Noise-Limiters

Venue Sound-Control

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.

Why Noise-Limiters Are Used

Noise-limiters are are usually installed for one of two reasons:

Environmental

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.

Health and Safety

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.

Setting-Up Noise-Limiters

Noise-limiters should generally be set up as follows:

Position the limiter's microphone at an arbitrary point in the room. The best position is generally as close as possible to and pointing towards the stage area, as this gives less opportunity for other factors (e.g. crowd noise) to affect the system. However, many noise-limiter manuals suggest a position more typical of an audience member (i.e. further from the sound source). This isn't going to make much difference in practice unless audience noise is likely to trigger the limiter.
Make some noise where the noise usually happens (this may involve hiring in a loudspeaker system if there isn't an in-house system that can make enough noise). Pink noise with a 6dB crest factor is probably as good a noise to use as any.
Measure the noise at a practical reference position: if protection of bar staff is the aim, measure the level at the bar; if keeping noise from neighbouring properties is required, measure the level outside the property at a known distance from it, then calculate the level at the nearest neighbouring property using the inverse square law.
Adjust the limiter so that it triggers when the target continuous level is exceeded for more than a set time (from ten to twenty seconds is a useful starting point).

Measuring the noise requires a calibrated sound-level meter, which is seldom included with a noise-limiter. Professional-standard meters can cost more than some noise-limiters.

Noise-Limiter Misuse

Noise-limiters may be incorrectly set up so that:

They are triggered by the highest-volume high-frequency content (generally lead vocals, but sometimes snare drum or cymbals) when their purpose is environmental.
They are triggered by low-frequency content (generally kick drum or bass guitar) when their purpose is health and safety.
They are triggered at very modest levels (although this may also be because target levels don't really permit live music at all).

Noise-limiters may be set incorrectly because:

A calibrated meter wasn't used.
The venue owner or manager has hyperacusis and set the level at his/her comfort threshold.

What to Do if a Noise-Limiter is Installed

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).

Maximise the available level

Place speakers as far as possible from the noise-limiter microphone.
As far as possible angle speakers away from the noise-limiter microphone. Bear in mind, however, that the microphone is probably situated in a position that makes this difficult to achieve without also angling them away from your audience.
Equalise your system so that there are no prominent peaks, especially at the noise-limiter's most sensitive frequencies. You can establish where these are - it may involve a lot of interruptions because of cutting out - by raising a pink-noise signal (with 6dB crest factor) to just below the cut-off point, and then boosting the signal using two or three adjacent graphic EQ faders at a time to find the worst areas. Then cut the output on the graphics in those areas by 6-9dB.

Minimise your output

Damp the drums. Get some drum mufflers or mute-pad sets. Otherwise, make hoops - three to four inches in diameter - from gaffer tape, with the sticky side on the outside of the hoop, and stick these on the underside of the drum skins, and on the inside of the kick-drum skin.
Get the drummer to use low-volume/practice drumsticks.
Put a rug/carpet under the drums, or, if you can manage it, cover the whole stage area in carpet.
Damp the walls around the stage area with anything you can. Open-plan office partitions are good if you can hire or borrow some; or make a backdrop from a blanket, a pole, and a couple of stands (even mic stands will do for this).
All sound sources add to the overall level, so keep backline levels to an absolute minimum (and position and angle any backline cabs towards the relevant musician and away from everyone else). This will also help you to
Keep monitor levels down (they also add to the overall level), or do without them altogether if it is humanly possible.
Set your final levels during sound-check to allow at least a couple of decibels between your loudest material and the noise-limiter's cut-off point.

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:

Most digital mixers and system controllers - ours included - take at least a few seconds to ‘wake up’. If you are using backing-tracks, midi files, digital consoles, or anything that is software-driven you will probably lose your place in the sequence. As well as having to wait for the noise-limiter to reset, you may have to wait for computer-based systems to reboot - and for anything that needs to reload - before you can even begin setting everything back to where it was before the power went off. The upshot of this is that you may not be able to resume where you left off at all quickly, or even at all.
Sudden power loss can cause damage (although this is not a usual result): it can corrupt hard drives, cause electronic component failure and even - in extreme cases - blow loudspeaker drivers.

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:

Do help to keep sound inside the building, by reminding guests or ticket-holders to keep doors closed.
Do keep the noise down when loading out.
Don't make a difficult situation worse by being antagonistic.

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