Building Acoustics

160 Building acoustics As derived in Chapter 3 (section 3.5.1.1), the RMS-value of the sound pressure at a given frequency may b ...

Sound absorbers 161 ref () p() 20lg px Lx p ⎛⎞ =⋅⎜⎟ ⎝⎠   , and exhibiting alternating maxima and minima, is shown in Figure 5. ...

162 Building acoustics {} {} { } {} r1 r 2 12 i1 i 2 F(, F(, (,) , ( ,) , F(, F(, pxt pxt Rx f Rx f pxt px t == (5.6) and a tran ...

Sound absorbers 163 where d = x 2 - x 1. This is the basic equation when using this two-microphone method to determine reflectio ...

164 Building acoustics 00S 55.3 55.3 , 4 VV T cAcA mV =⋅=⋅ + (5.14) where V is the volume of the room and A is the total equival ...

Sound absorbers 165 Examples will be given in section 5.7 where we shall include matrices representing porous materials based on ...

166 Building acoustics acoustical equations derived previously. We shall use both approaches, starting with a resonator where th ...

Sound absorbers 167 jj 00 a j ˆˆ ˆˆ kd kd ir kd kd xd ir p cpe pe Z vS S pe p e ρ − − = ⎛⎞ + ⎜⎟==⋅ ⎝⎠⋅ − j . (5.20) As we assume ...

168 Building acoustics 5.4.1.3 Acoustical resistance To calculate energy losses due to viscous forces, we have to modify the sim ...

Sound absorbers 169 () () 1 1 0 0 2 Jj 1 jJj s s s ρρ. − ⎛⎞− =−⎜ ⎜− − ⎝⎠ ⎟ ⎟ (5.30) Assuming that the length d of the tube in qu ...

170 Building acoustics 1 0 tan( ) j=j 1^2 2 s kb Zdd kb ρω ρ ω. ′ − ⎛⎞ ⎜⎟ =−⎜ ′ ⎜⎟ ⎝⎠ ⎟ (5.35) d b z x y Figure 5.10 A single sl ...

Sound absorbers 171 (^) () 2 0 radiation 0 1 8 j a 23 a Z cS ρω ωρ ππ ⎛ ≈+⋅⎜ ⎝⎠ 0 ⎞, ⎟ (5.37) where S and a are the piston radiu ...

172 Building acoustics situation, which was mentioned in section 5.2.3, are when using the so-called micro- perforated panels, p ...

Sound absorbers 173 Figure 5.12 Absorption factor at normal incidence. Hole-perforated plate backed by a cavity of depth 100 mm. ...

174 Building acoustics As mentioned several times already, it is possible to obtain a sufficiently high resistance just by makin ...

Sound absorbers 175 2 ln sin. 2 b d πε π ⎡ ⎛⎞⎤ Δ=− ⋅⎢ ⎜⎟⎥ ⎣ ⎝⎠⎦ (5.40) The quantity b is the width of the slot, and ε is the rat ...

176 Building acoustics 5.4.1.6 Membrane absorbers These absorbers are, as the name suggests, ideally, an impervious membrane str ...

Sound absorbers 177 model has to be modified. Kang and Fuchs (1999) have presented measured and predicted results for such micro ...

178 Building acoustics frame is completely stiff resulting only in a movement of the air contained in the pores, this being subj ...

Sound absorbers 179 Denoting the mean value of the particle velocity as vm will give the following equation of force (^) 0m 2 m ...