Classification and Characteristics of

sound

Harsh ParmarID: 16BEITG005

Sub: Physics Seminar

What Is Sound ??

Sound is a Vibration In an Elastic Medium With

definite Frequency & Intensity…

Longitudinal wave .

requires a medium .

cannot travel in a vacuum.

Classification Of Sound

Infrasound f<50 Hz

Audible Sound 20 Hz To 20kHz

Ultrasound f>50 Hz

Classification of Audible Sound

• The Sound Which Produces Pleasing Effect On The ear is Called Musical Sound.

• Sounds Of Sitar, Violin, Flute

Musical

• The sound That Produces a jarring effect on the ear and unpleasant to hear is called noise.

• Sound Of Road Traffic, Crackers ,Aeroplan

Noise

Properties Of Musical Sound

Regular in Shape.

Have definite Periodicity.

They do not undergo a sudden change in amplitude.

Properties Of Noise

Irregular in Shape.

Do not have Definite Periodicity.

They Undergo a Sudden Change In Amplitude.

Characteristics Of Musical Sound

PitchRelated To Frequency Of Sound

LoudnessRelated To Intensity Of Sound

TimbreRelated To Quality Of Sound

Pitch

We can describe pitch by frequency. Rapid vibrations of the sound source(high frequency)produce sound of a high pitch.

Slow vibrations (low frequency) produce a low pitch.

Different musical notes are obtained by changing the frequency of the vibrating sound source.

Loudness

Loudness is Characteristics which is Common to all sound

■ Loudness & Intensity are Releted to each other by relation

L log I

L = K log IWhere K Is Constant

Timbre

Quality Of Sound Which Enables us to distinguish between two sounds having the same loudness & Pitch.

Depends on the Presence of overtones.

■ It helps Us To Distinguish musical notes emitted by different musical instruments & Voices Of different Person Even Though the Sound have Same

A sound produced in a volume is reflected multiple times from the various surfaces. As a result sound persists in the volume for sometime of gradually decreasing intensity even the source stop emitting the sound. This persistence of the sound in a room due to multiple reflections, even when the source stops, is known as reverberation.

Reverberation

Reverberation time: It is defined as the time during which the sound energy falls from its steady state value to 10-6 times after the source is cut off.

Coefficient of absorption: It is a ratio of sound energy absorbed by its surface to that of total sound energy incident on the surface.

Sabine or Open Window Unit (OWU): 1 m2 Sabine is the amount of sound absorbed by one square meter area of fully open window.

Sabine’s formula works for large enclosures.However, it leads to paradox for highly absorptivesurfaces. For instance when a = 1, all sound energy

incident on the surface is absorbed and T = 0. Suchroom is called dead room in acoustical terms.

Sabine’s formula does not leads to T = 0 when a =1. Actually, experiments shows that Sabine’s

formula is valid only for a 7 0.2.

Eyeing proposed modification in the equation asFollowing.

EYRING’S EQUATION:

Sabine’s FormulaSabine’s formula is given by the following:

RT60 is the reverberation time (to drop 60 dB)V is the volume of the room

c20 is the speed of sound at 20°C (room temperature)Sa is the total absorption in sabins

The sabin unit has the same dimension as area (e.g. m2). A one square meter surface with an absorption coefficient of 0.75 would be considered 0.75 sabins. The absorption coefficient has a

range of 0 to 1, where a coefficient of 0 indicates none of the sound is absorbed, and a coefficient of 1 indicates that 100% of it is absorbed.

Since we know the speed of sound at 20°C is 343 m/s, we can do a little math and reduce the formula to:

Thank You