Building Services Engineering 5th Edition Handbook

Room acoustics 335
SRI = sound reduction index of common surface dB
S 4 = area of surface common to both rooms m 2
T 2 = reverberation time of intermediate space s
V 2 = volume of intermediate space m 3
EXAMPLE 14.6
A showroom has floor dimensions of 25 m × 10 m and a height of 3.6 m to a suspended
tile ceiling. The average height of the ceiling void is 1.8 m. An air-conditioning system
has distribution ductwork in the roof void above the suspended acoustic ceiling tiles. The
air-handling plant room is adjacent to the roof void and there is a common plant room
wall of 5 m × 2.5 m high in the roof void. The sound pressure level in the plant room is
expected to be 50 dB. The reverberation time of the roof void is 0.8 s. The plant room
wall adjoining the roof void has a sound reduction index of 10 dB. Calculate the sound
pressure level that is produced within the roof void as the result of the air-handling plant
room noise.
SPL 3 = 50 dB
SRI = 10 dB
S 4 = 12.5 m 2
T 2 = 0.8 s
V 2 = 25 × 10 × 1.8 m 3
= 450 m 3
SPL 3 = SPL 1 − SRI + 10 × log(T 2 ) − 10 × log(0.16 × V 2 ) dB
= 50 − 10 + 10 × log(12.5) + 10 × log(0.8) − 10 × log(0.16 × 450) dB
= 50 − 10 + 10 + 0 − 11 dB
= 39 dB
Sound pressure level in the target room
The sound pressure level in the target occupied room or space can be taken as:
SPL 4 = SPL 3 − SRI + 10 × log(S 5 ) + 10 × log(T 3 ) − 10 × log(0.16 × V 3 ) dB
(Sound Research Laboratories Limited), where
SPL 4 = sound pressure level in target room dB
SPL 3 = sound pressure in adjacent room dB
SRI = sound reduction index of common surface dB
S 5 = area of surface common to both rooms m 2
T 3 = reverberation time of target room s
V 3 = volume of target room m 3