Loudspeaker sensitivity and listening distance

Read the sensitivity line carefully

A loudspeaker might be specified as 90 dB at 1 W/1 m or 90 dB at 2.83 V/1 m. At 8 Ω, 2.83 V is approximately 1 W. At 4 Ω, the same voltage is approximately 2 W, giving the voltage-based figure a 3 dB advantage over a true 1 W comparison.

Also note bandwidth and measurement space. Anechoic, half-space and in-room figures are not interchangeable.

Allow for distance

For a point source in free field, level falls approximately 6 dB every time distance doubles. A loudspeaker producing 90 dB at one metre would therefore produce roughly 84 dB at two metres and 78 dB at four metres before room reflections and boundary effects.

Rooms reduce the loss at some frequencies, and multiple loudspeakers do not simply add together at every seat. Use the calculation as a design baseline, then verify the commissioned system.

Turn decibels into power

Every 3 dB increase requires twice the amplifier power. If one watt produces 84 dB at the seat, 2 W gives about 87 dB, 4 W about 90 dB and 100 W about 104 dB in ideal conditions. Add the desired peak headroom, then check that both amplifier and loudspeaker can deliver it cleanly.

Cinema-specific considerations

Bass management reduces deep-bass demand on small main loudspeakers, but the chosen crossover must suit their capability. High-sensitivity cinema loudspeakers need less power yet can reveal amplifier hiss and gain-structure problems. Long distances and low-sensitivity designs increase voltage and current requirements quickly.