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28 TRG-TRC007-EN
notes
period two
Sound Perception and
Rating Methods
Octave-Band Rating Method
A more useful method of rating sound level is to use the octave bands
discussed earlier. While octave-band data is not as simple to interpret as a
single-number rating, it provides much more information about the character of
the sound.
Both sound-power levels and sound-pressure levels can be presented in
octave-band format. When equipment sound data is provided in terms of
sound-power level in each octave band, an “apples to apples” comparison
can be made between various pieces of equipment. In addition, this sound-
power data can be converted to sound-pressure levels when the details of the
environment are known. This type of analysis will be discussed further in
Period Three.
Sound-pressure levels in each octave band, whether predicted from sound-
power data or measured in an existing environment, reveal much more about
the character of sound than any of the single-number rating methods. It is
important to note that any of the single-number ratings described in this section
can be calculated from octave-band sound-pressure data. However, octave-
band data cannot be derived from any of the single-number ratings.
Octave-Band Rating Method
octave
band
1
2
3
4
5
6
7
8
octave
band
1
2
3
4
5
6
7
8
center
frequency (Hz)
63
125
250
500
1,000
2,000
4,000
8,000
center
frequency (Hz)
63
125
250
500
1,000
2,000
4,000
8,000
equipment
sound power
(dB ref 10
-12
W)
103
104
100
101
98
93
88
85
equipment
sound power
(dB ref 10
-12
W)
103
104
100
101
98
93
88
85
sound pressure
in the space
(dB ref 20 m
mm
mPa)
63
52
45
38
31
24
16
10
sound pressure
in the space
(dB ref 20 m
mm
mPa)
63
52
45
38
31
24
16
10
Figure 32