Trane TRG-TRC007-EN Manuel D’Utilisation

TRG-TRC007-EN

21

period two

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

soun

d pres

su

re,

 d

B ref

 2

0 

soun

d pre

ss

ure,

 d

B ref

 2

0 

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

approximate threshold for 

approximate threshold for 

hearing continuous noise

hearing continuous noise