## The Decibe- Loudnessl

The decibel is the unit of sound intensity. The smallest audible sound is 0 dB and from this point the sound intensity increases logarithmically so a sound 10 times more powerful is 10 dB, a sound 100 times more powerful is 20 dB and a sound 1,000 times more powerful than near total silence is 30 dB. Some common sounds and their decibel ratings:

• A whisper - 15 dB

• Normal conversation - 60 dB

• A lawnmower - 90 dB

• A car horn - 110 dB

• A rock concert or a jet engine - 120 dB

• A gunshot or firecracker - 140 dB

Because the decimal scale is a log scale two sounds differ by 10 decibels if one is 10 rimes bigger than the other:

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and by 20 decibels if one istimes bigger than the other:

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Since the human ear is not equally sensitive to all sound frequencies, noise levels at maximum human sensitivity — somewhere between 2 and 4 kHz — the decimal scale does not accurately measure the sounds experienced by the ear. Despite this we can make the following generalizations

Any sound above 85 dB can cause hearing loss, and the loss is related both to the power of the sound as well as the length of exposure. Eight hours of 90-dB sound can cause damage to your ears; any exposure to 140-dB sound causes immediate damage (and causes actual pain).

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