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

period two

Sound Perception and

Rating Methods

notes

Room Criteria (RC) Curves

	80	A
mPa	70	B
	60
ref 20
dB	50
pressure,	40								RC-50
									RC-45
sound	30								RC-40
	20								RC-35
									RC-30
approximate threshold for
									RC-25
hearing continuous noise	10
		31.5	63	125	250	500	1,000	2,000	4,000

octave-band frequency, Hz Figure 28

Room criteria (RC) curves are similar to NC curves in that they are used to provide a rating for sound-pressure levels in indoor environments. The major difference is that RC curves give an additional indication of sound character. As discussed in the previous example, sound spectrums can be unbalanced in ways that result in poor acoustical quality. Too much low-frequency sound results in a rumble, and too much high-frequency sound produces a hiss.

RC curves provide a means of identifying these imbalances. An RC rating consists of two descriptors. The first descriptor is a number representing the speech interference level (SIL) of the sound. The second descriptor is a letter denoting the character of the sound as a subjective observer might describe it.

nN identifies a neutral or balanced spectrum

nR indicates a “rumble”

nH represents a “hiss”

nRV denotes perceptible vibration

Calculating an RC value from octave-band sound-pressure data is not quite as easy as determining an NC value, but it is still fairly simple. The RC value is based on sound-pressure data from the eight octave bands between 31.5 Hz and 4,000 Hz. Note that these are different than the octave bands included on the NC chart.

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