Bi-amping with six speakers?!

Discussion in 'Home Cinema Speakers' started by great_sushi, Jan 10, 2012.

  1. great_sushi

    great_sushi
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    I have two amplifiers, both 4-16 ohms. I also have a 3-way 100watt pair @ 4ohms, and two two-way pairs, one at 6 ohms (50watts) and the other 8 ohms (100watts).
    Whats the best configuration for me, im thinking of bi amping and having one amp powering all the subs, and the other for the mids and tweeters. Just concerning the power of the amps and the speakers... the amps can power the speakers but im worried about the impedance.
    One amp is bi wire able. not that that helps the situation much.
    The 3-way:
    subs approx 80 watts nominal 10"
    mids approx 50 watts nominal 4"
    tweets approx 45 watts 25mm
    4 ohms for the speaker set, and they have a decent crossover network.

    The other two speakers have one mid and a tweeter.

    Ask for any other info if u cant answer otherwise, but any help will be welcomed!
    Thanks
     
  2. MaturityDodger

    MaturityDodger
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    What is the setting for this? It sounds implausible that three pairs of possible mismatched speakers is going to be better than one unless the room is massive and they are spaced far apart from each other (like a PA setting). In which case, you'd probably want to buy another amp.

    As for your impedances, each amplifier can go to a minimum of 4 ohms. However you split the speaker inputs between amp channels (splitting woofers/tweeter etc), each input will still have the same conductance and these conductances will sum when put in parallel with each other.
    For example, your 4-ohm speakers have a conductance of 1/4. This might be 1/8 for the woofer and 1/8 for the mid and tweeter combined (so woofer's impedance is 8-ohm, and the mid and tweeter in parallel combine to 8-ohm).

    So let's assume you use one amp to its full capacity and give it a 4-ohm load.
    For argument's sake, we'll say you're using it solely for the 4-ohm pair.
    This leaves the 6 and 8 ohm pairs for the other amp. Their combined impedance when put in parallel is:
    1 / ((1/6) + (1/8)) = 3.43. This is below the amp's rating.
    In the best case, the amp's specs aren't accurate, and it's fine to go lower.
    In the worst case, things could heat up with the extra current being drawn, and get damaged.
    More likely is that your sound quality will be reduced as the amp struggles to send enough current when needed. You'll probably notice a lack of control in the bass, among other things.


    Now as for your proposed setup method: all LF on one amp and all mid/HF on the other.
    This could turn out even worse, as when there's a lot of demand in certain bands, one amp has to pay for it threefold.
    The bi-amping model is also slightly broken, as there are still different drivers on each amp channel. So each will have impedance nodes at different frequencies (no speakers are perfect) and affect the other drivers as they do so.

    If you do need to have all three pairs of speakers, then I suggest that you get another amp, and run one pair of speakers per amp.
    As mentioned at the top, knowing more about your setting might help me. I'm guessing it's not a regular domestic system.
     
  3. great_sushi

    great_sushi
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    Thanks for the quick reply!
    I think ill leave out the 50 watt 6ohm pair. I dont really have any need for a third pair, it was more curiosity than anything.
    Is it possible to say, put the two 10" subs through one amp, share the 4 mids through both and have the tweeters through the other amp.
    I've just realised that the 100 watts 8ohm speaker pair are 6 ohms not 8!
    I think that means that;
    1st Amp: 1 x 10" 4ohm subs + 1 x 4" 4ohm mid in series = 8ohms total per channel... right?
    2nd Amp: 1 x 6ohm mid + 1 x 6ohm tweeter + 1 x 4 ohm tweet = 16 ohms per channel.
    would this work?
    Thanks
     
  4. MaturityDodger

    MaturityDodger
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    You generally wire speakers in parallel, not in series. They'll affect each other in funny ways as their impedances change according to frequency, and you won't get accurate production. The only time you might want to go in series is if you have identical speakers.

    I really don't see why you want to split the drivers as you're suggesting. Improvement in sound quality due to bi-wiring doesn't happen just because HF and LF are separated. It's because each amp channel is presented with a simpler load, with fewer low-impedance frequency points etc. And also because the channel gets presented with a higher impedance.
    So splitting as you're suggesting still doesn't solve that problem.

    A speaker, incorporating all of its drivers and its crossover network is designed not to be too disruptive to an amp channel, or between individual frequency bands.
    Hi/mid/low bands on different speakers won't be designed to play nicely together.

    My advice remains to stick with one amp per pair of speakers.


    P.S. Some people even claim that bi-amping makes little to no difference anyway. I've never tried it in a side-by-side comparison, so wouldn't want to come down on either side. The theory is sound though, unlike a magical audiophile power cable or SATA cable (yes, they exist, and professionals have written articles extolling their virtues).
     
    Last edited: Jan 10, 2012
  5. BlueWizard

    BlueWizard
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    Are we talking about Speakers here or drivers? Those are very different things.

    Is this three complete pairs of speakers, or is this one speaker with three drivers in it?

    Also, when you say Subs do you actually mean Subwoofers? The Bass driver in a multi-driver speaker system in not a subswoofer, it is merely a woofer or bass driver. Given this, your terminology confuses me.

    Steve/bluewizard
     

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