AR-3A Woofer Repair Suggestions

[Guest marklm]

So I come home from work to find that one of my 1969 12" woofers lying on my concrete basement floor.(It had been on a 3' high table when I left it.) I reminded myself to breathe.

It looked normal. I hooked it up. I've got decent volume, but absolutely no excursion. It is locked tight! I applied some manual pressure on the cone, to no avail. It's not bottomed out, but more in the neutral position.

Before I start cutting and unsoldering, I thought I'd ask for suggestions.

Mark in olympia

[roundhome]

Hello Mark

I'm in spokane you are lucky your magnet is not in a lot of little parts. I had a 15" fall off and its now junk.

what might have hapened is that you losened the magnet and it is now binding the voice coil. not sure of a fix for that. I will have to look at one of my 12s that is broken apart I know the bottom plate is riveted on with the mag glued to that. don't try to move it if you can get the mag off cafully it might be able to be shimed and glued back on our at least save the cone and voice coil.

Jim

ps is it a bolt on magnet? if so this would be better For Tom or Ken to talk to you.

[tysontom]

>So I come home from work to find that one of my 1969 12"

>woofers lying on my concrete basement floor.(It had been on a

>3' high table when I left it.) I reminded myself to breathe.

>

>It looked normal. I hooked it up. I've got decent volume, but

>absolutely no excursion. It is locked tight! I applied some

>manual pressure on the cone, to no avail. It's not bottomed

>out, but more in the neutral position.

>

>Before I start cutting and unsoldering, I thought I'd ask for

>suggestions.

>

>Mark in olympia

Mark,

It is likely that if it landed on the magnet end, the magnet has shifted enough to bind the coil. It is also possible that the driver landed on the frame and warped it, causing the voice coil and spider assembly to be out of alignment. In any event, the tolerances for the voice coil in the gap are in millimeters, and very little is required to cause the coil to bind.

The glue on the magnet assembly is there to hold the magnet to the top and bottom plate (the "iron") of the magnet structure, but also to keep the magnet from shifting if a speaker is jolted in shipment, etc. In the case of the newer AR-3a woofer, the bottom plate and pole piece are riveted together, and the top plate is riveted to the basket. Glue and magnetic force together hold the magnet to the bottom and top plate.

The odds of repairing the damage you describe are not high. Even if you could get the magnet back in alignment, most likely the voice coil has been bent or scratched severely, and would never perform properly again. Good luck, but I'd start looking for another AR-3a woofer. You mentioned 1969; is your woofer a ceramic or Alnico woofer with the cast-aluminum frame? The earlier Alnico version will actually sustain a fall better than the newer one because it is bolted all the way through the magnet in three places.

--Tom Tyson

[Guest marklm]

Thanks Tom,

The plates had shifted. It is the old type with the three bolts. I dissambled the magnet assembly from the basket, took the iron plates off the magnet assembly, cleaned them, applied a little adhesive, and

replaced them using shims,(vinyl Levelor blind pieces, four thick.)

Some slight tweaking with a small hammer, and it's done. Free motion and good sound! I consider myself lucky. And I'm very impressed with how such a delicate sounding instrument can be built so incredibly sturdy. An elegant piece of engineering.

Thanks,

Mark in Olympia