Basic Documentation

Chapter 5–HVAC System Sound Analysis
To determine the attenuation and subsequently the sound power level a person would
experience standing mid way between the two terminals (about a 7 foot distance from the
person’s ears to each point in the ceiling just below the terminals), the Space Effect (Schultz)
equation is used:
RLp = 5 Log (V) + 10 Log (r) - 25 + 3 Log (f)
Where:
RLp = Attenuation due to distance and room size.
V = Room Volume (240 sq ft x 10 ft).
R = Distance from the sound source (7 ft).
F = Octave band frequency Hz.
RLp = 5 Log (2,400) + 10 Log (7) - 25 + 3 Log (f)
= 16.9 + 8.5 - 25 + 3 Log (f)
= 0.4 + 3 Log (f)
Substituting each octave band frequency in the equation’s (f) term will yield the following
room dB attenuation values at each octave band:
125 250 500 1,000 2,000 4,000
Hz Hz Hz Hz Hz Hz
6 dB 7 dB 8 dB 9 dB 10 dB 10 dB
Subtracting these values from the radiated sound level at the ceiling yields the following room
sound pressure level at 5 feet above the floor from each terminal:
125 250 500 1,000 2,000 4,000
Hz Hz Hz Hz Hz Hz
33 dB 24 dB 16 dB 10 dB 4 dB 0 dB
Since each of the two exhaust terminals generates a sound pressure level of equal value that
converge at the same point, add 3 dB to the individual sound pressure level value (per Table
3), to determine the resulting sound pressure level at that point. The result is listed in the
following table:
125 250 500 1,000 2,000 4,000
Hz Hz Hz Hz Hz Hz
36 dB 28 dB 21 dB 13 dB 7 dB 0 dB
The values determined for the radiated sound pressure level are quite low and will not
adversely affect the laboratory noise criteria level of 40 dB. Remember that these values are
for the radiated sound pressure level component; there is also the discharge sound power
component that must be addressed.
92 Siemens Building Technologies, Inc.