Definition of sound
What is sound?
Sound is a form of energy that produces the sensation of hearing. It is created when an object vibrates. Sound is vibrations that travel through a medium (solid, liquid, or gas) and can be heard.
Vibration: It means back-and-forth movement of an object. Examples: Strings of a guitar/sitar/veena vibrate to produce sound.
How sound is produced?
When an object vibrates, it disturbs nearby air particles. These disturbances travel as sound waves. We hear sound and when these waves reach our ears.
Medium of sound: Sound needs a medium to travel: a) Air b) Liquids c) solids
Sound cannot travel in vacuum (no medium).
Propagation of sound: Sound travels in all directions from its source. Similar to water waves when a stone dropped in a pond.
Types of sound: a) Pleasant b) Unpleasant
a) Pleasant sound: Pleasant sounds are those sounds which are soft, soothing and comfortable to hear. They make us feel relaxed and happy. Examples: Music, birds chirping.
b) Unpleasant sound: Unpleasant sounds are those sounds which are loud, harsh and disturbing to hear. They make us feel relaxed and happy. Examples: Noise, shouting, traffic
Hearing Range: Human can hear sounds between 20 Hz to 20,000 Hz.
Physical and psychological attributes of sound
We hear many types of sounds around us like a bell, drum, horn, or mosquito. These sounds are different because they vary in frequency and intensity. Some sounds are loud, others are soft. Some can be heard from far away, others only from nearby. The two main properties that describe sound are: 1. Frequency 2. Intensity
Frequency (Pitch of Sound)
Frequency is the number of vibration made by an object in one second. It’s unit is Hertz (Hz). When an object vibrates: If it vibrates fast, more vibrations per second is known as high frequency. If it vibrates slowly, fewer vibrations is known as low frequency. So, frequency depends on how fast something vibrates.
High frequency—–> High Pitch (Sharp/thin sound)
Low frequency—–> Low pitch (deep/heavy sound)
Examples: Drum vibrates slowly (Low frequency, Low pitch)
Bell (pooja bell) vibrates fast (High frequency, High pitch)
Human speech is the mixture of different frequencies.
Intensity (Loudness of Sound)
Intensity is the amount of force or energy used to produce a sound. It’s unit is Decibel (dB). If you hit or produce sound with more force sound becomes louder. If less force is used sound become softer. It depends on: a) Force applied b) Distance from the sound source
High Intensity—–> Loud Sound
Low Intensity—–> Soft Sound
Examples: Bird chirping (Low intensity, soft sound)
Fighter jet (High intensity, very loud sound)
TV: standing close (louder), Moving away (softer)
Other properties of the sound
Duration: How long a sound lasts. Example: Bell ringing for a few seconds.
Timbre (Quality): Helps us identify different sounds even if they are loud or soft. Example: Sound of a guitar and piano are different even at same loudness.
Types of Sound
Simple sound: Single frequency. Example tuning fork.
Complex sound: Many frequencies. Example: human speech, music
Range of human hearing
The range of human hearing refers to the frequencies and intensities of sound that a normal human ear can hear.
The human ear can hear sounds in a wide range of:
Frequency: 20 Hz to 20,000 Hz
Intensity: 0 dB HL to 120 dB HL, where 0 dB HL—–> softest sound heard and 120 dB HL—–> painful or uncomfortable.
Speech Range: Frequency: 200 Hz to 8,000 Hz
Whisper: ~30 dB SPL
Normal conversation: 55-65 dB SPL
Development of auditory behaviour
Auditory behaviour means how a child responds to sounds at different ages. As a child grows, their response to sound develops gradually. New born baby shows startle responses (sudden body movement) to loud sounds. Around 1 year, turn head when name is called and responds to familiar sounds. Hearing responses become more purposeful and clear with age, moving from simple reactions (startle) to recognizing and responding to sounds and names.
| Infant’s Age in months | Response |
| At birth | Arousal from sleep for 90 dB SPL |
| 3-4 | Rudimentary head turn for normal conversation (50-60 dB SPL) |
| 4-7 | Head turn to side for soft sound (40-50 dB SPL) |
| 7-9 | Head turn to side and indirectly below for a loud whisper (30-40 dB SPL) |
| 9-13 | Head turn to side and below to a loud whisper (30-40 dB SPL) |
| 13-16 | Head turn to side, below and indirectly above to soft sounds |
| 16-21 | Head turn directly to the side, below and above to a whisper |
| 21-24 | Locate directly even a soft sound from any angle |
As the infant grows, they start responding to softer (low intensity) sounds. Responses before 4 months: a) Startle response to loud sounds b) Searching response (trying to locate sound) c) Widening of eyes d) Waking up from light sleep. After 4 months, child begins to turn head towards sound. By 2 years, child can respond to sounds from all directions and can hear and respond even to soft sounds. Auditory development moves from basic reflex actions to active listening and sound localization as the child grows.
Functions of hearing
Hearing is one of the five important senses of human beings. Hearing helps us detect danger. Example: Hearing a bus horn and moving away from the road. Hearing is used for enjoyment and relaxation. Example: Listening to music, watching movies or drama. Hearing helps in understanding speech. It is essential for effective communication. Example: Listening and responding in conversations. Hearing helps in learning to speak. Children learn speech by listening and imitating others. Example: A child speaks like parents or people around them. Hearing helps in gaining knowledge about the world. It is important for understanding lectures and instructions. Example: Students learn better by listening in class. Hearing is important for safety, enjoyment, speech, learning and communication in daily life.
Role of hearing in learning
Hearing is essential for speech development. Babies learn to speak by listening and imitating others. They associated sounds with objects and actions, which helps in language development. Hearing helps us learn learn continuously throughout life. We learn new words and ideas by listening to others. Learning happens through limitation of speech sounds we hear. Hearing helps us listen to our own speech. This allows us to check and correct our pronunciation. Thus, hearing is important for the development of speech and language and to learn new things. It is also important for the maintenance of speech and language once we have developed these abilities.
