Acoustics
Acoustic Control
The aim is to produce sound for the human ear, be it live or monitored, that is as accurate as the original source with no colouration, excess reverberation or deadness.
The magic word is RT60 – this is how we express reverberation as a standard – RT60 is the measurement of the time it takes for a sound to decay by 60 decibels and therefore irrelevant to speech or quality. There have been many models studied to agree the ideal RT60. We use the ‘Stephens and Bate’ or Sabine methods to determine what the ideal RT60 time would be for a space depending on the volume of the area and the actual use.
The sounds that are generated within an area can take several seconds to decay and therefore, from any listening position, you hear not only the source sound but also many reflections from the walls floor and ceiling. With sound travelling at over 340 m per second, sound generated within a large room could travel over 1000 metres before it decays to an unperceivable level.
This means that you will hear sounds not only directly, but the same sound delayed and reflected off 1 surface, delayed still further and reflected off 2 surfaces, delayed still further and reflected off 3 surfaces, etc., etc., etc. This can make comprehension of speech almost impossible from any distance and reasonable recording of drama or music impossible.
A factor of sound is that the high frequencies dissipate faster than the low frequencies, so we design acoustic absorbent walls that absorb different frequencies at different rates to ensure that the overall RT time is within specification. At an RT of 1.3sec the full acoustic range reduces by 60dB at 1.3 sec – no more no less.
We have to ensure that the resultant perceived sound is neither too bright nor to dead.