When endeavoring to design a good acoustic environment, there are two main factors to be aware of: the ambient noise within the room and the reverberation time of the space. Teddy D’Souza, Director, Operations, Knauf AMF, India writes on the need to control unwanted noise and effects of sound when designing a new building or refurbishing an existing space.
The Whispering Gallery in St Paul’s Cathedral attracts around 50,000 tourists a year, many of whom visit to hear their hushed voices travel from one side of the 111m high dome to be heard clearly around the other side. This acoustic effect was not an intentional feature of the dome’s design but has become an entertaining tourist attraction.
But not all acoustic effects in buildings are entertaining. In office buildings background noise can have a negative impact on staff performance. In schools the situation is even more critical, where poor acoustics can have a detrimental effect on student concentration, behavior and academic achievement.
Ambient noise can come from a number of sources including sound transferring from adjacent rooms or corridors, speech, mechanical equipment inside the space and noises coming in from outside. Sound insulation or attenuation prevents noise from outside disturbing those inside the building and is measured as a decibel (dB) value. The highest performance dB rating a suspended ceiling alone would provide is in the region of 45dB. The dB rating is actually a minus figure; generally speaking, if the sound source measures 100dB in a room, by installing a 40dB ceiling tile, the sound heard in the adjacent room is 60dB.
Reverberation is the time in seconds required for reverberate sound in an enclosed space to reduce by 60dB of its original level after the source of the sound has ceased. Reverberation times can vary from half a second to up to eight seconds in a large room with hard walls, floors and ceiling surfaces. Acoustic absorption within a room is important if you want to reduce the reverberation time which can help improve speech intelligibility and clarity.
By installing sound absorption and insulation materials architects are able to control and alter the reverberation time in a space. This high sound absorption is achieved because of the light weight porous materials the ceilings are made from; which is why suspended ceilings are an extremely cost-effective solution for controlling ambient noise and reverberation.
There is a growing trend in modern architecture towards the use of hard reflective materials such as concrete, steel and glass in large areas like atriums in office buildings. These areas are prone to high levels of reverberation with reflected sound bouncing off the many surfaces.