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  1. #1

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    Default Technical question: JB Weld and Magnets

    So during my recent 2B upgrade spree I used J-B Weld on the four MW magnets. It didn't occur to me before putting the stuff on that since one component of the epoxy is a steel slurry it interacted in an interesting way with the magnet. The magnet actually pulled the mixed epoxy off the applicator (not a lot, just a noticable amount) and seemed to make it want to flow over the edge of the magnets, so I had to be pretty careful about how much I was using.

    Anyway, I know that J-B Weld is pretty much the approved solution for avoiding magnet shift and that it's not supposed to affect the sound at all, but I was wondering if putting a bunch of steel-bearing goop around the magnet could have any impact on the magnetic field the driver depends on?

    I might go back and do this to the drivers in some Monitor 5Jr's I recently tweaked, and was also wondering if the Dayton USB Woofer tester sold by PE might be able to detect any before-and-after differences.

    Has anyone tried doing a before-and-after test of the woofers using that gadget or know enough about it to know whether it would be worth trying?

    TIA!

  2. #2

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    Quote Originally Posted by On3s&Z3r0s View Post
    Has anyone tried doing a before-and-after test of the woofers using that gadget or know enough about it to know whether it would be worth trying?
    Yes, and there was no change.
    Polk SDA SRS 2
    Polk RTA 15tl
    Polk Monitor 7C
    Polk Monitor 4.6
    Polk Lsi9

    Infinity RS-II (modded)
    Infinity RS-IIIa (modded)
    Infinity RS 2.5 x 2

    Magnepan 1.6QR (modded)

    System: http://forum.audiogon.com/cgi-bin/fr...vol&1290711373

  3. #3

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    Quote Originally Posted by geoff727 View Post
    Yes, and there was no change.
    Cool, thank you! Just saved me 100 bucks.

  4. #4

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    Are you putting it all around the magnet?? If so there is no need to do so, four places around the top and bottom of the magnet.. Your 5jrs may need it around the basket and magnet as well, some of the older Polk drivers magnets are not rivited to the basket.. You can take a flashlight and shine it in the spider area to see if they are or not..

  5. #5

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    Quote Originally Posted by TOOLFORLIFEFAN View Post
    Are you putting it all around the magnet?? If so there is no need to do so, four places around the top and bottom of the magnet.. Your 5jrs may need it around the basket and magnet as well, some of the older Polk drivers magnets are not rivited to the basket.. You can take a flashlight and shine it in the spider area to see if they are or not..
    I did put it all around the magnets on the 2B's. The first pics I found using the J-B Weld (I think they were Geoff727's actually) had it all around the magnets top and bottom. After that was done and when I was putting on the Dynamat I found your thread that just had the J-B Weld in four segments top and bottom. That was the reason I was a little concerned over having used too much and maybe having affected something in a bad way.

    I did check for the rivets and all the drivers in the 2B's have them. I'll definitely check for those and be a little more sparing with the JBW otherwise when I do the 5Jr's. Thanks for the input, and thanks to you and Geoff for posting up your pics of the mods as well. It really helps a lot to know what you're shooting for. I would have posted up some of my own, but frankly you did a much better job covering the whole process. Thanks again!
    Last edited by On3s&Z3r0s; 04-20-2011 at 05:06 PM.

  6. #6

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    Quote Originally Posted by On3s&Z3r0s View Post
    I did check for the rivets and all the drivers in the 2B's have them. I'll definitely check for those and be a little more sparing with the JBW otherwise when I do the 5Jr's. Thanks for the input, and thanks to you and Geoff for posting up your pics of the mods as well. It really helps a lot to know what you're shooting for. I would have posted up some of my own, but frankly you did a much better job covering the whole process. Thanks again!
    If I'm reading the first sentence correctly.....where the front plate of the magnet attaches to the basket is not necessarily where the concern should be, obviously since these are riveted (like Larry said, some aren't). It's the joints in between the magnet, the front plate, and the back plate where things 'let go'. I am just using a thin bead of JBW around both those seams, smoothed with my fingertip, and cleaned from the magnet with Goof-Off (this is cosmetically motivated).

    Post some pics anyway! Why would we not want to see a speaker with new life breathed into it? Have you done any cosmetic enhancements?

    Sorry we didn't see you at the get-together on Saturday. We definitely had some good listening. Next year maybe? I was kind of hoping you'd show up with your enhanced Monitor 5's.

    G~
    Polk SDA SRS 2
    Polk RTA 15tl
    Polk Monitor 7C
    Polk Monitor 4.6
    Polk Lsi9

    Infinity RS-II (modded)
    Infinity RS-IIIa (modded)
    Infinity RS 2.5 x 2

    Magnepan 1.6QR (modded)

    System: http://forum.audiogon.com/cgi-bin/fr...vol&1290711373

  7. #7

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    Yes, after making sure all the drivers in the 2Bs did have the rivets joining the front plate to the baskets I didn't put any JBW there. I tried to duplicate what I saw in your pics with a thin bead around the entire perimeter of the magnet where it's joined to the front and rear plates. The Goof-Off is a great idea... wish I had asked before starting. My first attempt was a little sloppy. Trying to smooth the bead with a finger in a latex glove doesn't work so good. It didn't work out too bad except some smearing on the side of the magnet where the Goof-Off would have come in handy. I then switched to using some bamboo grill skewers to apply and smooth a more targeted bead. I got that to work reasonably well.

    Unfortunately, I didn't take any pics of the JB Weld and Dynamat on the drivers before I put them back in the cabs. But they look basically identical to the pics of other folks' Dynamat jobs. I haven't done anything with them cosmetically. They are some plain-jane lookin' all black studio 2B's. But I'll get some pics of them when I at least get that gorgeous "Black Oak" veneer polished up a bit. I also spiked them and upgraded the binding posts plus one for the SDA IC. I was thinking of posting some pics documenting that process since that doesn't seem to be covered in quite the same level of detail as some other mods. Not especially tricky, but maybe worth a thread. At least folks can tell me what I did wrong.

    And about the Seattle PF, I was bummed to have to miss that. I had a competing engagement. I can't imagine you guys could have had more fun than I did bowling with a bunch of other peoples kids. I definitely hope to meet some more of the WA/PNW Polkies next time one happens.
    Last edited by On3s&Z3r0s; 04-21-2011 at 12:51 AM.

  8. #8

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    Actually, the JBW will come off the magnet with some careful scraping with a utility knife. That will clean it up a little bit.

    Any thoughts about putting some real wood veneer on these? It would not be that tough, & they would look really sharp.

    You (and all Seattle-area/PNW folks) always have a standing invitation at my place....if listening to a pair of plain old Magnepans is something on your list of things that sound interesting!
    Polk SDA SRS 2
    Polk RTA 15tl
    Polk Monitor 7C
    Polk Monitor 4.6
    Polk Lsi9

    Infinity RS-II (modded)
    Infinity RS-IIIa (modded)
    Infinity RS 2.5 x 2

    Magnepan 1.6QR (modded)

    System: http://forum.audiogon.com/cgi-bin/fr...vol&1290711373

  9. #9

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    I did give some thought to veneer having seen the results you've been able to acheive. But I've never worked with it before, so would have to go through that learning curve and also would need to find some time to do it. Unfortunately I have a backlog of home/yard repair projects to get to and when the weather warms up my wife gets cranky if I spend too much time sequestered away playing with the audio gear. Wives.

    But if I can find some time I'll definitely take you up on an audition of those Maggies (love your writeup on the 'Gon, BTW), and maybe I can take some veneer notes as well. Thanks very much for the offer!

  10. #10

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    Yep, just let me know.

    G~
    Polk SDA SRS 2
    Polk RTA 15tl
    Polk Monitor 7C
    Polk Monitor 4.6
    Polk Lsi9

    Infinity RS-II (modded)
    Infinity RS-IIIa (modded)
    Infinity RS 2.5 x 2

    Magnepan 1.6QR (modded)

    System: http://forum.audiogon.com/cgi-bin/fr...vol&1290711373

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