[Mayhem]

Interesting trick John. You could also use "polyswitches" which do a similar job. Essentially, these components (which look like ceramic capacitors) go "open" when they get too hot and then as they cool down, they close the circuit again. You need to match them to the wattage and impedence of the speaker being protected and they work very well. The bonus here is that unlike the globe that needs to be replaced, backing off the power will cool down the polyswitch, allowing the gig to continue.

Also, Mosfet power amps are prone to oscillation at higher frequencies whcih also will take out speakers. This is a lot harder to detect as it is past the audiable range. I do not know all that much about it but I am lead to belive that the polyswitches can offer protection from this as well.

John - are you able to add to this?

Another point regarding clipping - this actually means that you are sending DC or direct current to the speakers which is bad. The reason that I mention this is that you may hear someone suggest "checking if an amp has DC at the outputs". This is what they are checking for.