What's loud, and how loud are Watts? Paul Trynka turns up the controls and boldly goes in search of strange new volume levels.

There's a rumour that most guitarists going around with long hair, damaged hearing/brain, and stacks big enough for squatters to move into think that the loudest guitar amp you can buy is one with a volume control that goes up to 11. The technical arguments against this might be somewhat dubious, but we won't go into that here. What we are dealing with here is the somewhat similar notion that the more Watts you have sitting in your amplifier, the louder it will be. Like most things in this most profound and convoluted world we have the existential misfortune to in habit, things ain't quite so simple.

In the first place a 200w amplifier is not twice as loud as a 100w amplifier, it merely throws the sound twice as far. In fact, the difference between the sound levels of two such amplifiers corresponds to the smallest change in volume which the human ear can detect. That's why, if you've got a half power switch on your amplifier you can hardly tell the difference between the two levels. Unless it's just me and my hearing's gone because I had my amplifier on 11 again.

Secondly, any minor differences between volume levels is swamped by the varying efficiencies of the speaker you use. Loudness is measured in deciBels, and the efficiency figure quoted for a speaker measures how many deciBels you get out for every Watt you stuff in. Thus, a more efficient speaker has a more advanced hearing damaging potential, which is what we all want. Unfortunately, though, it's not quite as simple as that; in many cases a speaker is engineered for high efficiency, but this is achieved at the expense of a flat frequency response. As my personal guru and spiritual guide says, the large print giveth and the small print taketh away. For the purposes of more usable volume, a speaker needs to be more efficient over the whole frequency range you're going to use.

This brings me nicely to the next point, which is the box you put your speaker in. Speaker enclosure design largely dictates the low-frequency performance of a speaker. A well-designed ported cabinet can extend bass response down an octave, and it's those funky gut-churning low frequencies which provide the subjective sensation of welly. By treating the cabinet as part of a system in the same way as resistors or capacitors are, you can thus improve your welly-inducing potential. Cabinet loading also affects the way speaker vibrations couple with the air they're trying to move — the number of speakers used also has a similar effect, and using the correct number of speakers means an amplifier will be able to deliver its full rated wattage.

Ah yes, wattages again. At this point, in order to confuse the situation somewhat, it might be useful to note that there are two kinds of wattages; RMS and Peak. They're both ways of trying to put an average figure to power levels, and put simplistically, which comes naturally to me, Peak or Music Power wattage ratings mean that someone's trying to make the figure look bigger. However, they can still provide some information about how an amplifier delivers power in short bursts.

Now, you remember that old chestnut about a 200W amplifier not being twice as loud as a 100W amplifier? That's still true, but did you know that two 100W amplifiers can be twice as loud as one 100W amplifier? Yes, this amazing transformation is possible if you split the frequency range in two using a crossover, and then amplify each half of the frequency spectrum separately. This is all thanks to that phenomenon known as the 'constant-gain-bandwidth-product', a term which is always worth dropping in casual conversation. Like all scientific facts, though, this is only true every now and then, but still greatly improves available power. Using this method with an active crossover will also increase the system's headroom, which can be regarded as a kind of aural overdraft, and helps stop your tweeters sending you a solicitor's letter.

This brings me to my conclusion, which is that the loudness level of your amplifier is directly related to the size of your overdraft. That's why I've only got a 20W guitar amplifier but it still sounds very loud.

However, I should mention that I've got a very rare early 60s Jazzmaster with a volume control which goes up to 11...