After reading recent comments regarding the planning application for a nearby wedding venue, I was reminded about my earlier life when for a brief period I was an Industrial Noise Consultant.
Noise can be a very emotional subject, so I thought that I'd refresh myself of the physics -- a very un-emotional subject!!
I started by looking at government information on noise:
There is no specific legislation setting noise limits for audience exposure to noise. However, HSE strongly recommends that the A-weighted equivalent continuous sound level over the duration of the event (Event LAeq), in any part of the audience area should not exceed 107 dB, and that the C-weighted peak sound pressure level should not exceed 140 dB -- the C-weighted pressure level looks more at the effect of low frequency sounds on the human ear, compared with the A-weighting. As we all know, bass sounds often carry further than other, higher frequencies.
The above sound-level exposure values are for the whole of the audience area. For practical purposes, it is usual for audience sound-level exposure to be monitored close to the front of house sound mixing position -- i.e. near the front loudspeakers.
Where practical, the audience should not be allowed within 3m of any loudspeaker.
I'm using these maximum levels to be those at 3m from the loudspeakers.
The physics is that sound levels drop about 6dB for every doubling of the distance from the source. This means that theoretically, the sound levels at certain Audlem locations could be:
OK, so these values are calculated for still air -- in reality they are probably the maximum levels. Noise is affected, normally being attenuated, by wind speed and direction. In reality, temperature and humidity have very little affect on live sound for most outdoor live shows. Typically higher frequencies are attenuated more than lower ones -- hence why particular types of music such as dance music often cause more of a problem due to their strong bass beat, which tends to carry further.
You may ask whether the marquee would help to reduce the propagation of the noise. Even if the marque were specially constructed with sound insulation, the reality is that the marquee will be open and people will be spilling out. In this situation the sound reduction performance of the marquee would be negligible. Even if the marquee was totally sealed it would not provide any sound reduction against low frequency sounds 40 – 120 Hz -- The Bass Sound!
I'm also ignoring the impact of any trees and buildings.
Trees don't really provide an effective noise barrier so do not rely on them.
Buildings can help attenuate noise, but also noise may be reflected off nearby buildings and this may direct the sound in unexpected directions.
Sorry if this has come across as a bit pompous -- I simply wanted to play the physicist again!!!
There isn't too much available online that gives more guidance.
The following is an interesting report done for East Suffolk"
An interesting outdoor event guide produced by Lambeth Council: