Using one set of speakers inputs for two sets of speakers

Discussion in 'Speakers' started by Brian Perry, Jul 31, 2003.

  1. Brian Perry

    Brian Perry Cinematographer

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    I'm helping a friend with his new stereo (an Onkyo receiver) and in addition to the normal 5.1 connections, he has two sets of outdoor speakers he wants to connect (one on his back porch and another on his patio). The Onkyo receiver has an extra set of speaker connections for Zone 2. I tried connecting both sets of outdoor speakers to this one set of speakers inputs simultaneously. Everything seemed to work okay, but the unit shuts off after a few minutes of listening to Zone 2, perhaps because the protection cicuit is kicking in.

    Did I create a short circuit by connecting two sets of speakers to one set of speaker outputs? If so, what is the best way to achieve my friend's goal of having two sets of speakers in Zone 2?

    Thanks.
     
  2. David_Stein

    David_Stein Second Unit

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    wiring two sets of speakers in parallel, which is what you are doing when you connect two to the same speaker output lowers the impedence that the amp sees. the actual law is 1/Rtotal=1/R1+1/R2, where Rtotal is the total impedence, and R1 and R2 are the impedences of the two sets of speakers you are connecting. with speakers this can really be simplified since most likely the impedences are the same. if you have two pairs in parallel, then the impedence is half of that. so what your amp is seeing is a 4ohm load and it obviously is unable to stablely power that. im taking a stab here, but what i think happens is that the total current that an amp can "push" is limited, but the current that the speaker is in effect asking for is determined by the voltage and the impedence. the voltage is determined by the reciever and and the source material and volume control and your impedences is halved. I=V/R, so basically you were asking your reciever to supply twice as much current and it just couldnt handle it.

    one way that you can connect it is to to put the speakers in series. someone should back me up before you do this, but what you do is take both of the Right speakers, hook the positive terminal up from the receiver to the positive terminmal in right speaker one, then hook the negative terminal from speaker one up to the positive terminal of right speaker two, and then the negative terminal from right speaker two to the negative terminal in the reciever. do the same with the left speakers. what this does, when resistances are in series, is double the impendence (making it 16ohms) and halving the current the reciever is asked for. it wont play as loud, but it should work.
     
  3. Brian Perry

    Brian Perry Cinematographer

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    Thanks, Dave, I'll try that. Also, the Onkyo has a menu where I can specify 6 ohms or 4 ohms. Maybe I should try switching the setting to 4 ohms?
     
  4. David_Stein

    David_Stein Second Unit

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    what onkyo reciever model is it? i can try to find an online manual that i can check about that in.

    if it has a setting that can stablely handle 4 ohm loads (ie. if thats what that menu option is really about) then it should work, but im guessing more likely its a menu its a option for switching between 6ohms and 8ohm. i think there are very few non-pro audio speakers or high end audio that are 4ohm. 6 and 8 ohms are the usual speaker impedences as far as i know.
     
  5. Brian Perry

    Brian Perry Cinematographer

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    It's the TX-NR900. I verified the choice is 4 or 6 ohms, but I think it's intended for the impedance of one set of speakers. I think you're original suggestion of wiring them in series will be best. Thanks!
     
  6. Wayne A. Pflughaupt

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    Brian,

    Your friend might want to consider getting a speaker selector like this one from Radio Shack. It allows for multiple speaker connections without overloading the amp.


    [​IMG]


    Regards,
    Wayne A. Pflughaupt
     
  7. David_Stein

    David_Stein Second Unit

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    Does that speaker selector allow you to drive two pairs of speakers at once and maintain an 8ohm load? or does it just switch between up to 4 pairs (one pair being driven at a time)? ill admit to not being very well versed in speaker selectors, but i think his friend is wanting to drive both pairs of speakers at once.
     
  8. Patrick Sun

    Patrick Sun Moderator
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    You can't maintain an 8 ohm load if both speakers are nominal 8 ohm speakers (connected in either parallel fashion, or in series). Wiring in series is the best way to not cause the protection circuits to kick in if the receiver's amp section isn't robust enough to supply the necessary current demands with a parallel speaker hookup, but the volume level won't be real loud (YMMV due to the speaker sensitivities).
     
  9. Terry Montlick

    Terry Montlick Stunt Coordinator

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    An alternative is to use transformers to match impedance while splitting the signal. You keep 8 ohms presented to the amp, even though you are driving two 8 ohm speakers. But you can't beat Patrick's series wiring recommendation for cost.

    Regards,
    Terry
     

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