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Sensitivity of Loudspeakers


Why do I have over five kilowatts of amplifier power driving speakers with a mid band sensitivity of 105db/watt?
A discussion of sensitivity and power requirements of loudspeakers, C.Hendricson, extracted from handbook of sound engineering.

" Listening for hi-fi pleasure at 3m (10ft) from the loudspeaker looses about 10db (ref 1m) and a 90 db level is certainly a typcial and pleasureable one if the music comes out clean: 100db is more typical of studio control room levels, which is often exceeded. On top of this, peak to average levels of 15 to 20 db are realistically available from a tape master, direct to disk, or digital source. Real life is this way, especially the spectacular and agresssive music that is enjoyed by and produced for the American public.

One watt into an 85 db/1W/1m loudspeaker will give about 75db at 3m. To listen at 80 db and expect a peak to average of 15db means we need a 3.2W average and a 420W total to handle peaks. The amplifier is still enormous and expensive and may damage the loudspeakers. The fact is that many so called hifi loudspeakers are really misnamed because they cannot handle realistic swings in pressure and only reproduce on axis (not power) response approaching hi-fi with a 1-W input.

A look a larger loudspeaker systems, such as recording monitors, shows that average sensitivities range from 96 to 100db/1w/1m. At 98db/1w/1m we have 88db available at 3m and need +2db or 1.6w to listen at 90db, 160w (+20db) to handle peaks. This is definitely a real world pracitcality. However, as 100db levels are reached, 1600W is required for 20db peaks. Most large power amplifiers are limited to 200 to 400w per side in sterio; 1600w may be approached by bridgeing an amplifier, but the loudspeaker may be damaged.

For 100db listening levels, a 15db peak to average will be handled by a 500w amplifier, something more realizable. "


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