Bass with guitar amp

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SunDevilSunDevil Frets: 511
No doubt this has been covered before, so apologies!

I’m thinking of getting a bass - if I use a guitar valve amp with a Power Station, does this pose any risk to the speakers?

..I’m guessing it’s a ‘no’ but it might not have big enough coupling caps to do the bass justice?

So..

If I get a 300w tranny bass amp and play it at home volumes through a cab with say, 2 creambacks (either semi or closed back) am I taking a risk?

Finally, what about the tranny amp with a bass speaker in a semi open guitar cab?

cheers

Baz
The answer was never 42 - it's 1/137 (..ish)
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Comments

  • ecc83ecc83 Frets: 1589
    You don't really want to put 300W* of bass through anything but a proper bass speaker unit of adequate power rating (and take THOSE with a handful of salt!) . I know the early bass cabs were 4X12 guitar speakers of about 30W rating each and a 50W valve amp but I don't think they lasted that long!

    The coupling caps in most valve amps are if anything TOO big as a rule, doubt that will bother you and things should be ok with an attenuator.

    *Yes, I KNOW you said "home volumes" but ***t'appen.

    Dave.
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  • ICBMICBM Frets: 71950
    It will be fine as long as you’re sensible. Home volume even for bass is no more than a few watts. It will probably sound OK too, at low volume the EQ should be able to overcome the natural voicing limitations.

    Whether a 300W amp is a risk to a 2x12” with Creambacks at all also depends on the cab impedance - the 300W will be at 4 ohms, and if the cab is 16 ohms the amp will only be capable of around 100W into it anyway.

    It will also be safe with a bass speaker in an open-back cab unless you’re really thrashing it. Something like an Eminence Delta 12A is rated for 400W, and you won’t even come close to stressing that at any volume you can be in the room with.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • SunDevilSunDevil Frets: 511
    Thanks Gents (as ever!)

    The answer was never 42 - it's 1/137 (..ish)
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  • SunDevilSunDevil Frets: 511
    Dust off..

    I trust the advice of this forum more than that of someone with a sales angle, but let me just play back what I was told this morning, when I spoke to a speaker vendor

    I said I was planning on putting a single 12" bass speaker into a 212 which a guitar speaker in the other slot, but with only the bass speaker wired up. The cab is convertible one with 3 screw on back pieces. All for home volumes

     I was told that the bass speaker wouldn't like not being in an air tight enclosure and would 'chuff' and that the non-wired guitar speaker would act as a dampener 

    I'm sure there's a mix of fact and up-selling in this

    Options are:
    1) As above - single bass driver in a closed back (but not air tight) 212 with a guitar speaker effectively acting as a baffle
    2) Add a second bass driver to the cab and wire them both up
    3) As above but get single piece of ply to make a solid back panel for the cab
    4) Double my spend on whole new cab - likely a 210

    I want a good tone, but this is only for home playing - what to do?


    Baz

    The answer was never 42 - it's 1/137 (..ish)
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  • ecc83ecc83 Frets: 1589
    A second, unwired driver in a fairly airtight cab will act as a "drone cone" as used in some hi fi and monitor speakers. This application is much the same as a ported enclosure but has some extra benefits. However a guitar speaker will have a much higher resonance frequency than the bass driver and the result will probably honk like a monster goose on steroids!  Might be interesting though and you could try shorting the voice coil tags. The speaker will then be very well damped and might..."Ah say might mind you!" Sound quite good.

    Whatever you try do not think a speaker is a "baffle", the cone is virtually transparent to sound i.e. might as well have a hole!

    Dave.


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  • ICBMICBM Frets: 71950
    edited December 2018
    All these things would be issues for a proper bass cab at 'real' volume, but at the sort of volumes you're talking about, none of it matters. It will sound fine either open or closed-back, just try it either way and see which you prefer. My guess is that the cab may vibrate a bit too much with it closed, but it depends on the fit on the back panels.

    If the back is closed, yes the unconnected guitar speaker will try to act as a 'passive radiator' - meaning that the air pressure inside the cab will push the cone, and make it move in the opposite direction to the bass speaker. This may or may not sound good - the concept is deliberately used in some hi-fi speakers, but with a tuned enclosure so the same rules don't apply - again, try it and see. If the cab is open it won't do much, almost all the air pressure will go straight out through the back.

    Adding a second bass driver would be better, but it's a lot more money for very little advantage and the cab may still not be ideal for bass - and it would defeat the purpose to some extent as it will increase the volume.

    In fact, if the cab has dual input jacks you could easily wire the guitar speaker to the other one and have a dual-purpose cab.

    Edit - aha, Dave posted something similar while I was still typing away :). I'd forgotten about shorting the unused speaker to stiffen it too.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • SunDevilSunDevil Frets: 511
    Thanks Dave - especially like the concept of the monster goose on steroids :-)

    So that rules out option 1 ..will 2 or 3 work?
    The answer was never 42 - it's 1/137 (..ish)
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  • ICBMICBM Frets: 71950
    SunDevil said:

    So that rules out option 1 ..
    No, it doesn't - try it and see first, since it's the easiest and least cost initially.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • what is your budget for option 4?? there are plenty of used bass cabs available for very little money..


    My trading feedback

    is it crazy how saying sentences backwards creates backwards sentences saying how crazy it is?

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  • SunDevilSunDevil Frets: 511
    Thanks all - @bloodandtears - not really wanting to go down this route if I can avoid it for space reasons

    @ecc83 @ICBM - shorting the unused speaker - is this as simple as linking the pos and negative leads?
    The answer was never 42 - it's 1/137 (..ish)
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  • ICBMICBM Frets: 71950
    SunDevil said:

    @ecc83 @ICBM - shorting the unused speaker - is this as simple as linking the pos and negative leads?
    Yes.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • SunDevilSunDevil Frets: 511
    Quick update, Eminence Alpha 12” fitted into semi open cab with a G12H55 sat next to it, unwired

    Cheap Vintage Jazz bass into EZG50 with everything at noon through a Rock Crusher

    I am a happy chap - I’m sure a proper bassist would scoff, but it’s enough to keep me happy for a while.

    So the dedicated valve bass amp goes on hold and I’ll get a bass DI with a headphone jack until I get up to speed - thinking the Ampeg one, but open to suggestions?






    The answer was never 42 - it's 1/137 (..ish)
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  • SunDevilSunDevil Frets: 511
    Okey doke..

    So now I’m getting a bit more enthusiastic with my bass playing (same amp - EZG50, same settings - everything at noon, but I’m  just hitting harder) I’m starting to get some slightly unpleasant break up on open E strings

    I currently have the middle 4” panel on the back of the cab open. Cab volume is conservatively 70l

    According to the spec sheet, the  Eminence Alpha 12” wants a closed cab up to 22l and an open configuration between 70 and 125l, so best I can tell, it should work as is

    So I guess the question is whether the distortion coming from the amp or the speaker not being supported properly?

    I’ve totally lost myself in Thiele parameter calculations and came out with needing 55l for a closed cab with 1 driver (..no idea how this and the 22l that Eminence state relate, or Whether I’m going around in circles very badly?)

    Tomorrow I’ll try the cab closed back with the unwired driver shorted and hope this solves it, otherwise I think I’m getting a bass cab or small bass combo

    Baz
    The answer was never 42 - it's 1/137 (..ish)
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