MASTER'S THESIS Game engine based auralization of airborne sound insulation JIMMY FORSMAN June,2018 Master’sthesis,Civilingenjörsprogrammetitekniskfysik,UmeåUniversity. JimmyForsman, [email protected]. Gameenginebasedauralizationofairbornesoundinsulation isaprojectdoneinthecourseMaster’sThesisinEngineeringPhysics,30.0ECTS attheDepartmentofPhysics,UmeåUniversity,incollaborationwithTyrénsAB. Supervisor: RikardÖqvist,Acousticsdepartment,TyrénsAB. Examiner: KristerWiklund,DepartmentofPhysics,UmeåUniversity. Abstract Describing planned acoustic design by single number ratings yields a weak link to the subjective event, especiallywhenthesinglenumberratingsareinterpretedbyothersthanexperiencedacousticians. When developinginfrastructure, toolsfordecisionmakingneedstoaddressvisualandauralperception. Visual perceptioncanbeaddressedusinggameenginesandthishasenabledtheestablishmentoftoolsforvisu- alizations of planned constructions in virtual reality. Audio engines accounting for sound propagation in thegameengineenvironmentaresteadilydevelopingandhaverecentlybeenmadeavailable. Theaimof thisprojectistosimulateairbornesoundinsulationbyextendingthesupportofrecentlydevelopedaudio enginesdirectedtowardsvirtualrealityapplications. Thecasestudiedwasairbornesoundinsulationbetweentwoadjacentroomsinabuilding, thesound transmittedtothereceivingroomthroughthebuildingstructureresultingfromsoundpressureexcitingthe structural elements in the adjacent source room into vibration. The receiving room composed modelled spaceinthegameengineUnrealEngineandSteamAudiowastheconsideredaudioengine. Soundtrans- missionwasmodelledbyfilteringbasedoncalculationsoftransmissionlossviadirectandflankingpaths usingthemodelincludedinthestandardEN12354-1. Itwasverifiedthatthefilteringtechniqueformodellingsoundtransmissionreproducedattenuationsin correspondencewiththepredictedtransmissionloss. Methodologywasestablishedtoquantifythequality oftheaudioengineroomacousticssimulations. Aroomacousticssimulationwasevaluatedbycomparing the reverberation time derived from simulation with theoretical predictions and the simulated reverber- ation time showed fair agreement with Eyring’s formula above its frequency threshold. The quality of thesimulationofairbornesoundinsulationwasevaluatedrelatingthesoundfieldinsimulationtoinsula- tion classification by the standardized level difference. The spectrum of the simulated standardized level differencewascomparedwiththecorrespondingsoundtransmissioncalculationforamodelledscenario. The simulated data displayed noticeable deviations from the transmission calculation, caused by the au- dio engine room acoustics simulation. However, the simulated data exhibited cancellation of favourable and unfavourable deviations from the transmission calculation resulting in a mean difference across the spectrumbelowthejustnoticeabledifferenceofabout1dB.Singlenumberratingswascomparedandthe simulated single number rating was within the standard deviation of how the transmission model calcu- latespredictionsforacorrespondingpracticalscenariomeasuredinsitu. Thus, thesimulateddatashows potentialandcomparisonsbetweensimulateddata,establishedroomacousticssimulationsoftwareandin situmeasurementsshouldfurtherbemadetodeducewhetherthedeviationsentailsdefectsintheairborne soundinsulationpredictionorisanerrorimposedbytheaudioengineroomacousticssimulation. Keywords: Auralization, Building acoustics, Airborne sound insulation, EN 12354-1, Room acoustics, Audioenginesforvirtualreality,Gameengine. iii Acknowledgement First of all, I would like to address the exceptional effort by my supervisor Rikard, thank you for your support,yourenthusiasmandmostimportantly,foralwaysbroadeningmyperspective. Rikard,yourcon- tributionstretchesfarbeyondthisMaster’sthesisproject. I would also like to express my gratitude towards Tyréns AB enabling me to perform this project, providing equipment, premises and trips, a great working environment and I have been fortunate to be surroundedwithpleasantpeopleondailybasis,thisacknowledgementisdedicatedtoyouaswell. Further, IwouldlikeshowmyappreciationtowardsallofyoufromtheTyrénsofficesatUmeå,LuleåandStockholm takingyourtimeguidingmeandshowinginterest. Arne, thankyouforyoursupportfromthebeginning ofthisprojectandforallhelpfuldiscussionsprovidingmewithdirection. Philip, yourtime,interestand expertiseinroomacousticshavebeensignificant. One thing that I particularly appreciate about Umeå University and would like to acknowledge is the openenvironmentallowingfordirectinteractionbetweenstudentsandteachers. Therehavebeenplentyof influential teachers at Umeå University during my engineering physics studies that deserves recognition. Inconnectiontothisproject, IwouldliketoaddresstheeffortsbyyouKrister, yoursupporttowardsthe studentsismajorandyourguidanceintheprocessofmythesisprojecthasbeenvaluable. Iwouldaswell liketothankyouPetterfortakingyourtimeandsupportingmeinthewritingprocess. ThisacknowledgementwoulddefinitelybeincompletewithoutaddressingthegreatpeopleIhavehad achancetobesurroundedwithduringthesefiveyearsofengineeringphysics,youthatIhavehadachance toworkwitheverydayaswellashavingstrictlunchhourswith! Viktor,yougotmethroughthisandyou havemadeeverythingbearable. Carl,amongmanythings,Iwouldnothavemanagedwithouttheruthless answerstoanyquestion! Karl-Johan,yourenergy(andexpertiseindenim)havebeensignificant. Iwould alsoliketoaddress: Youwhowasalwayslighteningthemood,whenawakeandwhennot,itwouldhave beenlessfuntimeswithoutyou! YouwhowaswonderinghowIwasreasoningandgavemethenickname thatstuck. Thisisalsotothemostefficientpersonevertoproceedanengineeringphysicseducation,safe! To the champ with the neon sign, I would like to get a chance to claim the title some day. Additionally, thisdefinitelycallsfortheglassversion! Ihavemissedplenty,butIamgladyouaretoomanytoannounce here. I must stress that the endless support from my family deserves a proper acknowledgement, because your support has been crucial. Finally, I would like to dedicate this to my friends, for instance, always readyforadegandalwaysreadyforacruisewhenvisiting,aswellastoyouwhoIalmostneverseemto runintoexceptatFridaylunch. JimmyForsman, Umeå,Sweden, 11June,2018. iv Contents 1 Introduction 1 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Aim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.4 Disposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 Theory 4 2.1 Acoustics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1.1 Planewaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1.2 Energytransport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1.3 Soundpressurelevel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1.4 Standardizedfrequencybands . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2 Soundmodellinginrooms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.1 Surfaceabsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.2 Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.3 Geometricalacoustics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.4 Diffusefields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.5 Theoreticalreverberationtimeprediction . . . . . . . . . . . . . . . . . . . . . . 9 2.3 Soundtransmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3.1 Airbornesoundinsulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3.2 ThestandardEN12354-1andflankingtransmission . . . . . . . . . . . . . . . . 12 2.4 Signaltheoryforauralization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.4.1 Fouriertransform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.4.2 Convolution,impulseresponseandtransferfunction . . . . . . . . . . . . . . . . 16 2.4.3 Retrievinganimpulseresponse–Diracdeltafunction . . . . . . . . . . . . . . . 16 2.5 Reverberationtimederivation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.6 Roomimpulseresponse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.7 Theconceptofheadrelatedtransferfunctions . . . . . . . . . . . . . . . . . . . . . . . . 19 2.8 Ambisonics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3 Method 21 3.1 Modellingapproach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2 Transmissionlossbasedfiltering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.1 Performanceparameterinputdata . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2.2 Designingwall-filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.2.3 Wall-filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.3 Receivingroomsimulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.3.1 Audioengine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.4 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 3.4.1 Evaluationsetup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.4.2 Filteredsecondarysourcesignals . . . . . . . . . . . . . . . . . . . . . . . . . . 33 v CONTENTS 3.4.3 Reverberationtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.4.4 Virtualsoundinsulationmeasurement . . . . . . . . . . . . . . . . . . . . . . . . 35 4 Results 39 4.1 Transmissionlossbasedfiltering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 4.2 Reverberationtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4.3 Virtualsoundinsulationmeasurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 5 Discussion 47 5.1 Transmissionlossbasedfiltering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 5.2 Reverberationtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 5.3 Virtualsoundinsulationmeasurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 6 Conclusions&outlook 51 6.1 Futurework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Bibliography 54 vi Chapter 1 Introduction 1.1 Background The current population growth demands a high rate of developing infrastructure. The United Nations predicts that 66 percent of the world’s population will reside in urban areas by 2050, compared to the 54 percent in 2014. The estimated population growth then corresponds to adding 2.5 billion people to urbanareasinthetimespan2014to2050[1]. Ahighrateofurbanizationrequiresagiledecisionmaking from involved engineers, clients and contractors. Availability of efficient support for decision making is desirable to make proper judgements early in the building process for preventing the rapid development fromexertingunnecessarymarksontheenvironmentbyinhindsightrevisingbuiltconstructions. Support for making the technical decisions is crucial, however, the development would not be sustainable if the inhabitants of the constructed environments are neglected. Therefore, tools for rational decision making arerequiredtomanagehowplannedconstructionsmaybeperceived. Theusageofvirtualrealitysystemsaretodayappliedinvariousdisciplinesinscienceandengineering, whereamajoraspectofitsusefulnessistheabilitytoaddresshumanperception.Virtualrealityapplications commonly aim to manage the human visual system. A broader modality is strived for to improve the abilityofmanagingperceptionandcanbeachievedthroughconsolidatingthevisualstimulationwithaural stimulation. Virtualrealitysystemsoftenreliesongametechnologywheresufficientvisualstimulationfor manypurposescanbeachievedutilizingtechniquesofcomputergraphics,thusallowsforcomprehensive visualizations. Tobroadenmodalityofvirtualrealitysystemsthevisualizationistobesupplementedbyits audioanalogue,auralization. Auralizationisatermintroducedinapaperfrom1993byKleineretal. [2] andcanbeconsideredtorenderaudiblesoundfieldsforsimulatingtheacousticsofmodelledspace. The integration of auralization into virtual reality systems based on established game engines have not been conductedtothesameextentduetotherelativelylessdevelopedsupportofthegameenginesinsimulating soundpropagatinginthevirtualenvironment. TyrénsABhavedevelopedaplatformforvisualizationaimedtowardssustainabledevelopmentincon- nectiontocivilengineering[3]. Thevisualizationplatformcanbeusedinthedesignprocesswhendevel- opinginfrastructureandprovidesanimpressionofhowaplannedprojectmaybevisuallyperceivedpriorto construction. Thevisualizationplatform—TyrEngine—isbasedonthegameengineUnrealEnginewhich allowsforimmersinganobserverbymeansofvirtualrealityintoplannedconstructionsforreal-timevisu- alizationofthreedimensionalenvironments. TyrEngineishencebasedoncomputergametechnologyand thewelldevelopedgraphicalsupportofthegameenginehaveinvariousprojectsprovensufficientforad- dressingthehumanvisualsystem. However,TyrEnginehascurrentlynosupportforaddressingthehuman auditorysystem. Supportforaddressingauralperception wouldenableforcommunicatingtheeffectsof acousticdesign. Onereasonforthelackingsupportisthenduetothemuchlessdevelopedfeaturesofthe gameenginefortakingintoaccounttherelevantphysicalpropertiesofsoundpropagatinginthemodelled environment. Recently, companies such as Valve and Google have devoted attention to the development of audio engines aimed towards integration with game engines providing more detailed modelling of how sound interactswiththevirtualenvironment. Duringthepastyear,thenewlydevelopedaudioengineshavebeen 1 1.2. AIM madeavailable[4,5]. Itisofinteresttoinvestigatehowtherecentlydevelopedaudioenginescanbeutil- izedforcivilengineeringapplicationsperforminggameenginebasedauralizationsimulatingperceivable effectsofdifferentacousticsolutions. ThisMaster’sthesiswillfocusontakingtheinitialstepsforbroad- eningmodalityofgameenginebasedvisualizationplatformscombiningvisualizationwithauralizationby utilizingtheinherentfeatures,aswellasextendingthesupport,ofrecentlydevelopedaudioengines. Often, acoustical engineers describes the performance of a construction in isolating against airborne soundbyprovidingsinglenumbersratingsandgraphsindicatinginsulationpropertiesinfrequencybands. Dataintermsofsinglenumberratingsandgraphsarefarfromanexhaustivedescriptionofthesubjective eventthatclearlyillustratesperceptualconsequencesofplannedacousticdesign, hardlyaneffectivetool facilitatingprudentdecisionmaking. Thus,singlenumberratingsasadecisionbasiswheninterpretedby othersthanexperiencedacousticiansimposesrisksofsub-optimalconstructionsresultinginunsustainable developmentregardinghumanhealth. In this thesis, development towards vivid descriptors of sound insulation to function as adequate de- cisionmakingtoolswillbecarriedoutbystudyingacaseinvolving—auralizationofairbornesoundinsu- lation—themodellingandsimulationofthesoundfieldinsidethereceivingroomasaneffectofairborne sound transmitted from the adjacent source room. To entail possibilities of supplementing high quality visualizationsbyauralization, simulationswillbeconfinedtothegameengineenvironment, specifically, UnrealEngine[6]usingValve’sSteamAudio[7]asabasisformodellingsoundpropagationinthevirtual environment. Theaiminafutureperspectiveistoenableforphysicallyaccuratevirtualrealitypresenta- tionsofacousticdesignproceedingfromtheversatilegameengineenvironment.Thefirststepistoproceed from algorithms developed for auralization of airborne sound insulation [8, 9], performing modifications adapting the algorithms to the game engine environment and further performing objective evaluations of this approach for building acoustical auralization. Objective verifications of game engine based building acousticalauralizationwillbenefitthedevelopmentoftoolsforclearlydescribingtheinfluenceofacous- tical design in civil engineering. Thereby simplifying decision making for engineers, clients as well as contractors when striving towards creating sustainable, acoustical, environments. The initial steps in the developmentprocesswillbetakenduringthecourseofthisthesis. 1.2 Aim The aim of this project is to simulate airborne sound insulation by extending the support of recently de- velopedaudioenginesdirectedtowardsvirtualrealityapplications. 1.3 Goals Thefollowinggoalsarespecified: i. Performandevaluateagameenginebasedroomacousticssimulation. ii. Simulate airborne sound transmission between two adjacent rooms in a building using established modelsdedicatedtosoundtransmissioncalculations. iii. Evaluatethequalityofthesimulationusingstandardizedbuildingacousticalmethodologytorelate thesimulatedsoundfieldtonumericaldescriptorsofsoundinsulation. iv. Delivermethodologytobeusedwithrecentlydevelopedaudioenginesforperformingandevaluating gameenginebasedauralization. 1.4 Disposition AcousticsisbrieflyintroducedinChapter2proceedingfromwavetheory.Centralconceptsforauralization arethenaddressedafterdealingwithcommonmodelsinroomandbuildingacoustics. Themodellingof soundtransmissionaswellasmethodologyforperformingandevaluatinggameenginebasedauralization isthetopicofChapter3. ResultsfromvariousevaluationsareprovidedinChapter4,analysedinChapter 2 CHAPTER1. INTRODUCTION 5andconcludingremarksfromtheanalysisinconnectiontothespecifiedgoalsarepresentedinChapter 6. Chapter 6 is then finished off by emphasizing where to proceed with further research from what is establishedinthisthesis. 3 Chapter 2 Theory 2.1 Acoustics Acousticsintermsofforinstanceairborneorstructure-bornesoundconcernswavesinairorsolidmedia. Here,wewillintroducecentralacousticalconceptsproceedingfromwavetheory. Particles in a sound wave follows a space and and time dependent displacement vector, s, describing relativedisplacementfromparticleequilibriumwithparticlevelocity,v,givenbythederivativeofswith respecttotimeas ∂s v= . (1) ∂t For airborne and structure-borne sound the particles then concerns air molecules and atoms in a crystal lattice. The related density and pressure fluctuations, ρ and p, of the medium which the sound wave propagatesthroughcanbeexpressed ρ =ρ −ρ , (2) tot 0 p=p −P, (3) tot 0 wherethetotalsindicatestheeffectivequantitiesofthemediumasaresultofthedisplacementsfromthe equilibriumdensityρ andpressureP,respectively. Thesoundpressure, p,isthemainquantityofinterest 0 0 and it is the sound pressure that relates sound waves to human hearing [10]. We will mainly deal with soundwavesinfluidmediafornowandfocusonairbornesound. Thepressurefluctuationsduetosound wavesisassumedtofulfillthewaveequation ∂2p c2∇2p− =0, (4) ∂t2 wherecisthespeedofsoundandwestickwithphysicsnotationssuchthat∇2denotestheLaplacian. The soundspeedisthephasespeedofthesoundwaveinthemedium,thatis,anobserverfollowingthesound wave at speed c would experience a constant phase and see no change in the wave pattern, thus, phase speed[11]. 2.1.1 Planewaves We will introduce necessary concepts of wave theory related to acoustics and therefore we consider a solutionofthewaveequationasaplaneharmonicwave p(r,t)=pˆei(ωt−k·r), (5) where pˆ isthe,generallycomplex,pressureamplitude,ω istheangularfrequency,kisthewavenumber vectorandrdenotesthepositionvector.Notethatwhendealingwithactualphysicalquantitiesweconsider onlytherealpart. Now,considerthepositionvectorrforaCartesiancoordinatesystemwherer∈R3,we 4