Reverberation –

It means the prolonged reflection of sound form walls, floor of hall or room. It simply means persistence of sound even after the source of sound has stopped.

Reverberation Time –

Reverberation time is defined as time interval between the initial direct note up to minimum audibility level.

Design for good Acoustics –

A)  Selection of Proper site –

Avoid noisy places like railway tracks, roads with heavy traffic, airports, industrial vicinity for auditorium. Also it should be away from the lift to avoid electromagnetic interference.

B)  Volume –

It should be optimum. Small halls cause irregular distribution of sound due to formation of standing waves, while big halls cause weaker intensity & large reverberation as per Sabine's formula viz $T=0.161\times \dfrac {V}{A} \$.

C) Shape –

The sidewalls and ceilings are usefully reflecting surfaces therefore they should be carefully designed to maximize their usefulness. The rear walls & floor are potential sources of useless and harmful reflection which are to be avoided. Parallel hard walls create echo problems. Use of splayed side walls greatly reduce the problem & increase the acoustical quality. A concave surface focuses sound reflection therefore must be avoided.

D) Use of absorbents –

Specially rear walls & ceiling must be provided with good absorbent like good quality thick wall paper & false ceiling respectively. The floor must be covered with thick soft carpet to suppress unwanted reflections & audience noise. We can also use open windows wherever possible cloth suspended at the centre of the hall can be absorb the echo.

E) Reverberation –

Reverberation time must not be too short or too large for lecture hall, concert hall & cinema halls it must be atleast 0.5 sec, 12 sec, 2sec respectively. It is decided by use of absorbent, sufficient audience people, presence of open window & furniture.

F) Echelon Effect –

A set of railings, staircase or any regular spacing of the reflected surface may produce a musical note due to regular production of echoes of original sound. This effect is called echelon which distorts the original sound. To avoid it thick carpet must be used to cover such surfaces.

G)  Seating Arrangement –

The seats may be arranged in concentric arcs of circle for good hearing. The successive rows are must be raised. If balconies provided are too high, sound shadow are formed and the person seating below do not receive ceiling reflections. Suitable sound reflectors should be positioned at proper place to avoid this defect of sound shadows.