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POLK Model 7 Replacement speaker

R

robback

Active Member
I picked up a pair of Model 7's and one of the pair is distorting badly. I'm assuming it's the mid/woofer (not the passive), and I also have read that these guys tend to have magnets shift.

I looked for replacements but I'm WAY lost because of all the different versions of the model 7.

Can anyone help me figure out what I would need to order. I'm in Canada, but it's probably worth the money, since the one working speaker sounds really nice.
 
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robback said:
I picked up a pair of Model 7's and one of the pair is distorting badly. I'm assuming it's the mid/woofer (not the passive), and I also have read that these guys tend to have magnets shift.

I looked for replacements but I'm WAY lost because of all the different versions of the model 7.

Can anyone help me figure out what I would need to order. I'm in Canada, but it's probably worth the money, since the one working speaker sounds really nice.
Click to expand...
Post pictures of the speaker terminal assembly on the back so we can see if there is an external fuse, and also of the front of the speakers. We need to verify if they are 7A's, 7B's, or 7C's.

These are 7B's


IMG_0673_zps9a2zjrjd.jpg


https://www.midwestspeakerrepair.com/home-audio/woofers/polk-audio
 

Ok, I'm 95% sure that those are 7A's, which came with two fuses (one for the tweeter and one for the whole system). There are some later 7A's that only had one fuse, but I'm not aware of any 7B's, or 7C's that had two fuses.

That said, you're looking for the MW6502, which was the original driver. You can look on ebay for a used one, or try one of these. https://www.midwestspeakerrepair.com/polk-audio-mw6502-6-5-inch-oem-woofer I have no first hand experience with purchasing from midwest speaker repair, so caveat emptor.

Recap the crossovers while you're at it. There are only two capacitors in each crossover, and it will make a huge difference in the sound quality. Mine sounded like poop when I picked them up from someone on Craigslist, but the drivers were in perfect shape. For around $40.00 in parts, and a 1 hour job, you can replace the capacitors (if you are even halfway handy with a soldering pencil) and you will be amazed at how good these speakers sound.
 
There's a guy on the polk forum that will fixed shifted magnets for free, you just pay shipping. Might have to do some research to find him but he's on there.
 
MitsuMan said:
Ok, I'm 95% sure that those are 7A's, which came with two fuses (one for the tweeter and one for the whole system). There are some later 7A's that only had one fuse, but I'm not aware of any 7B's, or 7C's that had two fuses.

That said, you're looking for the MW6502, which was the original driver. You can look on ebay for a used one, or try one of these. https://www.midwestspeakerrepair.com/polk-audio-mw6502-6-5-inch-oem-woofer I have no first hand experience with purchasing from midwest speaker repair, so caveat emptor.

Recap the crossovers while you're at it. There are only two capacitors in each crossover, and it will make a huge difference in the sound quality. Mine sounded like poop when I picked them up from someone on Craigslist, but the drivers were in perfect shape. For around $40.00 in parts, and a 1 hour job, you can replace the capacitors (if you are even halfway handy with a soldering pencil) and you will be amazed at how good these speakers sound.
Click to expand...

Thanks, That's great. I will indeed do the caps - got to check what's in my parts bin. The thing about buying the new replacement is that after I add the 30% exchange rate for Canada, plus the shipping, I'm starting to hit $100, so I'll need to do some hunting first. And ideally, it would probably be best to change out both in the pair.
 
bryblob said:
There's a guy on the polk forum that will fixed shifted magnets for free, you just pay shipping. Might have to do some research to find him but he's on there.
Click to expand...

Thanks. Again the problem comes with shipping over a border and costs, believe it or not. I don't know what shipping both ways would cost, but it wouldn't surprise me if it was at lwast $50 U.S,
 
robback said:
I picked up a pair of Model 7's and one of the pair is distorting badly. I'm assuming it's the mid/woofer (not the passive), and I also have read that these guys tend to have magnets shift.

I looked for replacements but I'm WAY lost because of all the different versions of the model 7.

Can anyone help me figure out what I would need to order. I'm in Canada, but it's probably worth the money, since the one working speaker sounds really nice.
Click to expand...

As mentioned, those are 7A's.

Before you start looking for a replacement driver you need to put two screws in the binding post plate as the missing screws create an air leaks, which will affect the damping ability of the driver and could be the cause of the distortion. You still may have a bad driver though. However, the magnet shift issue usually results in a locked driver that makes no sound.

If you need a new driver, Polk sells them direct. Note, you will have to trim the rubber around the screw holes otherwise you will damage the surrounds.

The repair of magnet shifted drivers is offered to Club Polk members only, but it's easy to join.

I should have mentioned that since you are in Canada you have to purchase Polk parts through the Canadian rep.
 
robback said:
Thanks, That's great. I will indeed do the caps - got to check what's in my parts bin. The thing about buying the new replacement is that after I add the 30% exchange rate for Canada, plus the shipping, I'm starting to hit $100, so I'll need to do some hunting first. And ideally, it would probably be best to change out both in the pair.
Click to expand...

Don't replace the original electrolytics with new electrolytics. Use high quality film/foil caps such as Sonicap or Clarity and replace the resistors with Mills. You will be rewarded many times over with much better sound quality.
 
Also if you join up as a member of the Polk Forum and call Polk c/s you get a discount on the driver w/ free shipping. Polk backs just about all their vintage drivers . I had a set on original M7s and I have an extra driver less than E-Bay or Polk direct for sale. As Dswankey said (w/ that great Phil Lesh Alembic) F-1 is one of the original Polkies and knows about generations and parts for modding. Off topic, personally I liked that bass better than his next model w/ the star shape around the knobs. Then he went w/ Modulus basses. Photo of # label not so good w/ flash but it's a new #6502IMG_4171[1].jpg IMG_4172[1].jpg
 
Thanks all for the valuable advice and support. I'm going to swap the drivers to make sure it's a driver problem. WHile I'm at it, I'll take pics of the innards for reference purposes. Then I'll have to decide if I want to break it down into parts and get rid of it (the cabinets are rough), or find a better priced source. The shipping alone for the speaker new would cost almost as much as the driver.
 
Thanks all, and F1nut on the screws. I often leave some off if I know I'm going to be "going back in" soon.

So, here's the report, in case someone else stumbles across the same issue of distortion from the 6.5 inch. I'll skip the detective work part.

By LOOSENING the screws that hold the mid/woofer, while music playing, I was able to eliminate the distortion. When the screws were tightened really tight, the driver stopped completely. By easing back a bit at a time on the screws, I hit the sweet spot.

I don't know WHY this is the case, whether the frame is bent, or the magnet is starting to slip, but right now, given I got them for 5 bucks, and they sound great. I'm happy.
 
did you take the midbass drivers out and check the connections to them? The only thing that would make sense to me is that you have a poor connection to the metal tabs or an internal wire in the driver itself that's bad.
 
F1nut said:
That's a new one on me and makes no sense.
Click to expand...

Well, there it be, though. I've tested it several times...tightening --> distortion and then no output, loosen until sound returns, then normalizes. Again, I leave the cause to those with a better understanding of the structure of drivers, but it kind of does make sense to me, when you have a driver that is very close to being completely out of spec because of voice coil shifting, frame flexing, that kind of thing, where even minor torque and strain can cause it to go completely out of spec.
 
bryblob said:
did you take the midbass drivers out and check the connections to them? The only thing that would make sense to me is that you have a poor connection to the metal tabs or an internal wire in the driver itself that's bad.
Click to expand...

No, I didn't do that, since I found the cause, if not the root cause, and could fix it simply. It's got to be, I mean GOT to be a physical problem, rather than an electrical one. Tightening or loosening the mounting screws simply wouldn't have any effect on the electrical connections. My thinking is that tightening the screws warps the frame "just enough" to cause voice coil rub, or something of that nature, because the tolerances required for proper sound vs. improper are so narrow due to the age and and shifting of something structural.

Just trying to logic it out at this point.
 
I know those drivers inside and out. I just can't see the frame warping by tightening the screws. Suggest you take it out for a look see. If you find nothing obvious swap it with the other speaker.
 
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