Importance of rear sub in HT setup

Discussion in 'Speakers & Subwoofers' started by Arup, May 7, 2003.

  1. Arup

    Arup Stunt Coordinator

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    How many agree that a rear sub is neccesary for a proper HT setup?

    Using a rear sub enables one to use LARGE speaker setting for rear speakers in the HT receiver/amp. In my experience, it widens and opens up the soundstage significantly and adds the resonace in DTS. Most DTS setups call for large full range speakers in the rear. By using a active sub, one can use bookshelf speakers for better imaging and avoid a logistical nightmare of placment. Also an active sub uses it's own power, thereby relieving the HT amp to give high dynamics to the rear speakers and leaving the power robbing job of bass to the sub.

    In my opinion, a rear sub is way more important than a rear center speaker.
     
  2. Arup

    Arup Stunt Coordinator

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    What happens when you have a high powered main amp and high quality floor standing speakers with good response up to 40Hz. Isn't it a waste to set the main speakers to SMALL in that case. Also the most powerful sub will never give you the residual bass the way a rear sub does. Specialy in DTS, the difference is astonishing.
     
  3. Leon O

    Leon O Stunt Coordinator

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    Are you sending high level inputs from the surrounds into the rear sub and using its on-board amp to perform the crossover functions?
     
  4. StevieP

    StevieP Stunt Coordinator

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    I agree with Arup, although have tried it both ways ( with/without)

    Presently I am running the rear sub with high level inputs, and letting it do the crossover for my Def Tech BP1X surrounds.

    Gonna try it with sub out on receiver as soon as I get another cable. Problem with that is you can't cut the low end to the surrounds.

    Maybe I wouldn't need it if I had SVS[​IMG] But thats down the road a bit.
     
  5. David Smith

    David Smith Stunt Coordinator

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    Leon O,

    It appears from his post that he is indeed running the rears "large". I'm sure the point you're trying to make is the same as me. I don't think it's easier on the HT amp at all. The amp is still sending the full range signal since the crossover is on the sub, after the signal has been sent.

    Right?

    With the rears set to small, the HT amp only needs to worry about signals above the internal crossover pojnt, 80hz etc.
     
  6. Arup

    Arup Stunt Coordinator

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    The HT amp is not being taxed as the sub's crossovers are taking over the bass robbing signals and are sending the mid and highs to the rears. I have seen significant improvement in the mid and high dynamics.

    I am also running two 800W subs for main front in addition to full towers for main and a seperate 260wpc main amp. My speaker settings are all LARGE and for sub I have BOTH selected.
     
  7. Brett DiMichele

    Brett DiMichele Producer

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    All I can see this creating is major phase cancelation
    issues as the standing waves smack into themselves 180
    degrees out of phase..

    I dunno.. Considering Bass *is* non directional (fact) it
    just seems moote to me to have a rear SW when the Surrounds
    are set to small.. Anything 80Hz and below is going to the
    sub anyway (If it's the standard THX XO)


    But at the end of the day. If it sounds better to your
    ears that is all that matters! [​IMG]
     
  8. RichardHOS

    RichardHOS Second Unit

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    I could go either way on this one, depending on exactly where the multiple subs were placed, and what XO points are used. Sometimes multiple subs reduce the variation in room response caused by modal peaks and nulls... sometimes they exacerbate them.
     
  9. Edward J M

    Edward J M Cinematographer

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    I can see and appreciate both sides, but I'm firmly in Brett's camp on this one.

    Setting up full range speaks all around with multiple subs is much harder to do right than all speaks to small and one/two great subs co-located on the front stage.

    With that said, even though the bass might be acoustically non-directional, it CAN be localized by vibration transmission through the floor or by air pressure felt from behind.

    Setting the speaks to small does not waste their bass capabilities. The high pass filter rate is not a brick wall and is typically 12 dB/ocatve, and the speaks will still see significant bass below the filter point. I think 80 Hz is perfect for vigorous HT applications, and if you doubt how much bass the speaks still get on small at 80, just power off the sub and give it a listen - bet you'll be surprised. If anyone thinks 80 Hz is too high, many pre-pros and AVRs allow the high/low pass filter point to be adjusted anywhere from 40-120 Hz.

    Also, setting the speaks to large does indeed stress the HT amplifier more, as this mode sends a full range, full current signal to the subwoofer, which in turn absorbs and filters this signal before passing it back to the speaker in question. Small filters the signal at the pre/pro stage, before it hits the amp stage and this is much easier on the amp, since the majority of the current requirements at high volume are in the bass frequencies.

    Regards,

    Ed
     
  10. StevieP

    StevieP Stunt Coordinator

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    Actually, I have my surrounds set to small, and the crossover set to 40hz.

    My rear sub is small, Def Tech 10" located in the back of the room on the left wall approx 8' forward of the back wall just below the left surround. So i'm not asking much of it, but it does fill in the upper bass nicely that the small BPX1s are lacking. Also it doesn't seem to cause phase problems with the 15" sub in the front left corner.
     

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