Sound Intensity Formula

Sound intensity is described as sound per unit area perpendicular to the path of the sound waves and which is represented by I. The sound intensity SI unit is W/m2 (watt per square meter).
The SI unit of sound intensity is watt per square meter (W/m2). The standard definition is the calculation of noise sound intensity in the air at the listener position as a quantity of sound energy.

The Formula for sound intensity is expressed as

\(\begin{array}{l}I=\frac{P}{A}\end{array} \)


P = sound power

A = area

In order to measure the sound intensity level, need to compare the given sound intensity value with standard intensity value.

The formula of Sound Intensity Level is expressed as

\(\begin{array}{l}I_{L} = 10 log_{10}\frac{I}{I_{0}}\end{array} \)


I = sound intensity and

Io = reference intensity

The unit of sound intensity is expressed in decibels (dB)

Solved examples on Sound Intensity

Example 1

A person whistles with the power of 0.9 × 10-4 W. Calculate the sound intensity at a distance of 7m.



P = 0.9 × 10-4 W

A = 7m

Sound intensity formula is

I = P / A

I = 0.9×104 / 7

I = 1.28 x 10-5 W/m2

Example 2

Determine the intensity level which is equivalent to an intensity 1 nW/m2.


Intensity Level formula is given by

IL = 10 log10 I / I0


I = 1 nWm-2 = 1 × 10-9 Wm2

Io = 10-12 Wm-2

IL= 10 log10 (1×109) / 1012

IL = 10 log10 103

IL = 30.


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