# Sound intensity: Definition, Types of Sound, and Examples

#### Sound intensity: Definition, Types of Sound, and Examples

Physics is the branch of science that deals with the properties and nature of energy and matter. Sound intensity is widely used in physics. The sound intensity tells the intensity of the sound and how many decibels are required for normal conversion or other conversions.

This intensity is decreasing with increasing distance among persons. It is inversely related to the sound wave. In this post, we will learn about the definition, types, and examples of the intensity of the sound.

## What is sound intensity?

Before going to the definition of the sound intensity, we must be acknowledged with the sound. Let’s learn about sound.

In physics, a vibration that spreads through a medium in the form of mechanical waves, (for propagation they have to use material medium), in the direction of one of the types of mechanical wave known as a longitudinal wave is known as a sound.

The material medium required for the propagation of the vibration to produce can be solid, liquid, or gas. The movement of the sound waves is faster in the solids as compared to liquid and gases.

The reason for the fast speed in solids is that the molecules in solids are much closer but in liquid and gases, the molecules are not closed together.

Sound intensity is sated as the amount of energy flowing with the help of unit area in per unit time and is perpendicular to the path where the waves of the sounds travel. In simple words, the sound per unit area is perpendicular in the direction in which waves of the sound are traveling.

It is usually denoted by I. And the SI unit of sound intensity is watt per square meter (Wm-2). The most frequent definition of sound intensity is to calculate the sound intensity of the noise present in the air. That noise is at the listener’s position due to the amount of sound energy.

The expression for the sound intensity is written as.

Sound intensity = sound power / area

Sound intensity = I = P/A

And the equation for the sound intensity level is written as.

Sound intensity level = SIL = 10 log10 (I/I0)

Usually, sound intensity and the sound intensity level are different. In sound intensity, we have to find the intensity of the sound. While in sound intensity level we have to find the level of the sound relative to a reference intensity.

## Types of Sound

There are different types of sound but three types are used widely in the theory of sound.

• Mechanical waves
• Longitudinal waves
• Pressure waves

Let’s discuss these types briefly.

## (i) Mechanical waves

The waves that are not able of transferring their energy along a vacuum are known as mechanical waves. For transferring their energy from one direction to another, mechanical waves require a medium. Mediums like rock, liquid, solid, or gas.

These waves contain sound waves, waves on ropes, water waves, and waves on springs. These waves are not capable of traveling along with a vacuum.

## (ii) Longitudinal waves

The waves that consist of vibrations or periodic disturbance that takes place similar direction as the advance of the motion of the waves is said to be the longitudinal wave. For example, the waves of ultrasound, compressed coiled spring, and seismic are longitudinal waves.

## (iii) Pressure waves

The waves that are in the form of a regular pattern of high-pressure and low-pressure regions are known as pressure waves. These waves are called pressure waves because these waves travel away from their source.

The pressure waves are also known as the traveling waves or standing waves. But keep in mind that all the traveling waves are not pressuring waves. For example, a drum being hit by a drummer is a pressure wave.

## How to calculate sound intensity?

Sound intensity and the sound intensity levels are calculated by using formulas. There is another way to calculate the sound intensity and the sound intensity level by using a sound intensity calculator in which you have to put your input and the required output will come in a couple of seconds.

Example 1

Find the sound intensity and the sound intensity level if the pressure is 2 and radius is 4?

Solution

Step 1: Identify the given values.

Pressure = P = 2

Step 2: Take the general formula of sound intensity.

Sound intensity = I = P/A

Sound intensity = I = P/4πr2

Step 3: Put the values in the above formula to calculate the sound intensity.

Sound intensity = I = P/4πr2

= 2/4π (4)2

= 2/4π (16)

= 2/64π

= 1/32π

Sound intensity = I = 0.009947

Step 4: Now take the general formula of sound intensity level.

Sound intensity level = SIL = 10 log10 (I/I0)

Step 5: Choose the reference sound intensity and take the calculated sound intensity.

Reference sound intensity = I0 = 1 x 10-12 w/m2

Sound intensity = I = 0.009947 w/m2

Step 6: Now put these values in the formula of sound intensity level.

Sound intensity level = SIL = 10 log10 (I/I0)

= 10 log10 (0.009947 /1 x 10-12)

= 10 log10 (9.947 x 10-15)

Sound intensity level = SIL = 99.977 db

Example 2

Find the sound intensity and the sound intensity level if the pressure is 12 and radius is 5?

Solution

Step 1: Identify the given values.

Pressure = P = 12

Step 2: Take the general formula of sound intensity.

Sound intensity = I = P/A

Sound intensity = I = P/4πr2

Step 3: Put the values in the above formula to calculate the sound intensity.

Sound intensity = I = P/4πr2

= 12/4π (5)2

= 12/4π (25)

= 12/100π

= 3/25π

Sound intensity = I = 0.0382

Step 4: Now take the general formula of sound intensity level.

Sound intensity level = SIL = 10 log10 (I/I0)

Step 5: Choose the reference sound intensity and take the calculated sound intensity.

Reference sound intensity = I0 = 1 x 10-12 w/m2

Sound intensity = I = 0.0382 w/m2

Step 6: Now put these values in the formula of sound intensity level.

Sound intensity level = SIL = 10 log10 (I/I0)

= 10 log10 (0.0382/1 x 10-12)

= 10 log10 (3.82 x 10-14)

Sound intensity level = SIL =105.82 db

## Summary

Sound intensity and the sound intensity levels are very essential for knowing the intensity and the level of the sound. The level of the sound intensity is measured in decibel and denoted by db. You can solve all the problems related to sound intensity just by following the above examples.