The Intensity of Sound

The amplitude of the wave translates into the loudness or intensity of the sound, which is related to the power of the wave.

I = P/A, where I = Intensity, P = Power, and A = Area.

Power is in metric units of Watts and Area is in metric units of m², therefore, Intensity results in W/m².

A scale has been developed which gives relative intensities of sounds compared to a threshold of hearing at zero decibels.

The threshold of pain is considered to be 120 dB.

To find the dB reading of a sound, use the equation dB = 10 log (I / I₀), where I = intensity in W/m² of the sound and I₀ = the intensity of the threshold of hearing at 1 x 10^-12 W/m². Notice from the website reading (that follows) that every increase of 10 dB means an increase in a power of ten of W/m². Going from 30 to 60 dB is actually a 1000 times increase in intensity! (10 x 10 x 10, or 10³ increase)

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