How loud should it be? A better question might be “How loud shouldn’t it be?” There is no danger of being injured by a sound that is too soft, but there is definitely an upper limit to what people should be exposed to.
The eardrum is a pressure-sensitive stretched diaphragm, much like a drumhead. And if you hit it too hard it will break, much to the displeasure of its owner.
According to OHSA, exposures that exceed 95 dBA-Slow for more than an hour or so are a problem for human listeners. With this in mind, let’s look at typical levels encountered on stage with a live band.
Chain Of Command
We will start with the source that is the least adjustable in level – the acoustic drum kit. The levels generated for the other musicians can easily exceed 90 dBA-Slow.
The other musicians will naturally desire to balance their own level with the drum kit, so we will assume that each is producing the same SPL as the drums.
The combined level of all of these sources might be on the order of 90 dBA + 10logN.
If there are four sources (drums, guitar, keys, bass) the level on stage might be 96 dBA-Slow. If we factor in the level contribution from reflected sound (from the stage floor, ceiling and rear wall), we can easily expect another 6 dB for a total of 102 dBA.
Next, the musicians need to hear the vocals, so the floor monitor levels must be set to balance with the stage level of the instruments. And since musicians are spread all over the stage, the monitor system might also be expected to reinforce the instruments to produce a better mix for each musician.
It’s a bit difficult to calculate, but it is safe to say that the monitors will easily add another 3 dB to the overall stage level. So, the base-line levels generated by an acoustic drum kit practically guarantee a total on-stage sound pressure level of 105 dBA, and potentially much higher.