CHAPTER FIVEACOUSTIC ENCLOSURES AND BARRIERS 5.1 SOUND TRANSMISSION LOSSAirborne STL is defined as follows: 101STL10logWhere is:1. Airborne STL Transmitted soundRefracted and absorbed soundIncident soundReflected soundAbsorption coefficient:iriIIITransmission coefficient: tiIIIncident: Incident: I Ii i Reflected: Reflected: I Ir rAbsorbed: Absorbed: I Ia aTransmitted: Transmitted: I It tSound Insertion loss (IL) The difference in sound pressure measured in a single location with and without a noise-control device located between the source and receiver. The difference in the sound pressure measured in the occupied space with the wall versus without the wall is the IL of the wallSound transmission loss (TL) It equals to the ratio of the airborne sound power incident on the partition to the sound power transmitted by the partition and radiated on the other side.IL and TL101TL10logSourceBarrierIn a roomWe have known:i= absorption coefficient of i th surfaceiiiASFor i th surface:niiiAS For a whole room: the room-averaged sound absorption coefficient , : niiiSSASS is the total surface area of the room.Also, in a roomTransmitted soundRefracted and absorbed soundIncident soundReflected soundeqiiSS iieqSStiII10Also, in a roomeqiiSS iieqSSThe corresponding sound transmission loss is given by :101STL10logeq101R10logeqWe assume :Another form :exampleWall: 20m2, walldoorwindows5110Door: 2m2, Windows: 3m2, 32102310Calculate the STL.exampleWall: 20m2, walldoorwindows5110Door: 2m2, Windows: 3m2, 32102310STL=10log105=50 dBSTL=10log103=30 dBSTL=10log102=20 dBAverage transmission loss required for various levels of speech privacyAverage Transmission loss of wall, dBHearing conditionsRating30 or lessNormal speech can be understood quite easily and distinctly through the wall.Poor30-35Loud speech can be understood fairly well. Normal speech can be heard but not easily understood.Fair35-40Loud speech can be heard, but is easily intelligible. Normal speech can be heard only faintly, if at all.Good not40-45Loud speech can be faintly heard but not understood. Normal speech is inaudible.Very goodrecommended for dividing walls between apartments.45 or greaterVery loud sounds, such as loud singing, brass musical instruments, or a radio at full volume can be heard only faintly or not at all.Excellentrecommended for band rooms, music practice rooms, radio and sound studios,2. STL in a separated roomSound transmission loss is calculated by:SpeakerMicrophone(Receiver)Room2Partition(Source)12Room11210STL10logSLLAL1L2The is obtained as follows: The sound power impinging on the test specimen from the source side is 24sspWScS= surface area of test specimen, m2 ssWI S(4.8)4scI22spc1210STL10logSLLAIn the source roomIn the receiver room The rate of energy transmission into the room equals the rate of energy absorption, at steady-state conditions. Thus (4.12)rWIA24rrp AWcOr(4.8)4cI22rpcL1SpeakerMicrophone(Receiver)Room2Partition(Source)12Room1Sound transmission loss is calculated:24sspWScL224rrp AWcrsWWtiII22srp SpA From the definition of transmission coefficient: 22srp Sp A210210logsrp SSTLp A22101022/10log10log/srefrrefppSppA221010102210log10log10logsrrefrefppSppA121010logSLLA3. Sound transmission class STC STC is a single-number rating used primarily to rate the speech privacy of a barrier or other structure. It is determined from a plot of STL data measured in 1/3-octave bands (or octave bands) from 125 to 4000 Hz. (NRC)STC following conditions:1. The STL value at any frequency cannot be more than 8 dB below the STC contour.2. The sum of all deficiencies (STL less than contour value) at all frequencies cannot exceed 32 dB. 3. The STC value is obtained from the STL value of the highest-valued contour at 500 Hz. The sound transmission class number is used to rate the acoustic performance of walls, floors, ceilings, doors, folding partitions, panels and other architectural structures. Test data curveSTC 46STC contourTransimission loss, dBBand center frequency, Hz125 200 320 500 800 1250 2000 3200 5000100 160 250 400 630 1000 1600 2500 4000 63006050403020100頻率頻率參考量參考量100-19125-16160-13200-10250-7315-4400-1500063018002100031250416004200042500431504 Can we always find the STC for sound transmission loss of a panel?STC ratings for various levels of speech privacy25303540454850NormalLoudLoudLoudMustSomeLoudSpeech can be understood quite easilySpeech can be understood fairly wellSpeech audible but not intelligibleSpeech audible as a murmurstrain to hear loud speechLoud speech barely audibleSpeech not audibleSTC ratings for common building materialsMaterial STC rating1/4-in steel plate361/4-in plate glass263/4-in plywood284-in brick wall416-in concrete-block wall421/2-in gypsum board on both sides of 2 x 4studs3312-in reinforced-concrete wall5614-in cavity wall (8-in brick2-in air space 4-in brick)65 國家標(biāo)準(zhǔn)民用建筑隔聲設(shè)計規(guī)范（GBJ118-88）中，對住宅分戶墻的隔聲性能規(guī)定是：一級住宅50dB，二級住宅45dB，三級住宅40dB . 參考發(fā)達(dá)國家相關(guān)標(biāo)準(zhǔn)，將我國住宅分戶隔墻的空氣聲計權(quán)隔聲量的實驗室測量值均定為不應(yīng)小于50dB，現(xiàn)場測量值不應(yīng)小于45dB；套內(nèi)分室隔墻的空氣聲計權(quán)隔聲量，實驗室測量值均定為不應(yīng)小于35dB，現(xiàn)場測量值不應(yīng)小于30dB。 表表 各國住宅分戶隔墻隔聲最低要求對比表各國住宅分戶隔墻隔聲最低要求對比表 單位： dB注：Rw和DnT，w分別為墻體隔聲量的實驗室測量值和現(xiàn)場測量值。國家隔聲澳大利亞一戶居室與另一戶廚房、衛(wèi)生間相鄰時其間分戶墻Rw50，其余Rw45英國Rw50德國Rw54丹麥Rw54新西蘭Rw55美國STC（Rw）50或DnT，w45dB中國現(xiàn)場測量隔聲量404. Insulation value of combined structural elements It is often necessary to calculate the net insulation value of two structural elements acting in combination. The net insulation of a wall with a window, a partition with a door or a roof with a rooflight, can be obtained by calculation if the insulation values of each element are known. exampleWall: 20m2, walldoorwindows5110door: 2m2, windows: 3m2, 32102310iieqSS101TL10logeq532315 102 103 101.6 1020eq 101TL10log27eqdBExample: Let us assume that a class rooms have 6mm fixed glazing of average insulation 26 dB set in a wall with an insulation value of 50 dB and that the ratio of window to wall is 2:1. calculate the Insulation value of combined windows and wall?wallWindowsglazing0 5 10 15 20 25 30 35 40 45 50 55 60 dB1 3 5 10 15 20 25 30 35 40 45 50 55 60 dB Difference1:2501:1251:641:321:161:81:41:21:12:14:18:1Loss of insulation (deduct from higher insulation)Ration of two areas (lower to higher insulation)Ratio of areas: 2:1Difference in insulation: 50 26 = 24 dBFrom graph, loss of insulation = 23 dBTherefore net insulation of wall and window = 50 23 =27 dBWall 50dBWindowsGlazing 26 dB0 5 10 15 20 25 30 35 40 45 50 55 60 dB1 3 5 10 15 20 25 30 35 40 45 50 55 60 dB Difference1:2501:1251:641:321:161:81:41:21:12:14:18:1Loss of insulation (deduct from higher insulation)Ration of two areas (lower to higher insulation)exercise A class rooms have fixed glazing of average insulation 20 dB set in a wall with an insulation value of 45 dB and that the ratio of window to wall is 1:4. calculate the Insulation value of combined windows and wall?The hole effects of STL on the wall 1 12212SSSSFor the wall and hole, we set:102111S2S21 12212SSSS121201SSSS 212SSSUsually, 12SS21SS102121SSS2/S1STL dB1/1000301/100201/10101/23Equal STLwallwindow21SSIn our design, We assume:1122SSWhich means if we want to improve the STL, we should improve the windows STL .Ratio of areas: 2:1Difference in insulation: 50 26 = 24 dBFrom graph, loss of insulation = 23 dBTherefore net insulation of wall and window = 50 23 =27 dB Wall 50dBWindowsGlazing 26 dBAttenuation versus Dissipation of Acoustic Energy Note !Transmitted soundRefracted and absorbed soundIncident soundReflected soundAbsorption coefficient:iriIIITransmission coefficient: tiIIIncident: Incident: I Ii i Reflected: Reflected: I Ir rAbsorbed: Absorbed: I Ia aTransmitted: Transmitted: I It t The guideline that a good absorber is a poor barrier is illustrated by the following example. Consider a sound wave impinging on the surface of an absorbing structure. If 80 percent of the incident intensity is absorbed, 10 percent is reflected, and 10 percent is transmitted, then 1.0STL10log10dB0.1=10log=10dB=33dBabsorbedabsorbedreflectedreflectedtransm ittedtransm ittedE1E1E1E1E1E1E1E1=10log1011081010.11.0TL10096.5TL0.00051.01000.0510031010Absorption and transmission-loss characteristics of absorbers and barriers end