Sound transmission in buildings. Flanking sound transmission - Building Acoustics - page 340

The constant ε is equal to 1.0 in the case of totally absorbing sidewalls and equal to 2.0
for totally reflecting ones. The corresponding sound reduction index for the transmission
path through the suspended ceiling, assuming minor attenuation in the plenum, is then
given by

2

⎡ ⎤

ε L

R

RRR =+−⋅ ⎢ 10 lg ,

⎥

cl S R

4 h (9.20)

⎣ ⎦

where R =− ⋅ 10 lg τ and R =− ⋅ 10 lg τ .

S S R R

The transmission factors τ S and τ R are calculated from Equation (9.14) .

80

70

60

50

40

30

20

Via ceiling
ex/ attenuation
Plasterboard
40 mm abs.

10

0

63 125 250 500 1000 2000 4000

Frequency (Hz)

Figure 9.12 Sound reduction index R cl for transmission by way of a suspended ceiling and plenum. Suspending
ceiling of 9.5 mm plasterboard with 40 mm thick porous absorber. Calculated sound reduction index of
plasterboard and absorber is presented by separate curves. The sound reduction index R cl is also shown for the
case of no attenuation in the plenum, (Equation (9.20) ).