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Acoustic Reflectors

It is very important to provide as much natural reinforcement for the unamplified voice as possible. This applies equally in smaller rooms, classrooms, meeting rooms etc, but is particularly important for larger spaces where the distance between the speaker and the listener is greater.

Natural reinforcement is achieved by the strategic placement of reflective surfaces. For example in theatres it is common to place reflectors above the stage, and to angle these to give useful reflections, particularly to the back of the auditorium. Hard flat surfaces can be considered to reflect sound in a similar manner to thye way that a mirror reflects light (i.e the angle of incidence equals the angle of reflection.

Convex surfaces will scatter sound and concave surfaces can cause focussing of sound. Focussing of sound is usually avoided because, whilst it increases the sound level for listeners at the focus , those outside the focus do not benefit. The sound level would therefore vary considerably throughout the auditorium. For this reason, convex surfaces are usually used.

Any reflected sound that arrives within 50 milliseconds of the direct sound will help to reinforce the speech. Reflections arriving later than 50 milliseconds might be heard as a distinct echo and will degrade intelligibility. 50 milliseconds is the time it takes sound to travel 17 meters, so reflective surfaces/panels should be designed so that the reflective sound has to travel no more than 17 meters further than the direct sound to reach the listener.

In smaller rooms like meeting rooms, the main reflections come from the central part of the ceiling. This therefore should be made reflective. Architects often specify acoustically absorbing ceiling tiles in meeting rooms to reduce the reverberant sound levels, but listening conditions would be improved by making the central portion non-absorbing.

 

Acoustic Reflectors