Thermal Distortion your loudspeaker most likely suffers from it. But do you care?


 Thermal Distortion is much more serious than just a maximum power handling limitation or side effect.TD is overlooked by most manufacturers as there is no easy (low cost) solution and TD is audible and measurable most of the time at most power levels. TD is caused by the conductive metal (aluminum, copper, or silver) voice coil getting hotter when you pass electrical energy through it. The more power you pass through it the hotter the metal gets. The hotter the metal gets the more the electrical resistance increase. The efficiency goes down and you need to ram in more and more power for smaller and smaller increases in SPL. It can be the reason you get fatigued while listening. If you are running massive power you are creating more TD in your transducers. But do you care? And is it a reason some prefer horn-loaded designs or SET-powered systems since they have the least problems with TD? 

128x128johnk

Pannels don't suffer from it but they have their own design limitations related to limited excursions, dipole effect cancellations, beaming, and pannel size reducing higher frequency. Nothings perfect.

+1 @ieales … another #metoo attempt, and this time trying to sneak in panels as a heat stroke sufferer.

Insignificant in properly designed loudspeakers. High efficiency helps keep distortion to a minimum.

Back when tubes were king, high efficiency speakers were very common because tube power was (and continues to be) expensive.

When solid state amps were commonplace, speaker efficiency started to go down.

The problem here is that it never helps to have an amplifier drive a speaker that is a difficult load and in particular low efficiency. The result will be higher distortion from the amplifier if nothing else, and that distortion usually manifests as higher ordered harmonics, to which the ear assigns the tonality of 'harsh and bright' and is keenly sensitive to their presence since it uses them to sense sound pressure.

So we've been hearing 'harsh and bright' for 50 years now. Some is the fault of amplifier design of course, but difficult to drive speakers don't help. 

So inefficient and low impedance speakers should be avoided if you want to get the most out of your amplifier dollar investment.