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
Passive radiator rings CNC cut, drilled, painted and passive radiators fitted. URL as above.
Anisotropic Alnico magnets are theoretically the best magnets for subwoofers but they are more expensive so Ferrite magnets are much more common. Ferrite magnets work well and are harder to demagnetize they just have to be larger. 
’’Alnico magnets are theoretically the best magnets for subwoofers’’.

That Is why JBL chose Alnico 5dg magnet for the JBL 1501al-2 woofer and not Ferrite. Alnico Is the best for making permanent magnet speaker drivers. JBL engineers discovered that more then 75 years ago. Probably the only better driver Is a field coil. The JBL 1501al-2 cost is $1500.00 each.



http://www.audioheritage.org/vbulletin/showthread.php?33557-1501al-2