Speaker spacing & SPL: check coverage before the quote

A loudspeaker covers a cone of sound. The higher the ceiling and the narrower the coverage angle, the larger the spacing can be. The lower the ceiling, the closer the speakers must be.

The count follows the spacing: area divided by the coverage per speaker, plus the edge conditions. The tap setting then follows the required level.

Use the finished ceiling height and the loudspeaker’s coverage angle to calculate the coverage diameter at the listener plane. Add the mounting height and the listener ear height to get the actual throw.

A speaker with a wide angle at a low ceiling gives a small coverage circle. A narrow-angle speaker at the same height covers less, but may be more intelligible in a reverberant room.

Two rules are easy to check without software: no listener more than 15 m from the nearest loudspeaker, and no more than 8 m from the last corridor loudspeaker to the corridor end.

These rules are a design check, not a complete acoustic model. They catch the common error of a corridor with a speaker at one end and a listener at the other.

Sound pressure level falls with distance. A useful starting formula is SPL = SPL at 1 m − 20 log10(distance). The tap setting and the loudspeaker sensitivity give the SPL at 1 m.

Use the formula to compare tap settings, not to replace a measurement. The room, the surfaces and the background noise change the result.

The emergency message must be at least 15 dB above the ambient noise. Measure or estimate the noise in each zone, then set the tap and the amplifier level to reach the target.

A factory with 85 dB ambient noise needs a much higher level than an office. The loudspeaker and the tap must be selected for the noisiest condition, not the quietest.

Take a corridor 60 m long, 2.4 m wide and 3 m high, with a target of even speech coverage. The 8 m corridor rule sets the last speaker no more than 8 m from the end; the spacing along the corridor follows the coverage pattern.

The most common mistakes are counting speakers without checking the ceiling height, setting every tap to maximum, and ignoring the corridor end rule. Each one produces either poor intelligibility or an oversized amplifier.

Send the room dimensions, ceiling height, room use, ambient noise and a plan with the speaker positions. Add the target SPL or the local code requirement.

We will return a spacing calculation, a speaker count and a tap-load estimate. The final model is confirmed against the room data.