12trx problems baffle science!

[CaptnBob]

I've got a pair of Electro-Voice 12TRXs from, I'm guessing, the middle 1960s. They have both been reconed several times over their long and checkered lives. One was dropped by UPS so hard that the magnet structure was knocked off the frame, destroying the cone. Nothing was shattered, however, so after several tries, I managed to get everything lined up again and reassembled. Then I had the guy Electro-Voice recommended recone it, using original no kidding really EV parts - cone, surround, spider, and voice coil. Both drivers have matching parts numbers on the cones.

The problem is this. The output is much lower than the other 12trx - at least 10 db and probably more. The cone moves freely, with no rubbing, and mechanically feels about as stiff as the other one.

The problem persists with the woofer section connected directly to the amp, thus bypassing any crossover culpability. The tweeters have about the same output. So my question is, "what gives?" Did the UPS induced trauma cause the magnet to lose some of its power? I can attest there is still plenty there, having almost lost fingers during a couple of my attempts to reassemble the thing. Can it be fixed? Or should I sail the treacherous waters of ebay to look for another? I'd sell them, but they were a wedding present and it might be awkward.

Thank you for any ideas.

Capt'n Bob

[Malcolm]

No takers yet on this? I'll take a stab, then.

I would have made UPS eat the speaker.

The only possibilities I can think of are a problem with the magnet circuit or a difference in the parts that were replaced. The spontaneous dissasmbly certainly did not do the magnet circuit any good.

Did the reconer recharge the magnet?

Where did the reconer get EV parts? I was told years ago by EV that parts were no longer available, except of course for the tweeter. Unless something has changed, the reconer would have to be using NOS parts or aftermarket parts.

FWIW I would have reconed both speakers at the same time to minimize any differences between them.

[jnorv]

Long tread under "Technical" called Re-charging Alnico Magnets, that deals with this. There is also info on the Lansing site with some of the same contributers.

http://www.audioheritage.org/cgi-bin/gforum.cgi?guest=6021

J Norvell

[CaptnBob]

Thanks, guys, I was beginning to feel neglected. Being dropped hard enough to "energetically disassemble" the loudspeaker certainly seems like it might have caused the magnet to lose some of it's punch.

The reconer did not recharge the magnet. He said he would look into it when he got back from vacation. Those posts stating the speaker would have to be reconed again afterwords are a bit disturbing.

Lloyd (the rebuilder) bought out another speaker tech when the older man retired. The 12trx recone kit was in a big stack of parts he got with the deal. (Before anyone gets on the phone, he did not have any parts for a 15WK. I asked.) The part numbers on both 12trx cones are the same.

Actually, the company that packed the speakers "ate" the damage - I got the money after only four or five months. (I guess UPS doesn't feel bolting a speaker in a 3/4" mdf box, then surrounding it with bubble wrap, then putting everything in a cardboard box, was sufficient.) When I pointed out to the packing company in California it would cost them a great deal of money to get the damaged speakers back, they decided to let me keep them. The cabinets were a total write-off, but I wanted to see what could be done with the driver.

Capt'n Bob