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w6-2144 Transmission Line Issues

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  • w6-2144 Transmission Line Issues

    I have been trying to delve into the Transmission Line cabinets for some time now with mixed results. I picked up a set of T angband W6-2144 full range drivers when they were on sale a few weeks ago. Thought they would be a great candidate for this style of enclosure. But, I have been getting very frustrated with this project. The stated Fs of the driver is 45Hz with a Vas of 34.6, so I used these parameters, along with the rest of the T/S to design an expanding MLTL. Here is a picture of the cabinet.



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    The cabinet was designed using the Leonard Audio Program. I then installed the driver and ran OmniMic on it, the results were very disappointing.
    Click image for larger version

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    It basically has very little bass, really falls off below 100 Hz. This information was gathered with no stuffing. I then ran an impedance on the enclosure and here are the results.
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    So the enclosure looked fine. When designing the speaker I used the published data from Tangband so I decided to get the T/S parameters using DATs, the results showed huge discrepancies:

    Tangband Stated DATS measured
    Re 6.8 6.4
    Fas 45 Hz 63 Hz
    L(e) .01mH .08mH (10K)
    Vas 34.6 liter 14.6 liter
    Qts .45 .47
    Qms 1.73 1.63
    Qes .62 .66
    Mms 8.98 10.8

    I'm assuming the correct answer is to build a new cabinet with the measured T/S parameters. I guess I have a couple of questions:
    1) Can anyone see if there is something blatant I'm missing here?
    2) Has anyone seen this kind of discrepancies in the T/S parameters between stated and measured. I thought I had to be doing something wrong. So, I measured both drivers twice and came up with very similar results.

    Any thoughts would be greatly appreciated.


  • #2
    DATS is pretty foolproof (as long as you don't have a motor vent blocked/restricted) re: all measurements except Vas (which CAN vary due to op "experience").
    Bottom end reach is based on Qts and Fs, so... THAT driver misses it's advertised F3 by maybe 15Hz? (SEEMs like a lot)

    If you broke in the driver('s suspension - spider mostly) by hand (carefully pushing to Xmax several times) or electrically, you could expect a drop in Fs (with a corresponding drop in Qts, and an increase in Vas). I don't think it would greatly change your box model though.

    YOUR measurements are what you should use. If you feel as though the driver can't live up to your plans, you could try to return it and pick something more appropriate.

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    • #3
      If that's the impedance curve with the enclosure unstuffed, then you've got some losses going on there somewhere. The dip between the peaks should be quite a bit deeper, almost reaching the driver's Re.
      Brian Steele
      www.diysubwoofers.org

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      • #4

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        • #5
          This was after sealing the speaker wires and installing the driver gasket. Thanks for the reply Brian. Very surprised that such small amounts of leaks can change things like that.

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          • #6
            Looks like you've still got some leaks somewhere. That dip should be a bit deeper.
            Brian Steele
            www.diysubwoofers.org

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            • #7
              Originally posted by grubby65 View Post
              This was after sealing the speaker wires and installing the driver gasket. Thanks for the reply Brian. Very surprised that such small amounts of leaks can change things like that.
              Yep. Early on, I tried "sealing" temporary boxes with blue painters tape. The impedance measurements were useless and confusing.
              Use thick weatherstripping if necessary and screw or clamp panels tight.

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