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TRG-TRC007-EN 23
period two
Sound Perception and
Rating Methods
notes
Room criteria (RC) curves are similar to NC curves in that they are used to
provide a rating for sound-pressure levels in indoor environments. The major
difference is that RC curves give an additional indication of sound character.
As discussed in the previous example, sound spectrums can be unbalanced in
ways that result in poor acoustical quality. Too much low-frequency sound
results in a rumble, and too much high-frequency sound produces a hiss.
RC curves provide a means of identifying these imbalances. An RC rating
consists of two descriptors. The first descriptor is a number representing the
speech interference level (SIL) of the sound. The second descriptor is a letter
denoting the character of the sound as a subjective observer might describe it.
n N identifies a neutral or balanced spectrum
n R indicates a “rumble”
n H represents a “hiss”
n RV denotes perceptible vibration
Calculating an RC value from octave-band sound-pressure data is not quite as
easy as determining an NC value, but it is still fairly simple. The RC value is
based on sound-pressure data from the eight octave bands between 31.5 Hz
and 4,000 Hz. Note that these are different than the octave bands included on
the NC chart.
Room Criteria (RC) Curves
approximate threshold for
approximate threshold for
hearing continuous noise
hearing continuous noise
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
Figure 28