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82 CHAPTER 5. SOUND INSULATIONthe transmission of the sound (and vibrations) energy from one room to theother. This indirect way of transmission throughall those other boundaries /paths (other than directly through the partition which separates the rooms)is called ’flanking’ transmission (see Figure 5.1). Consequently a distinctionmustbemadebetweenthesoundinsulationRofaseparatingstructurewhichis called the ’sound reduction index’ in the international ISO140 norm, andthesoundinsulation D n between two roomswhich iscalled ’the normalizedlevel difference’ in the ISO140 norm.Figure 5.1: Flanking (2 to 4) and direct (1) transmission.It is obvious that in practice, i.e. in the acoustics of a construction,only the sound insulation D n between two rooms matters because flankingtransmission is always present. Normally we will perform the so-called ’fieldmeasurements’ of the insulation between two given rooms, where we ignorethesoundpathbetweenthesource-andreceivingroom. ThesoundinsulationD n is expressed in dB. To characterize the quality of a partition constructionby measurements all the flanking effects must be eliminated and thus a fieldmeasurement is not an option. A ’laboratory-only measurement’ must beperformed (see Figure 5.2) Such a laboratory consists of two rooms : thesource- and receiving room are independent with regard to vibrations, andthe sound transmission occurs only through the structure under test. Thisenables us to determine the sound insulation R (this is typically larger thanD n ).We will now give the formula that enables us to experimentally determinethe sound insulation as function of the frequency. Let S represent theseparation plane consisting of the wall to be tested (10 m 2 is required for
5.1. MEASURING SOUND INSULATION 83Figure 5.2: Laboratory for measuring sound insulation of a separating structure.measurements in laboratory). Because of the fact that sound transmission isa transfer of energy, we will consider the sound intensity levels :R = L I1 −L I2 = 10log I 1I 2(5.2)with I 1 the incident intensity and I 2 the transmitted intensity at the otherside of the wall. Now, the intensity level I 2 transmitted through the wallis quite difficult to measure because also the walls will contribute to themeasured sound level in the receiving room (in the normalized laboratorythe hard walls create a diffuse field). For this reason we will use the meanintensity Ī2 in the receiving room and convert this to the intensity I 2 . Bothintensities are related to each other by :I 2 S = Ī2A (the transmitted energyis absorbed by the walls with total absorption A). This means that we canwrite the sound insulation as follows :R = 10log I 1I 2= 10log p2 1because I 1 = p2 14ρcI 2 4ρcin a diffuse field.p 2 1= 10log4ρcĪ2 A Swith SI 2 = AĪ2= 10log p2 1p 2 2 A S
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VRIJE UNIVERSITEITBRUSSELAcousticsB
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iiWhen sound becomes noise, it will
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ContentsI Introduction to acoustics
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CONTENTSvii4.3 Measuring the acoust
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Part IIntroduction to acoustics1
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4 CHAPTER 1. FUNDAMENTAL CONCEPTS O
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10 CHAPTER 1. FUNDAMENTAL CONCEPTS
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24 CHAPTER 2. THE HUMAN HEARING SYS
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Page 69 and 70: Chapter 4Sound AbsorptionAll(constr
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Page 125 and 126: 6.4. RADIATION NOISE 115Figure 6.17
Page 127 and 128: 6.4. RADIATION NOISE 117Figure 6.20
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132 CHAPTER 8. NOISE ON THE WORK FL
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140 CHAPTER 9. COMMUNITY NOISE2. No
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142 CHAPTER 9. COMMUNITY NOISE
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144 APPENDIX A. MATERIAL PROPERTIES
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152 BIBLIOGRAPHY[12] Bruel and Kjae
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