How Do We Hear Sound

Key Concepts

1. Audible and inaudible sounds
2. The human ear
3. Hearing aid

Introduction: How Do We Hear Sound

We humans are able to hear a variety of sounds. However, we cannot hear all kinds of sounds. Moreover, there are many parts of the human ear involved in making a sound heard. Some people cannot hear clearly, for which they may use hearing aids. 

Explanation: 

Audible and inaudible sounds: 

We human beings can hear sounds of frequencies ranging from 20 Hz to 20 kHz only. Children and some animals such as dogs can hear sounds up to 25 kHz. As we grow older our ears become less sensitive to higher frequencies. 

The sounds with frequencies less than 20 Hz are called infrasonic sound or infrasound. The sounds with frequencies more than 20 kHz are called ultrasonic sound or ultrasound. 

The infrasound is used by animals such as elephants and rhinoceros to communicate with each other. Ultrasound is primarily used for medical purposes such as echocardiography and sonography. 

The human ear: 

We humans are able to hear sound by the help of a sense organ called the ear. The sound waves propagate through a medium as density or pressure variations. These pressure variations when reach our ear, gets converted to electrical signals, which are then sent to our brain, where they are interpreted. 

A human ear is divided into three sections, namely,  

1. The outer ear 

2. The middle ear and  

3. The inner ear 

The outer ear:  

• The outer ear consists of the ear pinna, the ear canal, and the ear drum. 

• The ear pinna collects the sound waves from the surroundings and sends it into the ear canal. 
• The ear canal serves as a passage for the sound waves leading them to the ear drum. 
• The ear drum is a membrane, which vibrates when it encounters the pressure variations of a sound wave. 
• When the ear drum encounters a compression, the pressure near it increases. This pushes the ear drum inward. 
• On the other hand, when it encounters a rarefaction, the pressure near it decreases. This pulls it outward. 

• This leads to the vibration of the ear drum. 

The middle ear: 

• There are three small bones in the middle ear, namely, Hammer, Anvil and Stirrup. 
• The vibrations of the ear drum vibrate these bones, which amplify the vibrations several times. 
• These amplified pressure variations are then transmitted to the inner ear. 

The inner ear: 

• The amplified pressure variations are then converted to electrical signals by the cochlea. 
• These electrical signals are then sent to the brain by the auditory nerve, where these signals are interpreted as sound. 

Hearing aid: 

• Some people suffer from hearing loss. Such people use hearing aids to hear clearly. 

• Hearing aids are battery operated electronic devices. 
• Each hearing aid contains a microphone which receives the sound from the surroundings and converts them into electrical signals. 
• These electrical signals are amplified by an amplifier. 
• These amplified electrical signals are given to a speaker of the hearing aid. 

• The speaker then converts the amplified electrical signal to sound and sends, which ensures a clear hearing. 

Summary:

• An average human can hear sounds of frequencies ranging from 20 Hz to 20 kHz only.
• The sounds with frequencies less than 20 Hz are called infrasonic sound or infrasound.
• The sounds with frequencies more than 20 kHz are called ultrasonic sound or ultrasound.
• A human ear is divided into three sections, namely, the outer ear, the middle ear and the inner ear.
• The outer ear consists of the ear pinna, ear canal and the ear drum. It collects the sound from the surrounding and direct it towards the middle ear.
• The middle ear consists of 3 small bones namely, hammer, anvil and stirrup. These bones amplify the pressure variations coming from the outer ear.
• The inner ear consists of cochlea and auditory nerve whose functions are to convert the amplified pressure variations into electrical signals and carrying them to the brain respectively.
• People who suffer from hearing loss use hearing aids to hear clearly. These are battery operated devices which amplify the surrounding sound to make it clear to the person.