ReMagnetizing Question

[RonSSS]

How prevelant is the need to remagnetize?
I have a 416-8B alnico driver that has no apparant cone problems. No rubs etc. Yet the T/S parameters measure WAY OFF spec. The mate to that driver is dead on.
I can have the unit re-coned locally with parts bought from GPA, but if it's a magnet problem, a re-cone won't fix it.
I bought these drivers new in 1977, and the bad one is completely original. Never dropped, overheated etc. The other one had to be re-coned about 15 years ago because it began to rub.
The local re-coner BTW does excellent work and used to be a factory authorized Altec service center before Altec went TU. But I don't think they can remagnetize.
Thanks,
Ron

[Art J.]

Hi Ron, Congrats on the new 19's and my fingers stay crossed for Dylanl.
You might want to try an experiment that I tried a while back to test for
magnetism. I put a woofer on a long wood table and slid a boy scout compass
toward the woofer until the needle started to deflect. I marked the spot
on the table and repeated the procedure with the other woofer. In my
case they both were the same so I really don't know if this method is reliable
but it was the only method I was equipped to perform.. What do you think?
Is it worth a try? Art

[Altec19]

Hi Ron,

Remagnetization is like replacing worn out shock absorbers on a car: You don't know how bad they where until you experience the new ones. I had GPA remag a pair of 416-8B's and the difference in my case was significant. Even my kids noticed it. This is the reason I prefer having 416-8C's in my Model 19's. Ferrite doesn't fade. Besides, I'm not sure I buy into the notion that the human ear can discern the difference between sound created by the interaction of an electromagnetic field with a permanent magnetic field originating from ferrite versus Alnico. Assuming, of course, that both were of the same intensity to begin with.

Later . . .

Later . . .

[gearjammer]

There is no difference in the sound,do not believe the hype.The only thing alnico has going for it is it looks better and works with CRT's in the home theatre.

[RonSSS]

I don't believe the hype. I just know that one of my alnico units doesn't meet specs, not even close. I'm wondering if a simple re-cone will fix it.

[dgwojo]

I'd check the DC impedance with an ohm meter on both woofers without them connected to the crossover. Maybe the DC impedance is way different, I have a 515-8LF from Altec that has a 16 ohm coil, no idea how it got past quality control, it was brand new in the box when I bought it from an authorized dealer!! I realize impedance should be measured at 1khz but the DC measurement can also give some indications, under 8 ohms = 8 ohm coil, over 8 but under 16 = 16 ohm coil. I think yours should read around 6 ohms!!

[joyspring]

Ron,

Have both drivers reconed and remagnetised at the same time; it's a prudent measure regardless.

Even a loud on/off transient can significantly demagnetise an Alnico driver, and most do change timbre/sensitivity between remagnetisations.


Gearjammer:

You're quite right about the Alnico vs. Ferrite debate being hype in terms of Altec 416/515; both utilise underhung voice coils so any consideration regarding symmetric flux lines outside the magnetic gap, etc. are essentially irrelevant.

However, the Alnico driver is subject to demagnetisation although the closed magnetic circuit is definitely helpful in proximity to CRTs.

BobR

[Altec19]

I wonder if Altec changed the tuning of the Model 19's when they went from the 416-8B to the 8C? If T/S is significantly different then I could understand a discernable difference between the two drivers in the same cabinet.

[RonSSS]

My guess would be that they didn't change a thing......I was wondering the same thing. But I guess after I get these things down to the listening room, I can swap a woofer in one cabinet and do the measurements to see where the tuning point is. The woofs come out real easy.
Ron

[RonSSS]

One thing,
The 416-8B and the 416-8C do have different Theil Small parameters, so each would require a different box tuning. So in the exact same box, they just might sound different. But not because of the magnet material.

Dwojo, I did check the VC resistance when I measured the T/S parameters, and they were the same. The bad speaker measure very non linear.

Ron