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Acoustic 408 problem

Discussion in 'Amps and Cabs [BG]' started by jj4001, Jan 21, 2012.

  1. jj4001


    Dec 27, 2010
    Providence, RI
    I just got a 408 today. It has the original Eminence drivers in it from '78. The bottom two speakers work fine (and sound real nice, too). The top two speakers have problems, though. They sound like there is metal vibrating against metal somewhere. I took the speakers out to inspect them and the inside of the cab. Everything looks fine except for one of the bad speakers has a dented dust cap that has an inch long split from the cone. The other bad speaker has no visible damage.

    I tried the 9 volt battery test and all four speakers moved in unison. Any more than that is beyond my expertise. :help:

    I'd very much prefer repairing the speakers to replacing them, if possible.

    Any advice or recommendations? Anyone know of a good speaker tech in the RI/MA area?
  2. I don't know any speaker repair places but I definitely recommend getting them fixed. I have a blown speaker in my 408 so I have it wired as a 2x15 at the moment (4 ohms) and it still sounds awesome. My blown speaker is non original though so I'm just looking for an original to replace it with. Great cab. I love the stock speakers. You can play it as a 2x15 like I am until you get those two fixed (unless your amp pushes more than 150w). Good luck.

    Also, my third good original speaker didn't seem like it was working at first because it wasn't getting signal from my blown speaker since it was wired after in the chain. But it passed the battery test and sounds fine on its own. Try it out on its own or wired in a 2x15 (within the cab itself) to make sure it's bad before you send it off. Though it could still be buzzing even with no physical damage. It's worth a try if you haven't done it yet.
  3. craig.p


    Sep 28, 2008
    New Hampshire
  4. jj4001


    Dec 27, 2010
    Providence, RI
    Appreciate the advice, fellas.

    My main amp is an Acoustic 320 and I bought the 408 to have the matching cab. I believe the 320 is 225 watts at 4 Ohms so I'd be a little nervous running it into the 408 as a 2x15. The cab I've been gigging with is an Acoustic 402 loaded with two 15" Peavey Black Widows and this thing is a beast on its own so at least I don't need to rush into a decision on the stock 408 drivers.

    Like I said, the two bad speakers sound like metal vibrating against metal. I don't recall any blown speakers I've come across sounding quite like this (although I have no prior experience with vintage Eminence speakers). I hope this doesn't sound like a stupid question, but does this noise typically indicate a re-cone is necessary or is there anything else that could be causing the issue?
  5. Are you sure it's BOTH of the top speakers ?

    The seperating dust cap will definitely cause some issues.
  6. jj4001


    Dec 27, 2010
    Providence, RI
    Yes, it's both of the top two speakers. I tested them individually and they both sound the same.

    I haven't tried out the bottom two speakers individually because they sounded fantastic when I took the top two out.
  7. Hmmmm........................

    Have you checked for voice coil rub (gently pushing cone in/out with hands) ?

    Possible warped frame/bad gasket (try rotating the driver and remounting) ?

    Wires or leads that go into the cone/voice coil vibrating against the back of the cone ?
  8. jj4001


    Dec 27, 2010
    Providence, RI
    The two offending speakers have been rotated and remounted. The frames aren't warped and the gaskets seem to be as they should.

    I did not check the voice coil since I'm not too experienced with this stuff. (I used to just bring things to a tech before discovering TB!) I'll be sure to try this when I get home later. What exactly should I be looking for when I try this? I would imaging rubbing against a side, correct?

    Also, I'll have to re-check the speaker wired inside. It really does sound like they could be the culprit because they aren't tied down. It sounds like the metallic sounding vibration is coming from inside the cab as opposed to the speakers. That could be my imagination, though as it seems wires as light as these wouldn't make that much noise, but again, I'm far from an expert.

    Again, thank you for taking the time to reply. I want to figure this out so I'm not throwing money at the wrong issue.
  9. Take the speaker out of the cab and lay it down face up. With both hands, gently and slowly move the cone in and allow it to return out (with fingers still touching). The cone should move freely. If there is voice coil rubbing, you will feel it as "scratchy".

    And yes, something as small as a wire touching the back of the cone while vibrating will give off a terrible sound.

    Check the interior of the cab thoroughly too. Since you say it sounds like vibrating metal INSIDE the cab, there could be loose bracing, a loose baffle, or loose hardware causing the issue.

    Try eliminating all the possible culprits before reconing/replacing the speakers. It would surely suck to replace them only to have the same thing happen because of an issue with the cab and not the speakers themselves.
  10. jj4001


    Dec 27, 2010
    Providence, RI
    OK, just checked the voice coils. The two bad speakers are scratchy and the two good speakers are not.
  11. Bummer - sounds like recone/replace time
  12. jj4001


    Dec 27, 2010
    Providence, RI

    Thanks so much for the help. Time to find a good speaker guy. Hope the pretty white dust caps can be saved!
  13. rad69cam


    Aug 31, 2007
    So Cal, USA
    Unfortunately that likely won't happen. Best of luck.
  14. jj4001


    Dec 27, 2010
    Providence, RI
    Just got off the phone with a speaker guy who has a great reputation locally. He says saving the white dust caps shouldn't be a problem. I'll be bringing the speakers to his shop tomorrow so we'll see what happens.

    If the dust caps can't be saved, I guess I'll just put them in the cab's internal chamber and put the remaining good speakers in the top and bottom, outward facing position.
  15. Muziekschuur


    May 25, 2009
    Were you able to save the white dust caps?
  16. jj4001


    Dec 27, 2010
    Providence, RI

    They came out great. I ended up mounting the re-coned speakers into the internal chamber so you can't see the dust caps without shining a light in there but they look and sound great.

    I've only gigged this 408 twice since my 2x15 is more than enough but I did record an album with it. No DI on the album at all, just a mic on one of the frontward firing, non-reconed, original speakers. Very happy with the results.

  17. jungleheat

    jungleheat Banned

    Jun 19, 2011
    I have a 408 problem too... I don't own one.


    Jan 28, 2013
    Do the speakers have the same phase (they all go out when the battery was applied) my 408 has no wiring

    Please thank you
  19. jj4001


    Dec 27, 2010
    Providence, RI
    Yes they do. The cab is sounding really good these days.
  20. Bassmec


    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    That's an utterly great cab!, I have one with the original alnico drivers and it does sound amazing.
    I think I might get buried in mine.:bassist:
    Mine was a lot better after I lagged it with 1" polyester batting.

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