Contrary to popular belief, distortion does not cause speaker damage. Distortion is merely the audible detection of signal "clipping". Clipping is when an audio component can no longer provide enough power supply voltage to "cleanly" amplify the audio signal. Clipping can occur at any point in the signal chain (souce unit, signal processor, amplifier, etc.) The popular belief is that if an amplifier "clips" it will send D.C. current to the speaker's voice coil and "burn" it. THIS IS NOT TRUE. It would surprise you to realize nearly every car audio system's amplifier "clips" when listening to music at moderate -to- loud levels. Electrically overpowering a speaker is caused by continually playing the audio system loud, resulting in applying more power to the speaker than it's "rated" specifications. This is what causes speaker voice coils to "burn".