Are my floor-standing speakers too far from the wall?

Discussion in 'Speakers' started by John Pine, Mar 3, 2005.

  1. John Pine

    John Pine Supporting Actor

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    When testing with AutoSound 2000 #101, I’m getting an 18dB+ drop around 62Hz with my JBL S-310 II’s. I’m using an analog RS meter and I did compensate by using SVS’s recommended numbers. My towers both are approximately two feet from the wall. I moved them that far out to make them physically parallel with my S-Center II, that sits on my TV. Could that distant cause a mid-bass drop-out around 62-70Hz? Hmmm...or maybe it’s just the speakers. Any feedback?

    p.s. For testing, I’m using a optic connection from my 2900 and the two-channel “Surr Off” mode with the cross-over set to 40Hz on my 525.


    My 5.1 setup:

    Toshiba 35"
    harman/kardon AVR 525 (preamp)
    Parasound HCA-2003 (mains & center)
    harman/kardon PA 2000 (rears)
    Denon DVD-2900
    JBL S310-II's
    JBL S-Center II
    JBL S36-II's
    SVS PC-Ultra
    All Better Cable interconnects,
    Panamax MAX 4300
    18'x23'x12' vaulted ceiling (LxWxH)
     
  2. Greg_Hammond

    Greg_Hammond Agent

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    See if you can set your AVR to full-range with no crossover to ensure that you're not filtering out the < 62 Hz frequencies going to the fronts. I doubt that moving the fronts 2 feet away from the wall would cause that sharp of a drop in frequency response in that range.

    If removing the crossover setting doesn't help any, try hooking your front mains directly to the AVR 525 and using the on-board amplifiers to see if there is a response difference. Naturally, you won't get the power output that you do from your Parasound, but you can at least remove a link from the diagnostic chain.

    If I had to put my finger on it, I'd say you got some odd crossover settings in the receiver that are cutting the low frequencies from the mains. The HK has independant crossover settings for fronts and center, it may be possible the unit isn't behaving the way you expect it to.

    Greg
     
  3. John Pine

    John Pine Supporting Actor

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    "See if you can set your AVR to full-range with no crossover to ensure that you're not filtering out the < 62 Hz frequencies going to the fronts. I doubt that moving the fronts 2 feet away from the wall would cause that sharp of a drop in frequency response in that range."

    Thanks, good idea Greg. I'll retest with the 525 set to large for the mains. Should I turn the sub off?
     
  4. Rich Malloy

    Rich Malloy Producer

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    I'm not sure why you're getting that particular suck-out, but two feet off the front wall is by no means "too far". I'd say it's only barely far enough (and particularly if you have a large boxy TV jutting out in-between). I know there exists some software to determine room nodes that might help in your placement... it might even be possible that moving them further into the room can counter a particular node in that frequency range even as that placement also has the effect of otherwise reducing the bass support you get off the front wall.
     
  5. John Pine

    John Pine Supporting Actor

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    "I'm not sure why you're getting that particular suck-out, but two feet off the front wall is by no means "too far". I'd say it's only barely far enough (and particularly if you have a large boxy TV jutting out in-between)."

    Good info Rich, that's what I was thinking as well. I thought if they were too close to the back wall, I would be getting mid-bass (boost) coloration.
     
  6. BrianWoerndle

    BrianWoerndle Supporting Actor

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    You are probably getting a room mode cancellation. It could also partly be the native response of the speaker. Unless you can take readings in an anechoic chamber, you will never know the speaker, room, or electronics.
     
  7. Kevin C Brown

    Kevin C Brown Producer

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    I have always liked Vandersteen's suggestion for distances:

    He says the best setup is speakers at 1/3 the distance into the room from the front wall, and seating 1/3 from the back wall. (The distance from the speaker to the side walls should *not* be equal to the distance from the front wall.)

    If you can't do 1/3's, he says try moving the speakers to the 1/5 point, 1/7 point, etc. That way, you *minimize* the interaction of the speaker to the nodes in the room. (Nodal points are always at 1/2, 1/4, 1/8, etc.)

    Also, that distance is from the wall to the "acoustical center" of the speaker. That point is usually a few inches behind the front face of the speaker. Basically, where the voice coil of the lowest freq driver is.
     
  8. Chris Quinn

    Chris Quinn Screenwriter

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    Try modeling your room here.
     

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