Sound Volume and the Ear - Alec Nisbett

Intensity (sound wave power or energy/time) and volume (subjective loudness) As it happens the ratio of intensities in 3 dB is about 2:1. This is convenient to remember, because if we double up a sound source we double the intensity (at a given distance). So if we have one soprano bawling her head off and another joins her singing equaly loudly the sound level will go up 3dB (not all that much more than the minimum detectable by the human ear). But to raise the level by another 3dB two more sopranos are needed. Four are needed for the next 3dB -and so on. Before we get very we are having to add sopranos at the rate of 64 or 128 a time to get any appreciable change of volume. (euroelectron note, this should also explain why low power amps can sound much louder that we expect them to sound). Extract from the excellent book The Use of Microphones - Alec Nisbett. Vicky's gift.