Pitch, Loudness , Quality of Sound Wave

(a) Pitch: Pitch is the characteristic of a wave by which sound wave appears shrill or grave. It depends upon the frequency of the wave.

Higher the frequency higher will be the pitch and vice-versa.

Frequency and hence the pitch of a female voice is more than the frequency and the pitch of a male voice and hence female voice is shrill and male voice is grave.

You might have seen in tape recorders that the voice is shrill when its rpm is more than the normal (high frequency and high pitch) and the voice is grave (low frequency, low pitch) when it runs at lower rpm then the normal.

(b) Loudness: Loudness of sound depends upon the intensity of sound. It is found that.

L ∝ Log I

i.e. greater the amplitude, greater will be the intensity (I ∝ A2) and so louder will be the sound.

The Unit of loudness is decibels (dB) and-

$ \displaystyle L = 10Log\frac{I}{I_o} \;(in \; dB) $

Here Io is constant i.e. minimum intensity (Io =10-12 W/m2) just audible at intermediate frequencies.

The loudness of normal talks is about 60 dB.

(c) Quality : It is the sensation received by the ear by which, we are able to differentiate two sounds (even if they are of same pitch and loudness).

The quality actually depends on the shape of wave form and the number of overtones .

e.g. the two wave forms shown in the figure are of the same frequency and same amplitude, but since their shape is different they will have different quality.

We differentiate the sound of a mouth organ and guitar because of different quality. A pleasant sound has certain well defined frequencies which have considerable amplitudes.

On the other hand a noise has frequencies that do not bear any well defined relationship among themselves.

Exercise  : What is the level of loudness of a sound of intensity 10-12 w/m2 ?

Also Read :

→ Wave & Wave Function
→ progressive wave , Equation of a Plane Progressive Wave
→ Speed of Wave in a String
→ Sound Waves , Infrasonic & Ultrasonic Wave
→ Velocity of Sound : Newton’s Formula & Laplace’s correction
→ Factor affecting Velocity of Sound
→ Displacement wave & Pressure wave
→ Reflection, Refraction & Superposition of Waves
→ Standing Waves in a String
→ Vibration of strings
→ Vibration of air columns : Closed & Open organ Pipe
→ Beats
→ Doppler Effect

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