Ragged Sub Response - Suggestions?

Discussion in 'Archived Threads 2001-2004' started by Bob U, Jan 25, 2002.

  1. Bob U

    Bob U Stunt Coordinator

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    Hi there,
    I have two Sunfire True Subs Mark II's running from the LFE out of my pre/proc that have a very ragged response no matter how I seem to place them in the room.The proc xover is set to 80Hz, the subs crossovers all the way up. In phase seems to be better at 80Hz by a dB or two.
    Since I have floor to ceiling bass traps behind my mains in the front corners, I keep the subs away from the corners. And since they fire both front and rear, I have the active drivers firing forward. This is audibly better than against the front walland firing to the sides.
    The room dimensions are 9' x 16.75' x ?? as the dining room and hallway are connected. I have put up a spread sheet with a room diagram and layout as well as curves for 5 different room locations at Room Layout and Test Link. You can see a reasonable representation of the room there and you'll note that all of the responses have dramatic peaks and dips.
    Is there anything I can do to smooth this without an EQ? Would front firing subs improve the response curves?
    I'd appreciate any and all suggestions.
    -=Bob=-
     
  2. joe logston

    joe logston Stunt Coordinator

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    try puting them back to back, and move them around the room, it would be like a side fireing subyou want them to fire to the front and to the back try it and get back to me thank you, joe
     
  3. Bob U

    Bob U Stunt Coordinator

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    Joe,

    They already fire front and back which I suspect is part of the problem. No way to arrange Sunfires as you suggest.

    -=Bob=-
     
  4. ColinM

    ColinM Cinematographer

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    Have you ever stacked them?
     
  5. Bob U

    Bob U Stunt Coordinator

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    No, I haven't. I actually ran them in stereo for quite awhile and in some ways much preferred that.

    I would think the main advantage of stacking is increasing output level, and I have more than enough of that. Just a very ragged speaker/room response curve.

    But for the hell of it, I'll disconnect one tomorrow and see if the response is any smoother with only one operating.

    -=Bob=-
     
  6. Wayne A. Pflughaupt

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    Bob,
    The problem starts with your split configuration, and is compounded by the out-in-the-room placement.
    When the sound wave from the sub hits the wall it reflects back, out of phase. Thus there is cancellation at a specific distance-related frequency as the sub interacts with each boundary in the room. (The affected frequency at 6ft. is about 56Hz; affected frequencies are lower at longer distances and higher with shorter distances.) As a consequence, out-in-the-room placement results in cancellation at four different frequencies.
    In your asymmetrical room, the subs each have different boundary situations, which only adds to the number of affected frequencies. In addition, the half-way point between the two subs acts like a boundary, so there is yet another canceled frequency.
    Thus, Bob, it is no surprise that your low frequency response is hopelessly ragged, due to the large number of boundary-affected (cancelled) frequencies.
    You will have the best results by putting both subs in the corner, one with the longest uninterrupted wall length in both directions. The front left corner (i.e., away from the stairs) looks idea from your picture. With corner placement, two boundaries are so close to the sub that the sound waves reflect out of the corner in-phase with the original signal, essentially doubling output (and the second sub doubles output again). The wall at the end of the dinning room is so far away that the cancelled frequency will be well below the sub’s operating range. That only leaves the wall at the staircase as a cancellation issue.
    So, corner placement will not only significantly increase output, the numerous cancellation issues are reduced to one. You can still expect a response peak or two, naturally, but they can be easily addressed with a parametric equalizer -- unlike the ragged response we had before, which is often so bad in many cases not even an equalizer can fix it.
    Speaking of equalizers, I hate to be the one to break it to you Bob, but achieving smooth response in most rooms without one is wishful thinking. With an equalizer you can usually achieve excellent sub response, but without one the best you can hope for is response you can live with.
    However, the good news is that a dedicated sub equalizer is inexpensive – a fraction of what your two Sunfires set you back. It really makes no sense to buy top-fight subs and never get the best from them.
    Another suggestion: Get a test disk with at least 1/6 octave resolution. This will get much better results than the 1/3 readings you are getting now.
    Regards,
    Wayne A. Pflughaupt
     
  7. Bob U

    Bob U Stunt Coordinator

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    Thanks for the thoughtful reply, Wayne.

    Do you think that corner placement even with bass traps there is the way to go? When I was "just" stereo, they did such a fine job of tightening the bottom on my mains, and still do. I haven't put the Sunfires there because of the lack of corner, so to speak, but it seems worth a try.

    And I do have 1/6th octave test signals, just posted 1/3rd for simplicity. And with -8 +22dB curves, the 1/6ths would probably only look worse.

    -=Bob=-
     
  8. Bob U

    Bob U Stunt Coordinator

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    Well, I couldn't wait until morning so moved both subs into the corners even with the bass traps there. The curve smoothed *very* little, surprisingly. Now -4.5 / + 21 dB.
    I've updated the tables on my spreadsheet at Link to Room Layout and Response Curves .
    In the morning I'll try just one sub to see if that is smoother.
    -=Bob=-
     
  9. joe logston

    joe logston Stunt Coordinator

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    you missed under stood me,i was saying face one of the drivers to the front wall, and face the other to the back wall, put both subs back to back, sorry for not explaning it to good. but the sunfire subs are already harsh to my ears they are over powerd they got to give them that much power to get the low bass # in a small space thats what the problem is a larger incloser is better for a sub. thank you,joe
     
  10. Bob U

    Bob U Stunt Coordinator

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    Just updated the charts on the link above by using just one sub in the corner. Level dropped from 6-10dB in places, which is to be expected. Lost a lot at 20Hz, but from 22.5Hz to 80Hz is now -5 +15.5 dB.

    Not as good as I might have thought, but the smoothest curve yet in this room.

    If I had nothing else to do and a lot of energy, I'd pull out the bass traps and test again. But at this point, I'm thinking about a compromise placement and a parametric.

    What do you all recommend in an analog parametric or 1/6th octave graphic? I have had bad Behringer experiences so I will avoid the BFD.

    -=Bob=-
     
  11. Wayne A. Pflughaupt

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  12. joe logston

    joe logston Stunt Coordinator

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    all the eqs. going to do is roll the subs off at the bottem it mite work but you should try again for placementtry one in each corner on opposite sides one in the back one in the front and reverse the phase 180 degrees on one of them try that dont give up yet. thank you,joe
     
  13. joe logston

    joe logston Stunt Coordinator

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    on that set up it would be like a push pull configeration one pushing the air and the other is sucking the air it mite work thanks again, joe
     
  14. Wayne A. Pflughaupt

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    Joe,

    Equalizers to not inherently roll off the bottom end. You would have to intentionally set it that way.

    Bob,

    You’ve already found the spot with the best unequalized response. Build on that. No need to keep moving the sub around.

    Regards,

    Wayne A. Pflughaupt
     
  15. BruceD

    BruceD Screenwriter

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    Joe,
    Your suggestion of a sub in opposite corners, "on that set up it would be like a push pull configeration one pushing the air and the other is sucking the air it mite work thanks again, joe "
    Is not a good recommendation. That positioning is typically the absolute worst possible configuration for smooth bass response in a room with multiple subs.
    TomV at SVS subs also agrees this is typically the worst possible setup configuration.
    Also go to the end of this thread where Wayne talks about opposite corners specifically. here
    First, one should try both subs in the same corner with the longest wall and farthest away from any openings.
     
  16. ling_w

    ling_w Second Unit

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    BruceD,
    I don't think opposite corner is the worse way to place a sub (although I don't quite agree with the out of phase hookup.) Opposite corners frequently will result in the inability for odd room modes to not build up, since the 2nd sub would pretty much produce a signal that is 180 deg out of phase for wavelength 2x the room length/width, and so on.
    If you are not so concerned about room width mode, subs at the opposite ends of a room, along the same length of a wall would have the same result as above.
    A paper describing it is shown here:
    http://www.sonicdesign.se/subplace.html
    As far as the Wayne's test. It dealt with out of phase, and the test only involved direct sound, since the 2nd sub was not near any boundary for the standing waves generated by the 1st sub to interact with the 2nd sub.
     
  17. BruceD

    BruceD Screenwriter

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    ling,

    You didn't correctly read that paper you provided a link to as it relates to the discussion of opposite corner subs. The paper describes the 2 front corners, while we have been discussing the front left and right rear (opposite corners) here.

    So again, I say opposite corners as I described above is the worst positioning of 2 subs.
     
  18. ling_w

    ling_w Second Unit

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    Having 1 sub in each corner would eliminate both the room length and width standing wave. A poor man's implementation would be to have the subs in opposite corner, since the existing subs would cover for the missing ones in terms of producing waveforms in the length and width-wise direction. The length and width-wise soundwave from one sub might not interfere with the sub in the opposite corner with its direct soundwave, but might take a few bounces to reach the other side of the room. This is still better than full room mode resonance, where T60 runs much longer than the time it takes sound to bounce back and forth a few times along the length of the room.
     

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