Audible and Inaudible Sound

Sound can be defined as one form of energy and is created by vibrating objects or bodies. Sound needs a medium to propagate. This medium is called a transmission medium and it can be anything solid, liquid, or gas. There are two different waves discussed while talking about sounds. They are longitudinal waves and transverse waves. Longitudinal waves are nothing but waves that are produced in the same direction as the vibrating particles of a certain medium. Transverse waves are produced if the waves’ direction of propagation acts perpendicular to the direction in which the particles vibrate. A source is needed to generate sound. A real-time example of this would be a sound speaker where the sound frequencies use the speaker as a source. The diaphragm in the speaker vibrates to generate sound.

The following paragraph will explain how a sound source works, in a detailed manner. The particles present in the medium vibrate when a source (sound) vibrates. These particles surround the sound source. Because of continuous vibration, the particles move further and further away from the actual sound source. The speed of the sound determines the propagation of the particles that vibrate away from the source. The above mentioned explains how a sound wave is being formed. Different elements such as pressure, displacement, and velocity in the medium can vary along with time. One notable thing is that the vibrating particles need not have to travel along the same direction as sound waves. It is more like these vibrating particles move further and interact with other stable particles and make them vibrate to produce high volume and frequency of sound. This is a continuous process.

Factors that affect the nature of propagation of sound

There are three major factors. They are -

1. Relationship between density and pressure

It is a significant possibility that density and pressure present in the medium can affect the speed of the sound. Varying temperatures can further affect this.

2. State of the propagating medium

If the medium is in a mobile state, then it will affect the sound speed by increasing it.

3. Medium viscosity

The viscosity of the medium decides whether the rate of quality of sound should be reduced or not.

Classification of sound waves

Based on some common features such as speed of sound, direction, and magnitude of propagation, amplitude, pressure, intensity, wavelength, and frequency of sound, sound waves can be classified.

Audible sound

Audible sound can be understood if all the frequencies range between 20 Hz and 20 kHz. Humans can hear them. Though this sound can be heard, there are other factors such as surroundings and environment which play a major role as well. Loud noises can cause hearing problems to our ears. It is quite hard to perceive higher frequency sounds. This is one reason why old people have lower hearing abilities.

Inaudible sound

These are nothing but frequencies that either fall below 20 Hz or go above 20 kHz. They cannot be heard by human ears. To describe sound frequencies less than 20 Hz with a term, infrasonic sound waves can be used. Likewise, frequencies above 20 kHz can be termed ultrasonic waves. An animal such as a dog can hear sound waves over 20 kHz. This is the reason dogs are trained in the police department where they use a separate whistle that has its frequency above 20 kHz. They can only be perceived by dogs and not humans. Applications of higher-level frequencies include the medical field, technological development, research field, etc.

Components of sound

The following are some components of sound:

1. Pitch

Pitch is found by obtaining the periodic nature of vibration. Pitch can be seen as sound waves. Based on frequency, we can classify a pitch into high and low.

2. Duration of sound

It is an identifiable sound when you just start to hear something. It lasts until you stop hearing that sound. In simple words, the duration of sound is nothing but the time period where one can hear the sound until it ends. Duration can either be short or long based on the situation.