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简介:Inthispaper,theenergyformulasofActiveSoundAbsorption(ASA)inspacesoundfieldhavebeenderivedfromthebasicsoundwaveequation,andASAincludingtherelevantconditionsofmultipolesecon-dary-source,suchasmonopole,dipoleandtripole,etc.,hasbeendis-cussed.Onthebasisofthediscussion,ithaspointedoutthatdipolesec-ondary-configuration(DAA)isthesimplestattenuator.TheresultsoftheexperimentsdoneinanechoicchamberhaveshownthatDAAhaseffectiveperformanceswhichjustprovidethefundationandfeasibilityofpracticaluse.
简介:Inthenormal-modetheoryofMorse,itgivesaseriesofnormalmodesasthesolutionofforcedvibrationinaroom.Butactuallythereisalwaysthedirectradiationbesidesthenormalmodeswhichrepresentthereverbrantsoundfieldonly.Thereasonisthatthenormalmodeswereassumedonlyinthesource,andnaturallynormalmodesonlyareobtainedinthesolution.Atheoryofdoublesourceisproposed,thatthesoundsourceisboththesourceofthedirectradiationasifinfreespacebeforetheboundarysurfaceswerereachedbythedirectradiation,andafterthefirstreflectionfromtheboundarysurfaces,thesourceofthereflectedwavelets,randomlydistributedbothinspaceanintimeontheboundarysurfacesthatbuildupthenormalmodesafterfurtherreflections.Thewaveequationisformedaccordingly,andthesolutionofthewaveequation,thesoundfieldinaroom,containsexplicitlyboththedirectradiationandthereverberantsoundformedofnormalmodes.Theapproximatemeansquaresoundpressureisfoundtobethedircetsounddeterminedbythesoundpowerofthesource,andreverberantsounddeterminedbythesoundpowerreducedbyafactorofπ/2,differentslightlyfromtheresultobtainedfromenergyconsideration,ifthesourceispuretone.Thereisessentiallynodifferenceforasourceofbandnoise.
简介:Itisconsiderednecessarythatanadditionaltermrepresentingthedirectsoundbeintroducedintotheclassicalnormalmodesolutionofsoundfieldinenclosures,toaccordwithpracticeandtomaketheformu-lamoreuseful.
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简介:Thispaperstudiestheinteractionofshockandgradientwave(soundwave)ofsolutionstothesystemofinviscidisentropicgasdynamicsasamodelforthecorrespondingproblemsfornonlinearhyperbolicsystems.Theproblemcanbereducedtoaboundaryvalueprobleminawedgeddormain,ByusingthemethodofconstructingasymptoticsolutionsandNewton'siterationprocessitisprovedthatifaweakshockhitsagradientwave,thenthegrandientwavewillsplitintotwogradientwaves,whiletheshockcontinusespropagating.Inthispapertheauthorreducestheproblemtoastandardformandconstructsasymptoticsolutionoftheproblem.Theexistenceofthegenuinesolutionwillhegiveninthefollowingpaper.
简介:Numericalanalysisofthree-dimensionalsoundpropagationinsoft-softorsoft-hardcircularductswithcircumferentialandaxialmodesofsoundsourcesattheinlethasbeencarriedout.Inthispaper,thenumericalmethodandthesamplesareofferedandtheeffectsofcircumferentialandaxialmodesonnumericalresultsarediscussedindetail.
简介:Thedeterminationofthesoundpowerofasourceissimpleinareverberationchamber,butusuallylowervalvesareobtainedatlowfrequenciesthanthefree-spacevalue.Itisshownthatthesoundpowerdeterminedinareverberationchamberdependsnotonlyonitsfree-spacepower,butalsoonthepositionsofthesourceandthereveiver,aswellasthewaythemeasurementsaremadeandaveraged.Exactandstatisticalformulasarederivedtoaccountforthesefactors.Theresultsexplainthediscrepancyandagreewellwithearlierexperiments.Basedonthetheory,parcticabletechniquesofsoundpowerdetermina-tionarepropesedandcorrectpowerformulaspresented.