Switching Impedance?

Discussion in 'Amps and Cabs [BG]' started by thehurlatron, Jan 6, 2005.

  1. One of the cabs I currently use is a EA VL-210.(500w@8ohms)
    Is there any simple way of changing the impedance to 4ohms?
    Some sort of "dummy load"?
    I see accugroove has their "accuswitch" on their cabs. Is this something I can add to my EA? It would be great to be able to switch back and forth for different rigs.
  2. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    accugrove's impedance selector is top secret technology. there really isnt a way to make that a 4 ohm cabinet. Your 8 ohm 210 is either two 16 ohm tens wired in parallel, or two 4 ohm speaker wired in series.
  3. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Well, there are ways. You could wire up an 8 ohm Weber MASS inside the cab with a switch, and wire it to give you either 8 ohms (just the speakers) or 4 ohms (speakers and MASS) total. But using the MASS would mean that the rig wouldn't be any louder at 4 ohms than at 8 ohms, since the MASS would be getting half the power.
  4. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA

    Exactly. The additional power would simply be dissipated as heat from the resistor, not directed to the speakers.

    So, yes you can get twice the water from the pipe, but you'll spill half on the ground.

    I do know a few guitarists who have rigged devices like this because they preferred the way that their tube amp sounded with a particular load and were not really looking for additional volume, but rather looking to change the behavior of the tubes and thus the tone.

    With a SS bass amp, it has no value.
  5. HMMM.... :( Well, I guess I'll just be running at 2.6Ohms??

    EA VL-210(500w/8ohms) + Ampeg BXT210M(400w/4ohms)

    In this case, are both cabs getting equal power, or is one of them sucking up more juice? DB750(mono) 975@2, 750@4
  6. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    Well, you certainly could do it with a transformer, but the downside is that the transformer would have an effect on the sound and some amount of power would be wasted in the transformer. Unlike the Weber mass solution, a transformer would result in a cab getting louder at 4 ohms.
  7. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    For the sake of argument, the 4 ohm Ampeg cabinet would receive twice as much power as the 8 ohm EA.

    If the EA is 3 dB more efficient, they'd produce the same "volume".

    Since the cabinets are not identical, only a sound check will let you know what they're going to sound like together.
  8. Yes, some companies even sell such transformers intended to change a cabs impedance.
  9. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    It could be done with loudspeaker drivers that have multiple, split, or tapped voice coils.

  10. The Ampeg is 99db the EA I believe is 101db (both 1w@1m)

    Would this then be "pretty close"?
    I get so confused with all this stuff, but I'm very interested. Is there a post or a book, or page, that explains reletively simply about all kinds of speaker lingo and amplifier lingo?
  11. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    this thread is a start...............click here

  12. Kudos on that thread!! Thanks for laying it out there, I have a better basic understanding of the terms and such now. :hyper:
  13. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    If I'm doing the math right, and assuming the amp puts out 800 watts into 2.7 ohms...

    SPL = Sensitivity dB + 10 log (Power in - 1) dB

    For the Ampeg 99 dB + 10 log 532 = 126.3 dB

    For the EA 101 dB + 10 log 266 = 125.2 dB

    So yes, they'd be very, very close.

    If I'm doing the math wrong, PLEASE correct me!!! I've offered this up in two threads today and would need to fix it...