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creating a 4 ohm load with two 4 ohm speakers

Discussion in 'Amps and Cabs [BG]' started by johnvice, Dec 10, 2004.


  1. johnvice

    johnvice

    Sep 7, 2004
    I want to use a pair of 4 ohm speakers cabinets from my amp that has a minimum 4 ohm load. How do I do this without frying my amp?
     
  2. MJ5150

    MJ5150 Terrific Twister

    Apr 12, 2001
    Lacey, WA
    unless you have a two channel amp, you can't do it.

    -Mike
     
  3. 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
    Leave one of them unconnected. ;)
     
  4. Rickenbackerman

    Rickenbackerman

    Apr 17, 2001
    Laurel MD
    Wire them in series.

    4 + 4 = 8
     
  5. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Find a transformer company that will make you a huge, heavy and probably extremely expensive 2 ohm to 4 ohm impedance matching transformer.

    -or-

    Connect one 4 ohm cabinet to your existing amp and buy a power amp that can be used to drive the second 4 ohm cabinet.
     
  6. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    Jump up and down and yell profanities?

    Well, I didn't say it was a good idea.

    Sorry, you are out of luck. You can't combine two 4 ohm cabs and end up with a 4 ohm load. The can be either 2 ohms, 8 ohms, or stereo 4 ohm loads.
     
  7. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    best freaking thing i've read in a while............lmao

    but seriously, you can't do it. for soem good info on ohms, (if i do say so myself), click here
     
  8. Doesn't Mark Wright at Accugroove have a cabinet that will do this?
     
  9. Tez

    Tez

    Jan 24, 2004
    Australia
    You Have to create an 8 ohm dummy load I do this by using an electric jug element (the exposed element type) they have a 16 ohm resistance) mount it in a box and tap off in the centre of the heating coil . that gives an 8 ohm resistor ,then wire in parrallel to the 2 speakers that you wire in series. 4 plus 4 in series = 8 8+8 in parallel = 4. I have one made up in a plastic box that I keep in by gig box in case I need a dummy load to test an amp head or to ballance my P A foldback if I dont use all my speakers at a gig .

    I can post photos later if you want .
     
  10. Tez

    Tez

    Jan 24, 2004
    Australia
    By the way I have a Ber%#@r 120 watt that states it has a 4ohm min load and I have been using that at 2 ohm without problems (So Far)
     
  11. IvanMike

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

    Nov 10, 2002
    Middletown CT, USA
    oh. it'll work...............................but for how long????????
    besides you void your warranty that way. and you could even start a nifty fire too!!
     
  12. Tez

    Tez

    Jan 24, 2004
    Australia
    I dont crank the amp and i pull most of the tone settings way down so I dont push that much power through the head I just use 2 twelves to move more air
     
  13. Tim__x

    Tim__x

    Aug 13, 2002
    Alberta, Canada
    Why in the world would you ever do that? All the extra power put out by your amp at 4 ohms will go into the heater element, it's a waste of power, time and work, not to mention being a fire hazard.
     
  14. Joe P

    Joe P

    Jul 15, 2004
    Milwaukee, WI
    Hey - that's not a bad Idea, I can tell you.

    I've been in the transformer buisness for over ten years (QA tech), and it's quite a reasonable thing to do. There's a type called an 'autotransformer' that has very tight, accurate and efficient coupling, and a 500W (we'd say "0.5KVA") unit would not be that huge!

    Another thing that's pretty cool about them is that while you're at it, a simple little tertiary winding could be fairly easily designed-in that would give you a high-quality, fully-isolated, true transformer-balanced direct out.

    An autotransformer that's been properly designed around a Metglass C-core would have extremely wide frequency response, but I bet that common M6-type 'audio grade' transformer steel in regular off-the-shelf E-I laminations would be fine. A smart designer could probably even design the taps ratios to be a one-does-everything - 2 to 4, 8, or 16; 4 to 2, 8, or 16; 8 to 2, 4, or 16; and 16 to 2, 4, or 8. One thing that makes this application pretty easy is that an amp has a low output impedance; it's high-Z and high-voltage sources that get more tricky. This would definately be easier to design and manufacture than a tube amp's output transformer (high voltage AND high-Z plate circuit)!

    What we're talking about is a fairly straightforward design, but they have magnetic FEA programs now that allow transformers to be designed for applications that weren't even possible before.

    I'd also like to see a TRANSISTOR amp with an output transformer!

    Joe
     
  15. hands5

    hands5

    Jan 15, 2003
    good 'ol USA/Tampa fla.
    none
    I don't tink this is correct either.
     
  16. Rickenbackerman

    Rickenbackerman

    Apr 17, 2001
    Laurel MD
    I've got a broken McIntosh MC2100 on my bench that has one - full power (210w) at 8, 4, and 2 ohms. Pretty cool! The thing weighs 60lbs, though.

    I think somebody famous used a few of these as bass amps - anybody know who?
     
  17. Rickenbackerman

    Rickenbackerman

    Apr 17, 2001
    Laurel MD
    It's correct if he wants to run an 8 ohm load on his amp. It won't make full power, but it won't fry the amp, either.
     
  18. I'm in the process of designing a single-ended MOSFET hifi amplifier using an OT. Or more accurately 'amplifiers.' The single-ended circuits will power the mid and tweeter of an active loudspeaker. In this case, I'm using fairly small transformers because I don't need strong low end response and I don't need much power. Preliminary prototyping shows promise...
     
  19. Well I tink it is, but it's a series connection, which needs special cables to make it work. Basically the plus side of the speaker cable goes to + on cab 1 and it's - goes to + on cab 2, and the - on cab 2 goes to the - on the amp. Make sense?

    It's the way they make 4 ohm cabs with four 4 ohm woofers. two sets of two series wired speakers wired in parallel.
     
  20. bassclef112

    bassclef112 Supporting Member

    Sep 2, 2003
    New York City, NY
    Get one of these:

    http://www.sherlockaudio.ca/

    "The MODEL FOUR for mono guitar or bass amp owners who want to run maximum four speaker cabinets - great for building a wall of sound!"

    "Your amp will see a load of about 6.5ohms"

    This is a direct quote from the maker of these regarding hooking in only (2) 4 ohm cabinets.