Bottom line, CLIPPING distortion eats up speakers. All other distortion is simply noise/sound/signal for the amp to recreate. If the amp is operating within its normal range, the speakers will play whatever is fed into the amp just fine.
Totally Agree about clipping. I.e. gaining the system properly is of paramount importance hence my reference to cleanly powering your amplifier. Most of what I see on the water are over gained systems and clipping the heck outta speakers with square waves. When I hold tweak and tunes on the water, this is 80% of what I do. Adjust gains.
Re: distortion: garbage in garbage out. Amplifiers reproduce. Pretty simple. I've yet to ever see a guitar pedal in the signal chain hehe.
But if you send garbage in, the garbage coming out will not tear up a speaker if the amp is not clipping. Careful upstream gain setting preserves the quality and faithful recreation of the sound up to the power amplifier input, and provides for an optimal gain structure through all points in the audio chain. Proper upstream gain setting with the head unit, its aux inputs, (if attenable) eqs, preamps, etc, do nothing to preserve speakers.
It is this very real semantical difference I am trying to point out, and that I think, (???) David is trying to point out. Your writing, (as one would read it and try to understand) quite literally seems to suggest that a clipped head unit signal, driving a clean operating amp will blow speakers. That is simply not true.
When you boil it down, distill it, the net-net-net cause of thermal failure is TOO MUCH POWER regardless of how you arrive at that power. Too much clean power can be an equal threat also.
Continuous power is power regardless of the waveform shape. However, you can have just as much continuous power without near the peak to peak power. So the same power can come in different shapes. The math will lead you to the same point....as measured continuous power. And that is the number that is of concern.
Does hard clipping an amplifier create extra power? Yes it does. Is that a threat? Yes. It expands the duty cycle to the point that the speaker has less opportunity to dissipate the heat. But you can accomplish the same danger with a larger unclipped signal.
The distortion is a byproduct of a severely over-driven amplifier. But in the final analysis it is the power that is the damaging component regardless of how you arrive at that power level.
A badly over-driven amplifier can put out much more power than its rating. It may not be clean power and it may not be useful power, but a smaller amplifier (rated under the speakers thermal rating) can generate enough power to do damage.
Now you could square wave an insignificant amount of power all day long without speaker damage IF that power is at a less than dangerous level for a particular speaker.
You can introduce all kinds of distortion into the signal path and if the output power does not approach or exceed the speaker's thermal capacity then the speaker is safe.
Again, POWER KILLS SPEAKERS. Distortion does not. Serious distortion happens to be a byproduct of a seriously over-driven amplifier.
Phil, from reading your material, we understand the problem exactly the same. Some of the language gets a bit clumsy though.