Noise Limit & dB Exposure.

Sound from a single point source drops by about 6 dB every time you double the distance from it, which is the inverse-square law in a free field. So a level of 120 dB at 1 metre falls to roughly 114 dB at 2 metres and around 86 dB at 50 metres. Real sites behave differently because of reflections off buildings, hard ground and weather, so the open-field figure is a best case and you should still measure on the day.

A plain dB reading counts all sound energy equally, while dBA applies an A-weighting filter that rolls off the very low and very high frequencies your ear is less sensitive to. Because human hearing and most noise regulations are based on perceived loudness, council limits and workplace noise standards are almost always written in dBA. Use dBA figures when you are checking exposure or compliance, and remember a sub-heavy show can read higher on an unweighted meter than the dBA number suggests.

Safe Work Australia sets the workplace standard at 85 dBA averaged over an 8 hour day, with a 3 dB exchange rate. That means every 3 dB increase halves the safe time, so 88 dBA is safe for about 4 hours, 91 dBA for about 2 hours and 100 dBA for only around 15 minutes. Above the 85 dBA action level you should provide hearing protection for crew and limit how long anyone stands in the loudest zones.

There is no single national number because allowable levels are set by local council noise regulations and usually depend on the time of day and how close the nearest homes are. Many residential limits sit somewhere in the 50 to 65 dBA range at the boundary, and they tighten in the evening and overnight. Always check the specific limit in your council's local laws or environmental health conditions, then use a distance calculation to work back to a safe level at the speakers.

Start from the limit measured at the nearest receiver, such as a residence boundary, then use the inverse-square law to work out how loud the speakers can be at source for that distance. Aiming the PA away from homes, keeping subs low and tight, raising boxes so sound carries to the audience rather than spilling sideways, and adding distance all help. The calculator gives you a planning estimate, but you should still take a sound-level reading at the boundary on the day and adjust.