pls help identify magnet type of speaker!

[tubo]

hi,

i just bought a pair telefunken speakers. what is the magnet type of the big speakers, for sure i tweets are alnico. thanks

[Cal Weldon]

I think they're alnico V as well

[planet10]

You have 4 of the famed Isophon 4" alnico tweeter... what is weird is they look like the older short cone aperiodic ones (the most desirable ones), which doesn't jive with the presence of the ceramic magnet ovals... what are the date codes?

dave

[Cal Weldon]

Dave,

Is it the lathe divot that tells you those are ceramics?

[planet10]

The shape. And that i've seen quite a few before -- dead ones became magnets + scrap metal.

dave

[Andrew Eckhardt]

Is that shrink wrap around those? I'd have to put a cut in it and peel it back a little to satisfy the curiosity about the magnet material. Although if they have a Qts below about 2, it's probably alnico.

Although the energy product for alnico 5 is almost the same as for ceramic 5, it has the flux density of neodyminum, so lower Q speakers are possible with smaller alnico magnets, although they wont take much power without a lot of it.

[planet10]

Originally Posted by Andrew Eckhardt

Is that shrink wrap around those?

It is a moulded plastic cover.

These are ceramic. No question.

dave

[Andrew Eckhardt]

If that's the case then they either have 0 coil overhang and a very small gap, or a Q above 2 (or lets say Well over 1). The only reason I'd be likely to go along with you is the fact that anything other than plug shapes were rare in that size, although rings were definitely being used for higher power speakers at the time. I wasn't designing magnetic components until 1993, so I'm not exactly aware of why small rings of alnico weren't common. If anyone wants to look at the demagnitization curves for all but the higher grades of neo magnets, Bunting Magnetics has them published on their site.

[Andrew Eckhardt]

Arnold Magnetics didn't start producing ferrite magnets until 1964. Ferrite materials were invented and produced in the 30's in Japan, but I'm not quite sure when commercial production of any ferrite permanent magnets began.

The plastic cover might have something to do with early fears about the brittleness of ceramic magnets. I'd still drill a small hole and look.

[planet10]

I have disassembled the same units...

dave