Impedence Question...

Discussion in 'Live Sound' started by rmccam, Nov 11, 2005.

  1. rmccam

    rmccam Guest

    This questions is sort of in conjunction with a previous post.

    If I'm running a 1400w (700w x 700w) stereo power amp and I'm using one side to power the mains and the other side to power wedge monitors, should I be concerned with having to match the impedence of each of the channels (to each other)? So if I have two old JBL wedges that are 8 ohms each running in series (so 16 ohms total?) on one channel, do I have to have speakers that equal 16 ohms on the other channel??

    If I don't need to match the impedence what is the output result of either channel?

  2. McCheese

    McCheese Well-Known Member

    Mar 24, 2005
    What kind of amp?
  3. MilesAway

    MilesAway Guest

    It's *probably* not an issue... Solid-State poweramps are pretty forgiving regarding impedance mismatches... certianly more-so than thier tube-driven counterparts. RTM just in case though...

    Another Q: How are you running 2 monitors in series? If you're running into 1, then using the out from that into the 2nd one, they're running in parallel (hence the "parallel out" jack). This will give you a 4ohm load, not 16...
  4. dpd

    dpd Active Member

    Sep 29, 2004
    Power amps do NOT match impedances to speakers. Power amps are designed essentially as voltage sources. They just keep putting out more current as the load impedance drops - up until the power supply can't source the current or the amp overheats.

    If you run one side at one laod impedance and the other side at a different load impedance you will get different power outputs on each side for equal drive level.

    However, if you do this and one side is providing more power than the other side you run the risk of crosstalk into the lesser-driven channel if the heavier-driven channel's power supply begins to limit the drive power. Especially if the amp has a single power supply for both channels.
  5. Kev

    Kev Well-Known Member

    Nov 13, 2001
    good answer/description from dpd
    it may seem geeky
    the above statement is the main point
  6. sheet

    sheet Well-Known Member

    May 28, 2003
    Kansas City, KS
    Home Page:
    Why are you running in series? Are you wanting to choke the amp on purpose? Your total load increases, your speaker's sensitivity stays the same, but your amp is putting out 350+/- watts vs. 700W at 4 ohms.

    Is your amp a dual mono amp, or an amp that shares one power supply, borrowing power from the other channel when needed? The question is resistance and not voltage. Most modern amps have built in protection for mismatched loads. Most pro amps do anyway. But this is not meant to be engaged for normal operation, and it will effect the sound of the amp.

    Ideally, you DO want to have matching loads on both sides. Run the monitors in parallel, and get an increase in power.
  7. rmccam

    rmccam Guest

    I think I got the jist of it...

    Read the manual, hope for two power supplies, try my best to match the loads, and run in parallel. Regardless, with solid state amps mismatching the loads shouldn't be a big issue.

    Is that about right?

    Thanks for the advice everyone!

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