By learning about the 4 important characteristics of sound, you shall discover why no two sounds are the same, whether it is the thundering cloud or the soft rustling of the wind.

Introduction

From the ticking of a clock in a quiet room at night to the deafening horns in a busy street at noon, sound surrounds us everywhere. But the questions are:

Questions about the Characteristics of Sound An Illustration of a Classroom

The answer lies in the characteristics of sound. These characteristics — loudness, pitch, quality, and intensity — allow us to distinguish one sound from another and understand how physics shapes our everyday hearing.

Before diving in, let us recall two simple wave features:

Amplitude → how “big” the vibration is from its mean position.
Frequency → how quickly the source vibrates back and forth.

Both amplitude and frequency are at the heart of how sound behaves.

4 Important Characteristics of Sound

1. Loudness

Loudness is the characteristic of sound that allows us to distinguish between loud and faint sounds.

Example

A girl whispering to her friend produces a soft sound, while a boy addressing a large group must speak much louder.

What is Loudness? _ Whispering vs Addressing

Factors Affecting Loudness

Amplitude of Vibration

Loudness is directly related to the amplitude of the sound wave.

Greater amplitude → louder sound
Smaller amplitude → softer sound

Example

Hitting a drum gently produces a soft sound, while hitting it harder produces a loud sound.

Area of Vibrating Surface

The area of a vibrating surface is directly related to loudness.

Larger vibrating surface → louder sound
Smaller vibrating surface → softer sound

Example

A large drum produces a louder sound than a small drum because the larger surface pushes more air particles.

Distance from the Source

Loudness decreases as you move away from the source. In fact, when the distance doubles, the sound becomes about one-fourth as loud.

$\text{Loudness} \propto \frac{1}{\text{Distance}^2}$

Example

A boy standing close to a beating drum hears it much louder than his friend standing farther away.

Factors Affecting Loudness Distance from the Source and Condition of the Listener's Ear

Condition of the Listener’s Ears

One of the most important factors affecting loudness is the sensitivity of the listener’s ears.

Sharp hearing → sound feels stronger (louder)
Poor hearing → sound feels weaker (softer)

Example

A child may hear the bang of a drum more sharply than an elderly person with weaker hearing.

Did you know?
If you strike a tuning fork and hold it in the air, the sound is faint. But if you place the base of the vibrating fork on a wooden table, the sound becomes much louder. The large surface of the table vibrates with the tuning fork, amplifying the sound.
It shows that loudness depends on how our ears perceive sound. It does not measure sound itself. For that, we use a related measurable quantity called intensity of sound (explained later).

2. Pitch

The characteristic of sound that helps us distinguish between shrill and grave sounds is called pitch.

Examples

A child’s or a woman’s voice has a higher pitch than a man’s voice because their vocal cords vibrate faster.
In music, the flute produces a high-pitched sound, while a drum produces a low-pitched sound.

Illustration of Pitch The Characteristic of Sound

Factors Affecting Pitch

Pitch depends on the frequency $\left(f\right)$ of vibration:

Higher $f$ → Higher pitch (shrill sound)
Lower $f$ → Lower pitch (deep/grave sound)

Did you know?
The pitch of a tuning fork depends on the mass of its prongs. Heavier prongs vibrate more slowly (lower frequency), producing a lower pitch (grave sound).

3. Quality (Timbre)

Quality, or timbre, is the property of sound that allows you to distinguish between two sounds of the same pitch and loudness.

Example

Even if two people sing the same note at the same loudness, you can still tell their voices apart because of the unique quality of each voice.
A clarinet and a flute playing the same musical note sound different because their waveforms are different.

Illustration of Characteristic of Sound - Quality

Did you know?
Quality is the main characteristic of sound that allows you to recognise your friend’s voice instantly, even in a noisy, crowded place.

4. Intensity

The intensity (or the intensity level) of sound is the amount of sound energy passing per second through a unit area, held perpendicular to the direction of sound propagation.

In simpler words, intensity tells us how much sound energy is flowing through a given area per second.

Key Characteristics of Intensity

It is a derived and scalar physical quantity, measured in watts per square metre (W/m²). It is represented by the symbol $I$ .

Range of Human Hearing

Faintest Audible Intensity → $10^{-12} \, W/m^2$
Painful Loudness → greater than $1 \, W/m^2$

This means our ears can detect an enormous range of intensities — from the tiniest whisper to the roar of a jet engine.

Mathematical Formulation

The intensity level (or sound level) in decibels is given by:

$\text{Intensity Level (in dB)} = 10 \, \log \frac{I}{I_0}$

where,

$I$ = Sound Intensity
$I_0$ = Reference Intensity $\left(10^{-12} \, W/m^2 \right)$

Why the Decibel (dB) Scale?

Since the range of audible intensities is so huge, scientists use a logarithmic scale to make it manageable.

Example

Whisper: around 30 dB
Normal conversation: around 60 dB
Jet engine (close): about 140 dB (painful)

Intensity of Sound Illustration of Intensity Level in Real Life

Did you know?
Intensity is physical, but loudness is psychological and depends on how our ears perceive sound.
Your ears are not equally sensitive to all frequencies. A sound at 3500 Hz feels much louder than a sound of the same intensity at 125 Hz.
Therefore, intensity alone does not fully explain loudness; it also depends on your ear’s sensitivity to frequency.

Other Characteristics of Sound

Apart from loudness, pitch, quality, and intensity, other characteristics of sound help us understand its nature perfectly.

1. Duration

Duration is the characteristic of sound that refers to how long a sound lasts. It depends on the time for which the source vibrates.

Duration - The Characteristic of Sound Illustration

Examples

The strike of a bell produces a sound that fades gradually, long duration.
Snapping your fingers produces a very short-duration sound.

2. Speed of Sound

The speed of sound is one of the most mesmerising characteristics of sound that intrigues scientists and engineers alike. It depends on the medium because sound is a longitudinal wave that needs particles to carry it.

Speed of Sound - The Characteristic of Sound Illustration

Example

In air at STP → about 343 m/s
In water → faster, around 1500 m/s
In solids → even faster, because particles are closely packed
On the Moon → no medium (like air) to carry sound waves

3. Resonance

Resonance is the phenomenon in which a body starts vibrating with a large amplitude when exposed to sound waves of its natural frequency.

Resonance - The Characteristic of Sound Illustration

Examples

The shattering of glass by a singer’s high-pitched note is a classic case of resonance.
A tuning fork placed near another tuning fork of the same frequency can make the second one vibrate.

Common Misconceptions about Sound

Myth	Truth
Sound can travel through space.	Sound needs a medium (air, water, or solid). Space is a vacuum, so sound cannot travel there.
Loudness and intensity are the same.	Intensity is a measurable physical quantity, while loudness is how our ears perceive that intensity.
High pitch means a loud sound.	Pitch depends on frequency, not loudness. A whistle and a drum can be equally loud but have very different pitches.

Conclusion

The characteristics of sound explain why every sound around us is unique. By understanding these properties, you not only learn the physics of sound but also appreciate the science behind music, speech, and everyday noises.

Frequently Asked Questions (FAQs)

Name 4 important characteristics of sound.

Loudness
Pitch
Quality
Intensity

Identify which part of these musical instruments vibrates to produce sound:

(a) electric bell (b) loud speaker (c) piano (d) violin (e) flute

Electric bell → metal gong
Loudspeaker → diaphragm (cone)
Piano → strings
Violin → strings
Flute → column of air

Suppose you and your friend are on the Moon. Will you be able to hear any sound produced by your friend?

No!

The reason is that sound needs a medium (like air, water, or a solid) to travel, but the Moon has no atmosphere.

What do you know about a silent whistle? Can you hear it?

A silent whistle produces sound at a very high frequency (20 kHz – 25 kHz). Humans cannot hear it because it is an ultrasound, but dogs can since their hearing range is higher.

Which property of a sound wave determines its: (a) loudness (b) pitch?

Loudness → amplitude of vibration
Pitch → frequency of vibration

What is the difference between loudness and intensity of sound?

Intensity: measurable, physical quantity of sound energy (W/m²).
Loudness: subjective perception of intensity by human ears.

Relationship

$L \propto \log(I)$

This is why we use a logarithmic scale (decibel) to measure sound intensity levels.

What do you mean by the term intensity level of the sound? Name and define its unit.

Intensity level is the ratio of sound intensity to a reference intensity that is expressed on a logarithmic scale.

$\text{Intensity Level (dB)} = 10 \log \frac{I}{I_0}$

It is measured in units of decibels (dB).

What are the units of loudness? Why do we use a logarithmic scale? On what factors does loudness depend?

Units

Loudness is not directly measurable (so no SI unit). It is expressed in phon or sone in psychoacoustics.

Logarithmic Scale

It is used because human hearing can detect intensities across an extremely wide range (from $10^{-12} \text{to } 1 W/m^{-2}$ ).

Factors

Loudness depends on amplitude, vibrating surface area, distance from the source, and the sensitivity of the listener’s ears.

What is the difference between frequency and pitch? Describe their relationship graphically. If the pitch of sound is increased, what are the changes in the following?

a. the frequency b. the wavelength c. the wave velocity d. the amplitude of the wave

Frequency: objective, measurable number of vibrations per second (Hz).
Pitch: subjective perception of frequency by the ear.

$\text{Higher frequency → higher pitch}$

Graphically

A rising frequency vs. pitch curve showing a direct proportional relationship.

Frequency vs Pitch _ Graphic Illustration

Changing Pitch of Sound

If pitch increases:

a. Frequency → increases

b. Wavelength → decreases

c. Amplitude → unaffected

d. Wave velocity → remains constant (in the same medium)

Describe the effect of a change in amplitude on loudness and a change in frequency on pitch.

Amplitude ↑ → Loudness ↑
Frequency ↑ → Pitch ↑

A student says that the two terms speed and frequency of the wave refer to the same thing. What is your response?

Incorrect.

Speed → how fast the wave travels through a medium (m/s).
Frequency → how many vibrations occur per second (Hz).

The two quantities are related by the formula:

$v = f \lambda$

Where.

$v = \text{speed}$
$f = \text{frequency}$
$\lambda = \text{wavelength}$

Two people are listening to the same music at the same distance. They disagree on its loudness. How?

Because loudness is subjective and depends on ear sensitivity. One may have sharper hearing than the other.

Will two separate 50 dB sounds together constitute a 100 dB sound?

No.

Decibels are logarithmic, not linear. Two 50 dB sounds combine to make about 53 dB, not 100 dB.

Table of Contents

Introduction

4 Important Characteristics of Sound

1. Loudness

Example

Factors Affecting Loudness

Amplitude of Vibration

Example

Area of Vibrating Surface

Example

Distance from the Source

Example

Condition of the Listener’s Ears

Example

2. Pitch

Examples

Factors Affecting Pitch

3. Quality (Timbre)

Example

4. Intensity

Key Characteristics of Intensity

Range of Human Hearing

Mathematical Formulation

Why the Decibel (dB) Scale?

Example

Other Characteristics of Sound

1. Duration

Examples

2. Speed of Sound

Example

3. Resonance

Examples

Common Misconceptions about Sound

Conclusion

Frequently Asked Questions (FAQs)

Name 4 important characteristics of sound.

Identify which part of these musical instruments vibrates to produce sound:

(a) electric bell (b) loud speaker (c) piano (d) violin (e) flute

Suppose you and your friend are on the Moon. Will you be able to hear any sound produced by your friend?

What do you know about a silent whistle? Can you hear it?

Which property of a sound wave determines its: (a) loudness (b) pitch?

What is the difference between loudness and intensity of sound?

What do you mean by the term intensity level of the sound? Name and define its unit.

What are the units of loudness? Why do we use a logarithmic scale? On what factors does loudness depend?

What is the difference between frequency and pitch? Describe their relationship graphically. If the pitch of sound is increased, what are the changes in the following?

a. the frequency b. the wavelength c. the wave velocity d. the amplitude of the wave

Describe the effect of a change in amplitude on loudness and a change in frequency on pitch.

A student says that the two terms speed and frequency of the wave refer to the same thing. What is your response?

Two people are listening to the same music at the same distance. They disagree on its loudness. How?

Will two separate 50 dB sounds together constitute a 100 dB sound?

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