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Thread: After 5 years it finally begins

  1. #16
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by sebackman View Post
    The left and right speakers will be rather shallow to look "smallish" on the wall. I know that will impact low end but with DSP and reasonable amount of power in a normal living room I think I can compensate for the fall off below 200hz. I will XO @ 70Hz towards the subs. I hope that will be fine.
    I have found shallow boxes to allow more midrange coloration to reflect back through the LF driver's cone. You may want to explore internal diffusers or Sonex foam on the back wall of the enclosure to help mitigate this.

    Have you mocked them up?


    Widget

  2. #17
    Member sebackman's Avatar
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    Hi Widget,

    Thank you for the input.

    I did experiment a little with current cabinets that are also shallow. However, in the end I just settled for a layer of wool felt (about 1/2") applied with excess material creating an un-even surface on the rear wall and some more damping in the box. There is also some bracing on the back wall that limits the flat surface.

    Once I get these new cabinets, I will have a go at checking if such addition of a diffusor foam at the back is audible. I do have some triangular shaped diffusor foam in the shop but I have no idea how it react over frequency. Good ideas must be tested.

    At reasonable levels in a living room I guess the potential distortion is limited. At higher volumes it may prove more problematic. My system rarely sees concert levels unfortunately. :-)

    The wool felt is actually the same wool felt I use in the drivers when removing the often-aged foam in the rear cover. I typically just remove the old foam and cut a circle of the wool mat and glue in. I cut the circle the same size as the outer diameter of the back cap and when I glue it in it will nicely cover the sides a little like in the 475Nd/476Nd. I recognize that they a have larger back caps but this works just fine. I also added a picture of my favourite diaphragm in the 2451 cores, now difficult to find.




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    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  3. #18
    Member sebackman's Avatar
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    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  4. #19
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    wow !

    Wow !

    Those cabs look nice !

  5. #20
    Member sebackman's Avatar
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    Christmas comes early this year.

    Sorry for picture being upside down. No idea how to fix that. Normally ok, but this was uploaded from an iPad.
    Attached Images Attached Images  
    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  6. #21
    Member sebackman's Avatar
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    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  7. #22
    Administrator Mr. Widget's Avatar
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    Looking great!
    Oh, and I fixed your previous image... much easier to see with it right side up.


    Widget

  8. #23
    Senior Member srm51555's Avatar
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    Yes looking great, progress is moving along pretty nicely.

  9. #24
    Member sebackman's Avatar
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    Still some work needed on the WG to make room for the 045. Slowly getting there.

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    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  10. #25
    Senior Member pos's Avatar
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    "RoB 1"

    Very cool looking Robert!
    That is a one of a kind and very refined system for sure, and with these top components and well executed integration it is going to be top notch for sure

  11. #26
    Member sebackman's Avatar
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    Hi POS,

    Rob1 was the first M2 WG sold as a spare part back in 2014. That is where it started.

    Now butchered to form something else.

    More info to follow.
    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  12. #27
    Member sebackman's Avatar
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    Saturday fun in the shop.

    2430k, 2451/475Nd, 2451Be & 2453SL

    Impedance sweep naked, with VTX horn and M2 horns.

    Tomorrow frequency measurements on all combinations.

    Slowly getting there. :-)

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    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  13. #28
    Senior Member ivica's Avatar
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    Quote Originally Posted by sebackman View Post
    Saturday fun in the shop.

    2430k, 2451/475Nd, 2451Be & 2453SL

    Impedance sweep naked, with VTX horn and M2 horns.

    Tomorrow frequency measurements on all combinations.

    Slowly getting there. :-)
    Hi sebackman,

    Only JBL Be diaphragm the (476) is "missing"....
    Anxiously waiting the measurements...

    regards
    Ivica

  14. #29
    Member sebackman's Avatar
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    A peak

    2430K and 2451Be on M2 WG. Be is smoother but falls off sharpely after 15k.

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    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  15. #30
    Member sebackman's Avatar
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    Huge plans to cover some ground during the holidays was abandoned in the same pace they were made.

    At least the cabinets are now reinforced for wall hanging and wall mount cups for left and right installed. The baffle is cut out to make way for the 045’s.

    045 horns are attached to M2 wave guide and 045 drivers are attached to the horns.

    Later this week I will remove the remaining two 2451Be’s from the old system replacing them with 2453SL’s and changing them from 3-way way to 2-way.

    The measurements I did on D2’s with and without the passive JBL M2 filter show that the capacitor is mainly a protection cap and replacing it with a 6db filter in the BSS/DSP achieves nearly the same curve. The cap in the M2 filter is not a Butter slope, the D2 extends a little further down with the cap compared to 6db Butter I used in the DSP. Please see picture.

    The XO used in my measurement corresponds to HP 6db filter at 957Hz. The frequency is the result of running a backwards calculation from a calculated 20,8 ohms load that the 8mf in series in the original JBL filter would be seeing. The 20,8 ohms load seen from the cap is a result of the average impedance between 800Hz and 20kHz (26,3 ohms) of the D2 driver on the M2 and 13 ohms in series and the 11ohms shunt in the filter. Lowering the XO can probably mitigate some of the difference, but the passive cap is probably not a Butter curve with those resistor values.

    If you are building an exact M2 clone (this build are rather ClownsJ ) I would recommend keeping the passive filter to mimic the exact JBL curve. However, I do think it is possible to change the slope and/or the cut off frequency (lower) of the 6db filter in the DSP do achieve an identical curve without the cap’s, for the one willing to invest some time.

    In my build I will use 4” drivers with Be diaphragms and 045 UHF’s so I have no curve to adhere to, except for the almighty “straight line”, so I will not use capacitors for the 4” drivers, only an attenuator with -8db. They are sturdy enough.

    For the 045 UHF’s I will use a cap for protection as they are much more fragile than the 4” and I cannot use an attenuator for protection as the sensitivity is low, 87db @ 4ohms. That gives me about 90db when compared with the other drivers that are 8ohms. That will imply a real boost in the DSP anyway.


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    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

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