An increasing number of venues now use noise-limiters.
Noise-limiters are inserted between the 230V mains distribution board (AKA breaker box) and the 13A sockets supplying the stage area. Some have an internal microphone, some rely on an input from an external microphone, and some allow use of either an internal or external microphone. If the sound picked up by the microphone exceeds a set level (generally for a set period), they interrupt the 230V supply to the 13A sockets (usually for a set period, or until the unit is manually reset).
In effect, a noise‑limiter acts as a 230V mains cut-off if sound levels at the microphone exceed a preset (usually user-adjustable) threshold for a preset (usually user-adjustable) period.
The intention is that all touring sound systems and backline amplifiers use only sockets supplied by the noise-limiter, so that if the sound level exceeds limits set by the venue, the power to the equipment is interrupted, silencing it until the noise-limiter is reset.
Sometimes noise‑limiters also have weighting options, so that they are more easily triggered by particular types of sound. Generally, noise‑limiters used for environmental reasons (see below) need to respond to low-frequency sounds, as these travel furthest and penetrate obstacles - like a neighbour's wall - most. Conversely, noise‑limiters used for health and safety reasons need to respond to higher frequencies (especially in the range from 1kHz to 6.3kHz), as these are the most damaging to hearing.
Most noise-limiters incorporate a warning-light system to give performers and sound-engineers some advance indication - often only a few seconds (again, usually user-adjustable) - that power to stage sockets will be cut unless the level is reduced.
Noise-limiters are are usually installed for one of two reasons:
Where venues are near residential properties, they have a duty to keep any noise (usually measured at a residential property's boundary) to a reasonable level.
There isn't any fixed legal value for what that level should be: in the event of a complaint or dispute - or even simply a licence application - it will be determined by the local authority, taking a number of factors into account (including the context and frequency of the noise); generally, the threshold will be lower for a new wedding venue that will function every Saturday in a quiet rural area than for a city centre pub that puts on live entertainment a couple of times a year. In either case, however, the establishment's entertainment licence is at risk if there are noise complaints from residential neighbours. Also, some local authorities may impose a noise limiter on the venue as a condition of its entertainment licence (and some impose them on all applicants for an entertainment licence).
In this application a noise-limiter is generally a Cheap and Easy option (typically costing hundreds rather than thousands of pounds), but may make the venue unusable for any kind of live music apart from string quartets and the kind of folk music where someone in the audience always says SHHH! if anyone whispers anything to anyone else.
A better - Expensive and Difficult - option is to soundproof the venue adequately and prevent guests or ticket-holders from opening the balcony doors every thirty seconds while the band is playing. Adequate soundproofing (typically costing anywhere from several thousand pounds to eye-watering multiples of this) may add so much to capital costs that the project is not viable at all, while implementing a Fierce door-management regime has its own drawbacks: most Happy Couples don't appreciate an autocratic maitre d' barking at their nicotine-dependent guests. As most venue doors double as fire exits, locking them isn't usually an option.
The upshot, really, is if someone wants to host even moderately loud music (anything that involves a drum-kit) anywhere near a twitchy householder or residential estate, they are not going to get a very easy ride. If their solution is a noise-limiter and you are the noise creator, you may not have an easy night either.
There isn't yet any statutory requirement to protect customers or party guests - who are there voluntarily - from loud noises, but there is a requirement for employers to protect employees and contractors.
There are fixed legal values for what those levels should be, and recommendations for the types of remedy that an employer should adopt (see Sound and the Law for more details). If any employee - e.g. a waiter, bartender, or duty supervisor - has to be in the same room when the music is playing, their employer has to keep the overall volume as low as reasonably possible. One way to enforce this - bands and DJs don't often accept the limits voluntarily - is to use a noise limiter.
Venue owners generally seem far more nervous of neighbours (whose entitlements are more vague) than of employees (whose entitlements are clear), and more limiters are installed for Environmental than for Health and Safety reasons.
Noise-limiters should generally be set up as follows:
Measuring the noise requires a calibrated sound-level meter, which is seldom supplied with a noise-limiter (and professional-standard meters can cost more than some noise-limiters).
Noise-limiters may be incorrectly set up so that:
Noise-limiters may be set incorrectly because:
If you can't move the event to another venue - and if music is central to the event you really do need to consider this - or bypass the noise-limiter in some way, you only have two main strategies available (and you should employ both).
It is an unfortunate fact that all these measures combined may not be enough to prevent cut-off: if noise-limiters never engaged, there would be no purpose in having them.
If the power does go off, besides being - literally - a show-stopper, other consequences may follow:
In spite of this, if you have to work in a venue that has a noise-limiter, always respect the venue owner/manager, who may be terrified of losing the venue's licence (and his/her livelihood along with it), and who may dislike noise-limiters even more than you do: