Basic Documentation

Commentary on HVAC System Sound
Exhaust Terminal Reverberant Radiated Sound Power Level at 50% Maximum Airflow
125 250 500 1,000 2,000 4,000
Hz Hz Hz Hz Hz Hz
47 dB 41 dB 36 dB 32 dB 28 dB 23 dB
Exhaust Terminal Reverberant Discharge Sound Power Level at 50% Maximum Airflow
125 250 500 1,000 2,000 4,000
Hz Hz Hz Hz Hz Hz
61 dB 56 dB 53 dB 49 dB 45 dB 39 dB
NOTE: Exhaust terminal manufacturer’s sound ratings typically cover only the 125 to 4,000 Hz octave bands.
See Environmental Adjustment Factor in Chapter 4 to determine if the manufacturer’s sound
rating needs to be adjusted based upon the type of sound rating test (Free Field or
Reverberant).
Radiated Sound
First, we’ll determine the effect of the radiated sound pressure level of the two exhaust
terminals. With reference to the text covering Radiated Sound Attenuation, Table 25 gives
expected attenuation of typical dropped ceiling material on radiated sound that originates
above the ceiling.
Table 28. Attenuation of a Dropped Ceiling and Plenum on Radiated Sound (repeated).
Ceiling 63 125 250 500 1,000 2,000 4,000 8,000
Hz Hz Hz Hz Hz Hz Hz Hz
1/2-inch
Thick Tiles
Fiberglass
4 dB 7 dB 8 dB 9 dB 10 dB 11 dB 14 dB 18 dB
5/8-inch
Thick Tiles
Fiberglass
5 dB 8 dB 10 dB 12 dB 13 dB 14 dB 16 dB 19 dB
5/8-inch
Thick
Gypsum
Board
10 dB 15 dB 22 dB 26 dB 30 dB 28 dB 30 dB 30 dB
Subtracting the Table 28 values for 5/8 inch-thick fiberglass tiles from the manufacturer’s
rating data for the 125 Hz through 4,000 Hz bands, leaves the following radiated sound level
at the ceiling just below each terminal:
125 250 500 1,000 2,000 4,000
Hz Hz Hz Hz Hz Hz
39 dB 31 dB 24 dB 19 dB 14 dB 7 dB
Siemens Building Technologies, Inc. 91