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Sound Perception: Loudness

Our perception of the loudness of sound is related to the intensity of sound, but in a logrithmic way not a linear way. A sound that is 10 times the intensity of another sounds only about 2 times louder. The range of intensities which the human ear can detect is amazingly large: from the threshold of hearing (the softest detectable sound) to the threshold of pain (so loud it hurts!) This is a range of 10-12 W/m2(watts per square meter) to 101 W/m2. The pressure of the threshold of hearing corresponds to a pressure wave in which the molecules of air are displaced only one-billionth of a centimeter. The scale commonly used to measure the loudness or sound intensity level is the decibel. The threshold of hearing is assigned the sound intensity level of 0 dB. In general the the sound intensity level of a sound of intensity I is given by where I is the intensity in watts per square meter and I0 = 10-12 W/m2 (the threshold of hearing.)

Source
Intensity
Intensity
Level
# of Times
Greater Than TOH
Threshold of Hearing (TOH)
1*10-12 W/m2
0 dB
100
Rustling Leaves
1*10-11 W/m2
10 dB
101
Whisper
1*10-10 W/m2
20 dB
102
Normal Conversation
1*10-6 W/m2
60 dB
106
Busy Street Traffic
1*10-5 W/m2
70 dB
107
Vacuum Cleaner
1*10-4 W/m2
80 dB
108
Large Orchestra
6.3*10-3 W/m2
98 dB
109.8
Walkman at Maximum Level
1*10-2 W/m2
100 dB
1010
Front Rows of Rock Concert
1*10-1 W/m2
110 dB
1011
Threshold of Pain
1*101 W/m2
130 dB
1013
Military Jet Takeoff
1*102 W/m2
140 dB
1014
Instant Perforation of Eardrum
1*104 W/m2
160 dB
1016

 

The perceived loudness also depends upon the frequency of the sound.

 

 

Graphical rule
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