Remember to epoxy your woofer magnets!

13

Comments

  • StantonZ
    StantonZ Posts: 410
    edited September 1
    Thanks to this thread, I finally took care of this maintenance item. My 10B's are ~35 years old with (luckily) no magnet shift. It probably didn't hurt that they've been sitting in my family/media room for ~25 years; we're getting ready to move and they might have to spend some time in storage, so I can't predict how they will be handled. I used JB Weld (the quick dry kind from Amazon)...and it took me about an hour per speaker...and it sucked...but everything came out ok! I had previously rebuilt the crossovers and replaced/updated the tweeters, so I'm definitely in it for the long-haul.
    Yamaha RX-A2050 AVR (5.0.2)
    (4) Polk Monitor 10B's w/SoniCaps, Mills, and RDO-194 tweets (R/L F/R)
    (2) Polk Monitor 4's w/peerless tweets (Top Middle)
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  • F1nut
    F1nut Posts: 46,120
    Political Correctness'.........defined

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  • msg
    msg Posts: 6,597
    Any tips on applying that stuff neatly?
    I disabled signatures.
  • Gardenstater
    Gardenstater Posts: 1,992
    edited September 28
    It's pretty messy stuff. All I can suggest is a band of masking tape around the magnet, trimmed on both sides with a razor blade, and lots of throwaway nitrile (or other) gloves, and an appropriately sized troweling tool to tool the epoxy into the space. The speaker could be propped up against an iron angle plate with the magnetic attraction holding it in place to allow access to both sides of the magnet and it can be spun to work on it. I would seriously consider trying the 5m epoxy syringes that come with a couple of mixing nozzles. It may be on the thin side would be the only possible caveat.
    George / NJ

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  • lawdogg
    lawdogg Posts: 396
    edited September 30
    I use a wood stir stick to carefully spread a bead of epoxy where the magnet meets the basket / pole piece on the "shelf" created by the magnet. I mix the epoxy on a flat piece of plastic and kind of scoop it up with the stir stick a little at a time, then use the stir stick to spread the bead so it's neat and even.
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
  • pitdogg2
    pitdogg2 Posts: 19,236
    lawdogg wrote: »
    I use a wood stir stick to carefully spread a bead of epoxy where the magnet meets the basket / pole piece on the "shelf" created by the magnet. I mix the epoxy on a flat piece of plastic and kind of scoop it up with the stir stick a little at a time, then use the stir stick to spread the bead so it's neat and even.

    Yep I just went a bought some popsicle sticks from the craft store.
  • hytekrednek
    hytekrednek Posts: 115
    I used the 5 minute epoxy with the mixing nozzles. Worked great and not very messy. It does smell odd for a week but is very strong
  • Gardenstater
    Gardenstater Posts: 1,992
    I used the 5 minute epoxy with the mixing nozzles. Worked great and not very messy. It does smell odd for a week but is very strong

    Any issues with the viscosity of that......I mean did you have to do one side of the magnet and let it cure a while, and then flip the driver over and do the other side? Does it tend to stay where you put it or does it want to run?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    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
  • hytekrednek
    hytekrednek Posts: 115
    no issues at all. It stayed where I put it, but it was just thin enough to seep deeper into the corners without having to spread it manually.
  • hytekrednek
    hytekrednek Posts: 115
    I did both top and bottom of magnets at same time
  • pitdogg2
    pitdogg2 Posts: 19,236
    Check it in 6-8 months. I used some loctite clear epoxy and about a year later I could peel it off.
  • F1nut
    F1nut Posts: 46,120
    5 minute epoxy is the wrong product.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • joebass3
    joebass3 Posts: 49
    Is Loctite power grab ultimate still considered ok? I used it on a set of 1C's recently after reading favorable reviews.
  • pitdogg2
    pitdogg2 Posts: 19,236
    joebass3 wrote: »
    Is Loctite power grab ultimate still considered ok? I used it on a set of 1C's recently after reading favorable reviews.

    The problem is it doesn't grab the metal as well as JB-weld. I have also used the Power Grab on many as it was much easier to apply. I've also used the JB-weld years ago. I certainly wouldn't try and remove the Power Grab as you may damage the woofer by dislodging the magnet. Leave well enough alone and use JB-weld next time on a different woofer.
  • VSAT88
    VSAT88 Posts: 1,030
    pitdogg2 wrote: »
    lawdogg wrote: »
    I use a wood stir stick to carefully spread a bead of epoxy where the magnet meets the basket / pole piece on the "shelf" created by the magnet. I mix the epoxy on a flat piece of plastic and kind of scoop it up with the stir stick a little at a time, then use the stir stick to spread the bead so it's neat and even.

    Yep I just went a bought some popsicle sticks from the craft store.

    Try chopsticks. I just roll mine right on. Spreads it real well.
    Where in Alabama ?
  • VSAT88
    VSAT88 Posts: 1,030
    It's pretty messy stuff. All I can suggest is a band of masking tape around the magnet, trimmed on both sides with a razor blade, and lots of throwaway nitrile (or other) gloves, and an appropriately sized troweling tool to tool the epoxy into the space. The speaker could be propped up against an iron angle plate with the magnetic attraction holding it in place to allow access to both sides of the magnet and it can be spun to work on it. I would seriously consider trying the 5m epoxy syringes that come with a couple of mixing nozzles. It may be on the thin side would be the only possible caveat.

    Use an old turntable to sit the woofer on. :)
    Where in Alabama ?
  • VSAT88
    VSAT88 Posts: 1,030
    StantonZ wrote: »
    Thanks to this thread, I finally took care of this maintenance item. My 10B's are ~35 years old with (luckily) no magnet shift. It probably didn't hurt that they've been sitting in my family/media room for ~25 years; we're getting ready to move and they might have to spend some time in storage, so I can't predict how they will be handled. I used JB Weld (the quick dry kind from Amazon)...and it took me about an hour per speaker...and it sucked...but everything came out ok! I had previously rebuilt the crossovers and replaced/updated the tweeters, so I'm definitely in it for the long-haul.

    Quick dry kind??... Took an hour per speaker ?? How did you do that ???
    Where in Alabama ?
  • skrol
    skrol Posts: 3,092

    pitdogg2 wrote: »
    Yep I just went a bought some popsicle sticks from the craft store.

    I'd buy a box of popsicles and have fun eating them. Maybe share some with the kids.
    Stan

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  • invalid
    invalid Posts: 676
    F1nut wrote: »

    I used this JB weld on a cracked engine block and drove the truck for over a year with no problems.
  • BlueBirdMusic
    BlueBirdMusic Registered User Posts: 1,549
    invalid wrote: »
    F1nut wrote: »

    I used this JB weld on a cracked engine block and drove the truck for over a year with no problems.

    Did you have the speakers in the back of the truck for a year? :D
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  • Gardenstater
    Gardenstater Posts: 1,992
    edited October 8
    Here's some tensile strengths. It will of course depend upon the materials bonded but this gives a pretty good idea for comparisons. The first two show how much strength you lose in going to a fast setting epoxy from a standard. This is of course barring any adhesion issues with the two materials involved, which pitdogg2 observed with another 5m epoxy (loctite?). The last two show a comparison between loctite and gorilla construction adhesives. I used the Gorilla and found it to be very satisfactory. It shrinks a fair amount but I don't see that as an issue and it comes in a caulking gun style tube which means you can apply it without a lot of mess. Power Grab is clear also but it is a non-shrinking silane modified polymer with higher solids/ less VOCs. Doesn't seem to be very strong when bonding maple to maple and aluminum to aluminum. Gorilla doesn't seem to be forthcoming with tensile strength data and the 1500 psi figure was in answering a customer's question on homedepot.com. I'm going to ask them for more specific data. Edit to add - I shoulda mentioned this and I posted the data somwhere else but it is so hard to find past postings (need some way to search on one's own postings), but a key factor in adhesion over time is the ability to maintain adhesion with 2 materials of different coefficients of thermal expansion. In this case we're talking about Ferrite vs high iron content steel. I'll see if I can find those figures again. Anyway, not all adhesives are going to work best over time with this scenario and of course it depends upon how the speakers are stored climate control wise. A super rigid epoxy can lose bond over time if temperatures vary a lot and that is why West Systems G Flex *may* be better than a regular epoxy. It seems to me that the Modulus of Elasticity for the Gorilla Max Strength would be lower and that might be advantageous.



    JB-Weld (4 to 6 hr set, 15 to 24 hr cure): 5,020 psi
    JB-QwikWeld (6m set, 4 to 6 hr cure): 3,127 psi
    Loctite Power Grab Ultimate Crystal Clear Construction Adhesive: 161 psi
    Gorilla Max Strength Clear Construction Adhesive: 1500 psi
    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
    Crown D150 amp
    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
  • Gardenstater
    Gardenstater Posts: 1,992
    Having said all that ^^, an even bigger factor may be the difference in coefficient of thermal expansion between the *adhesive* and the objects being bonded. In any case flexibility and strength both would seem to be important for keeping the grip, not to mention mechanically abrading the surfaces. JB-Weld is a steel filled epoxy. That may make the expansion coefficient closer to steel than other epoxies.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    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
  • StantonZ
    StantonZ Posts: 410
    VSAT88 wrote: »
    StantonZ wrote: »
    Thanks to this thread, I finally took care of this maintenance item. My 10B's are ~35 years old with (luckily) no magnet shift. It probably didn't hurt that they've been sitting in my family/media room for ~25 years; we're getting ready to move and they might have to spend some time in storage, so I can't predict how they will be handled. I used JB Weld (the quick dry kind from Amazon)...and it took me about an hour per speaker...and it sucked...but everything came out ok! I had previously rebuilt the crossovers and replaced/updated the tweeters, so I'm definitely in it for the long-haul.

    Quick dry kind??... Took an hour per speaker ?? How did you do that ???

    I used the same stuff that @F1nut provided the (Amazon) link for above. I did 4 speakers (8 drivers) and it took (2) 10 oz packages. To say it's a "mess" is an understatement: lots of plastic spoons/knives, rubber gloves, packing paper (better than newspaper)...and I'm amazed I didn't get any on the floor/carpet. Took a bit over an hour per speaker and I split it into 2 days; my only other suggestion would be use in an area with good ventilation (the stuff stinks).
    Yamaha RX-A2050 AVR (5.0.2)
    (4) Polk Monitor 10B's w/SoniCaps, Mills, and RDO-194 tweets (R/L F/R)
    (2) Polk Monitor 4's w/peerless tweets (Top Middle)
    Polk CS300 center channel
    Analog: B&O TX2 Turntable, Nakamichi Cassette Deck 1
    Digital: Pioneer CLD-99 Elite LD, Panasonic DMP-UB900 UHD Blu-Ray
    LG 65EF9500 4K OLED
  • aprazer402
    aprazer402 Posts: 2,411
    Has anyone had a MW that they glued with any of the strong glues mentioned fail? Fail meaning the magnet came loose. If so, was the failure due to the glue itself just failing to hold over time or was it the result of the speaker being jarred or dropped which caused to glue to not retain the magnet in place?
  • audioluvr
    audioluvr Posts: 3,621
    JB-Weld (4 to 6 hr set, 15 to 24 hr cure): 5,020 psi
    JB-QwikWeld (6m set, 4 to 6 hr cure): 3,127 psi
    Loctite Power Grab Ultimate Crystal Clear Construction Adhesive: 161 psi
    Gorilla Max Strength Clear Construction Adhesive: 1500 psi

    You are over thinking this. Tensile strength is meaningless if it won't stay adhered to the two surfaces over time. I've used the power grab ultimate (non clear) for gluing wood shelves over my washer dryer that holds probably 100# of crap. It's subjected to heat, cold, vibration and hasn't failed.

    Best way to test the effective adhesion capabilities is to put a drop of each product on a piece of metal. Wait 24 hours, take a screwdriver and hammer and see what it takes to remove it.
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  • Gardenstater
    Gardenstater Posts: 1,992
    edited October 8
    Not overthinking. Tensile strength is a measure of bond strength. It is specific to the two materials being bonded and the adhesive doing the bonding. Manufacturers give a *general* tensile strength sometimes, without giving the specific materials being bonded. The good ones have technical data sheets where they do give the different tensile and sheer strengths of bonds with the materials being bonded specified. Here are the tensile strengths given by Loctite for Power Grab Ultimate Crystal Clear Construction Adhesive. Note the maximum of 161.2 psi which is much less than the maximum of 1500 psi for Gorilla (need to verify still): hhxd0wl9w2xk.jpg

    I believe I was addressing the issue of adhering over time by saying that flexibility (lower modulus of elasticity) may be important to deal with differing thermal expansion rates and enduring many cycles of temperature changes, so I never said that tensile and sheer strength are the only factors we need to concern ourselves with.

    I think doing tests like you mention are great, but how does that 24 hour test determine how it would hold up over many cycles of temperature changes? It doesn't.
    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
    Crown D150 amp
    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
  • F1nut
    F1nut Posts: 46,120
    Power Grab Ultimate Crystal Clear is the wrong product. I no longer have any tubes of the original Power Grab that we were using a few years ago and I don't recall the exact name, but Ultimate Crystal Clear was definitely not it.

    This is for the Power Grab All Purpose.

    Shear Strength:
    Wood to Wood: 870 to 1160 psi
    Wood to Aluminum: 870 to 1160 psi
    Wood to PVC: 435 to 725 psi

    No listing for metal to metal.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • F1nut
    F1nut Posts: 46,120
    Not sure where this came from as I couldn't find it anywhere.
    Gorilla Max Strength Clear Construction Adhesive: 1500 psi

    Gorilla has a spec for their heavy duty construction adhesive, 370 psi. It doesn't say with what material.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."


    President of Club Polk

  • Gardenstater
    Gardenstater Posts: 1,992
    F1nut wrote: »
    Not sure where this came from as I couldn't find it anywhere.
    Gorilla Max Strength Clear Construction Adhesive: 1500 psi

    Gorilla has a spec for their heavy duty construction adhesive, 370 psi. It doesn't say with what material.

    I found it searching the Q&A section on the word "tensile" on homedepot.com. I asked them for a technical data sheet with bond strengths for different materials and will share it with the forum *if* I get it. They (gorilla) are all over the place with their statements. They say on the product label that it is 2x stronger than Gorilla Heavy Duty Construction Adhesive Ultimate but their graphical info on product sheet shows for strength: Max Strength 8 bars, Heavy Duty Ultimate 6 bars, Heavy Duty 4 bars. Pretty wackadoodle lol. Here is what I found searching Q&A:

    3t2vcc4ibp5d.jpg
    34wffyr4v1g0.jpg
    enpcgogtocas.jpg
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    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