Question

In public halls and auditoriums, the sound persists even after the source of sound has ceased. This persistence of sound is called
1. Absorption
2. Echoes
3. Reverberation
4. Reflection of sound

Answer 1

Correct Answer - Option 3 : Reverberation

Concept:

Reverberation:

As per IS 2526:1963,

• The persistent sound even after the source has ceased is called Reverberation.
• The time taken by the reverberant sound to decay to 1/10⁵ of the sound intensity level existing at the the source of sound is stopped is called reverberation time.
• The optimum reverberation time for hall depends on the volume of the hall in m³.
• The number of absorption unit required to give desired reverberation time is given by Sabine's formula which is given below:

\(A=\frac{0.16V}{T}\)

Here,

A - Total sound absorption \(=\Sigma( α S)\)

V - Volume in m³

T - Reverberation time in seconds

α - absorption coefficient for corresponding surface

S - Area corresponding to α

• A distinct and discernible reflected sound arrives at the listener with a delay after the direct sound is called Echo. This delay is directly proportional to the distance of the reflecting surface from the source and the listener.
• The process in which the sound energy is lost when it comes into contact with an absorbent material like ceiling, walls, as a result sound is not reflected back in to the space is called absorption. The some of the sound absorbing materials are:

1. Wood particle board
2. Compressed wood wool
3. Acoustic plaster (Includes granulated insulation material with cement).