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Stiffening up a speaker cone in an old bass cab...will this work?

Discussion in 'Amps and Cabs [BG]' started by hater-ade, Dec 30, 2003.


  1. hater-ade

    hater-ade

    Feb 11, 2003
    I just purchased a used SWR Goliath Senior for $850 (Canadian!)at my local music store. The cab was for rental so its pretty beat up and old (it has a black grill and the SWR logo is slightly different, which I thought was wierd but I guess thats how SWR made these at first), but still sounds great.

    Anyways, I took the grill off today and i noticed that one of the speakers seem to have been driven so hard that the cone has actually creased a bit near the surround. The top 2 10's also have some very minor dents in the cone.

    I was wondering how i might be able so treat the cones as to stiffen them up and restore strength to the crease in one of the cones. I have experimented with a few things and found that epoxy seems to stiffen up cardboard-like paper (like the cones) a LOT without adding much weight. Does anyone know how this might affect the tone? I figure the bit of added weight would lower the driver's frequency of resonance a bit but i'm more concerned about the tone. I figure it would help it a lot because of the more rigid cone.

    The epoxy I used is very thin and runny (not like that 5 minute stuff from Lepage) and penetrates through the cardboard-paper i tested, and will probably do the same to the cones. I plan on covering the entire cone with the epoxy (not the surround but maybe the dustcap because its been hit and softened too).

    Thank you!


    -Kyle
     
  2. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    Once the cones are creased, they need to be replaced. Creasing occurs due to overexcursion of the driver's cone beyond that of its capability. Anything you put on them to "stiffen" them up will cause serious harm to their sonic performance. Example, epoxy will create a buzzing sound against the flexible paper, like humming into a couple of playing cards like a kazoo.

    There was an article in Bass Player Magazine concerning speaker creasing recently. Check it out, it explains everything, and concludes that the ONLY thing that can be done to restore performance is to replace or recone the entire driver.
     
  3. Nick Gann

    Nick Gann Talkbass' Tubist in Residence

    Mar 24, 2002
    Silver Spring, MD
    So you know what that means? Since you have to replace it, try it out, and if it doesn't work, then replace it. Who knows, you may find a new inexpensive treatment for old speakers!






    <--- is feeling surprisingly optimistic
     
  4. hater-ade

    hater-ade

    Feb 11, 2003
    Hey Eric, yes i know what you mean, I think you are thinking that the epoxy will just rest on the surface of the cone. The epoxy I'm thinking of using is very runny and completly penetrates the paper. I thought of that happening at first (thick epoxy will come loose and buzz on the cone, i think thats what you are trying to say) but what do you think of the stuff im going to use? Is reconing expensive? I really dont want to do that... :(
     
  5. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Actually creasing isn't usually from over excursion. It occurs when the cab is fed large signals at or near the tuned frequency of the cab. At this point the speaker cone's movement is at a minimum, but that's because the port is doing all the work. The air behind the cab effectively acts like a spring, offering enough resistance against the cone's movment to make it sit still for a while. The cone wants to move but can't because of the air resistance, and this places enormous pressure on the speaker cone. Speaker cones are designed to flex, but if the cone isn't up to the challange, is creases.

    I don't like that this stuff you're planning to use penetrates the paper. Remember cones are cupposed to flex. If you make the cone as stiff as a board, it may help against creasing at the cab's Fb, but my guess is it will put additional pressure on the suspension system at every other frequency. Further, if it makes the cone heavier, it will change the speaker's T/S parameters, throwing the cab design out of allingment.

    If you're gonna try coating the speakers, try using something that sits on the surface only and try to keep it a thin coat.
     
  6. hater-ade

    hater-ade

    Feb 11, 2003
    Thanks for all your input guys!

    I figured that since you said the cones will have to be replaced anyway i might as well try the epoxy. Well i did it to all the cones and it sounds great! The bottom end has been tightened up a bit and the cab seems to be a bit punchier. The drivers are now black because of the epoxy but thats ok, i think it looks better. The creases in the cones are now as solid as the rest of the cone. If you have a bass cab that you dont want to recone, give this a try first, just make sure you use a very thin and runny epoxy that wont add much weight to the cones. Oh yeah, the cones are now waterproof too which is nice.


    -Kyle
     
  7. Nick Gann

    Nick Gann Talkbass' Tubist in Residence

    Mar 24, 2002
    Silver Spring, MD
    See? Look at that. Like I said, just give it a try! I was the only one who supported you ;) And like I said, it looks like you discovered a new, cost effective way to repair speakers, without just replacing the whole thing. Good job :)