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Old 2008-11-11, 12:33 PM   #1
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Default Speaker re-magnetizing service available in Canada?

Hello,

Five years ago I bought four vintage twelve inch Tannoy coax speakers in a second hand pro-audio store.

Only last month did I finally complete building the cabinets.

Out of the four drivers, one woofer measures 7 db. down compared to the three other drivers.

Its companion tweeter is also 3 db. down because both HF and LF voice coils share the same magnet structure.

There are re-magnetizing services available in the U.S.

But before doing a cross-border shipping, I wanted to check first if such a service already exists in Canada.

Thanks for any leads.
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Old 2008-11-12, 05:27 PM   #2
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If you want local, I recommend finding a high end audio store in your neigbourhood and asking them for a recommendation.
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Old 2008-11-12, 06:50 PM   #3
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Wow, I didn't even know you could re-magnetise drivers. But I guess it makes sense, just never heard of it.

I'm just thinking out loud here... What kills magnetism? Usually it's heat. What else does heat (i.e. power) kill? Voicecoils! Have you taken the affected driver apart? I will presume you don't have a gaussmeter... Are you sure it's not a voicecoil with shorted turns reducing the output? Or some mechanical restriction? There is also something in there called a magnetic shunt, but supposedly that's mainly for increased low frequency flux. You probably know all this... If it was me, I'd take the bad and one good speaker apart. Without a gaussmeter, I'd compare each magnet for "picking up stuff", various weights, until I was convinced of the diff. I would only mail the magnet (or magnets, so they could match the good one), not the whole speaker.

Were these speakers used with live music amps? i.e run hard You are sure the bad speaker wasn't re-coned using some third-party crap? They will do that, and they're not the same. What I'm suggesting is heat is the only common thing to kill speaker magnetism in use, and there may be other problems that are now hidden. I would swap good/bad magnets to make sure. You've probably already done that... These drivers are too "valuable" to send out to "know-nothings" who don't appreciate them, you need to know exactly what's wrong so people don't dick around with them like they were doing a car repair...
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Old 2008-11-12, 09:55 PM   #4
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Thanks for the comments.

I have been in contact today with Tannoy Canada and they recommend that I swap the magnet structure between the two drivers to see if the problem moves with the structure.

Removing the structure requires me to first remove the woofer cone in order to expose the bolts hidden under the spider.

If the problem moves with the structure, I can further breakdown the structure into its three components, which are - one forward flux plate glued to the cylindrical-hollow magnet, a rear flux plate, and finally an inner waveguide core.

According to Tannoy, a faulty waveguide or rear flux plate can contribute as much to the problem as a weakened magnet.

These drivers were once in the studios of the C.B.C. (Radio-Canada) here in Montreal and came on the second hand market about 10 years ago. So they surely saw action during their tenure.

Tannoy Canada does not have a magnetizing apparatus, but feels confident that there is still at least one company in the Toronto area capable of remagnetizing.

Once we know which magnet part is responsible, then we will move on to the next step.

By the way, the voice coil resistances of both LF and HF are within 1/10 ohm of the values of the matching driver.
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Old 2008-11-13, 02:50 PM   #5
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Default Replacement magnet availability???

Quote:
Wow, I didn't even know you could re-magnetise drivers.
First time I hear about that my self. Since speakers use permanent magnets, it never occured to me that it would eventually demagnetize however, it does make sense as nothing last forever. I would more likely think they would replace the magnet portion ratter than re-magnetize. If you are to take apart that much, what are the chances Tannoy can send you the replacement magnet(s)? Keep in mind labor is usually the expensive portion of the work ratter than the replacement part(s)!

Cheers!
René
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Old 2008-11-13, 03:46 PM   #6
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These thirty plus year old Tannoy speaker magnets are collector's items.

At some point in the 1970's, the world supply of some rare earth minerals began to dry up and manufacturers looked to other alloys to approach, but not quite equal the force per pound characteristics of the ALNICO family of magnets.

All permenant magnets originally needed to be magnetized in the factory by placing them temporarily in an extremely strong magnet field generated by a high direct current passing through a coil of thick wire.

The polarity of any permenant magnet can deteriorate over time if subjected to the wrong conditions.

Complex magnet assemblies used in vintage Tannoy speakers are composed of four parts held together by fastening bolts. If the interface between any of these components becomes mis-alligned or less intimate over time, then that too can degrade performance.

I believe it is far cheaper to re-magnetize a vintage magnet rather than search for a replacement on EBAY which would require at least buying a vintage speaker with broken woofer and tweeter coils.

One company in Ohio charges 30$ to remagnetize. Vintage Tannoy speakers in working order sell for $400- $1000 per driver/crossover depending on year and model.
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Old 2008-11-13, 04:12 PM   #7
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Quote:
One company in Ohio charges 30$ to remagnetize.
Not worth looking at anything else at that price... What about your cost for shipping, insurance and all? What kind of warranty are they giving you on the success of the operation?

Cheers!
René
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Old 2008-11-13, 05:06 PM   #8
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Quote:
Originally Posted by TECHNOKID View Post
Not worth looking at anything else at that price... What about your cost for shipping, insurance and all? What kind of warranty are they giving you on the success of the operation?

Cheers!
René
I'm not too worried about the risk that they won't succeed in re-magnetizing the assembly. They do this all the time on Altec vintage loudspeakers like the famous 604E which has a similar profile to the Tannoy Monitor Gold.

The real problem will be to get this 10 pound item across the border twice without getting hit with a large customs brokerage fee.

And were it to be lost or damaged in transit, I would need well over a thousand dollars in insurance compensation in order to be able to purchase something close to identical on EBAY.

So the $30 fee will be minor compared to the other charges.

That is why I'm current looking in Canada for a service and I may have found one in Oakville.

They are currently evaluating my request.
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Old 2008-11-13, 05:24 PM   #9
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super!

bonne chance Montréal!
René
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Old 2008-11-13, 06:26 PM   #10
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Quote:
Originally Posted by TECHNOKID View Post
super!

bonne chance Montréal!
René
Merci bien Rene.
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Old 2008-11-13, 07:01 PM   #11
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Did you get the magnet(s) out yet? How hard is it? I've never disassembled a driver that far. My 12" ones are from '76, so sound about the same age as yours. Are you putting two of them in each cabinet, is that why you need them balanced?
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Old 2008-11-13, 07:15 PM   #12
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Quote:
Originally Posted by cfraser View Post
Did you get the magnet(s) out yet? How hard is it? I've never disassembled a driver that far. My 12" ones are from '76, so sound about the same age as yours. Are you putting two of them in each cabinet, is that why you need them balanced?
It will take some time to get the magnets out. Unlike other Tannoys of different sizes and different generations, my two HPD315s have their magnet structures attached by bolts whose heads are hidden under the spider.

So the woofer cone has to come off first. I'll do that next week.

I have 8 other Tannoys, three new ones (Saturn 6",8") and the other five dating between 1971 and 1978 (three 15", and two 12").

None of the vintage speakers have a magnet problem except this one driver in question.

It took me 15 months to build four new cabinets for all the 12" drivers, and yes it's one driver per cabinet.

With a 7 db. difference between the output within one pair, it makes no sense to boost the power by 4 times in order to create a balance. Better to get the magnet up to scratch.
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Old 2008-11-13, 07:57 PM   #13
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Ah yes, I can see the magnet assembly fastening screws in the cutaway pic I have, now that you mention them. Ummm...it's been a while, but doesn't removing the cones ruin the surrounds? IIRC I had to scrape them off the frame when reconing (expensive!).
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Old 2008-11-13, 08:15 PM   #14
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Quote:
Originally Posted by cfraser View Post
Ah yes, I can see the magnet assembly fastening screws in the cutaway pic I have, now that you mention them. Ummm...it's been a while, but doesn't removing the cones ruin the surrounds? IIRC I had to scrape them off the frame when reconing (expensive!).
I believe the early generation of Tannoy cones (late 1960s,early 1970s) did not use a glued on surround, the surround was formed by thining the extreme part of the woofer cone and gummy material was added to keep it flexible over time.

Removing these cones may have meant having to break the gummy glue bond between the frame and the cone.

Next generation cones used a seperate foam ring as a surround and a gummy material was not required, other than the thin brushed on latex paint only on the outer surface of the foam.

The back side of the foam is dry and should not be sticking to the frame. Unscrewing the four or more metal clips that hold the gasket sections should release the foam surround.
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Old 2008-11-13, 08:38 PM   #15
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But the deteriorated foam *does* kinda stick, even though my '76 HPD315As didn't have glue. It's part of the problem of the natural UV-caused deterioration, the foam turns kinda soft and gummy, and very easy to tear. To get back the flat surface on the frame I had to scrape them, that was by far the most time-consuming job when reconing, which is otherwise trivial with the Tannoy kits. Just a warning. Though your drivers may have been reconed at some point if they're that old and the surrounds may not be so fragile, usually 15-20 years is the upper limit for the surrounds of that vintage (before they changed the surround material to something more rubbery...the factory replacements are still foamy to maintain original sound characteristics). Anyway you'll get a good sense of it after you remove the 4 metal things that hold the surrounds, if the cones don't easily pop out.

Edit: I may be wrong in some of the details as it's been 6-7 years since I did a HPD315 reconing. But the part about the surrounds sticking is right though, hard to forget since it was a real nuisance...
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