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Speakers, 4 to 8 ohms

Discussion in 'Amps and Cabs [BG]' started by av_rockstar, Nov 19, 2003.

  1. av_rockstar


    Oct 4, 2003
    So. Cali.
    Yo Zupp.....
    I have 3 JBL 225H 15" speakers.
    (1) is a 8 ohm, the other (2) are 4 ohms...
    What or how can I change or run the (2) 4 ohm speaks @ 8 ohms? Can I just rewire them some-how ? I was told by someone else that I would have to re-cone them...Is this true...:confused:

    Any Help appreciated... ;)

  2. notabob


    Sep 20, 2003
    cincinnati ohio
    i was told that this is not possible
  3. embellisher

    embellisher Holy Ghost filled Bass Player Supporting Member

    I'm moving this to Amps where our resident speaker experts will see it.
  4. Hollow Man

    Hollow Man Supporting Member

    Apr 28, 2003
    Springfield, VA
    If the two speakers are four ohms each, then you may wire them in series to create an eight ohm strand. This means that half of whatever power you put into this strand will go to each speaker. This won't actually change the speakers, but it will change the way your signal is distributed between them.
  5. av_rockstar


    Oct 4, 2003
    So. Cali.
    What I have is a TR 225 cab. w/ 2 15's and a horn, the cab says 4 ohms and my QSC amp runs @ 8 ohms. Im assuming they are ran in series...
    What can be done if anything....

  6. De Teng

    De Teng

    Oct 27, 2003
    Utrecht, Holland
    Stop playing with the cab, until you're sure they are serial. When you connect a cab, which has a lower restistance then the amplifier, you will play your amp literally to ashes. Oh yes.. and dust. And smoke... and it stinks too!

    Moderator: This problem isn't so tough, we bassplayers are smart enough to solve it. ;)
  7. Hollow Man

    Hollow Man Supporting Member

    Apr 28, 2003
    Springfield, VA
    De Teng's right, don't screw with anything until you know exactly what you've got on your hands. If you overload your amp, you'll have quite the bonfire.

    Now let me see if I've got this straight. You 2x15 cab includes all three speakers you mentioned before (the one at eight ohms and the two at four ohms)? IF that's accurate, then it's reasonable to assume that your cab as a four ohm input impedance, as you suggested. This is fine in and of itself, but if your QSC power amp will only run at eight ohms, you must not connect this cab.

    I assume this is why you wanted to rewire your cab; you had hoped that you could make the normally four ohm cab operate with an eight ohm power amp. The best you could do is put all three speakers in series to give you a total impedance of 16 ohms, which would be compatible, but would only allow you to draw about 60% of your power amp's total output. You're more than likely better of buying a different eight ohm cab to use, or buying another four ohm cab to daisy-chain with your current 2x15.

    ....that is, assuming I understood your question.
  8. av_rockstar


    Oct 4, 2003
    So. Cali.
    :bawl: Rite on, Im thinkin I need another 8 ohm Cab....1 cab. has 1 15" and a horn rated @ 8 ohms.... The other Cab. has 2 15"s and a horn and says 4 ohms on back of cab...
    QSC amp runs @ 8 ohms....
    I hate having to be the sound guy for the band.:rolleyes:

  9. ESP-LTD


    Sep 9, 2001
    It's kind of unusual for a solid-state amp to only tolerate an 8 ohm load these days. Most will run "x" watts at 8 ohms, "y" watts at 4 ohms, and some will even push "z" watts into a 2 ohm load.

    What model is it exactly?
  10. Scott D

    Scott D

    Apr 21, 2003
    Minneapolis, MN
    Here's my take...

    All 15's are rated 8 ohms. the 2x15 is wired in parellel, so that makes it 2 8 ohm 15's (it's pretty rare to see a 2 ohm 15") so you could get it to 16 ohms, and that's about all you could do... What model QSC do you have? That sounds odd, a 1 channel @ 8 ohm poweramp...


    Mar 12, 2003
    USA, PNW
    Hint: If your amp isn't stable at 4 ohms, get rid of it. Unless it's one of those high-end esoteric amps.
  12. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    South Shore MA
    some older poweramps can only bridge into 8ohms...maybe it's one of those?
  13. ESP-LTD


    Sep 9, 2001
    Indeed, in which case bridging may not be very helpful in this situation, even though on the surface it might appear to be providing more power.
  14. av_rockstar


    Oct 4, 2003
    So. Cali.
    STEREO MODE, EIA: Both Channels Driven
    8 ohms EIA 1 kHz, 0.1% THD 200W 280W 360W 500W
    4 ohms EIA 1 kHz, 0.1% THD 300W 450W 600W 750W
    2 ohms EIA 1 kHz, 1% THD 430W 700W 900W 1200W

    Like this rite, I understand this, But..can say L side run @ 4ohms and R side run 8ohms
    :meh: Can I run both of my JBL-TR Cabs. together when 1 is 8ohm and the other is 4ohm..?
    Standard P.A. L/R out...w/o unduely stress to any componant.... TR225 and TR126 Ahhh..theres that word again.....STRESS...

    Rite On, the quest continues.....Make me understand......lol
  15. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Those are the per channel ratings. 360 watts per channel into 8 ohm loads, 600 watts per channel into 4 ohm loads

    Connect one speaker to one channel, the other speaker to the other channel. The 8 ohm cabinet can get up to 360 watts, the 4 ohm cabinet can get up to 600 watts. The loads on each channel can be different, you just can't go below the minimum rated impedance (which in this case is 2 ohms on each channel).

    The level control on each channel will control the relative loudness of each speaker.

    Have fun!!!!
  16. ESP-LTD


    Sep 9, 2001
    Yep, works just fine in non-bridge mode. I have an RMX 1450 and push a 2 ohm load on one channel (a pair of 4 ohm car audio subs) and a single 8 ohm cab on the otehr channel.

    Bridging can be handy some times, but I don't think it's doing you any good in this case.
  17. av_rockstar


    Oct 4, 2003
    So. Cali.
    Rite On, I hooked them up as they are...BAM
    Sounds Grt. Was just alittle worried about blowing something......Thanks for all the help all......We ride again....:bassist: