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Closing an open back (guitar) cab

Discussion in 'Amps and Cabs [BG]' started by oZZma, Dec 3, 2018.


  1. oZZma

    oZZma

    Sep 13, 2018
    IT
    is it safe?
     
  2. Maybe, maybe not.

    Some speaker parameters indicate that some speakers likes an open cab, some a sealed cab, and some like ports.
    There is a lot of science involved in the construction and matching of speaker enclosures to the speakers in the enclosures.

    What do you hope to achieve by doing this?
    What is your definition of "safe"?
     
    oZZma likes this.
  3. oZZma

    oZZma

    Sep 13, 2018
    IT
    The sound seems a little bit too "airy" to me and I'd like to try if a closed cab would sound more aggressive
    I can't afford another cab right now
    Which parameters should I check? Is there any reference I could study to understand if it can be done or not? My only concern is not to break anything, that's what I mean with "safe". If it sounds like sh*t I would just switch to the previous configuration...
     
  4. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If you seal the cab, you might want to add some damping material. You can use spun polyester from a fabric store. The rule is line a ported cab, stuff a sealed cab. Just try to keep it away from the speaker cone. You don’t want to impinge uponit.

    You won’t damage anything as long as you use common sense and listen when testing.

    The hard part is figuring out how to seal the back in a non destructive, fully reversible way.
     
    Last edited: Dec 3, 2018
    dBChad and oZZma like this.
  5. voided3

    voided3 Supporting Member

    Nov 11, 2008
    Guitar speakers are pretty forgiving, but some are better suited to open back designs and others are better suited to closed back/sealed. It won't hurt anything, but it might not be an improvement, especially if the cabinet is small (smaller closed back cabs can sound "nasal" or "boxy").

    The only closed back guitar cabinet I own at the moment is a Bogner oversized 2x12 and it has so much internal volume (barely smaller than an average 4x12) that it gets the drivers closer to being in free air space while still having the big closed cab bottom end. The tradeoff for a closed back is the sound is very directional, so tilt the cab up or raise it up on a stand or chair. My Bogner has an upward-angled baffle as it's based on the Marshall 1936 design.
     
    oZZma likes this.
  6. oZZma

    oZZma

    Sep 13, 2018
    IT
    thanks a lot for the tips!! :)
    I was thinking I could use the existing screw holes of the two panels... Because of course I want a full reversible mod, just to try if it's better at zero cost.

    The cab is similar to this (mine is an Engl but the back is built the same way):

    preview.
     
    Last edited: Dec 3, 2018
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  7. oZZma

    oZZma

    Sep 13, 2018
    IT
    yes, it's small
    It's a 2x10 :/
     
  8. buldog5151bass

    buldog5151bass Kibble, milkbones, and P Basses. And redheads.

    Oct 22, 2003
    Connecticut
    I would think you could first tape on a piece of hardboard, and do a test run.
     
    slobake, beans-on-toast and oZZma like this.
  9. oZZma

    oZZma

    Sep 13, 2018
    IT
    good idea!! :thumbsup:
     
  10. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    That makes it a lot easier to cover the hole.


    A small detail, but if the spare jack is the open type, it can suck and blow air. There are dummy plugs like this one that seals the hole:

    "Neutrik NDJ dummyPLUG for Neutrik 1/4" Jacks" from www.parts-express.com!

    If when you get the panel off the jack has a black plastic body, such as a Rean type jack, it is already sealed.
     
    Last edited: Dec 3, 2018
    oZZma likes this.
  11. oZZma

    oZZma

    Sep 13, 2018
    IT
    thanks!! I'll check that :thumbsup:
     
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  12. jshinal

    jshinal

    May 28, 2013
    Raleigh, NC
    I closed a VHT cab like that. I made a 'plug' of two pieces of plywood, one long piece to fit inside, and one short piece to fit in the gap. Mine fits very tightly and the cab has a really solid low end now.

    But it's quite heavy for a 2x12. If I were to do it again, I'd just replace the entire back, and paint it.
     
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  13. BogeyBass

    BogeyBass

    Sep 14, 2010
    You could seal the back.
    Vintage 30s and majority of guitar speakers work fine in sealed or open.

    Only thing is since they have parameters designed for open and sealed back they can be little boomy in smaller spaces.

    Might not be too bad really and should cure the airy sound. Should be simple with that amp as well
     
    oZZma likes this.
  14. oZZma

    oZZma

    Sep 13, 2018
    IT
    that would be a good solution for me, mine will not be heavy in any case, it's a really small cab...
    More that the low end (I'm almost totally killing the lows on the "guitar" signal) I'd like to have a sharper, more piercing sound (I already changed the head after only a few weeks :bag: now I like the head but I'm not convinced about the cab :bag::rolleyes:)

    this one has two Celestion V10-60 Silver series speakers, but I don't know much about speakers :bag: Almost every choice I've made until now was based on "reading on the internet" and "trial and error" :bag:
     
  15. BogeyBass

    BogeyBass

    Sep 14, 2010
    The 10" have much less likely hood of being boomy in a small box. Celestion has great thing about not posting speaker TS parameters.
    Don't really matter is what it is.

    Seal it up and have a listen, would help to stuff in some poly batten sheets.

    Only damage would be the usual way to damage speakers and that all follows common sense. These speakers and many others are literally designed to be driven into distortion by the way the voice coil is hung. But just follow common sense really
     
    oZZma likes this.
  16. Are you playing bass or guitar through these speakers?
    With Bass it's a big deal to get things right, guitar, not so much.
    Open air cabs are usually not good for bass. And just closing it up doesn't usually do the trick either.

    Google "Theile/Small parameters". Then Google open back vs sealed cabs and see what that tells you.

    The thing is, just closing the back doesn't mean the cab is sealed. I classify it more as being leaky. So just slapping a piece of wood on the back isn't really the way to go.

    I don't know where you are getting your information, but I don't think closing a cab will take it from airy sounding to aggressive. They do make pedals for that, though I know you're short on cash right now.

    I can't guarantee that you won't break anything. If you do this, start out at very low volume and work up gradually, at the point where your speakers sound like :poop:, back off.
     
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  17. oZZma

    oZZma

    Sep 13, 2018
    IT
    I play bass... But as a pseudo-guitar With that cab I play bass through a guitar head with almost zero lows in the attempt to have a guitar-like sound (I'm in a duo and we don't have a guitar, that's why... Not just mad or masochist :D )
    As for pedals, I used a Rat but that made not much difference as for the "airy" sound :sorry:(IMO the head alone with tons of gain sounds more aggressive...)
     
  18. mexicanyella

    mexicanyella

    Feb 16, 2015
    Have you tried your pseudo-guitar approach through the amp without closing the back?

    A few things to consider:

    If your duo is a low-volume act, maybe you don't need to change anything. I played guitar in a recording project once where the bassist used a Fender Jazz bass into a silverface Fender Deluxe Reverb amp...a 22-watt open-backed 1 x 12 guitar amp. He was just overdubbing his part into a microphone, not competing with an ensemble, so he was able to keep the volume low, but it sounded warm, full and fantastic. If you're not turning it up loud, maybe you can get away with your amp as is.

    But putting bass frequencies into undamped guitar speakers is going to give you a narrow margin of error. Listen carefully for speaker distress and be ready to back off.


    Closing the back of the cabinet will stop at least some of the low-frequency cancellation, in which the sound off the back of the speaker cancels some sound off the front of the speaker. But it won't help much to protect the guitar speakers from trying to reproduce bass signals. You're still using a speaker without enough cone and voice coil "travel" ("Xmax") to take much bass-frequency punishment. If you blow your speaker, you'd have been better off just hunting down a cheap used bass cab rather than having to buy lumber and replace the speaker anyway.
     
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  19. ZGotts

    ZGotts

    Sep 17, 2007
    Virginia
    WinISD is a free program, find the Thiele-Small parameters for your speaker, take some measurements on the box dimensions. I think with that big of an opening you could assume existing condition as Infinite Baffle, and then compare against sealed. If you're above the red line for your given wattage - you're in danger of blowing it.

    That said, I'd say what will happen to your tone will not be as easy to predict.
     
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  20. micguy

    micguy

    May 17, 2011
    Closing the back on an open guitar cabinet won’t cause the earth to self destruct - so long as you listen for signs of distress, it’s relatively “safe”.

    It will likely give you some more low end. It is unlikely, however, to be anywhere near as good for bass guitar as a well made bass cabinet designed for the purpose.
     
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