SpyCandy

Noise Limiters/Decibel Meters

The decibel scale is a logarithmic rather than a linear scale. That means it is not directly proportional to the energy or loudness of the noise. As an example, 66 dBA is not just 10% louder than 60 dBA - its nearly 75% louder! Similarly, 70 dBA is judged to be twice as loud as 60 dBA and four times as loud as 50 dBA.

Some approximate common noise levels:
Whispering: below 35 dBA
Talking with friends: 50-60 dBA
Hair dryer low speed: 82 dBA
Lawnmower: 90 dBA
Flute playing lively folk tunes: 88 dBA
Output of bagpipes: 109 dBA
Full orchestra peak: 110 dBA

Disco's and live bands should be expected to generate sound levels of around 100 - 110 dBA. While a Disco could easily turn down below this level, a live band cannot just as easily turn down a full drum kit, and an unamplified snare drum alone can expect to generate 80-85 dBA, and more when a drummer hits a high frequency "rim shot" - by hitting the drum stick on the metal edge of the snare drum, as well as the drum itself.

Controlling noise should not necessarily mean just installing a noise limiter. It should take into account the whole of the premises, its structure and ventilation, etc. Most noise levels in entertainment venues will be high - in excess of 95 dBA. Trying to maintain levels below this is generally unrealistic for music at genuine entertainment levels, particularly if a live band or karaoke is providing the music. However, this is the most common level that the Local Authority will impose upon a venue, when they have problems with sound containment and very close proximity to residential neighbours.

The most common types of "Noise Limiter" or "Decibel Meter" installed operate by using a microphone to monitor noise levels in the auditorium. There is a warning display to indicate when the limit level is being approached and exceeded. Once the level is exceeded for a predetermined length of time the device will cut the power supply. The advantages of this system are that it is quick and reasonably cheap to install, typically costing a few hundred pounds.

The disadvantages are that it needs to be able to operate in a high-music-noise environment otherwise it will be subject to interference by normal noise generated by the audience. Live bands, particularly, will constantly trigger the device if set below 95 dBA. Even a cheering/shouting audience can trigger the device at this level. They can also react to pitch (i.e. frequency of note) rather than straightforward volume, which means some instrument sounds - such as a trumpet, vocal or distorted rock guitar, can be more prone to set some of them off.

Most Noise Limiters will cut the power to all power sockets that they are routed to for a set level of time (usually a few 10's of seconds), then return the power back on. This can also cause problems to any equipment connected, because while the power cut is unlikely to cause damage, the sudden returning power surge may well do so. Large hi-tech PA's and amplifier systems often require a predetermined power on sequence, with gain levels turned down at power on.