Building Services Engineering 5th Edition Handbook

338 Room acoustics
Table 14.6 Noise rating applications.
Application Noise rating Comment
Acoustic laboratory NR 15 Critical acoustics
Radio studio NR 15 Critical acoustics
Concert hall NR 15 Critical acoustics
TV studio NR 20 Excellent listening
Large conference room NR 25 Very good listening
Hospital, home, hotel NR 30 Sleeping, relaxing
Library, private office NR 35 Good listening
Office, restaurant, retail NR 40 Fair listening
Cafeteria, corridor, workshop NR 45 Moderate listening
Commercial garage, factory NR 50 Minimum speech interference
Manufacturing NR 55 Speech interference
Heavy engineering to industrial NR 60 to NR 80 Sound levels judged on merits,
leading to risk of hearing damage
EXAMPLE 14.8
An air-conditioning fan produces the sound spectrum shown in Table 14.7 within an occupied
room. Calculate the sound pressure levels for noise ratings NR 35, NR 40, NR 45,
NR 50 and NR 55, and plot the noise rating curves for the frequency range from 31.5 to
8000 Hz. Plot the room sound pressure levels on the same graph and find which noise
rating is not exceeded.
Table 14.7 Noise spectrum in Example 14.8.
Frequency f (Hz) 31.5 63 125 250 500 1k 2k 4k 8k
Room SPL (dB) 39 44 48 52 55 49 36 33 28
A manually calculated example for one noise rating curve is shown. The reader should use the
spreadsheet graph or chart facilities to plot the whole figure. Calculate the SPL values for NR 55.
NR fd = 55
SPL = NR f × B f + A f dB
Calculate the SPL at each frequency for the values of B f and A f from Table 14.5. For 31.5 Hz,
SPL = 55 × 0.681 + 55.4 dB
= 92 dB
For 63 Hz,
SPL = 55 × 0.79 + 35.5 dB
= 78 dB