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Thread: JBL Master Reference Monitor

  1. #841
    Senior Member pos's Avatar
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    Quote Originally Posted by ivica View Post
    Hi POS,
    Ma be interesting study of : Maximizing Performance from Loudspeaker Ports

    http://koti.mbnet.fi/jahonen/Audio/P..._PortPaper.pdf

    regards
    ivica
    Interesting paper, thank you Ivica.

    Here is the patent listed in the M2 brochure:

    https://www.google.com/patents/US7890312
    as a pdf: http://www.patent2pdf.com/pdf/07890312.pdf

  2. #842
    Senior Member Valentin's Avatar
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    Hére aré some pics. Of the M2







    The internal measurements are
    28cm deep
    45cm wide
    116.5 tall

    all bracing is 21mm mdf

    the woofer is in the exact center of the enclosure

  3. #843
    Senior Member pos's Avatar
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    Thank you so much Valentin!

    So based on your data, the exploded view, and actual external dimensions (from Don McRitchie), it looks like the walls are probably 1"... or maybe a little more:

    width: 500mm exterior (the JBL description states 508mm ?...), 450mm interior, which leaves 2*25mm for the walls (or 2*29mm if using JBL's dimensions)
    height: 1220mm exterior (ignoring the 12mm "plate", and the feet), 1165mm interior, leaving 2*27.5mm for the walls. Might the interior dimension be closer to 1170mm?
    depth: 350mm exterior (ignoring the waveguide/additional baffle/grille/port plate), 280mm interior, leaving... 2*35mm for the walls???

    On the exploded view it looks like the rear wall in indeed thicker, but it might just be the perspective.
    The front baffle already has an additional ~12mm wall (to line up with the external gasket on the 2216).
    So it might be something like 25mm for the front baffle (+12mm from the additional baffle), and 45mm for the rear one?...
    That seems a bit too much.

    Any though?

  4. #844
    Senior Member Valentin's Avatar
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    Quote Originally Posted by pos View Post
    Thank you Valentin!
    Is there a tubular part in the middle, or is the profile constantly changing?
    Could you measure the smallest diameter inside the tube?

    I think a 70mm tube with large inner and outer flares needs to be around 8" to get a 27Hz tunings in a 140L box.
    There is no tubular part in the middle it is a two part port and it is symmetrical the fiscal length is 16cm the inner diameter is 60mm or so I could not get it exact
    it has a constant curvature
    hope this helps

  5. #845
    Senior Member pos's Avatar
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    I also noted two interesting things in Valentin's photos:
    - The M2 has a "M2 D2430K" sticker on it, which would support the idea of a specific (sorted?) D2430K version for the M2 (different part number, no diaphragm available, etc.)
    - The small Wima cap is a 3.3uF, and the PCB is marked "rev B" whereas the value of the smallest cap in the original (rev A?) network published in the technical manual is 4.7uF.

  6. #846
    Senior Member pos's Avatar
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    Quote Originally Posted by Valentin View Post
    hope this helps
    This helps a lot!

  7. #847
    Senior Member Valentin's Avatar
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    Quote Originally Posted by pos View Post
    Thank you so much Valentin!

    So based on your data, the exploded view, and actual external dimensions (from Don McRitchie), it looks like the walls are probably 1"... or maybe a little more:

    width: 500mm exterior (the JBL description states 508mm ?...), 450mm interior, which leaves 2*25mm for the walls (or 2*29mm if using JBL's dimensions)
    height: 1220mm exterior (ignoring the 12mm "plate", and the feet), 1165mm interior, leaving 2*27.5mm for the walls. Might the interior dimension be closer to 1170mm?
    depth: 350mm exterior (ignoring the waveguide/additional baffle/grille/port plate), 280mm interior, leaving... 2*35mm for the walls???

    On the exploded view it looks like the rear wall in indeed thicker, but it might just be the perspective.
    The front baffle already has an additional ~12mm wall (to line up with the external gasket on the 2216).
    So it might be something like 25mm for the front baffle (+12mm from the additional baffle), and 45mm for the rear one?...
    That seems a bit too much.

    Any though?
    Yes the walls are 1" and the front baffle has an extra 15mm in the woofer position more in the port area
    yes the high may be 117cm it was difficult too measure since I had to remove de fiber too some extent and with the laser measure it was not easy

    but the interior depth and wide are correct

  8. #848
    Senior Member pos's Avatar
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    This is the small cap: http://www.ebay.com/itm/2pcs-WIMA-MK...item233124e482

    Wima MKP 10, 3.3uF, 250 VDC / 180 VAC

    Name:  643438M2networkcap.jpg
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  9. #849
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    Thank you very much Valentin!

    So ~ 46" x 17-3/4" x 11 " = 5.2 cubic feet gross volume.

  10. #850
    Senior Member macaroonie's Avatar
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    I'm wondering how you chaps are planning on going about making the curved front of the baffle.

    Sure you can shape the add on 15mm but as we know MDF gets a bit nasty on the inside , all flaky and fibrous. This then leads to added complication with finishing if you are going for a paint finish.
    Veneering , not so bad as CA can be used to stabilize the MDF core.

    In my various researches I have come across a company in the US that does a natty line in curved birch plywood , even tubes.
    I seem to recall them doing curves up to 96" radius.

    http://www.aitwood.com/

    http://www.roberts-plywood.com/

    Plenty of scope for some alternative methods.

    M

  11. #851
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    Yep finishing an mdf curved panel is a pain, that's why I covered mine in leather.

  12. #852
    Senior Member Mctwins's Avatar
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    Nice Pictures

  13. #853
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    Quote Originally Posted by pos View Post
    .. specific (sorted?) D2430K version for the M2 (different part number, no diaphragm available, etc.)..
    so reconingspeakers's "JBL D2430K Tweeter for JBL M2 #5032754X" may be not "JBL D2430K Tweeter for JBL M2"?..
    el goregrind es cultura

  14. #854
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    Quote Originally Posted by Flaesh View Post
    so reconingspeakers's "JBL D2430K Tweeter for JBL M2 #5032754X" may be not "JBL D2430K Tweeter for JBL M2"?..
    What pos says makes sense ( & that philisophy usually applies to any studio monitor ) .

    ie ; Studio monitors generally get loaded with more tightly matched ( hand-picked ) components ( that actually live up to the design specification ) .

    I doubt that the common guy can buy "the very best" D2430K drivers .


  15. #855
    Member Flaesh's Avatar
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    Quote Originally Posted by Earl K View Post
    I doubt that the common guy can buy "the very best" D2430K drivers .

    Will see at the end of the month when, as reconingspeakers said, they must be in stock.
    el goregrind es cultura

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