An unfortunate side effect of a good disco is the noise created. Under the Environmental Protection Act 1990 local authorities are empowered to control noise levels at unsociable hours where the noise created causes a nuisance. As part of a venues entertainment licence they can be forced to install monitoring and control equipment to limit such noises.
They normally come as a result of noise complaints when venues are in residential areas. Bars and Clubs will have failed to control the noise levels resulting in complaints and the local authorities step in and threaten there entertainment licence and levy a fine. It's becoming the case that some new licences are only approved with the used of a sound control device.
So why do DJ's hate these so much your asking, surely they are there for a reason. Well, as explained above its normally because the venue has failed to control previous contractors. A few checks outside with a simple digital sound meter could save a load of hassle later on. Some venues are just simply in the wrong place and are not suitable for live music or a disco.
These devices work by using a mic to constantly measure the loudness of the noise inside the venue. It measures sound in decibel of dB which is a pretty difficult scale to understand as it uses a logarithmic scale. To give you some idea of the decibel scale, a conversation happens at around 60 dB, a truck driving past you walking would be around 80 dB where as a helicopter landing would be 100 dB and a police siren is 120 dB. The threshold of physical pain is 140 dB, a good set of powered speakers will have a max level of around 125-130 dB.
Sound dissipation over distance means that these levels are when you are right next to the source, as you move away the sound reduces. In a disco the speakers might be set around 100 dB but on the dance floor this would be closer to 85-90 dB. When working with sound the lower frequencies (we call bass) always travel furthest as they move the air more (vibration) and are generally stronger waves to treble and midrange. Bass is essential to a good music playout as it gives you the feeling and beat at the same time its normally the bass that causes the complaints.
When we work at a venue with a sound limiter we are legally obliged (or could be fined) to connect our equipment to the power supply that is connected to the sound limiter. If the limiter triggers the power is cut off immediately. Normally the limit must be reached for a period of 5 seconds to trigger but it can differ. There are 3 main issues here:
Our music is stored on a mechanical hard drive and sudden power loss or not being shut down correctly can cause them to fail and lose data. This as you can imagine is a DJs livelihood and not fast or easy to fix. This means DJs are very wary of working with a sound limiter.
The sudden loss of power can cause damage to the speakers amplifiers and in turn the cones. The loss of power causes a pop and rapid retraction towards the magnet.
You can't just set a safe level. Yeah you would think that all songs will play out at the same level but they don't. Differences in gain, production, strong bass, screams etc means no two songs are the same. Certain types of music are worse that others but at the end of the day the DJ has to have one eye on the limiter and another on the playout which makes life very hard.
Then you can add to this that no two limiters are the same. They are actually pretty poor at doing what they are installed for. Firstly the limit level changes, as does the location and age can affect them badly. Any venue with a limiter set below 90 dB is going to cause an issue. If you have live jazz or string musicians then 95 dB is required, a live band really needs 100 dB as they play off the unamplified drummer and they can't change their level.
We generally won't take a job or blacklist venues if the sound limiter is known to be problematic. We find it embarrassing and problematic to have the music suddenly disappear mid dance. We've worked with them many times and there really is no winning solution bar to play the music at such a low safe level it impinges on the reason you hired a disco in the first place. Make sure you always check with your venue before booking. It might look perfect but sometimes the devil is in the details.
Andy P