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  1. #1
    Senior Member srm51555's Avatar
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    Project M2 DIY Thread

    Since the JBL Master Reference Monitor thread is so massive I'm staring a thread that I and others can document our M2 DIY process if the. Here are some links that I was able to reference. Thank you for all of your contributions that made my and others project happen.

    Schematic of the M2 - Note: C2 in the schematic shows a value of 33.3uf, this is a typo. the correct value is 3.3uf

    DSP File

    Inside the M2

    Outside the M2

    M2 Dimensions

    Horn Mounting

    Horn Mounting pt2

  2. #2
    Senior Member srm51555's Avatar
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    Here is the photo progression of my project. Cabinets were glued with Titebond 2 and Spax MFD specific screws.

    I originally started out with using 1"x2" strips of particle board for bracing. After some recommendation I moved over to using Baltic Birch to achieve a better brace matrix. The particle boards were glued and screwed so they stayed in. With the extra volume they took up I was unable to brace exactly like the M2 in the top and bottom sections.
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    Next came the primer to seal the inside. It's a 2 part epoxy primer and I sprayed 2-3 coats of it on. I taped certain sections of the cabinet and bracing I could properly glue and screw baffle on.

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    Next came the dampening material. I was unable to locate the Owens Corning stuff POS recommended locally. I then was recommended two other options. Wrap on 16550 Bulk Roll Fiberglass or get the regular pink stuff from Home Depot and make it 1". My original plan was to use the Wrap on stuff but I realized I already had a roll of the pink stuff and figured I'd better use it since I've been storing it for this occasion.

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    I left the horn cutout process till after the baffle was installed because I wanted to be sure the horn was in the correct place.

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  3. #3
    Senior Member srm51555's Avatar
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    Current state, I still need to drill holes for the woofer and horn. Also I was original going to paint to standard black. Since then I've run the thought of painting it some other color, any thoughts. These will be in a dedicated room so WAF is not a problem.

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  4. #4
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    I think you'll want that fiberglass to be lining all the interior surfaces except the back of the baffle - especially behind the woofer.

  5. #5
    Senior Member srm51555's Avatar
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    That is the plan. I left it out because I was going to send it to paint. Since then it's gotten to dang cold to properly prep so I will most likely put it in so I can finally hear them and be left with an unfinished cabinet for the winter.

  6. #6
    Senior Member 1audiohack's Avatar
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    Well the M2 HF protection network comes with a small surprise.

    ATTACH]68669[/ATTACH]

    The cap values are 3.3µF and 4.7µF.
    Attached Images Attached Images  
    If we knew what the hell we were doing, we wouldn't call it research would we.

  7. #7
    Senior Member Hoerninger's Avatar
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    Us 7,890,312

    Method for predicting
    Loudspeaker port performance and
    optimizing loudspeaker port
    designs utilizing bi-directional
    fluid flow principles

    AES_PortPaper:
    http://koti.kapsi.fi/jahonen/Audio/P..._PortPaper.pdf
    ___________
    Peter
    Attached Images Attached Images

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    Member Fitero's Avatar
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    Thank you for the interesting technical information and gentle comments.

    I don't mean to be obtuse, but this is how I see it; the engineers at JBL have already completed the necessary port calculations, and through subsequent trial and error, have fitted ports that they deem the best compromise for this enclosure.

    Port design theory got them close. Listening and modification got them exactly how they wanted it to sound.
    It seems more prudent to defer to their experience and knowledge and build as closely as possible to theirs.
    By blindly copying their dimensions, I can save an enormous amount of time, and avoid making errors.

    Where I can surpass the original design is by making the ports with better flow characteristics. Their method of joining two bells in the center has left a sharp ridge, which for a venturi is anathema and results in disruption of laminar air flow.

    So again, a simple measurement of the bell diameters, port length and centre I.D. is all that is needed to make the copy.

    If that can't be obtained, then you are right in that I would have to rely on available port calculations to get a brute proximity.

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    Quote Originally Posted by srm51555 View Post
    Current state, I still need to drill holes for the woofer and horn. Also I was original going to paint to standard black. Since then I've run the thought of painting it some other color, any thoughts. These will be in a dedicated room so WAF is not a problem.

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    If you plan to use 'standard' fibreglass you may want to generously spray it with hairspray to fix those pesky fibres.

  10. #10
    Senior Member srm51555's Avatar
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    Thanks for the tip. Who knows, I may rip this stuff out and replace it with the wrap-on stuff, it's all pending on how sealed I can get the cabinet when painting it.

  11. #11
    Senior Member Lee in Montreal's Avatar
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    I suggest you router all corners with a straight bit, to make them flush. It will take 5 minutes per cabinet and they will look even better. ;-)

  12. #12
    Senior Member 1audiohack's Avatar
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    Hi All;

    I thought that since JBL did such a bang-up job with the M2 that to start out at least I should start with this little network in just to be sure I had the top end right.

    I am going to depart from the design with a 4435 type cabinet and four 2216's. I just like the form and two 15's close coupled gives me the sound I love. I have one but still have to buy two more I-Tech 5000Hd's, ouch! At first I will likely just run the woofers on a DBX260 and a pair of non DSP amps.

    I ran the drivers on the PWT and they are pretty well matched and have consecutive serial numbers, two nice surprises. The top curves are direct drive and the lower two are with the M2 network in series. The network pads the driver down 9.2dB from 3kHz on up and is down 12 dB by 250Hz.

    I can't wait for Christmas break to build cabinets!

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    If we knew what the hell we were doing, we wouldn't call it research would we.

  13. #13
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    Cabinet Mass, de coupling and frontal baffle

    Quote Originally Posted by srm51555 View Post
    Here is the photo progression of my project. Cabinets were glued with Titebond 2 and Spax MFD specific screws. I originally started out with using 1"x2" strips of particle board for bracing. After some recommendation I moved over to using Baltic Birch to achieve a better brace matrix. The particle boards were glued and screwed so they stayed in. With the extra volume they took up I was unable to brace exactly like the M2 in the top and bottom sections. Name:  IMG_3719.jpg
Views: 19556
Size:  150.2 KBName:  IMG_3717.jpg
Views: 18315
Size:  132.9 KBNext came the primer to seal the inside. It's a 2 part epoxy primer and I sprayed 2-3 coats of it on. I taped certain sections of the cabinet and bracing I could properly glue and screw baffle on.Name:  IMG_3723.jpg
Views: 17142
Size:  108.8 KBNext came the dampening material. I was unable to locate the Owens Corning stuff POS recommended locally. I then was recommended two other options. Wrap on 16550 Bulk Roll Fiberglass or get the regular pink stuff from Home Depot and make it 1". My original plan was to use the Wrap on stuff but I realized I already had a roll of the pink stuff and figured I'd better use it since I've been storing it for this occasion. Name:  IMG_3732.jpg
Views: 16881
Size:  176.5 KBI left the horn cutout process till after the baffle was installed because I wanted to be sure the horn was in the correct place.Name:  IMG_3741.jpg
Views: 16804
Size:  169.8 KB
    I would dampen the internal cabinet walls with metallic plates glued with silicon, after the paint, make a stronger frontal baffle, two mdf sandwiched with roofing tar, and silicon gaskets. Done with my projects and the gain in definition, clarity, attack is enormous.

  14. #14
    Senior Member pos's Avatar
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    Quote Originally Posted by srm51555 View Post
    As you know the schematic in this doc has a typo: C2 should read 3.3uF instead of 33.3uF.
    If you could edit your first post to make this clear that would probably be helpful.

    Here is the correct schematic, in appendix 3: https://docs.google.com/document/d/1...h.267sxg2itu1h

  15. #15
    Senior Member srm51555's Avatar
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    Quote Originally Posted by pos View Post
    As you know the schematic in this doc has a typo: C2 should read 3.3uF instead of 33.3uF.
    If you could edit your first post to make this clear that would probably be helpful.

    Here is the correct schematic, in appendix 3: https://docs.google.com/document/d/1...h.267sxg2itu1h
    Very good, post is updated. I was waiting for confirmation before I call Parts Express and try to return these out of the 45 day policy.

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