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Marshall Super Bass with open 2x12" cabs - how to improve?

Discussion in 'Amps [BG]' started by MBlom, Oct 18, 2012.

  1. MBlom

    MBlom

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    I bought a Super Bass a long time ago and when searching for cabinets I found an ad for two old PAs with 12" Greenbacks. Without knowing much about cabinets I thought these looked good and got them. Put two Vintage 30s in one of them so it could handle the output of the amp and for years I was quite satisfied with using just that one cabinet. But now I feel I miss more solid low frequencies (no ****! I know...). Thing is though, I really like those cabinets. Both the look of them and that they're easy to carry and transport. I don't play with the same people all the time so they're mostly at home and then I put the amp and a cab in my car when going to rehearse or jam.

    What I'd need some help with is to get the most out of these cabinets. I've thought about putting a piece of wood at the back of a cabinet to make them closed instead open but I have no idea whether this will make any improvement or maybe even making it worse. Another idea is to just get another set of high wattage 12"-speakers and use both cabinets. Maybe that would give me the extra boost that I need instead of modifying the cabinets. The last option is to buy new cabs altogether, but I really like the ones I have.

    Is there anyway you think I could improve the sound by using what I already have?




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  2. CL400Peavey

    CL400Peavey Supporting Member

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    Sell those guitar cabs., buy a bass cab.
  3. MBlom

    MBlom

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    Thanks. That really helped.
  4. PlungerModerno

    PlungerModerno

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    I think you'd be ruining two good guitar cabs to make two probably ineffective bass cabs.

    With the dosh you'd spend replacing the drivers you could likely pick up an OK used bass cab - or build one from scratch!

    It's my understanding that guitar cabs are generally all wrong in a number of areas - eg. volume, porting, bracing etc. making them a lot of work in mods to make suitable.

    I'm no expert though. :bag:
  5. Jazz Ad

    Jazz Ad Mi la ré sol Gold Supporting Member

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    I disagree with the general sentiment so far.
    These Celestions have well known specs.
    With minimal woodworking it should be easy enough to transform these into a decently designed pair of ported 1x12". Small speakers in big cabs can do wonders.
  6. Hopkins

    Hopkins Supporting Member

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    Its not the answer you wanted to hear, but it is the correct answer.

    You can spend all kinds of time, money, and effort trying to make those two guitar cabs work for bass, and in the end you would still be better off with a cheap bass cab.
  7. PlungerModerno

    PlungerModerno

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    Interesting - it may require a fair bit of tweaking but could it work?
    How best to do it would be far outside my experience.
    As I understand it there's a pretty essential early decision to be made - sealed or ported - eg. ports and port tuning. If you want loud lows you'll have to ditch the open back!
    Then there's bracing and dampening - which you'll likely want some more of . . . I've heard it's worth doing right.
  8. MBlom

    MBlom

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    Thanks for the input. (the lack of such was why I was a little sarcastic in the first reply). I'm not set on making any big cistly adjustments as some seem to think. I definitely don't want to do any sawing in the cabinets, my idea was just to replace the two backside panels with one large to make the open box closed. That wouldn't cost much and it could be undone without even an extra screwhole (?). However, if this would improve bass response is beyond my knowledge and therefore I ask you guys.

    Buying a new pair of V30's won't cost me much either and if that would give more boost (by being able to use both cabinets) it would surely be enough.

    So, those are my starting points. Not costly, complicated modifications.

    I'm not that unsatisfied with the sound I just wanted to know if there was someway of improving it. I mean, I'm not in Helmet, NIN or whatever and need that perfect well defined bass response. I just enjoy playing and think more about what and how I play, not mainly on how it sounds. Now, someone will probably think "with a good sound you play better because this and that..." and you might be correct. But that's not the way I want to go.
  9. MBlom

    MBlom

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    You mean, take out both Greenbacks and put a V30 in each cabinet? With closed backs then, I guess.
  10. Johnny DeVille

    Johnny DeVille

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    I vote for a used Bass cab. and Keep those PA speakers. I have never seen any in person.

    If you did add a new back panel to close it, I am pretty sure you would need to add at least 2 screws per side to prevent vibration.
  11. CL400Peavey

    CL400Peavey Supporting Member

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    As good as the speakers you have may be, they are not bass specific. They are guitar drivers. Depending on your tonal goal they may do just fine, but for the majority of bassists out there they will suck hard as far as volume/power handling goes and with not have the lows that most bassists want. That said you have a killer modular guitar rig that a lot of players would kill for.

    Sorry for my short initial reply, but it is the right answer. They need a signature tag for when people post from their phone.
  12. Jazz Ad

    Jazz Ad Mi la ré sol Gold Supporting Member

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    It's worth a study, if you want to keep them.
  13. RED J

    RED J Half Hip, Half Hick Supporting Member

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    I'm going to answer your request for an opinion by saying that you could try a closed back and port them for maximum results, such as they are. You can do anything you want, they're yours, just don't expect stellar results.

    On the other hand, they really are not designed for the purpose you intend, kinda like this picture.




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  14. MBlom

    MBlom

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    I really don't expect sterling sound. For that I know they won't deliver. Just thought I'd make an improvement with what I've got.
  15. MBlom

    MBlom

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    If I choose to make a back panel for a closed cabinet, should it have a hole in it for air transport (bass reflex or whatever it's called) and should there be any damping material within?
  16. dukeorock

    dukeorock Gold Supporting Member

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    Disclosures:
    Authorized fEARful/FEARLESS/greenboy designs builder
    It's a little trickier than just that, but the short answer to both questions is yes :)

    I gotta say, those cabs are so cool looking and so rarely seen, I'd also be afraid to mess with them.
  17. will33

    will33

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    Disclosures:
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    Sealing the backs would at least allow you to push them farther/dial in more bass before damage occurs. Seal the backs and add some stuffing.

    If you're thinking about buying different speakers, I'd at least make them more bass oriented speakers and not just other guitar speakers. Eminence Beta 12's woukd work in the sealed boxes, are affordable, and would add in some bottom that's missing from the guitar speakers.

    If you like the topend from the guitar speakers, you could leave one or two in the system and put a capacitor in front of them to starts rolling the bass out of them up around 300-400hz. That would again allow you to dial in more lows, push things louder before damage.

    All IMO there. Done right, any of those mods would be reversible.
  18. PlungerModerno

    PlungerModerno

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    I think it depends . . . You have three types as I understand it: Sealed, ported, and openbacked (which is not really used for bass cabs).

    If you seal the cab completely you still have to worry about the volume IIRC - You definitely need to consider the internal volume and the port (hole) size if you go for a ported cab design - and a ported design is, I understand, the best way to get a satisfying low end according to most people. IIRC you have to 'tune' the internal volume and port size to get the most even response and volume out of given drivers.

    If you go with two 12" drivers per cab or 1 12" driver per cab you'll need to 'take stock' on the existing cab construction. IF it's a sturdy well braced PA cab the cab might work great - if it's a guitar cab it might be very unsuitable - I've heard they aren't nearly rigid enough in a lot of cases.

    My advice is to read up on cab design - if you want to experiment, you might get it right first try, but more than likely you'll get little improvement - and may make it worse.
    If cash is available a used bass cab is an easier solution. But if more bracing reinforcement isn't needed, dampening is pretty cheap and you do say the drivers aren't outside your budget: Dig a little deeper, take some measurements of internal dimensions, figure out some amp tuning software and gauge the level of tweaks needed. How? I'm not sure.
    This could be a cool project but like CL400Peavey said, you might find it far better to start from scratch or trade your cabs for a purpose built bass cab or cabs.
  19. rpsands

    rpsands

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    I doubt that amp can push enough wattage down low to damage the speakers. most of those guitarish tube heads have a low end rolloff built into the transformer design from what I've seen.

    Played bass through guitar combos enough and not seen a lot of blown speakers.
  20. will33

    will33

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    Good points here.

    A lot of guitar speakers do have high xlim, made to be overdriven. But still, trying to dial lows in an openback cab can send them flying too far.

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