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

You’ve got more to worry about in passive crossovers than heat

VERY good information to add to my (limited) knowledge base.

Might also explain why it's extremely difficult for me to endure the 3rd (and featured) act of live performances?  As the evening progresses, the "tech" running the sound board bumps the sound levels up a few db during intervals.  By the time it gets to the 3rd set, it's downright painful.  The additive effects of distorted, dynamically compressed sound accompanied by much louder average sound levels is not what an aging audiophile appreciates at a live music venue.

@ditusa --

"Yes That is one of the many reason for using ALNICO in permanent magnet speakers, it’s impervious to heat so it’s flux is not affected by the change in temperature."

Alnico magnet’s were/are sometimes prone to demagnetize:

... there was one major disadvantage in Alnico loudspeakers that would have to be addressed � the susceptibility to permanent demagnetization due to overpowering.

This phenomenon is a result of variability in strength of the permanent magnetic field caused by interference from the voice coil�s electromagnetic field. This is referred to as flux modulation and is a leading cause of distortion in any dynamic loudspeaker. The electromagnetic field generated in the coil pushes against the global magnetic field set up by the permanent magnet and return circuit, causing it to �bend�. Under normal operating conditions, Alnico magnets actually resist this bending better than most other magnet materials. However, should this shift become large enough, it will exceed the coercivity of Alnico and cause it to partially demagnetize.

http://www.audioheritage.org/html/projectmay/technology/1500al.htm

Though in most cases, not least with high efficiency drivers used domestically I gather there are no real drawbacks with Alnico magnets to speak of.

@fiesta75 --

"You’ve got more to worry about in passive crossovers than heat"

Not least that they’re there in the first place, and their more complex iterations usually make matters worse. Heat at some point only adds to those issues, and used in low efficiency speakers this will only be more prevalent.

High eff. horn speakers ideally, or at least often call for steep filter slopes to avoid out-of-band irregularities, and as such active filters offer themselves much better here compared to passive XO’s.

Good info on Alnico magnets. They can be re-energized fairly easily too. I still enjoy them even with the increase Neodymium offers

The overpowering demag was mostly or only affecting a few JBL models when the switch was made from low tube power to higher power SS in PA use it is not an issue for other alnico magnet drivers. But it is still passed around as affecting all Alnico and that is just wrong I have dozens of old Alnico drivers meeting spec after lifetimes of use.