Dual Sub Placement & Calibration Questions

Discussion in 'Archived Threads 2001-2004' started by JayDaniel, Sep 6, 2002.

  1. JayDaniel

    JayDaniel Stunt Coordinator

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    I'm setting up my HT equip. in a new home. I've decided to use two subs in this house, rather than a single. After posting here a couple weeks ago about the benefits/tradeoffs of stacking the dual subs vs. placing them in opposite corners, I've decided to place them in the front corners of the 12'X18' room (instead of stacking in one corner). As info, the subs are 8" front firing, Bic bookshelf speakers (mains, center & surrounds), the ceiling is an 8' high drop ceiling, wooden walls, carpeted floors.

    First the placement questions. This may not matter, but should the subs be placed parallel to the side walls, or "caddy-cornered" with both pointing to the sweet spot?

    Calibration questions:

    How do I calibrate dual subs? In the past, I've calibrated my system (audio/video, including a single sub), using the S&V Home Theater Tune-Up disc and a Radio Shack SPL meter.

    Calibrating two subs baffles me. Do I do them one at a time? Or set both to the same SPL level, and calibrate them together?

    Any help would be appreciated. Thanks.

    JayDaniel
     
  2. Geoff L

    Geoff L Screenwriter

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    Hi Jay and welcome to HTF.

    Im not going to go into explaining a ton of stuff on you questions.

    Try a search for specific stuff your looking for. The questions you ask, have tons of info already posted and you will find enough stuff to make your head hurt!!!!!

    Then come back and post a thread for a specif thing if you can't grasp the information.
    I belive in the basic area their is info a plenty on sub calibration.

    Don't be discourged, it's just this subject has been hammered to death and people get tired of re-explaining things time and time again.

    Have at that "search fuction" and good luck, im sure we will here from you again.

    Regards
    Geoff
     
  3. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    Alright, I'll dictate what placement I would try but your listening position should be close to dead center of the room. If don't expect you to understand the physics behind placement but you might as well try it and see how it compares to 2 subs side by side in a corner...
    In theory, 2 subs against opposing walls would cancel out the odd order width resonances leaving one important one (2nd order). However, if you place the 2 subs in the nulls of the 2nd order resonance (equidistant from the walls) you should cancel them out as well.
    The location to put the subs would be about 1/4 of the distance from each side wall. So for a 10 foot wide room you'd place the subs (driver cone or port location) about 2.5 feet from each side wall. This should help a lot with those width axial room modes.
    Then place the subs 1/8th the distance from the front wall and the listener positioned in the middle of the room. This would leave only a 2nd order length mode "spike".
    Finally you may have a slight spike at 70hz if your mic is close to 4 feet from the ground from the first order (height) room resonance.
    The theory behind this is when you have one subwoofer producing a specific standing wave it begins at "+" phase, the signal will then flip(s) to "-" phase by the time it reaches the other subwoofer. This causes a cancellation of that room resonance. (Destructive cancellation ends up being good [​IMG])
    I will soon have graphs and data/pictures to back this all up and see how it holds true when I get my 2nd tempest (they are on back order).
    Here you can DL an EXCEL sheet that calculates all room modes I made and it can also graph room response if you have an SPL meter.
     
  4. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    BTW, the 2 subs should be in the same exact phase, signal, and output.

    I'd adjust it the same as you would one except when you change one, change the other the same way.

    The subs will be interacting with eachother and the room so placement, listener position, and room are equally crucial to how it will sound in the end.
     

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