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 Post subject: How to repair a seized speaker (or at least try)
PostPosted: Tue Sep 01, 2009 9:03 am 
Mad Scientist
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Location: Beaverton 48612
Here is my first attempt at a "how to", feel free to move it if it is worthy. Don't hold me responsible if you jack up your speakers even worse...

Anyhow, a little background, I got this set of XS 8's from Bogart on the phorum. They were known to be good when he shipped them, and were virtually new. They came well packed, but evidently our friendly neighborhood postal service still managed to beat them around enough to fuck them up.

So, both drivers are bound up. Knowing that they were in working order, I decided to take a stab at repairing them. Chris offered to buy me new ones, or have them reconed, but this wasn't his fault, and the speakers were part of a trade that was already way over the top... At one point in time I bought a JL12W6 on ebay that was tested good and arrived the same way, froze up. I figured out by destroying that one that the magnet epoxy/glue had broke free and the magnets slid binding the coil.

Rather than destroy these, I thought I would carefully pop the dust caps and see if I could tell what was going on. I didn't hold much hope that I would be able to salvage the dust caps, but 30 seconds with the heat gun and they popped right off.

Image

Interestingly, PG screened the caps on both sides, cool, they are reversible, lol...

Image

Next couple shots are of the VC and pole piece, you may not be able to see the contact point, as my camera sucks. I found on both of these that the pole piece was floating and had moved and bound the coil. My assumption is that the glue has just gotten old and failed.

Image

Image

Anyhow, this probably inst the best way to fix it, the best way would be to have a proper jig, and a magnetizer/demagnetizer to reset the speaker up perfectly and reglue the PP, but that shit costs over $10K used, so this will have to do. What we do is look at the coil to find the bind, then take a block of wood and light taps with a hammer get it centered as well as possible. You are going to be tapping on the back plate of the speaker, the metal piece that caps the back side of the magnet, this piece has the center pole attached to it and is called the pole piece. Here are the results of my careful persuasion.

Image

Not perfect, but the VC is now free and does not rub. Be careful not to get any crap in the gap, I also took a moment to blow the gap out with compressed air.

Next, reinstall the dust cap, I put it in place, and hit it with the hot air gun again for 30 seconds, pressed it down around the edge and let it cool. Presto, it is perfect:

Image

Next, carefully flip the speaker, being careful not to bump the PP and misalign it again. Face down on a table, be sure the cone is still moving free. Mix up some epoxy of your choice, preferably something with a long pot life and that is sandable when cured. I chose JB weld as I have a shit ton of it. Apply the epoxy to the pole piece and magnet, basically running a bead around the two. This should be sufficient to hold things in place, as the magnet holds the PP tight to itself. Let it cure 24 hours and sand it until it is as pretty as you can get it. It will never look perfect, but at least this side is normally buried in a panel/enclosure. Here are the results:

Image

Good Luck,
Jason



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M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
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 Post subject:
PostPosted: Tue Sep 01, 2009 10:27 am 
the Floor Sweeping Hack with Golden Ears

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neat stuff when you put jb weld on a magnet..........

The first time you do it you are like :shock:

We had a customer come in complaining that the drivers side tweeter was not working in his viper. The shop had put a swee system in it with dynaudio componants up front. When we pulled the door panel off to investigate we were amazed to see the magnet had completely fallen off.... IT was suprising to see it on such a nice speaker and when nick put some jb on it to put it back together he yelled out so we call all see it.

We were suprised to see that it had happened and didn't have any good reason why. When he asked how it might have happened I just mentioned that 0-60 in about 5.4 secs might have something to do with it. He just grinned and agreed...... It stopped working after a hard launch coincidentally, so he didn't even want us to replace it since it was working after the weld.


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PostPosted: Tue Sep 01, 2009 3:17 pm 
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sweet....I am oh so glad that this worked...those arn't so easy to find these days!!!! Once again Jason...sorry you had to work on em!!!


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PostPosted: Tue Sep 01, 2009 4:19 pm 
Short Bus Driver
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Good job so far with the fix, but I am pretty certain it will be in vain.

Gluing the bass plate/pole from the outside edge will not be that strong, the glue needs to be between the steel and the ceramic.

Here is a half assed suggestion...

Figure out a way to bolt the speaker basket down to something on your garage floor. Take a piece of pipe which just fits the vent hole. slide the pipe in the vent and put a bolt through it on the dustcap side. Bolt the speaker down, use a winch to pull the pipe and therefore the baseplate straight off the magnet structure. Find some plastic shim stock which fits snug between the pole and the voice coil former. You want that precision centered. Clean the ceramic and the baseplate, then re-glue with something very good.

It is critical the coil is perfectly centered on the pole. If not it will not move in one direction and will instead start to oscillate side to side as it plays. This will likely result in a rub and will kill the speaker or sound like crap.


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PostPosted: Tue Sep 01, 2009 4:24 pm 
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That makes a great deal of sense...ill bet it can be done...it was pressure fitted on so it should come back out with enough force. it would be interesting to see


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PostPosted: Tue Sep 01, 2009 4:58 pm 
Short Bus Driver
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If you are talking about the baseplate, it is not pressure fitted on. They are just glued using a special glue.

When I built prototype speakers at Rockford, we used a machined nylon fixture to center the ceramic magnet on the baseplate.

I would put a bead of glue down on the baseplate. I would then put some accelerator for the glue on the magnet. Slide the nylon fixture into the magnet and then put the assembly down on the pole piece. The glue would cure almost instantly. For double stacked magnets, just repeat the process.

Then using another nylon fixture I would glue the field plate on just the same.

Heat is the enemy of this glue. With enough heat the glue softens and the parts will shift. We had many a woofer do just that during power testing. When the coil is locked it would then either burn up or kill the amp connected too it.


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PostPosted: Tue Sep 01, 2009 4:59 pm 
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I guess for now it's a good thing you got those from hm instead of me. I forgot who had them to sell so I'm now going for a set of XS6 comps. that I have wanted for even longer.



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PostPosted: Wed Sep 02, 2009 7:13 am 
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Eric, I believe you are correct, and that this is definitely not the best way to do it. I have read a few articles online though, mostly dealing with old guitar speakers that have mentioned success doing it like this. If mixed and applied correctly, JB has tremendous adhesive and tensile strength and is pretty much impervious to heat until it hits 600° F or so. Hopefully this will work well enough. I am going to build some test enclosures and run them for a while to see. Time will tell.

As for pulling the BP/pole piece, trust me when I say I considered it. It would be a fairly simple job to make a puller that would pull the pole piece. The thing that turned me off from trying it was getting the SOB back in w/o loosing a finger. I think it would be next to impossible with the whole moving motor assembly still in place to drop the BP back in and avoid destroying the VC former. Maybe if you disassembled the entire driver, but I am not sure how difficult it would be to get the spider and surround free w/o ruining them. I don't think it would be easy to source a re-cone kit either, not for the carbon fiber or kevlar or whatever the hell it is cones.

Anyhow, here is a picture after the epoxy set up and I sanded it down. Be sure to block off the back vent to avoid filling the gap with crud. If you happened to use a metal filled epoxy like I did, be especially careful of the vent and blow the dust off frequently.

Here is the finished pic, I let you all know how they do over time.

Image

Later,
Jason



_________________
M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
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