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How can I use a 2 ohm cab?

Discussion in 'Amps and Cabs [BG]' started by BassBaron, Jul 31, 2001.


  1. BassBaron

    BassBaron

    Jul 20, 2001
    San Jose, CA
    I have an Acoustic 4x15 (that's right: two forward firing and an offset clamshell) but the cab is 2 ohm because of it's 4 parallel 8 ohm speakers. Is there a way I can rewire it to give me 4ohms? I am afraid it might fry my Hartke 3500 head at 2 ohms. Or is this cab even worth it at all? Does anyone have any experience with Acoustic gear or this cab in particular? (I think it is the 401 model, but don't quote me, I don't have it in front of me;~)

    thanks
     
  2. You could try adding a resistor to the cab, but i don't know if it will work..
     
  3. Paul A

    Paul A

    Dec 13, 1999
    Hertfordshire U.K!
    "Depending on the individual impedence of the speakers, a rewire may be possible, but YOU PROBABLY DON'T WANT TO DO IT!!! Assuming the speakers are eight ohms, you could rewire the cab to an eight ohm load, but the phase problems introduced by doing so (series wiring=very BAD for bass sound)"


    Why?........Surely all you have to do is make sure that the speakers are in phase?
    All you need is a 9 volt battery to check the polarity of the connections.
     
  4. This is pure hysteria. :D

    Nearly all 4x cabs are wired series-parallel unless the manufacturer makes a deal specifically to use 32 ohm drivers.

    Wire two pair in series (16 ohms total)
    Wire the two pair in parallel (8 ohm total load)

    Use a 1.5 to 9v battery to check phasing. Standard phasing is when the cones move forward (away from the magnet) when you make the circuit. If you have any drivers out of phase reverse the leads on that particular driver until all 4 drivers move the same direction.

    Incorrect phasing is very bad for bass, but series wiring is not. There are numerous visual examples out on the net if you need to see a picture. Do a Yahoo search for SERIES WIRING SPEAKERS and you will get pages of it.
     
  5. IMO, this is wishful thinking more than fact. I invite you to prove otherwise, and state your sources.

    Electron flow travels in wire at the rate of 1 nanosecond per 12 inches, approximately. The amount of mechanical delay alone in speaker moving assemblies introduces delays that are many orders of magnitude longer than electrical signal propagation.
     
  6. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Sorry, but this is simply false. Many, if not most, of the 8 ohm 4-10s out there use series-parallel wiring. Carvin, Eden, and SWR, for example.
     
  7. I can get flamed at work and get paid for it. You can rant at the wind now. End of discussion.
     
  8. Now if there's something you'd like to discuss, rather than make statements you are OH SO SURE about, then we'll talk. If you already know everything, there's no discussion possible. Why bother? What are you doing here?

    Doesn't it even slightly cross your mind, that, one way or another, you might be a little bit wrong, somewhere?????????

    Sarcasm intended.
     
  9. Luis Fabara

    Luis Fabara

    Aug 13, 2000
    Ecuador (South America)
    Audio Pro - Ecuador
    I believe Psycho has it right on the Phase Issue..
    There is a delay on the phase, specifically in the last speaker of the chain.
    Bass is decreased in a small ammount.
    Althought the delay is minimal to count as Phase Inversion (depends on the frequency), there is a delay in the signal wich is altering the sound.

    Instead of hearing Ego-Arguments, why Cant we just (I just read) post our Points on this issue.

    My question now is..
    If all of this affects the tone so much.
    Why do many manufacuturers use 8ohm Drivers and wire them Series-Parallel to get 8 Ohms?
    Instead of getting 32Ohm Drivers or 16 Ohm Drivers and wire them parallel (The Ampeg way)?
    Cost Effective?
     
  10. Just read all this -

    My take on series connection causing delay on the last speaker is that it is false. The are no appreciable capacitors to ground distributed between speakers, so the current that is moving through the first speaker coil is the EXACT same current moving through the last speaker coil. And since current causes the magnetic force, the magnetic forces are the same. Simple as that. We're not talking transmission lines here.

    Now, if there are any other factors thrown into the equation, there MAY be a slight difference in "tone" from series to parallel (but I don't think so). My Ampeg B25B cab is series wired, always has been.

    I haven't tried any of this switching the wiring experiment stuff as recommended by PBG, but I am under the impression that if you hook up a string of impedances in series, and there are no parallel paths to ground anywhere along the circuit, the current flowing in one end flows out the other. That's Kirchoff:

    KCL states that the algebraic sum of all currents
    entering a node is equal to the algebraic sum of all currents leaving that node.

    And if all the nodes are in one series string, all the currents are identical.

    Chris
     
  11. MikeyD

    MikeyD

    Sep 9, 2000
    Agreed. It was what I was thinking. Thanks, Chris, it was a very eloquent post.
    - Mike
     
  12. I have the solution!!!!!!! Buy an Ampeg SVT, it runs 300w @ 2 and 4 ohms...
     
  13. eli

    eli Mad showoff 7-stringer and Wish lover Supporting Member

    Dec 12, 1999
    NW suburban Chicago
    No, no; get another 415 cabinet and connect 'em in series!

    Seriously, what did you mean by "clamshell"? If you meant that there are two 15's facing each other, the wiring in the cabinet might be designed to reverse the phase of one of those opposed speakers, so their signals add in a "pushmi-pullyu" fashion. If that is the case, you really do NOT want to mess around rewiring this creature unless you are really sure what you have -- and what the results will be. You may wind up with the output of two of those 15's largely cancelling each other.

    But this is a fascinating thread (flames notwithstanding). Let us know what you find out!
     
  14. BassBaron

    BassBaron

    Jul 20, 2001
    San Jose, CA
    Look what I've started...

    You guys might want to take it down a notch or two, opinions need not be taken so seriously.

    Eli: The cab is two chambers with two drivers in each. One faces forward, the other faces towards a grilled-clothed-in cavity between the two chambers. The speakers facing the center on not on centerline; they about 5" offset and end up about 4" apart and are IN PHASE. I've heard that when speakers are arranged this way, the waves add together, provided the distance and offset are correct.

    Whether series or parallel, it appears I can only get 2 or 8 ohms load, 2 being dangerously low and 8 being too high. I'm not gonna drag around this frig-sized cab if I only have 240W to give it at 8ohm! My SWR Goliath II can handle more power than this novelty from a by-gone era anyway. This speaker is probably better suited as a PA sub, or something, if I can find another one.
     
  15. Hategear

    Hategear Workin' hard at hardly workin'.

    Apr 6, 2001
    Appleton, Swissconsin
    This whole thread has my brain throbbing! ;)
     
  16. So for the 1-2 dB in SPL difference you're not gonna use the cab? Going from 8 to 4 ohms, the difference is only 1 or 2 dB. 10 dB is a perceived doubling of volume.

    A bit of a piece of advice: don't look at the watts, look at the sound pressure level you'll get.

    My 0.04
     


  17. I do see where you're coming from.

    I'm just spurting off the standard theory on ideal series connections. All real world imperfections or differences between circuits, which definitely would exist, could change the "sound". I haven't messed around enough with it to know for sure. I just think that instead of series connection being "definitely bad", it's just "maybe different", and that difference may be bad or good depending on who's listening.

    You know what I mean. (Tequila makes deep thought really fun!):D

    Chris
     
  18. BassBaron

    BassBaron

    Jul 20, 2001
    San Jose, CA
    Point taken. I tried it wired at 8 ohms and it is somewhat more quiet than at 2, so you're right in that the difference between 4 and 8 would be even smaller. The sound (to my ear anyway) is aprox. the same, so I guess I'll keep it around for when I need that "extra push over the cliff" in bigger rooms. Thanks for all the interest guys!