Distinct LFE channel from unpowered sub?

Discussion in 'Archived Threads 2001-2004' started by Marc Rochkind, Jan 13, 2002.

  1. Marc Rochkind

    Marc Rochkind Second Unit

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    As I understand it, if you have an unpowered subwoofer that you're using with Dolby Digital 5:1, you would do this:

    1. Set up the receiver for no subwoofer and large left- and right-front speakers.

    2. Run wires from the left- and front-speaker receiver output jacks to the subwoofer.

    3. Run wires from the subwoofer's speaker outputs to the left- and right-front speakers.

    The crossover in this setup will occur in the subwoofer.

    But, my question is... do you still get the distinct .1 LFE channel? I guess you would if the receiver sends it out the left- and right-front jacks and then the subwoofer takes it from there, but is that in fact how it works?
     
  2. Justin Lane

    Justin Lane Cinematographer

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    With this setup you would not be gettting a true LFE just bass from your front mains.

    To utilize the LFE you would need to run the LFE out into another amp that powers the sub, or buy an amplified sub.

    J
     
  3. Marc Rochkind

    Marc Rochkind Second Unit

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    So, if Justin is right, then an HTB with an unpowered sub will not provide 6 DD channels? I wonder if that fact is somehow being suppressed...
     
  4. BruceD

    BruceD Screenwriter

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    Actually, in most cases LFE is still present and is being directed to the correct location or channel which in this case is the L&R.
    The only question is do you have the capacity to take advantage of it. The answer is no and here's why:
    Marc's example #1 (main L&R only).
    Typically doesn't have the capacity to properly produce the the re-directed bass from the center and surrounds and the LFE. It lacks the ability to generate high enough SPL levels and it lacks the ability to produce the lowest frequencies.
    Marc's example #2 (driving main L&R + non-powered sub from the same receiver outputs).
    This will most likely overdrive the amplifier and could cause distortion. You can adjust the sub's crossover, but both the mains and sub may be duplicating some frequencies making it tough to blend the two together.
    Marc's example #3 (driving the non-powered sub from the receiver outputs and then pass-through to the main L&R).
    This is actually no different than #2.
    The only way to get this right is to use the sub-out on the receiver and get a mono amp of some kind for the sub.
    Unless the L&R mains and sub were originally designed to work together as a single unit like example#3. But then I fear it would be no different performance-wise than example #1.
    ANOTHER EXAMPLE:
    For my system, I select sub=NO in my speaker setup and main=Large, center=Small, surround=Small. Then I put something called an external crossover between the L&R pre-outs and the L&R amp-ins.
    This external electronic crossover splits my mains and sub @60Hz.
    All the re-directed bass and LFE is sent to my main L&R, but gets split by the external crossover and sent to either sub or L&R.
    I don't lose any bass, I get everything and my mains don't get overloaded because I also have the sub (with it's own amp) there to.
     
  5. RichardH

    RichardH Supporting Actor

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    Proper bass management according to your setup should assure that the LFE doesn't get lost.
     

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