Some Term Related With Sound

Audibility

The range of frequencies which a listener can distinguish is known as range of audibility. The audible range of sound for the human being is 20HZ to 20,000HZ. TheSound of frequency below 20 Hz is called infrasonic sound or subsonic sound and sound with frequencies above 20,000 Hz are known as ultrasonic or ultrasound.

Properties of ultrasonic or ultrasound

• They produce heating effect in any substance through which they propagate.
• They produce coagulation ( the process by which liquid changes to a gel) in liquid.
• They can travel long distance without loss of energy.

Applications of ultrasonic or ultrasound

• They are used in diagnosis and cure some diseases.
• They are used in bloodless surgery.
• They can be used to detect cracks and flows in metal moldings.
• They are used in dry cleaning of clothes as they can remove grease and dirt.

Characteristics of notes

Single sound of a certain pitch and duration made by a musical instrument or voice is called note. Notes may be similar or different from each other in three aspects. They are pitch, loudness (or intensity) and quality (or timbre).

Pitch

Pitch is defined as the sharpness of sound. It depends only on the frequency of the sound vibrations.

Pitch depends on the following factor:

• Frequency of the sounding body: greater the frequency higher the pitch.
• Relative motion between the source and the listener: if the relative motion between source and listener is approaching, the pitch seems to be increasing and it they are receding, the pitch seems to be decreasing.

Intensity and loudness

Intensity of sound is the quantity of sound energy per unit time flowing across unit area hold normally to the direction of propagation of sound waves.

∴ Intensity of sound =

To find the intensity at a distance ‘r’ from small source of sound ‘O’, we consider a sphere of radius r. If E is the sound energy passes through the surface area in the given time‘t’. Then,

I =

∝ 1 ………………..(i)

If ‘a’ is the amplitude of the sound wave emitting from the source ‘O’. Then,

I ∝ a² ……………….(ii)

From (i) and (ii), we get

a²∝ 1 / …………… (iii)

∴ a ∝ 1/r