KLH Model 5 Woofer issue - Surround or Voice Coil?

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

  1. rocknroller

    rocknroller Active Member

    Messages:
    154
    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.
     
  2. tubed

    tubed Lunatic Member

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    12,568
    Location:
    Aztlan
    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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    2,894
    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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    Location:
    Northern Westchester Co, NY
    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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    3,082
    Location:
    NE Ohio
    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:
    VA Beach
    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:
    154
    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

    Messages:
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    Location:
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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.
     
  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

    Messages:
    11,883
    Location:
    Northern Westchester Co, NY
    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).
     

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