It's not the shape of a waveform that blows speakers when an amp clips. And the ouptut doesn't become DC, either. It's the excessive power that does it. When amp clips severely, the average power in the signal is much, much higher than if the signal were reduced to the point where it's clean. An amp could actually put out more power than its rating.

For an extreme example, let's say an amp driving an 8-ohm load puts out a sine wave that just starts to clip when the waveform peaks reach 60 volts. Its RMS voltage is 42.4 volts, and the power delivered to the load is 225 watts. A 60-volt square wave, OTOH, which would resemble a very severely clipped version of the sine wave, would deliver twice as much power--450 watts--into that same load.

While it's also true that clipping produces a lot of harmonic energy, that additional harmonic power in itself does not greatly endanger HF drivers in systems with passive crossovers. That's because even in a square wave, the fundamental is about 88% of the total power. Thus, if the amp is putting out a 60-volt square wave into an 8-ohm load (450 watts), the fundamental is about 400 watts and the rest of the power is in the 3rd, 5th, 7th, and higher-order odd harmonics.

-Bob Lee
Applications Engineer
QSC Audio Products, Inc.