Diagnosing & Fixing Shifted Polk MW Drivers

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  • bcwsrt
    bcwsrt Posts: 1,876
    The Polk logo embossed into the bottom of the surround on the MWs would then be upside down. How severe is your OCD?
    Brian

    One-owner Polk Audio RTA 15TL speakers refreshed w/ Sonicap, Vishay/Mills and Cardas components by "pitdogg2," "xschop" billet tweeter plates and BH5 | Stereo REL Acoustics T/5x subwoofers w/ Bassline Blue cables | Rogue Audio Cronus Magnum III integrated tube amp | Technics SL-1210G turntable w/ Ortofon 2M Black LVB 250 MM cart | Sony CDP-508ESD CD player (as a transport) | LampizatOr Baltic 4 tube DAC | Nordost & DH Labs cables/interconnects | APC H15 Power Conditioner | GIK Acoustics room treatments | Degritter RCM
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  • skipshot12
    skipshot12 Posts: 1,157
    My ocd is waaaaay f’d up but, my memory is worse.
    If I don’t remember it never happened.
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  • plastic_avatar
    plastic_avatar Posts: 708
    I rotated all of mine in all my old speakers..
    The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage
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  • robosdad
    robosdad Posts: 48
    Well I spoke too soon. One of my repair jobs missed the mark and I have some strangely intermittent coil rub. I can see the pole is just a tad off-center. Wish I had used the epoxy on the outside... Anybody have experience on loosening red loctite without a torch? :/
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  • plastic_avatar
    plastic_avatar Posts: 708
    @xschop and others !

    Midwoofer down!

    What can he do?
    The Thrifty Setups in Mah House Big thrifty stereo in the basement w/ my custom SDA-1C (built with help from kind forum members) * Beautiful 1966 MCM GE console upgraded w/ Bluetooth, Dual turntable, and Paradigm speakers in family room * Swanky 1980 Realistic system and great TEAC eq with dancing colored lights in the living room * custom 5B on a system for my Dad * Ye Olde college stereo in the garage
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  • xschop
    xschop Posts: 5,000
    You'll have to heat it with a butane torch. Put the flame directly on the flat top of the pole piece in a circular motion while plying with a putty knife between magnet and base plate.
    Don't take experimental gene therapies from known eugenicists.
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  • robosdad
    robosdad Posts: 48
    xschop wrote: »
    You'll have to heat it with a butane torch. Put the flame directly on the flat top of the pole piece in a circular motion while plying with a putty knife between magnet and base plate.

    Thanks @plastic_avatar and @xschop After my research online I'm afraid you're right. I think my friend has one. Next time I'll use the two part epoxy (and just do the outside edges right?).
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  • lawdogg
    lawdogg Posts: 455
    edited February 2023
    robosdad wrote: »
    Well I spoke too soon. One of my repair jobs missed the mark and I have some strangely intermittent coil rub. I can see the pole is just a tad off-center. Wish I had used the epoxy on the outside... Anybody have experience on loosening red loctite without a torch? :/


    That is a bummer! Do you think it re-shifted after you re-centered it, or do you think you might have missed it by a little when you re-centered it?

    (...and yes I just do the outer edge as noted in the write-up, haven't had an issue with re-shifting *knock on wood*)
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
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  • robosdad
    robosdad Posts: 48
    lawdogg wrote: »
    robosdad wrote: »
    Well I spoke too soon. One of my repair jobs missed the mark and I have some strangely intermittent coil rub. I can see the pole is just a tad off-center. Wish I had used the epoxy on the outside... Anybody have experience on loosening red loctite without a torch? :/


    That is a bummer! Do you think it re-shifted after you re-centered it, or do you think you might have missed it by a little when you re-centered it?

    (...and yes I just do the outer edge as noted in the write-up, haven't had an issue with re-shifting *knock on wood*)

    Strangely, it's intermittent. Right now it's working fine (sounds so good). I'm pretty sure the coil was moving freely when I glued it (I kept reveling in pushing it up and down with two fingers on either side of the dust cap every few hours when it was drying!)

    A bit more data (maybe there's a clue?):

    Yesterday I took the dustcap off and pushed the dust coil out to see if there's any damage or maybe something stuck, but the coil looks OK. And then it was fine- the rubbing stopped! But then it came back a couple of hours of use later. So I played with again (just kind of pushing in out by hand). And then the rubbing stopped again. (and so far hasn't come back...)

    The only thing I can see is that it isn't perfectly symmetrical (pole is just a little closer on one side). I did rotate the whole speaker so the smaller gap is at the bottom. I'm sure gravity wouldn't effect any thing, but why not...

    Anyway, right now it sounds great and my whole family took turns listening to Space Oddity last night. Super fun. We'll see what the future holds (possibly a butane torch, but I have an eBay alert for a MW6011 in the meantime!)...
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  • xschop
    xschop Posts: 5,000
    If it's a 6511, their suspensions are real saggy and can rub if they're not dead-center.
    Don't take experimental gene therapies from known eugenicists.
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  • Gardenstater
    Gardenstater Posts: 4,455
    These wouldn't be MW6500 would they? Those have a smaller radial clearance from the OD of VC to ID of front plate. Another possibility could be a particle between the VC former ID and the pole piece OD. Sometimes you can push it down out of the way with a shim.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • robosdad
    robosdad Posts: 48
    Gardenstater wrote: »
    These wouldn't be MW6500 would they? Those have a smaller radial clearance from the OD of VC to ID of front plate. Another possibility could be a particle between the VC former ID and the pole piece OD. Sometimes you can push it down out of the way with a shim.

    I mistyped- Its the MW6511 (mistakenly typed MW6011)
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  • lawdogg
    lawdogg Posts: 455
    edited February 2023
    I had someone send me a pair of woofers that he said rubbed a little, but I couldn't for the life of me get them to rub, so we agreed that I would just send them back, he re-installed them, and no more rub.

    Maybe that could have been a loose suspension issue as well? Point is - I've seen a case of intermittent rubbing in addition to yours.

    @robosdad Did you happen to mark the orientation when you heard the rubbing, compared to its orientation now, no longer rubbing?
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
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  • robosdad
    robosdad Posts: 48
    @lawdogg orientation of the entire speaker? If so, I do not remember orientation when I reinstalled the speaker the first time. After I took them out and played with them, I coincidentally put them back in the same as all the others, with the little wire nodes (at the rim of the dust cap) at the 6 o'clock position. I say coincidentally because I put them back in such that the smallest gap between the VC and the pole was at the bottom, thinking that gravity might possibly work in favor pulling the coil down.
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  • lawdogg
    lawdogg Posts: 455
    Ok, well, something to keep an eye on if it starts to rub again I suppose. But I hope it doesn't!
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
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  • robosdad
    robosdad Posts: 48
    edited February 2023
    One thing I forgot to add- when I first saw this thread, I didn't realize @lawdogg was offering to fix these things for free. Obviously, now, I see that his generous offer is embedded in his signature. On my computer, the long horizontal lines in the sig look like the long horizontal lines separating posts, so at the time I thought the sig was a post from a different user posting right after lawdogg's posts, and it was some kind of message board troublemaker that everyone was just ignoring, and that they were soliciting repair services with a "free" angle! Anyway, thought you all might get a kick out of that. Thanks again for the help- still loving the SDA-1c's (that one finicky woofer is still good to go!)
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  • lawdogg
    lawdogg Posts: 455
    Catch someone a fish and you feed them once; teach someone to fish and you feed them for life!
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
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  • pitdogg2
    pitdogg2 Posts: 25,411
    Solid advice!!
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  • odcics2
    odcics2 Posts: 331
    Got a pair of 7B speakers, one MW 6500 is seized. Measures 6.1 dc ohms, out of the cabinet.
    Good MW measures 6.0 dc ohms still being wired in the cabinet. (Is that a valid number, being still wired?
    Early in this thread, MW 6500 are stated to be 6.8 ohms.
    Any insight appreciated. Thanks.
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  • pitdogg2
    pitdogg2 Posts: 25,411
    @lawdogg
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  • Gardenstater
    Gardenstater Posts: 4,455
    edited March 2023
    odcics2 wrote: »
    Got a pair of 7B speakers, one MW 6500 is seized. Measures 6.1 dc ohms, out of the cabinet.
    Good MW measures 6.0 dc ohms still being wired in the cabinet. (Is that a valid number, being still wired?
    Early in this thread, MW 6500 are stated to be 6.8 ohms.
    Any insight appreciated. Thanks.

    They are supposed to be 6.50 Ohms across the driver terminals, out of circuit. I'd have to check mine to see what I get across the binding posts if that is what you are referring to.

    https://forum.polkaudio.com/discussion/133992/thiele-small-parameters-for-mw6500-drivers#latest

    PS: On a spare stock crossover I have I get around 0.7 and 0.8 Ohm (2 different meters) across the binding posts with no driver in the circuit and driver fastons held together. I do not trust these low resolution meter for this measurement however.
    Post edited by Gardenstater on
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • odcics2
    odcics2 Posts: 331
    I pulled the good speaker out of the cabinet and measured across the terminals, not at the speaker input.
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  • odcics2
    odcics2 Posts: 331
    Incidentally, the one good 7B is 100% airtight and the MW / PR combo sounds great. Goes deep on urban test music.

    Testing done in a garage, not my small dedicated room.
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  • Gardenstater
    Gardenstater Posts: 4,455
    odcics2 wrote: »
    I pulled the good speaker out of the cabinet and measured across the terminals, not at the speaker input.

    OK then I wasted my time I guess. That was not clear because for the one you said "still being wired in the cabinet".
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • odcics2
    odcics2 Posts: 331
    edited March 2023
    Sorry for not being clear and concise in how I measured the driver. :(

    So, driver out of the cabinet, measuring across the terminals which were still connected to the wires.

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  • Gardenstater
    Gardenstater Posts: 4,455
    edited March 2023
    No prob. But the answer to this is no and will give same reading across the driver terminals whether the fastons supply wires are connected or not. Should measure 6.5 Ohms. There are lots of cheap inexpensive meters that can be off however.

    "Good MW measures 6.0 dc ohms still being wired in the cabinet. (Is that a valid number, being still wired?"
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • odcics2
    odcics2 Posts: 331
    I should get myself a better ohm meter!!!
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  • Gardenstater
    Gardenstater Posts: 4,455
    odcics2 wrote: »
    I should get myself a better ohm meter!!!

    Most of what I own is questionable for measuring these low resistances, but I get around 6.4 Ohms on my drivers that I have measured. The way to find out would be to get some 1% tolerance resistors in the 1 to 7 ohms range and see how your meter does.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • Gardenstater
    Gardenstater Posts: 4,455
    @odcics2 If you wanted to check the accuracy of your ohmmeter you could get something like this:

    https://www.parts-express.com/Dayton-Audio-DPR10-6.5-6.5-Ohm-10-Watt-Precision-1-Audio-Grade-Resistor-006-6.5
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • lawdogg
    lawdogg Posts: 455
    I think I saw your post over on AK about the dog knocking it over!

    If the magnet flew off, how does the voice coil look? Visibly OK (e.g., nice and cylindrical, no discoloring)?
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
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