What UK Law Has to Say About Sound
There are two principal areas in which statutory provisions in UK law address Sound.
The first is Environmental: loud sounds can be a nuisance to other people, particularly in residential areas. Sound can travel remarkably well outdoors (especially at night, due to the refraction/reflection of sound waves caused by atmospheric conditions). If you are in any doubt about whether your planned event will constitute a nuisance:
If a Local Authority Environmental Officer or Policeman tells you to turn it down or off and you don't, they have the power to confiscate equipment (whoever owns it), and if it isn't yours - if you have hired it, for example - you might have to pay hire charges until the owner can recover it. They may not be able to recover it anytime soon.
The second area is Health & Safety. You have duties to any employees to provide ear protection and to take other action (e.g. limiting periods of exposure) when sound pressure exceeds certain levels.
A basic description of your responsibilities is provided on the Health & Safety Executive (HSE) website, with several leaflets in PDF format on the page dealing with the Music and Entertainment sectors. You can also download a (free) noise exposure calculator from the HSE site to translate concert sound levels into equivalent daily or weekly exposure levels.
For content that specifically addresses the music industry you will also find a good amount of useful information on the more recent Sound Advice website.
Generally, the ear is more tolerant of musical sounds, which differ in dynamic range and frequency content from the type of broadband noise caused by a bench grinder or pneumatic drill (although with some styles of music this may be a moot point). Also, typical exposure times are much shorter (typical concerts rarely exceed two hours of performance time), and are not an everyday occurrence unless you work in a venue. However, typical concerts also have much higher sound pressure levels than HSE action levels: even a folk duo will typically produce peaks exceeding 85dBA - the revised HSE second action level - and an unamplified snare drum can produce a peak sound pressure level (SPL) of over 120dBA. If the vocals (with a lot of energy in the ear's most sensitive range) need to be louder than the drum kit, the overall level can be very high, and potentially very damaging.
An increasing number of venues have SPL detectors that will interrupt the power to the circuits supplying amplifiers if the SPL exceeds a certain threshold.
If in doubt, you should at least:
However, if you are routinely involved with music production you would be well advised to read all relevant sections and documents on the HSE website, and if necessary take professional advice in implementing the steps the law now requires you to take.
Making Too Much Noise might bring you into contact with the law in other ways, as a Cautionary Tale in The Guardian shows.