A guide to reverberation…and why it matters
When sound waves strike a room surface, they may be reflected, scattered, absorbed or transmitted through the surface. Reflected sound is known as reverberation, and excessive reverberation – rather than simply excessive noise – is the number one cause of acoustic problems in modern buildings.
Reverberation time (RT) is the time taken for the sound wave to decay to an undetectable level. RT can be measured across a range of frequencies and in general terms we aim for a reverberation time of under 0.8 seconds in training rooms and general office space, and under 0.5 seconds in teleconference or video conference situations where microphones are being used.
Glass, plasterboard, wooden or ceramic floors and furniture are highly reflective and without additional reverb control measures will always adversely impact on productivity – the room will be too ‘live’ for the average person to concentrate for extended periods especially if sudden loud noises or intrusive speech are part of the acoustic ‘landscape’. Uncontrolled reverberation can result in people shouting to make themselves heard – this is a common phenomenon in arenas and entertainment venues but is obviously not desirable in the working environment.
By introducing sound absorbent surface finishes we can tune the acoustic performance of a room which has another major but often overlooked benefit……by reducing the sound pressure in the transmitting room we reduce noise transfer to adjacent rooms.
Reverberation reduces proportionally with the amount of absorbent material in the room, and increases with room volume. Therefore large spaces will typically require a lot of absorbent material to prevent reverberation becoming excessive.
When sound has been bouncing back and forth in the room for 80 to 120 milliseconds the reverberation will consist of a chaotic mix of reflections. Among acousticians this is referred to as “the late diffuse part of the reverberation” or ‘Lombard speech’; we call it the ‘Noisy Pub Syndrome’ where chaotic reverberation makes ordinary conversation impossible.