its the extra heat buildup from the current.....not the harmonics
the hotter the coil, the hotter the tinsels......and they can only take so much......
Not to get into the middle of you two's argument, but I think you are being a bit misleading here (unintentionally).
If you acknowledge its the excess amounts of heat that cause this, you shouldn't say clipping is the problem. Clipping isn't the culprit, over powering would be. If a less knowledgeable person read your answer on clipping and took it to heart, he'd think his 25watt amplifier would be capable of frying coils on a 1000 watt sub. Or he might be inclined to think his 250watt sub will be fine with a 1000 watt amp so long as it does not clip.
It may seem like Im splitting hairs here, but Im not. Its like the person who says that 'underpowering' kills speakers, when in reality that is merely symptom of why the problem finally occurred.
Clipping certainly can easily lead to overpowered, abused and melted coils. but 'clipping' is not the problem, it was the amount of power that was being applied that was the problem. Clipping merely helped create that problematic amount of power due to the size of the amplifier.
I think too many times anymore many of us just say 'clipping is the problem' as an easy answer to a more complex problem. That in turn evolves into something completely different, and wrong (like 'underpowering kills speakers' evolved from the idea of over-adjusting gains to make up for too small of an amplifier).