrangeofthesignalsused.Scalemodelscanbeusedbytes-ngathigherfrequencies.TypicalAnechoicchamberexperimentsincludemeasuringthetransferfunc-onofaloudspeakerorthedirec-vityofsoundradia-onfromindustrialmachinery.

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*Panelsdeadensoundisbyabsorbingsoundwaves.àlinedwithfiberglasswedgesthatcovertheen-receiling,floorandwallsMS’s:eachofitssixsurfacesislinedwithclustersof47-long(1.2m)wedgesofsoundabsorbingfoamààcreatesunevensurfaceofawedgenetworkprotrudingfromdifferentdirec-onsWhensoundwavesstrikethefiberglass,theyaretransferredtothebodyofawedge,wherethewaveenergyiseffec-velydissipated.Whenasoundwavecomesinsomeofitsenergyisspentsquishingthismaterialandit'sdissipatedasheatinsidethematerial.Anysoundwavesthatcomebackoutarenecessarilyquieter.*Theanglesdeadenedechoes.Anyresidualsound(wave)reflectsoffthewedgeatanangleandlandsonanotherwedgeundergoingthesameprocessagain,expendingalmostallofitsenergynotreflec-ngbackout,butbouncingupanddownbetweenthesepanels.Inthisway,alloftheenergyofasoundwaveisdissipated,sothere’snoechoandtheroombecomesunbearablyquiet,closetodeadsilence.

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*Ambientsoundofthechamberdoesn'twiggleyoureardrumsthewidthofasingleairmolecule,soitrestsatlowerthanthethresholdforhumanhearing.Soyoustartbeingabletohearthingslikeyourbloodpumpingthroughyourveins,andyourheartbeat,yourbrainmovingaroundinsideofyourskull,etc.“Whenit’squiet,earswilladapt.Thequietertheroom,themorethingsyouhear.You’llhearyourheartbea-ng,some-mesyoucanhearyourlungs,hearyourstomachgurglingloudly.Intheanechoicchamber,youbecomethesound.”–SteveOrfieldofOrfieldLabsHumanscantypicallyhearsoundsabove0dBA.Asaresult,ahumanwouldthinkthesurroundingsinanAnechoicchambertobevoidofsound.Manypeoplewhohavevisitedsuchchamberssaythatthelackofsoundisuncomfortableanddisorienta-ng.Howyouorientyourselfisthroughsoundsyouhearwhenyouwalk.Intheanechnoicchamber,youdon'thaveanycuesAnyoneinthechamberfor30+minutesmustbeseated,duetolossofbalance.

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BasicpremiseisthatthemetamaterialneedstobeshapedinsuchawaythatitsendsincomingsoundsbacktowheretheycamefromTestcase:Createdastructurethatcouldsilencealoudspeaker’ssound.Basedoncalcula-ons,theymodeledthephysicaldimensionsthatwouldmosteffec-velysilencenoises.3-Dprintedthemodeltocreateanopen,noise-cancelingstructuremadeofplas-c.ResearcherssealedtheloudspeakerintooneendofaPVCpipe.Ontheotherend,thetailor-madeacous-cmetamaterialwasfastenedintotheopening.Turningonthesound,theexperimentalloudspeakerset-upcameoh-so-quietlytolifeinthelab.Standingintheroom,basedonhearingalone,you'dneverknowthattheloudspeakerwasblas-nganirrita-nglyhigh-pitchednote.ThePVCpipe,howevershowedthevibra-onoftheloudspeaker'ssubwoofers.Themetamaterial,ringingaroundtheinternalperimeterofthepipe'smouth,actslikeamutebuLonun-lthemomentwhenitwasremoved.Suddenlythescreechingoftheloudspeakerechoedaroundthelab.Bycomparingsoundlevelswithand

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