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Carver AL-III Planar Rebuild - Loose Magnets
Carver AL-III Planar Rebuild - Loose Magnets
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Old 3rd July 2016, 10:28 PM   #1
CherylJosie is offline CherylJosie  United States
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Join Date: Sep 2011
Default Carver AL-III Planar Rebuild - Loose Magnets

Hello Everyone,

A kind person has given me a set of Carver AL-III speakers.

They seem like they may have been in excellent condition when I picked them up, except for the magnet adhesive that seems to be a problem with these older planars. Two magnets apparently came loose during moving, or were already loose when we arrived. At the time there was still crumbling foam in the front aperture and there is protective felt glued over the rear aperture so we could not tell if the magnets were in place or not (did not even suspect it could be a problem), but I did hear a 'clunk' as one speaker was tipped to get it through my door so at least one magnet shifted in transit whether it was loose already or not.

One of the magnets has clamped the Kapton diaphragm, the other seems to have just clamped to its lateral neighbor. Both diaphragms are still working although the pinched one seems to be taking a set with an indentation that is visible from the front aperture now that the crumbly grille foam has been vacuumed out.

Even with loose magnets they still sound good at low volume. I avoided powering them at high volume until after I discovered the loose magnets and ruled out a full test drive to avoid causing further damage.

I am considering the process of removing the drivers, opening them up, re-attaching all the magnets, and closing the drivers with the original diaphragms (since replacements are impossible to find and I am not planning on creating new diaphragms with Mylar that is not as stable or tough as the original .002 Kapton -- if I really want to go that route, I can send the drivers to someone on ebay with experience to mangle for me at high $$$).

So far I have come up with the following notes (sorry, it is on another site):

Carver AL-III Plus? - AVS Forum | Home Theater Discussions And Reviews

and this:

Speaker magnet glue

Does anyone here have any experience rebuilding such devices AFTER the magnets have shifted? I have never attempted anything with magnets before, beyond the typical neodymium/alnico dance of prying a couple of small magnets apart to marvel at how much force it takes, and how readily opposing magnets flip over and clamp to each other (even with your fingers in the way).

I am concerned that opening the drivers will dislodge more magnets and/or puncture the diaphragm. The only remedies I have come up with are:

  • Building an open/accessible bench fixture to attach the rear casing edgewise using its original baffle mount screws so that the entire assembly can be examined on front and rear sides as well as manipulated without having to hold it in hand at the same time.
  • Using very long screws to replace the existing case closure screws one by one so that the case can be opened gradually and evenly in controlled fashion under the compression force against the mutually repelling magnets on either side of the diaphragm.
  • Building a plywood plate with two short wooden slats attached to it that fit through the two parallel casing slots/aperture of the driver, and maintain separation between the magnets as the casing is opened despite the shifting forces, in case any more magnets come unstuck during disassembly. Eight plates with two slats each in front, eight plates in rear, one for each pair of case slots. I briefly considered making these slats long so that the casing can slide back along the slats, until I realized that in order for these slats to provide any realistic protection they need to remain level with the magnets they fit between so that no loose magnets from the opposing side can plunge through the gap between magnets and puncture the diaphragm (in a big way).

The magnets that are loose are already moved into the gap where the proposed fixturing slat belongs, with the loose magnet either attaching to the adjacent magnet in the first driver and/or the magnets on the opposite side of the diaphragm (on the other half of the case) in the second driver.

A short let alone long slat cannot even be inserted where there is a loose magnet. I will have to make the slats removable so that I can take one off if there is a magnet in the way. In fact I should attach the slats to their plates using a removable anchor such as a wood screw through a sloppy hole in the plate so that I can also adjust the center-center spacing and alignment. Then I don't need to be so careful about clearances and I can leave a slat floating inside the driver case while opening the case if I need to simply be removing the slat's mounting screw.

The diaphragm cannot be clamped to the front and rear plate simultaneously with multiple loose magnets! or I need to create some clamp that can reach in through the case slots and keep that loose magnet physically attached to its own case.

Even then I might still rip the opposing magnets off the opposite case as I try to pull the loose magnet off the opposing magnets it is stuck to. If that happens all bets are off because new loose magnets on the other side are also going to reposition as the case opens and probably destroy the diaphragm, unless I also find some way to hold/clamp magnets that have come loose from BOTH halves of the case simultaneously. That means removing slat fixturing from both halves of the case on either side of the diaphragm so that I can reach in with a clamp and grab the loose magnet, and seems very risky to me, especially when the new loose magnet still has not reached a magnetic equilibrium and could reposition itself at any time to be in contact with loose magnets on the other side of the diaphragm.

I have never done anything like this before. It seems like a potentially impossible task to disassemble these drivers without destroying the irreplaceable diaphragms.

If any of you have run into these issues opening a driver with loose magnets please tell me what you experienced and how you dealt with it? I would rather not totally destroy the diaphragms since they are likely the only diaphragms I will ever find for these drivers.

I still have not figured out how to clamp a loose magnet through the case either. The best I can come up with is something like a tiny adjustable woodworking clamp that has a long steel bar with ratchet-style sliding jaws, caliper-style, rubber coated, to grab the loose magnet by its ends. That sort of specialized tooling might already exist but it is a good bet I cannot create it on my own...

Any hints on flattening and re-tensioning an indented diaphragm to straighten it out are also welcome (the tension is likely way loose where the magnets have clamped the diaphragm and it will only get worse the longer it takes me to address the issue).

Thanks so much for any insights you may have!

'Forget it' is not insightful, but if that is the best you can offer, I will accept it in the spirit offered, provided you explain why you think that is my best choice. My alternative is to replace these planar drivers with a set of short ribbons or traditional 2" drivers (see that AVSForum thread for details) but I really am not looking forward to investing $1000 USD or more in a set of junk speakers that were given to me by someone who wanted these behemoths out of her home.

'Sell them' only counts if you are making me an offer.

OK, ready, aim, fire! Let me hear you!
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Old 4th July 2016, 01:28 AM   #2
lowmass is offline lowmass  United States
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Join Date: Jan 2016
McMaster-Carr

This is a very good adhesive for what you need to do. It uses an activator..

McMaster-Carr

it is a structural adhesive that is extreemly tough and will hold up under flexing of that thin metal sheet your mags are attached to.
As well this adhesive, when using the activator will set up andhold the magnet within about 1 min making repaires much easyer.

Some epoxy may work , things like JB weld are available at any harware store and cheap BUT!!! each magnet will have to be clamped for hours AND the result can be a brittle connection tht may no thold up under flex.

As for your diaphragm, well, likley it will be distroyed by dissasembly and tensioning is usually done with a larger diaphragm thats cut after gluing to frame.

Some have made their own diaphragms.
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Old 4th July 2016, 01:38 AM   #3
CherylJosie is offline CherylJosie  United States
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Join Date: Sep 2011
Hey thanks lots for the tips. I suppose if I get that far I could potentially make my own diaphragm, but it would have to be from small pieces of material. Full roll of Kapton is really expensive but Mylar is supposed to be more heat sensitive and unstable as well as thicker and more massive for similar strength, thus less treble and more resonance. What do modern drivers use?

Is there a thread here on making a diaphragm? The ones I saw were all DIY speakers and there were only about two threads. I am hoping to restore most of the performance, not make a science project. Absorptive acoustic room treatments are simple to design and not much more complicated to place, but speaker diaphragms are an art.
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Old 4th July 2016, 01:44 AM   #4
srinath is offline srinath  United States
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Join Date: Feb 2010
I have 2 pairs of the Al 3's. and the magnet issue and a ripped diaphragm has plagued one of them.
I opened it and will have to figure out glueing and shutting it back sometime soon.
In fact that magnet glueing business is what has been holding me back from slapping it back together and playing it and checking.
Cool.
Srinath.
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Old 4th July 2016, 02:52 AM   #5
CherylJosie is offline CherylJosie  United States
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Join Date: Sep 2011
Quote:
Originally Posted by srinath View Post
I have 2 pairs of the Al 3's. and the magnet issue and a ripped diaphragm has plagued one of them.
I opened it and will have to figure out glueing and shutting it back sometime soon.
In fact that magnet glueing business is what has been holding me back from slapping it back together and playing it and checking.
Cool.
Srinath.
so tell us how you opened it and etc pls? thx
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Old 4th July 2016, 03:05 AM   #6
tyu is offline tyu  United States
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Join Date: Jul 2009
lowmass....
well you send me your site...if you don't wont to post.... private message me..
thank you
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Old 4th July 2016, 03:49 AM   #7
srinath is offline srinath  United States
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Join Date: Feb 2010
Quote:
Originally Posted by CherylJosie View Post
so tell us how you opened it and etc pls? thx
Taking it apart is pretty easy, starting from the center unscrew them outward like 1/2 turn at a time.
Putting it back - whole other story presumably ~8-12 longer bolts can be used to get them closer together and then you put the original bolts in and tighten them 1/2 at a time as it gets closer and closer.
Then mine had a break in the conductor in 1 spot, I used a circuit writer and made the conductor and then used the sealer over it, and then put a small bit of scotch tape. But I have not bolted it back, cos I was looking for glue for the magnets.
Cool.
Srinath.
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Old 4th July 2016, 03:58 AM   #8
CherylJosie is offline CherylJosie  United States
diyAudio Member
 
Join Date: Sep 2011
Quote:
Originally Posted by lowmass View Post
McMaster-Carr

This is a very good adhesive for what you need to do. It uses an activator..

McMaster-Carr

it is a structural adhesive that is extreemly tough and will hold up under flexing of that thin metal sheet your mags are attached to.
As well this adhesive, when using the activator will set up andhold the magnet within about 1 min making repaires much easyer.

Some epoxy may work , things like JB weld are available at any harware store and cheap BUT!!! each magnet will have to be clamped for hours AND the result can be a brittle connection tht may no thold up under flex.

As for your diaphragm, well, likley it will be distroyed by dissasembly and tensioning is usually done with a larger diaphragm thats cut after gluing to frame.

Some have made their own diaphragms.
The loctite is similar to rear view mirror adhesive. It sticks strong but is similar to cyanoacrylate in its temperature characteristics (degrades easily when heated), plus I have had mirrors fall off again after using it...

Then there is the issue of leaving a gap to hold the glue. Without glass beads or maybe at least paper in the gap, the magnets will squeeze all the glue out, leaving nothing to hold the joint. Glue needs a certain minimum gap in order to actually hold on.

At least, that is what I read elsewhere... not an expert, not even a novice yet!
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Old 4th July 2016, 04:01 AM   #9
srinath is offline srinath  United States
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Join Date: Feb 2010
There was some adhesive used originally. I suspect it was closer to rubber cement than superglue, but it is there and visible when you move the magnets.
Thanks.
Srinath.
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Old 4th July 2016, 04:15 AM   #10
lowmass is offline lowmass  United States
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Join Date: Jan 2016
Quote:
Originally Posted by CherylJosie View Post
The loctite is similar to rear view mirror adhesive. It sticks strong but is similar to cyanoacrylate in its temperature characteristics (degrades easily when heated), plus I have had mirrors fall off again after using it...

Then there is the issue of leaving a gap to hold the glue. Without glass beads or maybe at least paper in the gap, the magnets will squeeze all the glue out, leaving nothing to hold the joint. Glue needs a certain minimum gap in order to actually hold on.

At least, that is what I read elsewhere... not an expert, not even a novice yet!
No not really, this adhesive may be similar to mirror adhesive chemicaly BUT not exactly. I have used this adhesive on many many magnet bonds and it is serious stuff. It wil literaly break the magnet tryig to remove and is very impact resistant. Also I have tested it to temps too hot to touch and it held fine. No need at all for special glass bead or specific gap. Just clean well with alcohol, apply activator, let dry, apply glue and place magnet.Truly great stuff.

You must remove all old adhesive though. Important to be clean. use alcohol as last thing to remove any cleaning solvents.

Last edited by lowmass; 4th July 2016 at 04:28 AM.
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