Speaker magnets


Three questions:
1) The coil in a speaker when fed with current from the amplifier will produce its own magnetic field, presumably 4 layer coils more so. Over time does this ever have any effect on the characteristics of the speaker magnet?
2) Modern speakers have massive magnets compared with most vintage speakers. What advantage do they give a modern speaker over a vintage speaker?
3) Does the magnet in a speaker deteriorate to any noticeable amount just due to age?
chris_w_uk
Plus 1 on weirdness and magnets. Can be very creep and/or surreal. Normal stuff like a fire truck using its flashing lights (no sound) and coming up the mountain road right by you, seems like a religious experience. But at least you realize why it’s happening (well placed warning signs that recommend limited exposure times). 
Bigger is not always better in woofer magnets. You need the right amount of gauss(related to magnet size) to give the right driver specs for the bass enclosure design to produce the bass control and roll off desired. Too small a magnet and you get boomy bass. But too big a magnet and you get over damped bass which starts to roll off too high and you end up with less bass.
The OP will need the Thiel-Small parameters for his drivers to design cabinets for them. These equations supersede the old cut-and-try method.
The Thiele-Small parameters are equations that will calculate the optimum box size for a particular woofer. Look up "How to measure Thiele-Small parameters". No need to futz around with old trial-and-error methods!