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24 TRG-TRC007-EN
notes
period two
Sound Perception and
Rating Methods
The following steps describe how to determine an RC rating.
1 Plot the octave-band sound-pressure levels on the RC chart.
2 Determine the SIL by calculating the arithmetic average of the sound-
pressure levels in the 500 Hz, 1,000 Hz, and 2,000 Hz octave bands. In this
example, the arithmetic average of 38 dB, 31 dB, and 24 dB is 31 dB.
3 Draw a line (C) with a slope of –5 dB per octave that passes through the
calculated SIL at the 1,000 Hz octave band. This is the reference line for
evaluating the character of the sound spectrum.
4 Between 31.5 Hz and 500 Hz, draw a line (D) that is 5 dB above the reference
line (C). Between 1,000 Hz and 4,000 Hz, draw a second line (E) that is 3 dB
above the reference line (C). These two boundary lines (D and E) represent
the maximum permitted deviation to receive a neutral (N) rating.
5 Judge the character of the sound quality by observing how the sound
spectrum deviates from the boundary lines drawn in Step Four. Use the
following criteria to choose the appropriate letter descriptor that
characterizes the subjective quality of the noise.
n Neutral (N): The sound level in each of the octave bands between
31.5 Hz and 500 Hz is below line D, and the sound level in each of
the octave bands between 1,000 Hz and 4,000 Hz is below line E.
n Rumble (R): The sound level in any octave band between 31.5 Hz
and 500 Hz is above line D.
n Hiss (H): The sound level in any octave band between 1,000 Hz and
4,000 Hz is above line E.
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
31.5
31.5
63
63
125
125
250
250
500
500
1,000
1,000
2,000
2,000 4,000
4,000
RC
RC
-
-
25
25
RC
RC
-
-
30
30
RC
RC
-
-
35
35
RC
RC
-
-
40
40
RC
RC
-
-
45
45
RC
RC
-
-
50
50
A
A
B
B
Room Criteria (RC) Curves
C
C
D
D
E
E
Figure 29