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Cabs with switchable Impedances

Discussion in 'Amps and Cabs [BG]' started by nicnoyd, Apr 11, 2003.


  1. nicnoyd

    nicnoyd Guest

    Feb 24, 2003
    Hey Guys...!

    Lately,I tried out a Tech 115 DCT and noticed that
    Impedances can be changed on these Cabs (2,4 or 8 Ohms)...
    BUT only on their 15" and 18" Cabs...

    For those that´d like to see them - check here !

    Now my Question is : Do you know other Brands
    whose Cabs have this Feature?
    Please let me know...
     
  2. i know mesa guitar cabs are like that, dont know about the bass ones though.
     
  3. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    Any cabinet with PAIRS of speakers (i.e. 2, 4, 6, 8, etc.) can be wired for multiple impedances but having a switch to select the impedance is rare as a factory feature, simple to add, though.

    Many Marshall cabs have impedance switches.
     
  4. Also, if you have drivers with dual voice coils which can be wired separately you can wire those either in series or in parallel (bassically as if you had two drivers)
     
  5. geshel

    geshel

    Oct 2, 2001
    Seattle
    I don't quite understand what they're claiming. As far as I know, you can't really switch a single speaker between 2, 4, 8 ohms. Unless it has a very complicated tapped-coil voice coil, which I seriously doubt.

    My guess is that they mean: you can purchase them as 2, 4, or 8-ohm cabinets.

    A multi-driver or dual-voice-coil single driver box may have an impedance switch, but usually one of the values must be 4x the other for instance, 4ohm or 16ohm. As others have noted, this is the difference between parallel and series.
     
  6. No, the Tech cabs really are switchable (only the 3-Way 1x18+1x10+Tweeter and the 2x15 cabs)
     
  7. geshel

    geshel

    Oct 2, 2001
    Seattle
    The website lists others as switchable too. (for example the 115t and 115dct that nicnoyd mentioned in the first place).

    Do you have any idea how difficult it would be to make a 1x18 + 1x10 + tweeter cab that was switchable from 2, 4, or 8 ohms?

    Or maybe I'm stuck in a rut, and they have some new method (an internal transformer??) that lets them do it.
     
  8. ok, I missed those two but all other cabs say something like 4 or 8 Ohm (no mention of switching), and as I said and you also said yourself tapped voicecoils would be a possibility, but you are right fore that 118 the wiring must be extremely complex if it is done that way
     
  9. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I built a home hi fi sub for a friend recently. He turned up with this single 12" driver but it had a double magnet and 2 voice coils. It was rated 4 ohms but to get that we could only wire one magnet and one voice coil. A series connection would have yielded 2 ohms and a parallel connection 8.

    Maybe these cabs use a similar driver, but add a switch????
     
  10. geshel

    geshel

    Oct 2, 2001
    Seattle
    You've got that backwards, series would be 8, parallel 2.

    I doubt it - then the 4 ohm option would have only half the power handling. And probably a different response too.
     
  11. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    OOPS!... that's what I meant to type:) You get the jist though.
     
  12. ttyR2

    ttyR2

    Feb 23, 2003
    Athena, OR
    older Ampeg V4B cabinet runs 2 15" EV speakers and has a 4/16 ohm switch on the back. Both woofers are 8 ohm. Pretty simple setup actually. Would be easy to replicate.
     
  13. lo-end

    lo-end

    Jun 15, 2001
    PA
    Mines 8 ohms only
     
  14. nicnoyd

    nicnoyd Guest

    Feb 24, 2003
    hey guys, sorry that i couldn´t reply earlier...i was out workin´...

    But now to the Tech again...

    Petebass,you got it right, they use double magnets
    and voice coils to achieve "switchability"!
    2 Ohms would be both coils in parallel, 4 Ohms = only one coil in use and 8 Ohms would be both in series...
    the 400 Wrms of the 115 DCT, for example, double up to 800 when the Cab is used in 2-,or 8Ohm-Mode...
    And this this Thing can actually handle some power - I had it hooked to my QSC RMX2450...
    And it´s ****in´ lightwheight... you can lift it with one hand...

    It´s a damn good standalone, but under a 4x10", it´s crushin´!
    Too bad the one I tested had a broken Tweeter,
    otherwise it would be here by my side!!!
     
  15. nicnoyd

    nicnoyd Guest

    Feb 24, 2003
    To Erik:

    Just like lo-end said, the Mesa Bass Cabs are not switchable...
    I have a Mesa 4x10 - 8 Ohms...!
     
  16. geshel

    geshel

    Oct 2, 2001
    Seattle
    Huh! Well I guess that's not too crazy then. A little weird perhaps. :) And, I guess for the 118 they have the 10" wired up the same way? I'm guessing they don't use DVC tweeters :D so that means when adjusting the impedance you'd need to give the tweeter level a little tweak to compensate (since it'll always be the same (4?) ohms) - but that's not too big a deal.
     
  17. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Add this to the list of brands I'd love to try but can't because they're not available in Australia :(

    Wierd can be good. Everyone thought an 8x10 cab was wierd when it first came out and look where that took us. Good to see someone trying something different IMO.

    Does anyone know what brand of drivers Tech uses?
     
  18. You can use resistors to modify the impedence of cabs. This is however, a bit flaky, and can generate heat. I've heard about this being done before, and it's probably how they do this.
     
  19. AFAIK Tech uses Tech drivers ;)

    Wierd cabs, hmmm... Tech also has a 3Ohm 6x12
     
  20. nicnoyd

    nicnoyd Guest

    Feb 24, 2003
    DavyO: Actually, the double voice coils they use to make cabs switchable work like a heat sink, because
    the heat can spread more than with a normal driver...

    Also,they use neodym magnets,but that´s only the reason for the Lightweight Factor,I guess...