Switchable series to series-parallel

Discussion in 'Amps and Cabs [BG]' started by rockness monsta, Sep 27, 2022.

  1. rockness monsta

    rockness monsta

    Sep 27, 2022
    We got our bass player a 4 x10 ampeg cab with blown speakers and ordered 4 x 10" new Eminence drivers for the puppy and it should rock!

    I know how to wire in series and I know how to wire in series-parallel. However, for the life of me, I cannot visualize how to put a switch in there to easily switch between the 2!

    I have an old low-profile DPDT switch from an ampeg 4x12 that I cannibalized that I can use (should be able to handle the voltage I would think).

    I've looked and looked for a diagram and found squat. Is this doable?

  2. Are you aware that bass cabs are designed around the speakers they were intended for, and just putting in something else may yield unwanted/undesirable results?
    You can get away with this for guitars, but for bass it's a real crapshoot. You might get lucky, but I wouldn't bet the farm on it.
    What cab are you using? Is it even a bass cab at all?

    How to wire may be the least of your issues. You need to resolve the question that asks if these speakers will work in this cab before you do anything else.

    Sorry to rain on your parade here on your first day. But welcome anyway, FWIW?
    Tell us what the cab is and exactly what speakers you ordered. Someone here might be able to help you figure this out. Once that's done, we can help with the wiring. But first things first.
    Last edited: Sep 27, 2022
  3. two fingers

    two fingers Opinionated blowhard. But not mad about it. Inactive

    Feb 7, 2005
    Eastern NC USA
    What is the purpose of the switch? In other words, WHY would you wire it to be switchable in the first place?

    Welcome to TalkBass by the way!
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  4. Razman

    Razman Supporting Member

    Feb 10, 2005
    Orange Park, FL
    Lots of assumptions here. Assuming you ordered exact replacements (with the same resistance rating) then just use the original wiring and it shouldn't need any further augmentation. And welcome to TB!!

    agedhorse likes this.
  5. rockness monsta

    rockness monsta

    Sep 27, 2022
    @Old Garage-Bander: I've been lurking regarding this issue for weeks now and have read numerous posts so I do understand that the cab is designed around the drivers. I don't have the bass cab info in front of me but it is a burly-as-f**k Ampeg ported 4 x 10 that was apparently designed for Victor Wooten or something. Seems like a legit piece of gear it just had blown cones (maybe water damage??? lots of rust on the hardware too). Anyway we took it apart and cleaned it up.

    After emailing eminence and asking about direct replacement of the drivers (the originals were Eminence) we ordered 4 x Eminence Legend BP102 4 ohm speakers thinking that 4 good speakers is better than 4 blown speakers. The original drivers were not available from Eminence.

    @two fingers: right now we're planning on driving the cab with an old Ampeg tube head (can't remember the type - all gear is in the practice space). Anyway the head only has 16 ohm outputs. Our bassist wants to upgrade to something more modern (maybe a Mesa Subway or something like that) so we thought that a 4 ohm input would make the cab more versatile for more modern equipment. Of course I could wire it series for now and rewire it in the future but why do that when I can have a more complicated project/problem!!
  6. rockness monsta

    rockness monsta

    Sep 27, 2022
    @Razman: initial drivers were 4ohm wired in series-parallel giving a 4 ohm load.
    Razman likes this.
  7. When you contacted Eminence did you give them the exact make/model of the cab? Did you inform them about the intended use for bass guitar? Was there any discussion between you and Eminence about TS parameters?

    You can have the world's best cab. You can have the world's best speakers. But if that world includes bass guitar and the speakers and the cab weren't designed for each other you run the risk of having four more blown drivers.

    As far as the advice to re-wire the cab for 16 Ohms now and make changes as needed at a later date, I'd stick with that plan. At this point, it isn't certain if you'll ever make it to the next iteration of this cab. Again, first things first.

    I really do hope this can all work out for you and your bass player. A lot of others will likely be along soon with more good advice. You don't need to like what I say, but when the majority of people here who have decades of solid experience, engineering degrees, or have played bass all their lives speak up, you'll do well to have a little listen-up.
    Last edited: Sep 27, 2022
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  8. rockness monsta

    rockness monsta

    Sep 27, 2022
    Honestly we didn’t get that far in depth with Eminence. We gave them the model number of the speaker we were trying to replace and said that we were looking at the aforementioned replacement. They seem to indicate that we would be very happy with that replacement.

    What are the ramifications for a driver or cabinet mismatch? Does it just sound crappy?Of course I’m a guitarist and used to dropping random 12 inch speakers in random cabinets and having it sound pretty good. Are we potentially in or something sounding crappy?
    mikewalker likes this.
  9. Redbrangus

    Redbrangus Supporting Member

    Nov 19, 2018
    Under The X In Texas
    Then you really don't want the cab impedance to be switchable - you'd be inviting a disaster. Why do you think you want a switchable impedance cab anyway? (Choice of 4 or 16 ohms? Huh?) Since you've already purchased the speakers, just wire it series-parallel for 4 ohms (presuming the amp has a 4-ohm output impedance available) and call it a day. Welcome to TB... we're a fun bunch of killjoys, aren't we? :D

    Edit: Plus, I don't think you can get where you're trying to go with a simple DPDT switch.

    Later Edit: OK, I missed the part where the amp only has a 16-ohm output. Nevermind.... I get wanting to switch the impedance. Still, don't do it - just wire it in series for 16 ohms.
    Last edited: Sep 27, 2022
  10. Let's assume that Eminence actually provided a legit replacement speaker with the same TS specs.

    OP says the current amp they use expects a 16 ohm load, but he rightfully would like to have an amp capable of being driven by an amp expecting a 4 ohm load, which is much more common (I have never hear of an amp expecting a 16 ohm load, but that is probably just me).

    With 4 4-ohm speakers, this is doable. To get the 16 ohm load, wire them all in series. To get the 4 ohm load, wire up to pairs each in series (giving 8 ohm) then wire those pairs in parallel (resulting in 4 ohm).

    This doesn't answer the OP's question as to what that wiring would look like to switch between the two, but something could be easily be figured out. I think writing up a truth table may help, but I would probably just do trial and error (with pencil - not with a soldering iron!). Easiest would be two switches - one for each pair, that switch between series and parallel for the pair. And then have the series after that. Trickier if you want more than one switch since perhaps you'd need 4 poles.
    mikewalker likes this.
  11. I believe from your well thought out post here, that Eminence didn't have enough information to make a proper recommendation. I'm not even sure if that is something they really do without at least involving their engineering dept.

    Can you cancel the order, or return the speakers until you get this sorted out?

    Here's a link that talks about the Thiele/Small parameters. These guys did all the research on the methods used in matching speakers and cabs.

    Thiele/Small Parameters Explained. A beginner's guide.

    As far as sounding crappy, that's one possible outcome. Of more concern is that a speaker's power often may need to be derated once you put it in a cabinet. And that's just the thermal rating... how much power you can run. There are also mechanical rating which come into play and those often get derated even more due to how bass frequencies act on the motion of the voice coil. This is where you break speakers.
    If things aren't working well together mechanically, you'll never need to worry about getting to the point of letting the smoke out. In the bass world, cabs and speakers are a finely tuned system, much like a race car. It might be fast, but you still need to know it's limits.
  12. Passinwind

    Passinwind I know nothing.

    With a tube amp? It depends on exactly what model Ampeg amp it is, but potentially a blown output transformer plus associated collateral damage if you go the other way than you're proposing. If you're going the other way (amp wants 16 but sees 4) it'll merely make less power and probably sound worse to many of us than it needs to. Best to wire for the correct impedance match now and change it if and when an actual need for that arises.
    Last edited: Sep 27, 2022
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    What model amp?
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  14. [​IMG]
    from another thread on tb
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  15. mcnach and lowendrv like this.
  16. Someone put some fresher eyes on this than mine to confirm...
    But if each pair of speakers are always hardwired in parallel, doesn't that preclude this from being able to switch between 16 Ohms and 4 Ohms? I think that was what the OP mentioned? Like I said a fresh set of eyes...

    Philosophically, an impedance switch on a cab makes sense. However, operationally if leaves open the possibility that the switch ends up in the wrong position which could do a lot of expensive damage to a tube amp, and at least degrade the performance of a solid state amp. It's better IMHO to forgo the convenience for the sake of equipment safety.
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  17. NKBassman

    NKBassman Lvl 10 Nerd Supporting Member

    Jun 16, 2009
    Winnipeg, MB, Canada
    Hardwire it for 16 ohms to suit the amp you have now. If and when you eventually upgrade the amp later, then revisit the cab.
  18. Boy! I don't know where this thread is goin' to end up. But one thing for sure @rockness monsta sure started off a doozie of a couple discussions. Thank you sir.

    BTW... get your bass player signed up here. Have him introduce himself. There's a lot more than just tech stuff going on. We have a lot of fun, and everybody picks up on something new sooner or later.
  19. rickdog

    rickdog Gold Supporting Member

    Mar 27, 2010
    Good catch. It looks like this switches between series-parallel and all parallel. If the drivers were 16 ohm, this would switch between 4 ohms and 16 ohms, but with 4 ohm drivers it switches between 1 ohm and 4 ohms.
  20. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz