KLH Model 5 Woofer issue - Surround or Voice Coil?

Discussion in 'Speakers' started by rocknroller, Oct 13, 2017.

  1. rocknroller

    rocknroller Active Member

    Messages:
    317
    I consider myself pretty experienced with speakers and speaker repair. I have replaced dozens and dozens of deteriorating surrounds, recap crossovers etc. However I have an issue with a KLH Model 5 cab that I'm not sure of and need some (expert) advice.

    When playing music and pushing any volume of bass, the woofer burps, which has always been an indication to me of voice coil rubbing when the surrounds appear to be good. I took the woofer out and pressed evenly on the cone in and out. What I expected to find was a rub throughout range or most of it. What I actually found was a rub only at the extremes (way in or way out.) When pulling the cone out, it feels like the cone is being stopped at the end. When pushing in, it's more of a typical rub at the far end. The surround is intact and I honestly wouldn't have thought twice that it might need replacing before, but now I'm wondering. The surround is is reverse surround type (meaning it scoops inwards towards the cabinet, unlike most surrounds that bow outwards) and made of a cloth surround, as opposed to more typical foam etc.. I've never actually done one that was this direction or of this rubber type, clearly a different material then typical surrounds.

    So my question is - is more like that the voice coil is really shot on this woofer, or that the surround simply is not strong enough to "hold" the woofer in place properly (not so much left/right/up down, sagging etc, but more from the point of the speaker excursion. As I mentioned, in what I would consider to be the normal excursion range of the speaker, I feel no rubbing. It only seems to be at the extremes.
     

     

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  2. tubed

    tubed Lunatic Member

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    MY guess is that the voice coil former has become "out of round" and perhaps even a bit bent at the bottom.
    I'd remove the dust cap( leaving a bit of a tab for reattaching).
    Once the dust cap is out of the way you can inspect the gap and former for anything out of alignment or bent.
    If so, a skinny but stout implement of choice can used to dexterously manhandle the form away from the pole piece until it's unhindered and moves freely once again.
    BTW, I've down this on more than one KLH woofer.
     
  3. woodj

    woodj Super Member

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    3,348
    If the surround is cloth, it may need sealing with AR sealer (nothing else); unsealed it may be allowing excessive excursion.
     
  4. GD70

    GD70 AK Subscriber Subscriber

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    Agree with the above comments.
    What you describe usually means the woofer VC bottomed out at some point.
    I had a AR-2a woofer that over extended from an amp power surge and the VC hung up on the top edge of the pole piece. I pulled the dust cap and reformed the VC with shims and it worked fine after that.
     
  5. RWood

    RWood The future is not what it used to be Subscriber

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    If you need a couple Five woofers, I've got two you can have for postage. One has a tear in the cone but a good VC, the other has a great cone but open VC. PM if you can use them.
     
  6. jlovda

    jlovda Things I loved from the 60's and 70's Subscriber

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    Location:
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    I had a similar problem with a pair of 5's. Sometime in the past, before I got them, they must have been subjected to an extremely large negative pulse. This jammed the VC down and it hit the bottom of the pole piece. It caused the bottom of the aluminum former to bend outward. At low volumes everything was fine but when the excursion got large the bent aluminum hit the upper pole piece on the way up causing it to stop and make a snapping sound. Your's may have had worse damage to the VC and former. I had one woofer repaired by a local expert. It cost $50. He had to remove the cone and VC completely from the basket and spider and bend the bottom edges of the former back straight. He said I was lucky the coil itself was not damaged. For the second woofer I just bought a nice replacement on ebay. Physically pushing the woofer cone down would never indicate a problem if you were looking to buy a pair. The problem was when the cone came up.
     
  7. borus

    borus Luthier tube guy Subscriber

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    Location:
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    As woodj said the surround needs sealing. The air suspension needed to control the woofers movement is compromised. It is just flapping around as the air in your environment allows. Once the air is trapped in the box it will stop the woofer from moving to far in and out. Fix that first the other fixes may not be needed. Don't look for it to be the worst Henry would have expected this.
     
  8. rocknroller

    rocknroller Active Member

    Messages:
    317
    OK - So two camps here, 1) to reseal the surround 2) fix the voice coil. I guess, I'm going to try the easy approach first. Seal the surround. I never had to take a dustcover off yet (thankfully) not sure how to do that yet still be resuable afterwards.
     
  9. jlovda

    jlovda Things I loved from the 60's and 70's Subscriber

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    If you're talking about removing the dust cover to fix a voice coil problem, it won't help. The problem is on the OUTSIDE of the VC. Removing the dust cover only allows you to shim the coil, not fix anything.
     

     

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  10. sberger

    sberger Hard Core Geezer Subscriber

    Absolutely a must. If you haven't done it, do it. Order the sealent from vintage-ar on the auction site. Made the biggest improvement for my 5's.
     
  11. GD70

    GD70 AK Subscriber Subscriber

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    Agree with this also! My first set of Sixs had a wild woofer, two coats of sealer tamed it quite nicely.
     
  12. sberger

    sberger Hard Core Geezer Subscriber

    I love the vintage-ar sealant. But be very careful and very conservative putting it on. You can easily make a good thing bad and impede the woofer by making the surround too stiff.

    Ask me how I know. Also ask me what you can do if this happens(hint: the answer is another thread on this forum).
     
  13. rocknroller

    rocknroller Active Member

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    317
    OK so an update - The sealant was a fail. Perhaps necessary anyway, but did not resolve the farting at all. I am convinced the issue is with the voice coil. I peeled the cap of the worst one and I notice two things:
    1) The coil appears to be centered (although the pics I uploaded show it off center, that's because I was pulling on the dust cap, trying take and pic and hold a light all at the same time - I can assure you that when "at rest" it is centered evenly around the magnet and the coil is not out of round. However, if I tap basically anywhere on the cone (12 o'clock, 3'oclock 6 o'c etc), the coil is hitting the magnet on the side I tap. It is simply too "woobly" in it's position and easily moved such that it comes in contact with the magnet. Confirmed this not only visually, but with a thin sheet of paper between to confirm the sound of the contact damped. The surround, post sealer treatment (2+ of them) would have to be stiffer than before but doesn't appear to be enough to prevent the simplest cone taps from angling the coil each time.

    2) By pulling the voice coil up and over the lip of the magnet, I was able to confirm the bottom edge was bent over. It was bent over facing inwards towards the magnet in a few spots. I was able to unpeel it and push back out straight, though you can see in the pic where there appears to be a little tear in it. This confirms on of the issue I had before such that when the cones excurts too far forward, it was hitting a blocking (where this coil was peeled back onto itself . I don't really have that blockage now that I unpeeled it.

    So The root cause right now seems to be the coil simply not staying vertically in the channel. On my other speaker, the tapping test only occurs in one quadrant, so the farting is not as noticeable, but on this speaker it is. Is this all due to the surround simply being too weak to hold the cone properly?? And if so, is there a stronger sealant that would hold it better than the AR sealant, which seems to be pretty lightweight. I realize anything stronger may be at the expensive of the general woofer audio quality but at this point the woofer is useless anyway so anything would be better. The coil probably should be replaced, given the peeling damage, but that's a bigger task then I'm comfortable with and if it can't be stabilized in the channel anyway, there's little point.
    IMG_6610[1].JPG IMG_6610[1].JPG IMG_6611[1].JPG
     
  14. woodj

    woodj Super Member

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    One last simple thought - farting can be a leak in the cabinet or some other portion of the envelope.
     
  15. rocknroller

    rocknroller Active Member

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    In this case - I'm convinced the coil is scrapping and is the cause
     
  16. borus

    borus Luthier tube guy Subscriber

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    Location:
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    The spider is where the coil is held in alignment more than the surround. Is it attached strongly?
     
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  17. GD70

    GD70 AK Subscriber Subscriber

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    Agree. I was just going to mention the spider and ask if it loose.
    If you have shims, they could be pushed down into the gaps to flatten out the bottom of the VC's where they bend inwards.
     

     

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  18. woodj

    woodj Super Member

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    I have done that, but with a light gauge sink tail piece which fit perfectly in the gap and around the VC.
    You might find something that might fit inside the former if the roll is toward the inside.
     
  19. rocknroller

    rocknroller Active Member

    Messages:
    317
    You were correct. Complete separation from the voice coil all the way around. Excellent call. See pic with the cone lifted up. I watched several youtube videos and users have used Locktight 5 minute epoxy to reglue these. My question is - would I run the bead of glue around the bottom of the speaker cone where it meets the voice coil and then push it back down to meet the spider, or better to try and get it on the top of the spider itself and push the cone down to meet? Or just set the cone down to meet and bead around at the joining point? Obviously concerned about getting glue on the coil or in the coil/magnet gap.

    FYI I do have some plastic shims that came with other surround kits so I'll put those in to make sure it's situated properly before glueing. I believe I already unbent everything previously and it actually took a bit of force with a screwdriver so not sure plastic shims would have done the job or not. Though to be fair I was fighting the magnet pull the whole time lol.

    IMG_6628[1].JPG
     
  20. rocknroller

    rocknroller Active Member

    Messages:
    317
    Another question - With the speaker out and held to the light - I can see a fair amount of light through the surrounds, even after multiple coats of the AR sealant. Is that to be expected, given the sealant is fairly clear?
     

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