Remember to epoxy your woofer magnets!

Hofy

I just lost a woofer on one of my Monitor 5jr today. It was working fine last night. Woke up this morning to listen to some music and things didnt sound quite right. One of the woofers is frozen. No bumps or drops. Just sitting there.

So, if you have been putting off securing the magnets on a set of speakers, get busy with the JB Weld or Loctite Power Grab!

honestaquarian

I keep reading about doing this,but I never see where exactly you are supposed to put the epoxy.

Hofy

I have 2 other pair of Polks I need to do. I will photo document the operation and post it. I know there are pics up here but I can not find them right now.

Polkaguy58

Just run a bead between the magnet and the speaker frame and wipe it with your index finger.
Power Grab is water soluable, so you can wash your finger off with no mess...............otherwise, don't scratch yourself until you do wash. (heh heh)

westmassguy

Note where the front plate and back plate meet, and sandwich the ceramic magnet.
This is where you apply the JB Weld/Epoxy or Power Grab.

Hofy

OK, looks like westmassguy beat me to it and has better pics too. Thanks!

Anyway here is my driver. You can see there is was not much of the original glue holding it together. I will build a jig and see if I can get it lined up right to bring it back to life.

Polkaguy58

I only added glue to the bottom half of the magnet, where the weight bearing area meets the frame.
Is there a history of the top part of the structure delaminating also ?

It seems that if you set the speaker face down, on top of a couple of pieces of 2x4 and re-glued the magnet with Power Grab, that one would have more than enough time before it set up, to re-allign the magnet structure by hand, while gently pushing up and down on the cone to see if it rubs or not, that is if the coil didn't get damaged by the shift.

westmassguy

Yes, the glue that holds the whole assembly together deteriorates

Hofy

Polkaguy58. I would run a second bead around the plate and magnet joint too.

The jig I need to make will help with fine adjustmemts when I put it all back together.

notified

Although it seems rather straight forward ,but has anyone ever made a [how to] You Tube video illustrating the recommended procedure for doing this?

gimpod

Polkaguy58 wrote: »

I only added glue to the bottom half of the magnet, where the weight bearing area meets the frame.
Is there a history of the top part of the structure delaminating also ?

It seems that if you set the speaker face down, on top of a couple of pieces of 2x4 and re-glued the magnet with Power Grab, that one would have more than enough time before it set up, to re-allign the magnet structure by hand, while gently pushing up and down on the cone to see if it rubs or not, that is if the coil didn't get damaged by the shift.

That magnet holds on pretty strong there is no gently adjusting it by hand you need to make a jig even then you only run about 50% chance of it working. Before you begin make sure the voice is good, also recheck the after it's fixed for it shorting out to the driver basket.

hears a few links on the process :

resetting a loose magnet with pictures

as promised pics of the magnet jig/

IMO: It's not worth the trouble for $48 get a new one from Polk.

Schurkey

Polkaguy58 wrote: »

I only added glue to the bottom half of the magnet, where the weight bearing area meets the frame.
Is there a history of the top part of the structure delaminating also ?

Both areas are susceptible to breaking the glue bond.

Polkaguy58 wrote: »

It seems that if you set the speaker face down, on top of a couple of pieces of 2x4 and re-glued the magnet with Power Grab, that one would have more than enough time before it set up, to re-allign the magnet structure by hand, while gently pushing up and down on the cone to see if it rubs or not, that is if the coil didn't get damaged by the shift.

NO!!!!

The epoxy or the Power Grab is used as "insurance" to supplement the original adhesive. This is done while the driver STILL WORKS.

If your magnets have popped-off so you have an actual REPAIR to perform, you use an entirely different adhesive, and then there's no need at all for the kludge of epoxy or Power Grab.

When I dropped a driver and knocked a magnet off, I cleaned the surfaces on BOTH SIDES of the magnet--the frame side and the pole-piece side--and reattached the magnet and the pole piece with Loctite 271 (or equivalent) red threadlocking anaerobic compound. The write-up is here:
http://forum.polkaudio.com/discussion/135716/lets-try-to-fix-a-mw6511-damaged-in-shipping/p1

My post to that thread is towards the end, near the bottom of the third page.

Hofy

I am first going to Loctite all my speakers drivers. Then i am going to try to save the bad driver. (I like to tinker so I will still have fun.) Then it looks like I will start stocking up on spare drivers.

Polkaguy58

This is how I'd try the job.
First I'd cut a 6" hole in a piece of scrap plywood and drill out 4 bolt holes to attach the speaker to.
Then I'd mix up some slow setting adhesive, stick the magnet back on and set the vioce coil as close as I could by hand.
With the speaker facing downward and the board suspended high enough on each side to reach my hand under to the cone, I'd start tapping the edge of the magnet with small wooden hammer (chisel handle etc.) while checking the coil rub and see if I could work it free by feel.
If you really wanted to make sure it was gapped right, you could pop the dust cap, insert a mylar shim (I make them from old plastic packaging, for guitar repairs) and tapp the magnet into place until the shim pulls free without any resistance.

I'd like to see how they do it at the factory.

gmcman

Yeah, I can attest to the fact of securing the magnet, I just lost a 6511 this weekend and a tube of JB is far cheaper than a new driver. This 6511 is 2 years old and was a new style replacement.

xschop

Is everyone else getting a mic'd reading of 3.320" dia. on their magnets?

Hofy

gmcman wrote: »

Yeah, I can attest to the fact of securing the magnet, I just lost a 6511 this weekend and a tube of JB is far cheaper than a new driver. This 6511 is 2 years old and was a new style replacement.

The glue on a 2 year old let go?

Hofy

xschop wrote: »

Is everyone else getting a mic'd reading of 3.320" dia. on their magnets?

85mm here on a MW6500 so that is close to 3 11/32"

westmassguy

gmcman wrote: »

Yeah, I can attest to the fact of securing the magnet, I just lost a 6511 this weekend and a tube of JB is far cheaper than a new driver. This 6511 is 2 years old and was a new style replacement.

That doesn't bode well for the future.

pitdogg2

Polkaguy58 wrote: »

This is how I'd try the job.
First I'd cut a 6" hole in a piece of scrap plywood and drill out 4 bolt holes to attach the speaker to.
Then I'd mix up some slow setting adhesive, stick the magnet back on and set the vioce coil as close as I could by hand.
With the speaker facing downward and the board suspended high enough on each side to reach my hand under to the cone, I'd start tapping the edge of the magnet with small wooden hammer (chisel handle etc.) while checking the coil rub and see if I could work it free by feel.
If you really wanted to make sure it was gapped right, you could pop the dust cap, insert a mylar shim (I make them from old plastic packaging, for guitar repairs) and tapp the magnet into place until the shim pulls free without any resistance.

I'd like to see how they do it at the factory.

you do realize that when they are built they are not magnetized yet right? IT is very difficult to do this when you're dealing with north and south poles

if you want to see how its done watch this

https://www.youtube.com/watch?v=VN0tmyyC0ak

google is your friend.

Schurkey

Polkaguy58 wrote: »

This is how I'd try the job.
First I'd cut a 6" hole in a piece of scrap plywood and drill out 4 bolt holes to attach the speaker to.
Then I'd mix up some slow setting adhesive, stick the magnet back on and set the vioce coil as close as I could by hand.

Don't use "slow-setting adhesive". Use anaerobic thread-locking compound or other anaerobic adhesive. Let the magnet/adhesive fully cure before putting the pole-piece in place.

Polkaguy58 wrote: »

With the speaker facing downward and the board suspended high enough on each side to reach my hand under to the cone, I'd start tapping the edge of the magnet with small wooden hammer (chisel handle etc.) while checking the coil rub and see if I could work it free by feel.

Pointless. Getting the MAGNET in place is easy enough to do using the fixture described in the thread I linked to earlier. The magnet practically snaps into place.

Getting the POLE PIECE in place without the voice-coil rubbing is the ****.

Polkaguy58

There's nothing "pointless" about trying any type of repair.
With the still wet glue acting as a lubricant and the weight of the magnet structure acting as a downward force, gentle tapping around the perimeter should be able to shift the pole from side to side.
If you remove the dust cap and set a cylindical shim in the groove, when things line up, the shim should come out smoothly.
Have I ever done it before ?
No.
Would I give it a try, if my other option was to buy a new speaker ?
Yes.
I find tinkering fun and you learn something no matter what the outcome.
Pardon me if I think outside the box.

xschop

Is 3.115" the standard OD of the front plate and rear plate on everyone else's drivers?

RandyCroissant

I think that a machined aluminum fixture that would support the basket at the flange with a mounting recess and screw holes then an aluminum cylinder coming up from the flange that matched the magnet diameter and extended up to the top of the pole piece all pieces would need to be centered with the basket flange. The last piece would be an aluminum washer that matched the pole piece diameter; this would or should keep the pole piece centered with the basket at least in theory.

xschop

I spun one up to 180 rpm after chucking it up on my Clausing. The magnet OD does not spin concentric but the front and back plates do. The Stamped basket OD at the MW flanges on all 4 of mine are 6.605 (+- 0.005) Randy's on the right track.

BTW, the Backplate's divot is a factory turning center. I imagine the plate was held by a magnetic chuck while the guidepost was turned to diameter. So it can be used as a jig guide.

RandyCroissant

Way to many good MWs get trashed when they could be fixed with the right jig, all we need is the right tool here!!!

xschop

I've already got the design down. It's the consensus on the magnet IDs and guidepost ODs that is the unknown, as I would also machine a centering dowel to go between the magnet ID and the guidepost OD for the first step.

Nightfall

That is very unfortunate that a driver from 2014 had the glue let go. Come on China, surely you can afford ten cents worth of better/more glue.

xschop

Too funny. But so true. It's like the Chinese water pumps that made their way into the Bosche packaging and ruined many NLA Porsche blocks....
On a lighter side all my MWs mic'd at 0.375" on their turn centers and the magnets were all 0.540" Blanche ground in my notes. That tells me the magnets are more than likely ID ground to tolerance.

gmcman

Hofy wrote: »

The glue on a 2 year old let go?

Looks like 6 years old, I purchased them 2 years ago in January but the date stamp tells otherwise.

pitdogg2

I would definitely call and let Polk know the problem exists ....STILL