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Thread: Repairing a split polypropylene bass driver

  1. #1
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 6,867
    I'm Lawrence.

    Default Repairing a split polypropylene bass driver

    I've got some Musical Fidelity MC4 speakers and sadly one woofer has a split right from the centre to the outer edge. I've tried them at moderate volume and strangely I can't hear any audible effect from it. However I'd still like to try a repair until I can find a new driver (rare as hens' teeth).

    I think I'm going to just put some speaker glue on both sides of the split and let it set but I was wondering if anyone has a better idea. It would look a bit messy but should keep it going as long as required.

    Sent from my HRY-LX1 using Tapatalk
    Last edited by Lawrence001; 16-09-2020 at 23:31.

  2. #2
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 6,867
    I'm Lawrence.

    Default

    Having looked it up I'm wondering if super glue is the best option for this. Or maybe a glue gun, which I've got.

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  3. #3
    Join Date: Apr 2012

    Location: N E Kent

    Posts: 51,624
    I'm Geoff.

    Default

    There is no ideal repair, but my inclination would be to apply a one layer strip of thin glassfibre tissue across and along the crack on the back of the cone (using epoxy of course). A glue gun may produce too much heat and distort the poly material.
    It is impossible for anything digital to sound analogue, because it isn't analogue!

  4. #4
    Join Date: Mar 2017

    Location: Seaford UK

    Posts: 1,861
    I'm Dennis.

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    In your position, and having had experience of using glue on polypropylene drivers, I would undoubtedly use superglue.
    (Loctite is the best quality).

    Polypropylene is notoriously difficult to glue, but I've glued sheet rubber to it on the back of my passives, (drone cones), which are the same cones as my drivers, but without the magnets and coils.

    The good thing from your point of view is that the fracture is probably intimate fitting, (like a broken cup, the bits fit each other), and a minimal amount is required for such a bond, and the Q of superglue is also not very different from that of polypropylene.

    I think it may even be so good that you will not need a replacement driver, but be careful not to apply too much, that will run all over the place, just enough to seep into the crack and run along. Use cotton buds to suck off excess or runs.

  5. #5
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 4,481
    I'm Alex.

    Default

    Decades ago I remember at work they were welding up polypropylene water tanks. I think that they also used a special adhesive for polypropylene as other have said it is difficult to glue.

    This looks interesting,
    https://www.gluegunsdirect.com/2013/...ypropylene-pp/
    Spendorman

  6. #6
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 6,867
    I'm Lawrence.

    Default

    Thanks all, like most other projects in recent years since the kids came along I'm wondering if I'll ever find the time. These might appear in the classifieds shortly..

    Sent from my HRY-LX1 using Tapatalk

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