... is dealing with the things that crawl out at you!!

Loudness is measured in terms of the air-pressure variations (sound-pressure level, or SPL) that we sense as sound waves. The scale is indeed base-10 logarhythmic, but the relationship to electrical power is not linear. [u]To double the SPL, you need 10 times as much power!![/u]

Just to confuse the issue even further, the efficiency, or lack of efficiency, of the speaker(s) makes a big difference in the loudness of a system.

You will see speaker efficiency specified in terms of how many dB SPL result from an input of [u]1 Watt[/u] at 1000 Hz, measured at a distance of 1 meter, in line with the centre of the cone. An efficient speaker will produce ~100 dB. Its not uncommon to see numbers closer to 90 dB.

Here's where things get strange. A 50 Watt amp driving the 90 dB speaker is going to produce the [u]same[/u] SPL as a 5 Watt amp driving the 100 dB speaker!

As for the tube/transistor conundrum, power ratings are measured at very low levels of distotion, typically much less than 1%.

A transistor amp stays clean right up to the point where it can't pass any more of the power supply voltage to the speakers. Then it 'clips' the signal, producing lots of very harsh distortion.

A tube amp starts to distort long before it 'runs out' of supply voltage, so it can deliver far more than its rated power, if you don't mind getting increased distortion along with the extra power. (You don't mind a little power-stage distortion, do you?)

The even-order harmonic content added to the original signal by tube distortion sounds more 'musical' than the odd-order harmonics that make up the waveform resulting from 'transistor' distortion. If you're feeling mathematically inquisitive, you can do some Fourier Transforms to see what I mean.

[Edited by Lordathestrings on 12-25-2001 at 07:13 PM]