Physics 1251 The Science and Technology of Musical SoundPhysics 1251 Unit 2 Session 18 Room AcousticsSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Physics 1251Physics 1251The Science and The Science and Technology of Musical Technology of Musical SoundSoundPhysics 1251Physics 1251The Science and The Science and Technology of Musical Technology of Musical SoundSoundUnit 2Unit 2Session 18 MWFSession 18 MWFRoom AcousticsRoom AcousticsUnit 2Unit 2Session 18 MWFSession 18 MWFRoom AcousticsRoom AcousticsPhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsFoolscap Quiz: Foolscap Quiz: Two tones of frequency 262 Hz and 264 Two tones of frequency 262 Hz and 264 Hz are sounded. What do you hear?Hz are sounded. What do you hear?Answer:Answer: A single tone of frequency 263 A single tone of frequency 263 Hz beating with a beat frequency of 2 Hz.Hz beating with a beat frequency of 2 Hz.ffmeanmean = (f = (f 11+ f+ f22)/2 = (262 + 264)/2 = 263 )/2 = (262 + 264)/2 = 263 Hz Hz ffbeatbeat = = f f 11- f- f22 = = 262-264262-264  = 2 Hz.= 2 Hz.Physics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsReflective ReviewReflective Review::•Wave motion is characterized byWave motion is characterized by•ReflectionReflection•RefractionRefraction•DiffractionDiffraction•Doppler ShiftDoppler Shift•Beats Beats •InterferenceInterferenceThe Reflective The Reflective Ref Ref Differed Differed Dopily, Dopily, Beating Beating Interference.Interference.Physics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsWhen the surface is smooth we have When the surface is smooth we have “specular” (mirror-like) reflection.“specular” (mirror-like) reflection.ReflectionReflectionSmooth SurfaceSmooth SurfaceRoughness Roughness ≲ ≲ λλPhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsRefractionRefraction occurs when a wave occurs when a wave “enters” a medium that has a “enters” a medium that has a different velocity?different velocity?RefractionRefractionVV11 < V < V22Physics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsWhat happens when a wave “is What happens when a wave “is partially obstructed?partially obstructed?DiffractionDiffractionDoppler Shift:Doppler Shift:Moving sourceMoving sourcePhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom Acousticsffobserverobserver = f = fsourcesource [v + v [v + vobserverobserver] / [v – v] / [v – vsourcesource] ] Higher fHigher fLower fLower fBeatsBeatsff11ff22Physics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsIn phaseIn phaseOut of phaseOut of phaseffmeanmeanffbeatbeatInterferenceInterferencePhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsConstructiveConstructiveDestructiveDestructiveLouderLouderSofterSofterPhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom Acoustics11′ Lecture:′ Lecture:Factors that most determine room Factors that most determine room acoustics:acoustics:•Direct soundDirect sound•Reverberant soundReverberant sound•Freedom from echo and interferenceFreedom from echo and interference•Background noise levelBackground noise levelPhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsGreek AmphitheaterGreek AmphitheaterAt Epidauros, GreeceAt Epidauros, GreecePhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsConstructiveConstructiveInterferenceInterferencePhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsGreek AmphitheaterGreek AmphitheaterAcousticsAcousticsDirect soundDirect soundReflected Reflected soundsoundPhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsMusiksvereinssaale ViennaMusiksvereinssaale ViennaPhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsRoyal Festival HallRoyal Festival Hallhttp://www.http://www.coxtcoxt..freeeservefreeeserve.co..co.ukuk/hall./hall.jpgjpgPhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsMorton Meyerson Symphony CenterMorton Meyerson Symphony CenterDallas, TexasDallas, TexasPhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsWinspear CenterWinspear CenterEdmonton, CanadaEdmonton, CanadaPhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom Acoustics80/2080/20Standards for “Good” Standards for “Good” Acoustics:Acoustics:•ClarityClarity•UniformityUniformity•EnvelopmentEnvelopment•SmoothnessSmoothness•ReverberationReverberation•Performer satisfactionPerformer satisfaction•Freedom from noiseFreedom from noise……little overlap of soundslittle overlap of sounds……everywhere the everywhere the samesame……sound from all directionssound from all directions……no echoesno echoes……appropriate length of appropriate length of timetime……reflected to stagereflected to stage……no competitionno competitionPhysics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom AcousticsCardinal Principle of Room AcousticsCardinal Principle of Room AcousticsThe temporal, spatial, intensity and phase The temporal, spatial, intensity and phase relationships between the direct and relationships between the direct and reflected sound ultimately determine the reflected sound ultimately determine the quality of the acoustics in a room.quality of the acoustics in a room.A room is an instrument that can dull the A room is an instrument that can dull the most illustrious performance by the most most illustrious performance by the most accomplished musician, or accomplished musician, or it can increase the pleasure of listening.it can increase the pleasure of listening.Physics 1251Physics 1251Unit 2 Session 18Unit 2 Session 18Room AcousticsRoom Acoustics80/20 80/20 Haas or Precedence EffectHaas or Precedence EffectThe earliest sound that arrives determines The earliest sound that arrives determines the sense of the origin of a sound, even if the sense of the origin of a sound, even if the later