Trane TRG-TRC007-EN manual A-B-CWeighting, Sound Perception and Rating Methods, period two

period two

Sound Perception and Rating Methods

notes

shall be X,” where X is a single-number descriptor conveying the desired quality of sound.

The most frequently used single-number descriptors are the A-weighting network, noise criteria (NC), and room criteria (RC). All three share a common problem, however: they unavoidably lose valuable information about the character, or quality, of sound. Each of these descriptors is based on octave- band sound data which, as noted earlier, may already mask tones. Further, the process of converting from eight octave bands to a single number overlooks even more sound data.

Despite this shortcoming, the single-number descriptors summarized in this clinic are valuable tools for defining sound levels in a space, and are widely used to specify the acoustical requirement of a space.

A–B–C Weighting

	0	C
dB	-10	B
response,
	-20			frequency responses for sound
				meter weighting characteristics
relative
	-30	A
	-40
	20	50	100	200	500	1,000 2,000	5,000	10,000

frequency, Hz Figure 23

One simple method for combining octave-band sound data into a single- number descriptor is A-,B-, or C-weighting. The weighting curves shown in Figure 23 compensate for the varying sensitivity of the human ear to different frequencies.

A-weighting, which is most appropriately used for low-volume (or quiet) sound levels, best approximates human response to sound in the range where no hearing protection is needed. B-weighting is used for medium-volume sound levels. C-weighting is used for high-volume (or loud) sound levels where the response of the ear is relatively flat.

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