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  • New three-way monkey coffins

    For some time now my brother has been wanting a three way system that has modern performance but styled as yesteryears designs - the design we colloquially refer to as 'Monkey Coffins'. I like the idea and its certainly back in fashion with plenty of manufacturers jumping back onto this format again.

    Broad criteria:
    Mid 30's to 20K response, as compact as possible
    Paper and textile woofers and tweeter
    Good power handling and a reasonably large woofer
    Driver costs not an issue

    Ok to compromise as follows:
    Size over bass depth
    Sonic quality over razor flat response
    Old school look/design over diffraction concerns

    My brother really likes the ATC Classic line of speakers and so we set out to design something similar.

    Now credit where credit is due - in researching a design like this you'd be a fool not to look at the work of Troels Gravesen. As so it was that one of his SBA designs was a close match for this criteria. So the eagle eyed observers here - yes this design takes a sizeable amount of inspiration from Troels in terms of format - but beyond form factor is not a replica.

    Landing on the same drivers, the SB Acoustics WO24P-8, MR13P-8 and TW29 tweeter. I've worked with the woofer and tweeter plenty before so I was leaning this way anyway and honestly the addition of the MR13P to round out this combo is simply a no brainer.

    So here's the basic cabinet design:
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    Offset mid range and tweeter (my signature move lol) keeps our diffraction issues to a minimum with a square, zero round over baffle!

    Aiming to keep to around 38-40L net for the woofer with a 28-30Hz tuning (to be tweaked once it all comes together). This gives us a magnitude response as follows:

    Magnitude response:
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    Cone excursion + power:
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    Tuning allows for a full 70Watts of power within the music spectrum. This tuning for this woofer forces the region where the cone unloads to below 25Hz...which is certainly well outside the normal music listening range and gives us mechanical power handing close to but within the thermal rating of the woofer. I like it!

    It also gives a nice gradual roll off in the lower octaves that yields an [email protected], [email protected]!! and [email protected] (nuts). We'll see how close to this we get once it all comes together and after woofer break-in.

    Should be good for 106db (less baffle step PLUS room gain).
    Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
    Refurbs: KLH 2 | Rega Ela Mk1

  • #2
    ..and so we begin!

    The Satori drivers arrived pronto from the wholesaler - these things are just beautiful!

    WO24P-8
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    MR13P-8
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    All the kids together - already looking amazing! :D
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    Starting out the construction with a layered offset wave sort of midrange enclosure. Now before y'all pile on in here about this - no I have no scientific approach for this and no evidence its of any material benefit - my operating assumptions were simply that we should limit parallel surfaces for the midrange and create an internal structure that sent reflections everywhere in a hope that it might more quickly dissipate the energy of the midrange back wave. I have no evidence it works or is better than just a square box - but I had the time and capacity to try and therefore why not!!

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    Layers all glues up and positioned within the box.

    This is the first picture of the box that I took unfortunately but it's a basic construction of 12mm (1/2 inch) MDF panel, sandwiched for a total 24mm (1inch) wall thickness with interlocking edges.

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    Last edited by DeZZar; 07-13-2022, 09:24 AM.
    Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
    Refurbs: KLH 2 | Rega Ela Mk1

    Comment


    • #3
      Gluing in the midrange enclosure. Its also braced to the back of the cabinet....

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      And then also braced to the side of the cabinet
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      A second brace is added just behind the woofer
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      And this is essentially the finished cab before internals and front baffle. Pretty simple one really and nice and solid.
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      Last edited by DeZZar; 07-13-2022, 09:25 AM.
      Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
      Refurbs: KLH 2 | Rega Ela Mk1

      Comment


      • LOUT
        LOUT commented
        Editing a comment
        That asymmetrical/side-bracing connecting the midwoofer compartment to the main cabinet made me do a "double take" before I remembered the mid+tweeter are offset, lol.

    • #4
      Now despite ones best efforts, due to the layered nature of that midrange enclosure its highly likely (as it was in my case) that not every layer comes together in such a way that the final product was perfectly square. No matter - I expected to need to compensate for this so the inside rabbeted edge received a final flattening with a router set on a jig to route down 12mm perfectly parallel to the outer edge of the box. This ensures when the baffle is glued down it will seal perfectly against the midrange enclosure as expected.

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      Then onto my favourite part (not!) - routing out the baffle for the drivers. When dealing with offset drivers - triple check you have marked out the two baffles as mirror images to each other (I learned that lesson the hard way some time ago!!)

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      Test fit....happy with that....

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      Last edited by DeZZar; 07-13-2022, 09:29 AM.
      Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
      Refurbs: KLH 2 | Rega Ela Mk1

      Comment


      • #5
        Test fit on the baffle - just to make sure....
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        Adding some deadening material to the side walls of the cabinets.

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        Followed by a layer of felt...

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        And the acoustic damping material
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        Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
        Refurbs: KLH 2 | Rega Ela Mk1

        Comment


        • #6
          The port for these needs a 90 degree elbow. It enters at the bottom corner of the box and needs to fit up through the window brace.

          I've used a commercially available port flare but 3D printed the elbow. I rather 3D print elbows and bends because I can ensure the diameter is perfectly maintained and a smooth transition around the bend (like mandrel bent pipe). A lot of the "plumbing" elbows available are (in my view) inadequate as they don't follow a constant radius or smooth transitions - usually just a right angle bend with a smooth outside curve but a 90 degree square on the inside.

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          The elbow is printed in two parts and glued together to avoid having to print support material (which is a pain to remove, lengthens the print time and wastes plastic). You can see the two halves of the second port in the background.


          Woofer and port mounted to start testing our tuning.

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          And here our impedance plot indicates we're right on our 28hz tuning target. I'm happy enough with this for now so wont be adjusting the port until the woofer has more hours on it.

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          Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
          Refurbs: KLH 2 | Rega Ela Mk1

          Comment


          • #7
            So lets button one of these up and get some measurements...

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            Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
            Refurbs: KLH 2 | Rega Ela Mk1

            Comment


            • djg
              djg commented
              Editing a comment
              It does look like one of Troel's 3 Way Classics, though he does seem to like front ports. A lot of impressive work.

              Q: What is your circle routing rig, it's like nothing I've seen?

              Q2: Can you get that unobtainable in U.S. black MDF Troels uses for baffles?

          • #8
            Here are the raw measurements for each driver....

            First up the tweeter. Having worked with these guys before there is a tendency for a rising response which is exhibited here as expected. @ 15 degrees off-axis things flatten out with a just a bit of a hump around 12K. Surprisingly we're not seeing any baffle edge diffraction issues here despite the sharp edges - a testament to carefully planning tweeter position with offset.

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            Midrange exhibits a rising response over 5k and associated breakup but should be usable up to 4-5K. I don't think I'll be taking it that high in this implementation - but always good to have some room to move. I haven't worked with this particular driver before so I took a little time to just to play it in its enclosure full range. Wow. Its absolutely wonderful. Some drivers with a response like this with breakup etc just sound dreadful on their own - but this driver (as with the other satori mid woofers/midrange) are pleasant to listen to - obviously not balanced, but the point is they don't shriek/squeal/shred your ears as a lot of the cheaper stuff does.
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            The nearfield measurement on the midrange shows just how smooth this thing is! This measurement is essentially un-gated (500ms) and has no smoothing applied!
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            And finally our nearfield woofer and port response. Woofer is again very smooth across the region we intend to use it. The aligned sum for the port and woofer show we are currently hitting an f3 of around 38Hz. Not quite 34Hz but I don't think its anything to get all disappointed about - driver break-in will likely impact this as well as the final quantity of acoustic stuffing etc so we'll leave it be for now and make any (if any) final tweaks to tuning later on.

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            My brother was very keen to get a 'sense' of how these might sound before he had to head home so I threw together a very quick and dirty crossover for a quick listening session....

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            Very promising.....more to come soon!
            Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
            Refurbs: KLH 2 | Rega Ela Mk1

            Comment


            • dkalsi
              dkalsi commented
              Editing a comment
              DeZZar - did you use VituixCAD to determine ideal driver placement/offset - if so, were you specifying the enclosure width based on the protruding baffle, or the full width of the speaker?

          • #9
            Great project and love the wood work so far.

            This is very similar to my project but I went for the Morel EM1308/ET448 and in a closed box but I think our goals are similar. Looking forward to see how it turns out and hearing what you think of the sound -

            https://techtalk.parts-express.com/f...ritique-please

            Comment


            • DeZZar
              DeZZar commented
              Editing a comment
              Yep very similar build! If you haven't already gotten the WO24P you'll love it - an incredible woofer! Somewhere around 38L is about as tight as you want to go ported I'd say and actually allows you to plug the port for an equally good sealed experience!

          • #10
            DeZZar - I freakin love your builds, and genuinely appreciate your willingness to document your process/build. I too have been meaning to build an "Old school look/design over diffraction concerns" - though I'll likely pull from drivers on hand (e.g. RS225, waver prepare mid, and wavecor tweeter). I'll likely take a lot of "inspiration" from this project.

            Any preliminary thoughts on where you plan on crossing the woofer to the mid?

            Also - are the port pieces already glued? If not - (and should you have an excess pipe on hand), it might be worth it to test a couple of port lengths to see if the magnitude of the port resonance can be tamed. Also - I've become a big fan of modeling the enclosure in Hornresp to test port placement.

            Comment


            • #11
              Wow, that midrange chamber! You must have some nice tools at your disposal. I liked the router trick you did to flatten the top of the midrange chamber.

              Very handsome build. excellent drivers. How can you go wrong?
              Isn't it about time we started answering rhetorical questions?

              Paul Carmody's DIY Audio Projects
              Twitter: @undefinition1

              Comment


              • DeZZar
                DeZZar commented
                Editing a comment
                Thanks Paul! The truth is I used a local CNC shop to cut out the patterns - got them to do several projects in one go to save some costs so I've had these little layers hanging around the shop for a while.

            • #12
              Originally posted by dkalsi View Post
              I freakin love your builds, and genuinely appreciate your willingness to document your process/build.
              Thanks man, appreciate it!

              Originally posted by dkalsi View Post
              Any preliminary thoughts on where you plan on crossing the woofer to the mid?
              I'm thinking somewhere around 300-400hz for this one - but we'll see where it lands in the end after some listening. I want to try and find that sweet spot where the woofer contributes enough to give a rich re-enforced lower midrange but stops short of colouring/overwhelming the upper midrange.....

              We've got plenty to work with here anyway as the C-t-C spacing of the drivers allows for up to 1500Hz (not that you'd ever go there).

              Originally posted by dkalsi View Post
              Also - are the port pieces already glued? If not - (and should you have an excess pipe on hand), it might be worth it to test a couple of port lengths to see if the magnitude of the port resonance can be tamed.
              No half the port isn't glued yet to allow for exactly that - final trimming/tuning. The last few sections are just taped together for now.

              Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
              Refurbs: KLH 2 | Rega Ela Mk1

              Comment


              • Ugg10
                Ugg10 commented
                Editing a comment
                I am guessing you have seen Troels Gravesen’s SBA941 which uses the same drivers. http://www.troelsgravesen.dk/SBA-941.htm

                He has comments on crossover point and ends up at 580hz.

                Also worth looking up Jeff Bagby’s Helios design and notes. He uses a Tank filter (small cap and resistor in parallel with the woofer inductor) to reduce the 3-4khz break up peak in the WO24p, you may not need to but it is a neat trick.

            • #13
              Originally posted by djg View Post
              It does look like one of Troel's 3 Way Classics, though he does seem to like front ports. A lot of impressive work.
              Thanks mate. If it was my personal project I probably would have gone with a front firing port as well which would have allowed me to sneak a slightly bigger box - but "compact" was the order so we landed here.

              Originally posted by djg View Post
              Q: What is your circle routing rig, it's like nothing I've seen?
              Haha. Well....its a self made creation. Basically just a piece of ply with a sliding pin attached to a threaded rod allowing for adjustment. I need to make another one with a few tweaks to the design and add in measurement markings to make it a little easier to make repeatable cuts and fine adjustments - but this one does ok for me for now!
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              Originally posted by djg View Post
              Q2: Can you get that unobtainable in U.S. black MDF Troels uses for baffles?
              Might as well be unobtanium over here in Aus too. I don't know if its the exact same stuff but there is a couple of places that sell "moisture resistant black core" MDF which looks the same. Its only $160 for a standard 4x8 1/2inch sheet!! Guess I'll make do with painting the baffle! :D
              Constructions: Dayton+SB 2-Way v1 | Dayton+SB 2-Way v2 | Fabios (SB Monitors)
              Refurbs: KLH 2 | Rega Ela Mk1

              Comment


              • djg
                djg commented
                Editing a comment
                Thank you, nice circle jig

            • #14
              Value! Should be great speakers - and your jig is brilliant.

              Geoff

              Comment


              • #15
                DeZZar is just brilliant.


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