Difficulty in matching passive sub to a single channel sattelite?

Discussion in 'Archived Threads 2001-2004' started by RichardHOS, Mar 11, 2003.

  1. RichardHOS

    RichardHOS Second Unit

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    Suppose you want your surround channels to be "full range", but don't want to add an extra channel of amplification for each surround channel (suppose it's four channels in a 7.1 setup). Instead, you're pondering the option of adding a smallish (10" maybe) "box" sub to compliment each sattelite, using passive crossovers and a common channel of amplification to drive both the sub and sat.

    Obviously, impedance matching, gain, crossover point, equalization, amplifier power, etc. will all be important issues to tackle. What I'm suggesting is essentially adding the driver that is left out in your sat vs. floorstanding models. This would greatly simplify amplification (four channels less), and remove the need for a four channel active crossover.

    In general, is this too difficult to accomplish? How would you guys approach something like this? What if you were dealing with abnormal sattelite speakers... say planar dipoles at 4 ohms? If matching an active (or seperately amplified) sub to each channel would work out well, could you approach the same result with this passive combo?

    I'd love to hear thoughts on this.
     
  2. Chuck Bogie

    Chuck Bogie Second Unit

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    What I've been seriously thinking of doing involves using PE 100 watt plate amps as the "low end" crossover, and running the signal through 'em, then back up to a two-way built into a (sealed) box on top. The PE's amp crosses the signal going out at 125hz...
     
  3. RichardHOS

    RichardHOS Second Unit

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    hmm... scratching my head a bit. So are you going to use the amp section in the PE plate, or just use it for a cheap crossover?

    I need to take a look at that plate amp to get a better idea of what you're suggesting. I'm guessing it has a set of line level outputs after the crossover section?
     
  4. ThomasW

    ThomasW Cinematographer

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    The primary problems with passive sub XO's are the large inductors needed, their cost, and their effect on the damping factor of the amp.

    Also it's difficult to get a good level match between a dynamic woofer and a planar with a passive XO.

    BTW, I use Maggie MMG's as rears.
     
  5. RichardHOS

    RichardHOS Second Unit

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    Cool, MMG's as surrounds looks like where I'm headed. I do understand the difficulties... just wondering if anyone had figured out a way to satisfactorily deal with them.

    The other option of course is a fairly cheap four channel amp, and a four channel active crossover. I guess the active/passive crossover prices will not be too different, so you're left with only the amp/eq cost increase.

    Probably easier to get good results... just doesn't seem as "elegant" for some reason. Twice the amp channels, extra electronics, twice the wire, etc. Just imagine... a nice little 8" or 10" sealed passive that, when added to your MMG's in series or parralel, created a really nice full range surround. [​IMG]


    BTW Thomas, are you just losing that low freq. information, or do you have a processor capable of shunting that off to mains or LFE channels?
     
  6. ThomasW

    ThomasW Cinematographer

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    Richard

    I use a 12 driver IB sub, so I'm not worried about the loss of the relatively small amount of LFE in the effects channels.

    The sub signal is created by a Marchand XM9 active XO placed after the pre/pro main L/R outputs.
     
  7. Chuck Bogie

    Chuck Bogie Second Unit

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    Well, I want some full-range speakers for music, but at the same time, I don't want to really go nuts on pushing power to 'em... Either my Denon 1803 (80 watts) or my "little" 30 watt/channel Marantz will work fine to run a pair of two ways, and since I can run the signal through the plate amps (which will power the larger driver on each), I'll still be able to get the volume with the bass...
     
  8. RichardHOS

    RichardHOS Second Unit

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    Sounds interesting... I'll have to take a closer look at those plate amps.
     
  9. Chuck Bogie

    Chuck Bogie Second Unit

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    At $100/each, they're cheaper than buying a bigger/better amp... Basically you feed 'em a full-range signal, and they cross it over at 125 hz (their "on board" crossover dial goes up to 160, but the outbound signal gets chopped at 125), and send that to the "satellite" speakers... I'm figuring that I'm going to go with a variant of the little two-way speaker kit that PE sells for the top end, and for the bottom end, I'm still waffling...
     
  10. RichardHOS

    RichardHOS Second Unit

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    OK, yeah, I checked out the PE plate amp you're talking about. That seems like a good way to go... 120W extra power for the sub, you get your crossover for the sub, and a high pass crossover for the sat. Specs seem "good enough" for a surround channel sub-reinforcement, and I'm assuming there is a gain as well on the amp so gain could be adjusted.

    Looks like all the parts are there. A good passive xover would probably cost about half of that per channel, so it does look like a great solution. Thanks for pointing me in the right direction!
     

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