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Rewiring a 4x10 8ohm into 2x 4ohms...?

Discussion in 'Amps and Cabs [BG]' started by klocwerk, Sep 16, 2005.

  1. klocwerk


    May 19, 2005
    Somerville, MA
    Ok, so here's the deal.
    Amp: Hartke 7000, bi-amp, 2x 350w@4ohm amps, not bridgable.
    Cab: Goliath II 4x10 8ohm, 500w RMS

    So. Since my head only puts out about 270 watts into 8ohms, I was thinking "why not take full advantage of the dual amps?"

    Cab should be wired series-parallel (it's not in my hands until tomorrow), so if I wire it so that two drivers are in parallel on each of two inputs, I'd have a stereo cab with 2x 4ohm circuits. I'll put the horn tweeter on one of the circuits and mark it so that I know which input is which.

    So my question here, with a 4x10 rated at 500w, does that mean that each speaker is only rated at 125w? Therefore, if I do the split, each input would only be rated at 250w..? With the amp putting out 350w per, that could be a problem if this is correct. Would I be running the risk of putting too much power through my drivers?

    Experience with this?
    General input?
  2. If your 4x10" cabinet uses four 8 ohm speakers, you should be able to wire it as two 4 ohm 2x10"s.

    From the Eden forum, I've read that the tweeter's crossover should be unaffected by the change in impedance.

    As for power handling, it would be reasonable to assume that each 2x10" is rated for 250W. 350W into each 2x10" is fine, as long as you don't push things too far. Just listen for the signs of overdriven speakers (farting, etc...).

    Having more power gives you headroom, and can actually be safer for the speakers than having too little and trying to achieve the same volume by clipping a smaller amp. Clipping is not good.
  3. The only way you'd be screwed is if all 4 drivers are wired in parallel, unlikely as an 8 ohm 4x10 would require 4 32 ohm speakers.

    You'd still be ok if it was 4 2 ohm drivers all in series.

  4. klocwerk


    May 19, 2005
    Somerville, MA

    Cool, good news, thanks.
    I think I'll give it a shot, and throw in a DPDT switch so I can swap it back to a mono 8ohm. Actually, not sure how that'll work, I'll have to draw me some circuits on paper...
    But yeah, thanks for the wattage info.
  5. That's true for Eden cabs, but we're not talking about Eden cabs here.
  6. klocwerk


    May 19, 2005
    Somerville, MA
    So is this something I'll need to worry about?
    I don't have the cab yet, but I can check the wiring on it tomorrow.
  7. True, but SWR may very well use a similar crossover design.

    I could be wrong....

    If I'm wrong, the impedance change will shift the crossover frequency. David Nordschow said this is not the case for Eden cabinets, and by family relatedness (Eden built early SWR cabinets), I suggest the same may be true for SWR as well.

    You can contact SWR and ask.
  8. klocwerk


    May 19, 2005
    Somerville, MA
    How drastic a change are we talking about?
    If it's a few hz, I'm not very concerned. If it's a few hundred hz, I might be.
    Any idea?
  9. If it is a single high pass filter for the tweeter it will not matter how your other speakers are configured. If it is a 2 way crossover your low pass will change but again your high pass will stay the same (I think). Hopefully someone can back me up on this.
  10. You aren't changing the crossover freq. You're changing the impedence of the woofers to get more woofer output.

    This would be the equivalent of taking a 4x10 cab with a tweeter and adding another 4x10 without a tweeter. You've gotten more woofers with lower impedence. How does that change the crossover freq of the tweeter?

    What it DOES do is change the relative balance between the woofers and tweeter, so you may want to boost the tweeter attenuator to compensate.

  11. klocwerk


    May 19, 2005
    Somerville, MA
    AH, that makes more sense. Thanks Randy.
    I'd been trying to google up references to the above info and failing miserably.
  12. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    If SWR is like most they don't have an actual crossover, only a high pass filter on the tweeter.