2 Sub-Woofers

Discussion in 'Speakers' started by Brooks, May 20, 2009.

  1. Brooks

    Brooks Extra

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    I've searched the forum and read the threads that relate to this question. I'm pretty sure I understand. Please bear with me.
    Here's my question:
    I have 2 sub-woofers - both have their own amps and thus only need pre-amp output from the receiver.
    I am about to install a Denon 3808-CI receiver.
    I want to drive both subs with it, of course.
    What is the best way to do so?

    Here are the answers that I think are correct:
    1) take the single sub-woofer pre-amp output and connect both sub-woofer amps to it. Each amp will see 4 rather than 8 ohms but it will work fine.
    OR
    2) Connect one amp to the sub pre-amp output and the other to the spare, assignable, fully powered, output on the receiver and monkey with the volume control on that second sub to equalize volume on the subs.

    I'd prefer to go with #1.
    Am I right that either will work and that choice #1 won't hurt the subs or the receiver?

    Thanks!
     
  2. Robert_J

    Robert_J Lead Actor

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    #1 is the correct method but some of your statements are incorrect. Since each sub has its own built-in amp, the receiver will not see 8 ohms nor 4 ohms. The receiver's sub-out will see a 5k to 10k ohm load because that is the resistance of the inputs of the sub amp.

    Also, most drivers used in powered home subs are in fact 4 ohm drivers. Pull out any driver from SVS, Hsu, Elemental Designs, Epik, etc and you will find them to be 4 ohms nominal. I run dual 2 ohms subs in my theater. But again, it doesn't matter to my receiver because the amp I use to power my subs is designed to drive two ohm loads.

    -Robert
     
  3. Brooks

    Brooks Extra

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    And that's why we all love this forum. I was right on what to do but misunderstood why. Now I know I'm doing it right AND I know the correct reason.

    Thanks Robert!
     
  4. brandonchenry

    brandonchenry Stunt Coordinator

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    This is the first thing I do with two subs- get them in phase. Two subs in perfect phase will be 6dB louder than one sub alone when both are calibrated (by themselves, one at a time) to the same level.

    75dB is reference level on MOST receiver test tones. Like Denon. So if you set the meter on a tripod and leave it in the middle, and then run ONE sub up to 75dB (0 deg phase for now); switch it off. Then do the second sub’s gain (no messing with the AVR now) to that same 75dB. Make sense? Both subs, one on at a time, both set to 75dB.

    Now switch them both on. You SHOULD be +6dB now with two subs going, or 81dB. But you can actually have LESS output than one if the subs are cancelling each other bad. Adjust one sub phase if you are not in the 80-81dB range. Change phase in small steps, like one hash mark at a time. It’s a crap shoot really but I have seen REALLY bad cancellation if two subs are out of phase entirely. Like measuring 12dB less shit.

    So, if you do one to 75, then the second to the same, then BOTH and get 81 db you are there. Don’t go crazy messing with phase. If it measures OK at 0deg too then let the Audyssey do the rest.

    Audyssey is your best friend. It will correct shit that would take you months of painstaking farting around to match. If you have a -CI model Denon AVR, know that it is unlockable/upgradable to the Audyssey Pro 3.0 software. This will require you going to Audyssey's website and finding an authorized Audyssey installer in your area. He will be able to enter an unlock code, and then use his computer's high processing power to run a much more robust version of the Audyssey software.

    Speaking of Audyssey and two subs, they have a box that is purposed just for this. It is an SVS product. It is called the AS-EQ1 subEQ. It is a fairly new product, and I think they are having a hard time keeping it in stock. Everybody wants one! Eq'ing a subwoofer takes bigger algerithems than any other speakers. The AS-EQ1 has extrodinary processing power. It can handle two subs, and make them play flawless in your room.

    If you are unfamilier with SVS, they are a factory direct subwoofer/speaker/electronics manufacturer. They build what other companies build- they only make it a little better and about half the price. worth a look-see for sure!
     

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