Wiring Multiple Surround Speakers per Channel?

Discussion in 'Speakers' started by Greig, May 9, 2006.

  1. Greig

    Greig Auditioning

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    Does anyone have first hand experience with setting up multi-speaker per channel for Surrounds?
    I am setting up 7.1 +Presence in a 13’x 22’room using -
    * for SPKR SYSTEM A:
    - 3x Jensen EHT-8 130W 6 ohm in walls for front stage
    - 2 EHT-6 110w 6 ohm for Presence speakers (to my Yamaha RX-V2600 AVR),
    - 2 home made subs, and
    - 6 EHT-4 110w x 6 ohm 40 degree- angled drivers in wall or ceiling (not yet sure) for (side) SURROUNDS: THE PROBLEM (see below)
    - 2 EHT-4 110w x 6 ohm 40 degree- angled drivers in wall or ceiling (not yet sure) for REAR surrounds.

    SYSTEM B: is my old pair of 5spkr x 4way Sansui SP1500 for stereo listening.

    Here’s the 7.1 problem area – I have 3 rows of seating so I have been trying to emulate the “multiple side” speakers in commercial theaters so that every row has the correct positioned (side) surrounds (i.e. before I came to know that comm Theatres us 10.2 and have all active (amplified) speakers). So I am trying to place 3 pairs of Surrounds along each side wall at 90 -110 degrees to each row. So do I wire –
    •3x PARALLEL, or
    •3 x SERIES, or
    •2x SERIES + 1 x PARALLEL, or
    •2 x PARALLEL + 1 x SERIES, or
    •Use an Impedance Compensation device of some sort (and what should/does that present as an impedance value to the surround channels of the AVR?)

    See I don’t want to cause EQ issues for the YPAO system, or degrade sound quality, or affect the “relative” volumes of SL and SR compared to the other channels for the listeners in each of the rows.

    Thoughts thus far: My first thought was to maintain 6 ohm load/surround-channel to be seen by the AVR so I don’t introduce quality/balance or danger problems to the AVR. To do this I can’t just wire as 3in Para = 2 ohm, 3 in Ser =18ohm, 2 Para + 1 Ser = 9 ohm, and 2 Ser + 1 Para = 9 ohm (Right???). So I’ve hunted for a “black box” only end up buying on recommendation (?) a no-brand one (1pr -> 4 pr) from Radio Shack/Tandy that was supposed to use combinations of series and parallel (?????) to maintain the impedance seen by the AVR at the same value as “the lowest impedance speaker in the array”. BUT it does not do that. I hooked them up and made measurements –
    •2 SPEAKERS-
    oSwitch 1 +2 = 6 -> 12ohm (obviously just series);
    oSwitch 3+4 = same (series);
    oeither (1 or 2) + either (3 or 4) =
     
  2. Mattak

    Mattak Stunt Coordinator

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    You can't do a parallel/series combination of 3 without the speakers getting different power levels - eg 2 parallel in series with 1 would give 50% power to the 1 and 50% power split between the parallel 2, so they'd see only 25% power. I think you either need to amp them seperately or put in 4/side. I've never been in a theater that had side surrounds for EVERY row - can't you space them so that all 4 are clumped together along the 3 rows? Amping them seperately would also be a pain with 3 because you're still stuck with 6x6ohm, 2x2/18ohm, or some combination like 2x6ohm + 2x3ohm/2x6ohm + 2x12ohm, none of which makes a great combo for a 4-8ohm amp.
     
  3. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Do NOT do a combination of series/parallel with 3 speakers. They will not operate evenly. Most of the power will go to either the one speaker or the other two speakers. (Mattak, your post slipped in before me.)

    Also do not put all 3 in parallel. Not worth the risk.

    I think the best way to go, since you apparently have pre-amp outputs, would be to use 6 channels of identical outboard amplification to drive the surrounds. This way there's no impedence issue and its easy to level-match the 3 pairs of surrounds to each other. Plus it off-loads some of the amplification duty from your receiver so now it only has to spread its power supply capacity across 5 speakers.

    One of the cheaper (compromise) solutions would be all 3 in series. There really are efficiency gains for driving an array of speakers such that the volume would be the same IF the 3 speakers were placed close together. Your concerns are valid - you're not planning to place them close together so there is some loss of SPL. But its probably not as much as you might think and you could certainly use the receiver's speaker level settings to boost them to match the other channels. The only question is if your receiver will have enough juice to drive them to your max listening levels.

    The other compromise solution would be as you suggested - use the Sansui to power 2 of the 3 pairs of surround speakers. Level matching probably won't be too difficult. But again, you'll have to figure out if this amp has enough juice to meet your listening levels.

    In the end it comes down to this - you can easily try both of the compromise solutions and it won't cost you anything but time. Ease up the volume slowly and back it down if any of the signals start to clip. If it works okay then you're done. Otherwise start shopping for more amplification.
     
  4. andySu

    andySu Cinematographer

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  5. andySu

    andySu Cinematographer

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  6. drobbins

    drobbins Screenwriter

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    Dave
    Greig,
    I am currently running a 6.1 Yamaha HT740 receiver with 9.2 speakers. I have a center above & below the screen and 2 pairs of surrounds for the 2 rows of seating. The doubled up speakers are run in parallel. I haven't had any issues with overheating. The front set is turned more forward and the rear set turned more backward trying to minimize and combing that might happen. I would be willing to bet that if you put one set of surrounds for the front row and another for the third row, you will have good coverage in the second row. Here is the link to my theater
    http://www.hometheaterforum.com/gallery1/main.php?g2_view=core.ShowItem&g2_itemId=3369
    Dave
     
  7. andySu

    andySu Cinematographer

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    There are risks of pulling to much from the amplifier, impendence changes with frequency and heat as well tends to build in the amplifier, due to it’s strain on the loudspeakers impudence.

    I have run a series to parallel mode before, and I boy did I get the math wrong on it, buy a friend who’ works in electronics helped me out in that department, which took a matter of minutes.
     

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