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Resetting a loose magnet (with pictures)

RayW

RayW

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After several threads asking about shifted magnets, I figured it might be time for a “tutorial” on resetting them. Note, this is based on a thread and method by Scootchu here. I just added a few more words and pictures.

First step is getting things apart. Be careful not to damage the coil when you’re pulling the magnet off. I usually use 3 screwdrivers to get it started and then wooden dowels working around the magnet until I can get it lifted off the plates far enough to pull it loose. On the pair I was working with, I had one on which the magnet and core/backplate were still attached but the magnet had come loose from the top plate and one where all 3 parts had separated. In this case, glue the magnet to the core/backplate using your eyes to center. This particular backplate has a raised area for centering the magnet. If yours doesn’t then it’s not a big deal. You just have to be close on this, not exact.


magnet1.jpg


magnet2.jpg
 
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Once you have it taken apart, clean the surface of the magnet and the plate. Make sure to get all the old adhesive off and then clean the plates with a cloth and your cleaner of choice. Make sure it’s something that will be removed completely and not leave a residue.

magnet%20cleaned.jpg
 
Now you need a jig. You’ll need a piece of PVC pipe that is big enough to fit over the magnet. For these (JBL) I used a 4” ID. Cut a slit along the length so that you can get it over the magnet and then cinch it down with the hose clamp. When I did a Pioneer (HPM-100) woofer I used 6” PVC and had to cut out a section so that it would cinch down and hold the magnet. Once you have the slit, you need to drill 6 holes (4 will work but is harder to center) more or less evenly around the jig. Make sure that they are high enough that the screws inserted in them will contact the top plate and not the magnet. You’ll have to figure out hole size based on the screws you use. I used ¼” x 20tpi screws. Scootchu used thumb screws, I used machine screws, either will work.


jig.jpg
 
I like to do a dry run to make sure that there’s nothing sinister going on. There are a couple of ways to get the magnet back on. Scootchu clinched the magnet in the jig, got it centered up close enough, and then release the jig so the magnet would jump into place. He used a rubber band and a couple of pencils to hold the cone/coil our of the way. Then did the fine work getting things centered. These particular woofers had a surround that was pretty tight and I couldn’t get the coil up out of the gap completely so I just dropped it in by hand while holding the coil up as high as I could and using my fingers to keep the magnet from snapping in from too far away. Be careful doing this as these are generally strong magnets and can pinch the heck out of you. With a finger completely between the magnet and plate it’s not too bad. Once I got the magnet on I slipped the jig over, tightened down the clamp, and started adjusting the screws.

in%20jig.jpg


You’ll have to have access to the gap so you will have to cut the dustcap out at least partially. These woofers had the cap cut out about 95% of the way around so they can be re-glued afterwards.

centered.jpg


You can look at the gap and get things close. Once the coil will move freely, I use a piece of paper (fairly thick letter stock in this case) as a feeler gauge. I work around the core looking for tight spots and adjust the screws accordingly. Once things are centered up as best I can get, I hook it up and listen to something paying attention for rubs or any other extraneous noises. If that looks good then I pull it apart again and do the same thing with glue involved. I used a 30 minute, 2 part epoxy. It’s pretty strong stuff. You have 30 minutes to get things centered up and 12 hours to wait for full cure.

gauge.jpg
 
Thanks for taking the time :thmbsp:

I'm guessing you need to use the glue very sparingly as once the mag clamps down you do not want it to squeeze into the VC gap. and methods for how much or pic of your glue on the baseplate before the mag got dropped?
 
kfa888 said:
Thanks for taking the time :thmbsp:

I'm guessing you need to use the glue very sparingly as once the mag clamps down you do not want it to squeeze into the VC gap. and methods for how much or pic of your glue on the baseplate before the mag got dropped?
Click to expand...

I'm glad there are folks like you to clean up after my messes, Kelly. :thmbsp: Yes, be careful to use just enough glue to get it done and I like to keep it towards the outside of the joint so if I do get some squeeze-out it'll go to the outside and not bind the coil up. Sorry, but I don't have pictures of that step. I'll try to remember the next time I do one.

Ray
 
Thanks, great work....

This process works great but for some reason I saw 4" and bought a four inch PVC coupler (if you don't want to buy a section of pipe). I only needed 3" for my Polk Speakers and had to go back and grab a 3" coupler, schedule 40. To get a really tight fit on the magnet I cut a 1/2" section out of the length of the coupler (with a chop saw) and used a band clamp to tighten around the magnet.

On my first version I used a drill to make undersized holes and then reamed them out with the same bit to get them close to my 1/4" bolts. The bolts will self-thread in the plastic, no need to use a tap and die set. The holes didn't line up very well when I did it by hand so I resorted to the drill press and then reamed out the holes with a hand drill, this worked much better.

I used hex-head bolts and a socket wrench for better control and set the magnet on top of the bolts before tighting the band clamp and lowering on the speaker.

I've got six total Polks that are getting the treatment, can't wait try them all out, thanks to all the guys that helped out with this thread..
 
Bone Yard said:
Thanks, great work....

This process works great but for some reason I saw 4" and bought a four inch PVC coupler (if you don't want to buy a section of pipe). I only needed 3" for my Polk Speakers and had to go back and grab a 3" coupler, schedule 40. To get a really tight fit on the magnet I cut a 1/2" section out of the length of the coupler (with a chop saw) and used a band clamp to tighten around the magnet.

On my first version I used a drill to make undersized holes and then reamed them out with the same bit to get them close to my 1/4" bolts. The bolts will self-thread in the plastic, no need to use a tap and die set. The holes didn't line up very well when I did it by hand so I resorted to the drill press and then reamed out the holes with a hand drill, this worked much better.

I used hex-head bolts and a socket wrench for better control and set the magnet on top of the bolts before tighting the band clamp and lowering on the speaker.

I've got six total Polks that are getting the treatment, can't wait try them all out, thanks to all the guys that helped out with this thread..
Click to expand...

what kind of glue was used? How did things work out for you?
 
another tool...

What a great thread Ray W., thanks for taking the time to document this! I was intent on keeping my thrift store Polk Monitor 10s a thrift buy and these instructions and jig helped immensly. Polk 6503 drivers are notorious for jettisoning magnets. I wanted to share a something that helped me out.

I was paranoid about dropping the backplate post into the jig and damaging the voicecoil. So I cut a piece of broom stick long enough to pass through the voice coil and support the backplate post. I used a piece of old molding for a stand and attached the dowel with a screw and glue.
IMG_3512-1.jpg
[/IMG]

I also used a paper sleeve to help align the backplate post to the dowel and guide ith through the coil. I first placed the paper sleeve through the voice coil then lowered the speaker over the dowel.
IMG_3515-1.jpg
[/IMG]

Then I put the alignment jig on the speaker (I used a 3" coupler from HD). No photos after this since I didn't pause after putting a thin bead of epoxy near the OD of the backplate. Lowered the backplate, positioning the post through the sleeve and then rested on the end of the dowel. Then just slowly raised the speaker to the backplate - no drama, no damage. I followed this thread's instuctions and succesfully aligned the magnet using the jig. Now if I can only learn how to repair the voicecoil on the other bad driver.:scratch2:
IMG_3518-1.jpg
[/IMG]
 
I just used this sticky to fix a focal car audio woofer. I guess I will know tomorrow if it was truly successful. I got no problem throwing it away if its not right. Thanks Ray.
 
Hey, My entire magent fell off(including the front flate) how would i re attach it.(even the metal thats supposed to be Pressure mashed inside the subwoofer to hold the magenet on is broken.)
 
Repaired a couple of Polk Monitor 7 mid's using this method, worked great. I used a PVC 4" coupler from home depot, had to take a chunk out to get it to the right size. Speakers are now in my office and I ran them pretty hard for a week. Used the gorilla'z ureathane quick setting, think it has a 5 minute open window. Made it easy to adjust when in the fixture. Thanks for the informative post!:banana:
 
Another thanks to the OP. I just fixed a Vifa D25AG using this method. 3" PVC coupler drilled and tapped holes for 12, 1" 10-24 allen screws - 6 for the magnet and 6 for the diaphragm mounting plate. Test fit everything before applying adhesive. I used 5min epoxy and wish I had used 10 or 15 minute at least to have a little more working time. Also -- be careful not to get any adhesive on the pole piece. I was careless but luckily it was all in a spot where I could quickly wipe it off. I actually think the tweeter sounds better than the other D25AG I have -- perhaps because I wiped up all the old ferrofluid in the process.
 
hi.. I am new to the board but have a question. I recently found a pair of monitor 10s in a thrift store for $20. a friend of mine had a smaller pair with single 6.5 and tweeter that I was very impressed by.. so I figured somes good mores better and bought them got them home and had great midrange up and no bass. took me several days of digging and bothering polk help desk before i pieced the story together.. slipped magnets. there are at least 4 different scenarios from using dayton classics to buying original MW6503 from polk. any solution I see using a working polk drivers involves immediately running a bead of epoxy to stabilize the magnets . I have also recently moved to Utah from NY for cancer treatment and have left 98% of my tools behind.. as in I don't have a vice or a drill press, clamps and all that out here. so the question I have is, if on inspection the magnet itself it reasonably centered or centerable, has anyone tried stabilizing the magnet on the base side with epoxy bead, remove the dust cover, then put the jig in the pictures above on the magnet and move the center without first removing the whole magnet? seems it would cut out a few steps and maybe note require a vice and all. any thoughts would be appreciated (a $20 find becomes less adventurous if you have to shell out 200 to make it work) so I am on for the centering the magnets as first choice but handicapped by not having access to my shop.
 
You didn't specify what tools you brought with you in that 2%, but the only ones I used were my trusty cordless drill to make the holes in the PVC, a hacksaw to cut the PVC so it fit over the magnet, and a screwdriver to turn the screws and hose clamp.

With the jig I used you wouldn't be able to center the magnet and put a bead around the outside because the jig would be covering that joint. If you center things and remove the jig the magnet will slide off center again. That's just what magnets do. :)

If you came up with a similar jig that was open instead of a continuous cylinder it might be possible.
 
RayW said:
After several threads asking about shifted magnets, I figured it might be time for a “tutorial” on resetting them. Note, this is based on a thread and method by Scootchu here. I just added a few more words and pictures.

First step is getting things apart. Be careful not to damage the coil when you’re pulling the magnet off. I usually use 3 screwdrivers to get it started and then wooden dowels working around the magnet until I can get it lifted off the plates far enough to pull it loose. On the pair I was working with, I had one on which the magnet and core/backplate were still attached but the magnet had come loose from the top plate and one where all 3 parts had separated. In this case, glue the magnet to the core/backplate using your eyes to center. This particular backplate has a raised area for centering the magnet. If yours doesn’t then it’s not a big deal. You just have to be close on this, not exact.

<images removed>
Click to expand...

Not to disagree but merely to add to your helpful post. Some speakers, like JBL LE series speakers have very tight VC gaps. For speakers like these you may have little choice but to shim. Now, I have not done any magnets, and I'm not aware of LE speakers having locating pins or ridges, so I may be out of line as it relates to JBL, but may still apply to other drivers. So, just a heads up on the matter and nothing more.

I WILL be using this post to remount the magnet structure on a 125a driver damaged in shipping. First time I've seen this.
 
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