@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.
