If I understand it right, I think the reason people say that low wattage amps are one of the biggest causes for blown speakers is because of clipping. As long as you don’t take your amp to the clipping point, then you are ok, but if you turn it up to the point were it starts to clip, this is very hard on a speaker. This is because if you look at the output of the amp when it is clipping on a scope, you can see it cutting off the tops and bottoms of the waveform, and this means that the speaker is being “told” by the amp to move completely in one position, and move completely in another position right away without any intermittent steps.
Example: If we were to put a perfect signwave of lets say 1k into the amp, and look at the output of the amp when it is not clipping, it looks perfectly round on the tops and bottoms of the wave, thus the speaker will move in and out very smoothly…this is good. But if you look at the same 1k signwave when the amp is clipping, it flattens out the tops and bottoms of the signwave, making it look more and more like a square wave the further you take it up. Depending on the quality of the amp, clipping can get very bad, very fast.
When the output of the amp looks like a squarewave it is telling the speaker to instantly move form the in position to the out position….this is very hard for the speakers to do, and isn’t good on them. This is also a very unnatural sound…..
Therefore, people say don’t run low powered amps on speakers, because they will clip sooner then higher powered amps. You still have to watch out that you don’t give the speakers more wattage then they are rated for, but at lease you will not damage the speaker before the speaker gets to its maximum wattage…..whereas you easily could with a under-powered amp if your running it hard…
Well, that is as I understand it….I could be wrong….we’ll see what Ian says….
