How do you calibrate a duel sub configuration ?

Discussion in 'Speakers & Subwoofers' started by Chip E, Apr 11, 2003.

  1. Chip E

    Chip E Screenwriter

    Joined:
    Nov 25, 2000
    Messages:
    1,165
    Likes Received:
    0
    Trophy Points:
    0
    In my upgrade trek, my SV sub is next. Right now i've got an SV 20-39PC w/original driver. If i was to go with duel subs, like let's say, duel 20-39PC+'s, how would i go about calibrating them ? With my current sub i just go to the test tone for my sub on my Ref50. Do i only turn one of them on and do one at a time ? Or, do you turn the amp and phase to identical positions on the back of the powered woofs ? Assuming these two subs would be right next to each other.. (left & right of each other or, front & back to each other ? ) Thanks gang..
     
  2. Chip E

    Chip E Screenwriter

    Joined:
    Nov 25, 2000
    Messages:
    1,165
    Likes Received:
    0
    Trophy Points:
    0
    /
     
  3. Bob McElfresh

    Bob McElfresh Producer

    Joined:
    May 22, 1999
    Messages:
    5,182
    Likes Received:
    0
    Trophy Points:
    0
    The guys as SVS do recommend putting multiple subs right next to each other to solve phase/cancelation issues.

    You want their individual phase knobs at the same spot and you use subwoofer test-tones to both with a SPL meter to level-adjust.

    You basically treat them as a single subwoofer unit.
     
  4. Chip E

    Chip E Screenwriter

    Joined:
    Nov 25, 2000
    Messages:
    1,165
    Likes Received:
    0
    Trophy Points:
    0
    Thanks Bob.. That sounds simple enough! Is it recommended to turn the amps all the way up and adjust from my pre ? (or as close to full vlome as the Ref50 will let me adjust downward?)I currently have my 20-39 amp volume set at around 1:00 to 2:00 position.
     
  5. Bob McElfresh

    Bob McElfresh Producer

    Joined:
    May 22, 1999
    Messages:
    5,182
    Likes Received:
    0
    Trophy Points:
    0
    In truth, it really does not make audible difference if you use the receiver LFE or the subwoofer volume knob when calibrating.

    But under the heading: "I want to do it right even if I cannot hear it": Turn the sub volume knob up to about 75%, keep the receiver LFE level down in the -5 range and adjust.

    There are 2 reasons behind this advice:
    • That sub knob was designed to work with the power needs of the sub. The people who designed/built the thing probably made sure it would work at all positions.
    • They found that the LFE port on many receivers create a LOT of distortion as the LFE setting is turned up. With regular speakers or amps you talk about something like 0.07% THD being the limit of acceptiable. But the LFE port produces 1-5% THD as you crank it up. Receivers have been doing this for years and nobody noticed til a few years ago when somebody hooked up a distortion analyzer to the LFE port.
     
  6. Chip E

    Chip E Screenwriter

    Joined:
    Nov 25, 2000
    Messages:
    1,165
    Likes Received:
    0
    Trophy Points:
    0
    Thanks again Bob...appreciate it.
     
  7. Geoff L

    Geoff L Screenwriter

    Joined:
    Dec 9, 2000
    Messages:
    1,693
    Likes Received:
    0
    Trophy Points:
    0
    Early Yammi Surround, & DD receivers where known for heavy distorion when their Recevers LFE was run high.

    Interesting and true with many units, that is, a Receivers or Pre's LFE "distortion output possibilitys" when running the LFE very high.

    One of the High End Mags measured a (mid line) Suround Sound, DD, "no-DTS" Yammi receiver with it's LFE gain at 3/4's up, at well over 1.5% distortion.
    At wide open it was approaching "4%"!
    LFE scale on the Yammi went from 0 to 20. It got excellent review except for that.
    Granted this was quite some time ago and certainly was not Yamahas top flight Receiver of the time.

    Always better to run the Receivers or Pre's LFE at it's mid point and if you need more volume to calibrate it's SPL output correctly, use the sub/s volume pot/s.

    Do any of todays Receivers or Pre's give distortion numbers for their max LFE out beside the min & max voltage output?

    Regards
    Geoff
     
  8. Edward J M

    Edward J M Cinematographer

    Joined:
    Sep 22, 2002
    Messages:
    2,031
    Likes Received:
    0
    Trophy Points:
    0
    I agree with the distortion theory of running the subwoofer level in the receiver at its midpoint or a bit lower and adjusting for SPL at the sub amp.

    If you will be placing the subs in the same location, keep the phase controls and the volume controls set the same. Remember, adding a second sub in the same location will add approximately 6 dB of volume, so accomodate for this calibrating.

    While it is much more work, the latest research on multiple subs suggests you might actually obtain the best overall results (i.e., flattest FR with the least peaks and nulls) with the subs in different locations. Along the same wall 1/3 from each corner seems to be a good starting point. With regard to the phase control settings, you will probably need to burn some test tones and plot the FR of one sub, and adjust its phase until it blends the best with the mains. Then bring the second sub on line and experiment with its phase control until you obtain the least cancellation with the first sub.

    Try these websites for more information:

    http://www.harman.com/wp/index.jsp?articleId=1003

    http://www.hometheaterhifi.com/volum...rs-9-2002.html

    http://www.guidetohometheater.com/shownews.cgi?388

    Good luck with your dual SVS Plus upgrade. I'm sure with a bit of work on your part, you will be thrilled.

    Regards,

    Ed
     

Share This Page