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TRG-TRC007-EN 21
period two
Sound Perception and
Rating Methods
notes
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.
NC
NC
-
-
15
15
NC
NC
-
-
20
20
NC
NC
-
-
25
25
NC
NC
-
-
30
30
NC
NC
-
-
35
35
NC
NC
-
-
40
40
NC
NC
-
-
45
45
NC
NC
-
-
50
50
NC
NC
-
-
55
55
NC
NC
-
-
60
60
NC
NC
-
-
65
65
70
70
50
50
40
40
30
30
20
20
10
10
sound pressure, dB ref 20
sound pressure, dB ref 20
m
m
Pa
Pa
80
80
60
60
octave
octave
-
-
band frequency, Hz
band frequency, Hz
63
63
125
125
250
250
500
500
1,000
1,000
2,000
2,000
4,000
4,000 8,000
8,000
Noise Criteria (NC) Curves
approximate threshold for
approximate threshold for
hearing continuous noise
hearing continuous noise
Figure 26