# Sound Intensity Formula

SoundÂ intensityÂ isÂ describedÂ asÂ soundÂ perÂ unitÂ areaÂ perpendicularÂ toÂ theÂ pathÂ ofÂ theÂ soundÂ waves and which is represented byÂ I.Â The sound intensity SI unit isÂ 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

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

Where

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 LevelÂ is expressed as

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

Where

I = sound intensity and

Io = reference intensity

The unit of sound intensity is expressed inÂ decibelsÂ (dB)

## Solved examples on Sound Intensity

Example 1

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

Solution:

Given

P = 0.9 Ã— 10-4 W

A = 7m

Sound intensity formula is

I = P / A

I = 0.9Ã—10âˆ’4 / 7

I = 1.28 x 10-5 W/m2

Example 2

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

Solution:

Intensity Level formula is given by

IL = 10 log10 I / I0

Here

I = 1 nWm-2 = 1 Ã— 10-9 Wm2

Io = 10-12 Wm-2

IL= 10 log10 (1Ã—10âˆ’9) / 10âˆ’12

ILÂ = 10 log10 103

ILÂ = 30.