Trane TRG-TRC007-EN Sound Perception and Rating Methods, period two, Room Criteria RC Curves

period two

Sound Perception and

Rating Methods

notes

Room Criteria (RC) Curves

	80	A
mPa	70	B
	60
dB ref 20
	50				D
pressure,	40	RC-31 (R)							RC-50
								E
						C			RC-45
sound	30								RC-40
	20								RC-35
									RC-30
	10								RC-25
		31.5	63	125	250	500	1,000	2,000	4,000

octave-band frequency, Hz Figure 30

If we plot the acoustical data for our example office space on the RC chart, we find that it results in a rating of RC-31(R). The SIL is 31 and the sound-pressure levels in the 63 Hz and 125 Hz octave bands are above line D, indicating a rumble characteristic of the sound.

This time, our objective and subjective analyses lead to the same conclusion. Although the space is quiet enough, the background noise is perceived as having a rumble. A sound spectrum that falls in the RC neutral category would be judged as excellent by most observers. It is this conformity of analysis results that makes the RC rating method a better tool than the other single- number descriptors for specifying acoustical requirements indoors. Despite the advantages of the RC rating system, it is less widely used than other single- number descriptors.

Finally, accurate determination of sound-power levels for the 16 Hz and 31.5 Hz octave bands requires a very large reverberant room. Most HVAC equipment manufacturers do not provide sound data in these two octave

bands due the cost of constructing such a large test room and the difficulty in qualifying it. This makes it difficult to predict sound-pressure levels in these octave bands.

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