Mumbai University > First Year Engineering > Sem 1 > Applied Physics 1

Marks: 5M

Year: May 2016

Size

1. Size of the hall also affects the reverberation time.
2. The hall should be big enough so that sound intensity spreads uniformly over its entire area. Smaller rooms lead to irregular distribution of sound because of formation of standing waves.
3. When the length of the hall, L is very large in comparison to the longest wavelength of sound, the room is considered to be large in the acoustical sense and the sound within such a hail may be regarded as spread uniformly.
4. The floor area of the hall is computed, excluding the stage, based on the requirement of 0.6 to 0.9 m^2/person.
5. The height of the hall is determined by the presence or absence of the balcony, ventilation requirement etc.
6. An average height of 6 m for small halls and 7.5 m for large halls are usually adopted.
7. It is desirable to provide slight increase in the height of ceiling near the center of the hall.

Nature of wall surface

1. The reverberation time can be controlled by the suitable choice of building materials and furnishing materials.
2. If the reverberation time of a hall is too long, it can be cut down by increasing the absorption or reducing volume and if it is too short, it can be increased by changing high absorption materials to materials of low absorption or by increasing volume. Since open windows allow the sound energy to flow out of the hall, there should be a limited number of windows.
3. They may be opened or closed to obtain optimum reverberation time. Cardboard sheds perforated sheets, felt, heavy curtains, thick carpets etc. are used to increase wall and floor surface absorption.
4. Therefore, the walls are to be provided with absorptive materials to the required extent and at suitable places. Heavy fold curtains may be used to increase the absorption. Covering the floor with carpet also increases the absorption.

Audience in an auditorium.

1. Audience also contributes to absorption of sound. The absorption coefficient of all individual is about 0.45 sabins.
2. In order to compensate for an increase in the reverberation time due to an unexpected decrease in audience strength, upholstered seats are to be provided in the hall.
3. Absorption due to an upholstered chair is equivalent to that of an individual. In the absence of audience the upholstered chair absorbs the sound energy and it does not contribute to absorption when it is occupied.