Trane TRG-TRC007-EN manual Noise Criteria NC Curves

period two

Sound Perception and

Rating Methods

notes

Noise Criteria (NC) Curves

	80
mPa	70
								NC-65
20	60
								NC-60
ref
								NC-55
dB	50
								NC-50
pressure,
	40							NC-45
								NC-40
								NC-35
sound	30
								NC-30
	20							NC-25
approximate threshold for								NC-20
hearing continuous noise	10							NC-15
	63	125	250	500	1,000	2,000	4,000	8,000

octave-band frequency, Hz Figure 26

Noise criteria (NC) curves are probably the most common single-number descriptor used to rate sound-pressure levels in indoor environments. Like the equal-loudness contours on which they are based, the loudness along each NC curve is about the same. Each NC curve slopes downward to reflect the increasing sensitivity of the ear to higher frequencies.

It should also be noted that NC charts do not include the 16 Hz and 31.5 Hz octave bands. Although HVAC equipment manufacturers typically do not provide data in these bands (because it is very difficult to obtain reliably), these octave bands do effect the acoustical comfort of the occupied space. Nevertheless, these octave bands can be measured in a space that is already built and may provide useful diagnostic information.

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