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woofer response dip at 50hz

Discussion in 'Archived Threads 2001-2004' started by SteveEdwards, May 13, 2002.

  1. SteveEdwards

    SteveEdwards Agent

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    Hey everyone! It's been a while since I've posted here! Anyway...
    [​IMG]
    On the factory frequency response graphs for just about every Eminence woofer, there is a huge dip between 40-50hz. Is there a reason for this? Most of the drivers have an fs of 40hz or below, and the dip is usually higher than that.
    When designing a box, should I assume the driver's usable response goes down to the fs or down to where the chart shows the dip?
     
  2. Patrick Sun

    Patrick Sun Studio Mogul

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    Are you sure it's not a room suck-out problem?
     
  3. Looks like a room induded null to me.
     
  4. Wayne A. Pflughaupt

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    Steve,

    Judging by the appearance of this chart (very flat response) and your statement, “On the frequency response graphs for just about every Eminence woofer, there is a huge dip between 40-50hz,“ I’m guessing this plot is provided from an Eminence brochure or website?

    If that’s the case, it’s nothing to loose sleep over. A manufacturer’s anechoic response plot bears little resemblance to the in-room performance the end product (although it’s nice to know you’re starting from a good place). The enclosure type and size and effects of the room will have an even greater effect on the sub’s response plot than the driver’s raw specs.

    As for your questions about usable response and fs, I’ll leave that to the more Thiele-Small literate among us.

    Regards,

    Wayne A. Pflughaupt
     
  5. SteveEdwards

    SteveEdwards Agent

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    These are Eminence factory charts. Why would they use an anechoic response plot with an in-room dip? Seems funny, especially when they're selling bass drivers to be used in huge rooms (even outdoors).

    BTW, I'm looking to build a 2-way DJing speaker with the Delta 12LF for mids and another 12LF for extra bass to bring to larger gigs. The 12LF has an F3 of 45hz in a 2ft^3 box... now that's portable!!! The Kappa 15LF looks good too, but the 2ft^3 box is too nice to pass up.
     
  6. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    The response chart can change a lot once you put in the box, ports, room/placement into the equation. I sure wish my speakers had a response curve as flat as the specs but I have more adjusting to do.

    That would be cool if you played a large sub outdoors and the sound waves could wrap around the earth forming a bass loop harmonic.
     
  7. Wayne A. Pflughaupt

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    Steve,

     
  8. Anchaic responce is relatively easy to achieve for the higher frequencies. ..to achieve anochaic in the 40hz area is a serious matter. Just visualize the damping material thickness they would need to achieve that low of an anochaic responce!!!

    ....so IMO, that is a room null...even though it is an anochaic responce.
     
  9. SteveEdwards

    SteveEdwards Agent

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    Eminence is the world's largest professional loudspeaker manufacturer. They should be able to afford this!
     
  10. Wayne A. Pflughaupt

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    Not to mention, there are methods to take ultra-quick readings before the room’s sound reflections begin to influence.

    Also the plot shows the dip is almost 1/3-octave wide. Room nulls are typically half that, 1/6-octave wide or less.

    Regards,

    Wayne A. Pflughaupt
     
  11. Mark Krawiec

    Mark Krawiec Agent

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    I'll give you my guess.

    This is a quasi-anechoic measurement and so the low frequency data is meaningless. Unfortunately, they don't say what is the low frequency cutoff. A nearfield plot could be used to look at the low frequency plots below 200-500(unfortunately, this plot is not given) and use their listed plots to measure fr response above say 200-300 (the exact number depends on the radius of the driver for a nearfield measurement and more on the end of the time interval of the mls response in the time domain...blah, blah, blah...)

    i.e. without the details of the measurement, you're not really sure.
     

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