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dB
Output Power. dBs Average value 160
in watts.
300
100
30
10
3
1
0.3
0.1
0.03
0.01
0.003
0.001
0.0003
0.0002 µ bar of pressure
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Jet engine
Community siren
Pneumatic riveter
Threshold of pain
Loud rock band, punch press
Chain saw
Very loud music
Loud music, heavy truck, subway train
Orchestra, highway traffic
Average conversation
Quiet music
Average residence, computer system
Background music
Quiet office, computer hard drive
Whispering
Faint sounds, paper rustling
Threshold of hearing
FIG. 23.5
Typical sound levels and their decibel levels.
Dynamic range ≅ 120 dB s
A common question regarding audio levels is how much the power
level of an acoustical source must be increased to double the sound
level received by the human ear. The question is not as simple as it
first seems due to considerations such as the frequency content of the
sound, the acoustical conditions of the surrounding area, the physical
characteristics of the surrounding medium, and—of course—the
unique characteristics of the human ear. However, a general conclusion
can be formulated that has practical value if we note the power
levels of an acoustical source appearing to the left of Fig. 23.5. Each
power level is associated with a particular decibel level, and a change
of 10 dB in the scale corresponds with an increase or a decrease in
power by a factor of 10. For instance, a change from 90 dB to 100 dB
is associated with a change in wattage from 3 W to 30 W. Through
experimentation it has been found that on an average basis the
loudness level will double for every 10-dB change in audio level—a
conclusion somewhat verified by the examples to the right of Fig.
23.5. Using the fact that a 10-dB change corresponds with a tenfold
increase in power level supports the following conclusion (on an
approximate basis): Through experimentation it has been found that on
an average basis, the loudness level will double for every 10-dB
change in audio level.
To double the sound level received by the human ear, the power
rating of the acoustical source (in watts) must be increased by a
factor of 10.
DECIBELS ⏐⏐⏐ 1025