I've seen other threads containing tips on how to repair a driver with a shifted magnet (actually a shifted pole piece), but never one with pictures, and never one specific to the drivers that many of us are using, the Polk MW series.
I recently sold a pair of MW6510's on ebay, to another forum member. Despite my careful packing, one of them still ended up with a shifted pole piece and frozen voice coil. I know that others have had unsuccessful attempts to repair these, so I decided to learn for myself why, and document with some pictures, for anyone wanting to try in the future. If the uploads don't work, I'll post some jpeg's.
First of all, the parts in the pictures are labelled as follows: FP=front plate, PP=pole piece, BP=backplate. The back plate and center pole piece are one assembly. Standard speaker parts.
When I disassembled the driver, I assumed (wrongly) that the front plate was held to the driver basket with adhesive. It's not. It's held on with 4 metal posts.... like rivets. I was tapping away to separate the basket and magnet assembly and put a ding in my tool. Separating these parts also resulted in the basket and driver cone distorting. Driver ruined at this point!
As you can see, there's a gasket between the basket and the front plate.
The front plate, magnet, and back plate/pole piece can come apart by gently tapping something wedged in between the parts.
In reality, this is what I should have done from the start. However, remember that the pole piece "wants" to be in the magnetic gap, and bringing it straight out of the gap without it slamming to one side of the gap is EXTREMELY difficult. In fact, one needs android precision to do it. If you try this, just know that the pole piece will probably be rubbing on the inside of the voice coil former as you pull it out of the gap. Obviously, the voice coil is pinched by this thing anyway, otherwise you wouldn't be taking it apart in the first place.
The best way to do this is to separate the back plate from the magnet with very gentle rubber mallet taps on the wedged piece, and progressivley using 'stand-offs' to gradually increase the distance between the back plate/pole piece and the magnetic gap. Be careful not to get your fingers in between the two. One small slip and the BP and magnet will slam back together with about 100 lbs. of force. It may not be that exactly, but your fingers will think so.
When I got the driver apart, you can see that the voice coil had one small spot of damage. This was due to my clumsiness, not the fact that the pole piece had shifted.
Looking at how the back plate, front plate, and magnet are held together, you can see the glue rings in between the 3. This is obviously the glue that fails when the driver gets whacked. That allows the pole peice to slam to one side of the magnetic gap, pinching the voice coil and coil former in position. Even though the glue may have failed, though, the strong magnetic attraction forces still keep the magnet and BP/PP assembly sandwiched together.
Now, say you didn't do what I did taking the whole magnetic assembly off. Instead, you successfully separated the back plate from the magnet and brought the pole piece out (TRICKY AND DANGEROUS TO FINGERS!). The real questions are....
1. Can you separate the magnet, then reglue it to the front plate to give it a stronger bond? Ya, probably.
2. Can you reglue the back plate to the magnet, inserting the pole piece into the magnetic gap to get a perfect ~1.5mm tolerance all the way around for the voice coil/coil former to go down into? For a non-android like me, definitely not.
As soon as you insert the pole piece into the magnetic gap, the natural tendencies of the magnetic field are to make the pole piece snap to one point of the inside of the gap. And, everyone knows what it's like trying to get two magnets to come together in the first place. Things get wobbly and inaccurate.
So, that's about 10,000 words just to say.....get a new driver. Oh well, I thought it might interest somebody.