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Slapshot MTM Build

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  • Slapshot MTM Build

    About two years ago, I decided I wanted to build a pair of MTM speakers using the Dayton RS series mid woofers. I don't recall my exact reasoning, except that it seemed to me there are lots of designs using this formula, so I think I figured there must be something to it. If I remember correctly, it seemed the most common formula was to use the Dayton RS tweeter, which I think was discontinued around that time. So for those poorly-remembered reasons, and possibly others as well, I landed on Curt Campbell's Slapshot MTM design, which uses two Dayton RS180-P midwoofers and a Morel CAT 378 tweeter. I bought the plans from Rhythm Audio Design (though now I cannot find the plans listed on their website). My wife bought me the drivers for Christmas 2018, and at that time my parents gifted me crossover parts. I had some birch plywood at my parents' house that I bought 20 years ago for building a 2x12 speaker cabinet for guitar (yes, literally 20 years ago, right after I graduated from school and was still living with my folks!).

    I sat on the plans and parts for two years, only recently finally getting the motivation to put it all together. I've built a few pairs of DIY speakers, but, excepting for the guitar speaker cabinet and a Paul Carmody Isetta, I've never done all the wood cuts myself, and built from flat-pack kits. My woodworking skills are mediocre at best! I don't have a table saw, and all the straight cuts were done on a too-small table, using a saw clamp-guide and circular saw. I bought a plunge router just for this project. I didn't have enough 20 year old birch ply to complete the project, so bought some more birch ply from the local hardware store. I think I counted five layers, I know it's not the best birch ply. (I once got a flat pack kit from Planet10, they used the 13-ply Baltic Birch wood that comes in 5x5 sheets - really nice.) After five sides of one box was glued together, I realized there was a slight bow to the side panels. I spent an embarrassing amount of time with Bondo and the belt sander!

    Almost all the speakers I've built have been finished in Duratex. I like a very plain, utilitarian aesthetic - Duratex fits the bill perfectly. It's easy to use, has a mild non-offensive odor, and cleans up with water. The textured finish also helps cover up my lousy woodworking!

    A special thanks to bungelow_ed ! The Slapshot MTM plans I got from Rhythm Audio Design included drawings for both the stand-mount MTM, and also bungelow_ed's floorstanding MLTL variant. My original plan was to build this floorstanding version, and Ed was very helpful in clarifying some of the details on the plans. Thank you Ed! But my wife veto'ed the MLTL version, and insisted I stick with the smaller stand mounts.

    Also, a big thanks to the folks at Rhythm Audio Design. The plans were missing a few details, and despite me buying them over two years ago, RAD was still very helpful in promptly and thoroughly answering all my (numerous) questions.

    These speakers are going in our basement. As you can see from the pictures, the basement is unfinished. But it still gets a lot of use by my family. Because it's unfinished, it's basically one big open area. Previously I was using a pair of Paul Carmody Speedsters. The Speedsters sound great! But I don't think anyone will be surprised to hear that they fall a little short when it comes to filling a large open area with sound. In this role, the Slapshots sound great! They certainly sound "big". I like fairly modest volume levels, but in this basement, to have an "even" sound in the whole area, the volume needs to be turned up a bit. The Slapshots sound very "effortless" to me: the sound is very clean, to the point where I want to play them louder than I normally like. Instrument separation is wonderful. They also don't seem very directional, especially compared to the Speedsters. In fact, I can stand to the side of one speaker (i.e. in the same plane as the pair) and it really doesn't seem all that different from standing in the sweet spot.

    Here's a clamping shot. Only after I had it all glued up did I realize I didn't have enough long clamps as I wanted to do the front-to-back clamping. So I rigged up the strap you can see in the picture to provide some front-to-back tension in the middle.

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    I pretty much followed the plans to the letter, except for the internal bracing. The plans called for cutting a couple "U" shaped pieces to go inside. I was afraid I wouldn't be able to pull of the necessary cut precision to do this, so I instead glued in some 1-inch dowels for bracing.

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    Here's one of the front baffles. I used a Jasper jig with my router for the circles. I free-handed the extra bit for the tweeter, and also free-handed the woofer vents.

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    Here's a shot of the inside, with crossovers and foam lining. I also stuffed these generously with poly fill.

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    Next post will have pics of the finished speakers, since there's a five attachment limit!

  • #2
    And here are pics of the finished speakers!

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    • #3
      Great job!

      now time to enjoy them.


      • #4
        Nice speakers! Geoff has a pair, and he speaks highly of them. Yours look like high end mix monitors, with the Duratex on them. I have some 225p's, and they're very nice for the cost. Glenn.


        • #5

          The Slapshots are indeed something; we love them and friends can't believe how good they sound: simple XO, too.

          Curt kindly modeled a MLTL for me, so the speakers are floor standing. A family friend made the cabinets from veneered MDF, stained "wenge" to match our room furniture. With most music and particularly LPs, we leave the sub off , the bass response and quality is excellent.

          The one thing I'd suggest is a grille over the tweeter, I have had to replace two fabric domes as a result of little fingers having a poke: and the Morels aren't cheap in Oz.

          Yours look beautiful, well done.

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          • Drummer
            Drummer commented
            Editing a comment
            Geoff, those look fantastic! I love that dark wenge stain over the veneer. What is the extension in the mltl? Glenn.

          • Geoff Millar
            Geoff Millar commented
            Editing a comment
            Thanks, you can tell I didn't make them.... our friend was a pattern-maker with GM-Holden, which unfortunately closed a few years ago so he was temporarily out of a job.

            I have the specs and graphs somewhere and I'll let you know. The stain was to match our stereo unit; one of the reasons I DIY'd was because we wanted a colour other than black and nearly every commercial model I looked at under A$2000 was black! Henry Ford would be proud.

            The cabinet size was a happy accident: I was going to build Paul Carmody's 'Cores' but realised they wouldn't fill up the room with Jimi.


            Update: I think the F3 is about 40Hz, the F6 about 35 from the graphs which Curt kindly provided.

            I don't have measuring equipment, unfortunately but they certainly dig low enough, not only that but the quality of the bass is really natural, not boomy or exaggerated. For example, I don't know the frequency, but the opening of the famous Bach organ prelude rattles the fireplace!
            Last edited by Geoff Millar; 10-13-2020, 04:17 AM.

        • #6
          Thank you for all the kind words, everyone!

          Originally posted by Drummer View Post
          Yours look like high end mix monitors, with the Duratex on them.
          It's funny you say that, because I originally wanted to build Jeff Bagby's RS180 MTM design, which he said he did for a recording studio. His design used the RS28AS-4 tweeter, which has been discontinued. The RS28A tweeter discontinuation is what sent me looking for another RS midwoofer based MTM design.

          Does anyone happen to have any data plots for the Slapshot MTMs, either modeled or measured? I'm always curious to see how my hearing perception aligns with measurement/modeling data. And to me, these do sound so "clean" I feel like they would indeed make good mix monitors.

          I actually have a measurement mic and have dabbled a bit with REW. I've done some frequency response measurements of my guitar amps, but I've found the measurements seem to be very sensitive to environmental conditions, especially microphone position. Does anyone have any links to particularly good tutorials for doing frequency response measuring with REW? I'd be happy to try my hand at taking measurements for the Slapshot MTMs, but I want to do them justice with good measuring technique.

          Thanks again everyone!


          • Drummer
            Drummer commented
            Editing a comment
            I'm not the one to answer your question on measuring, but you could send a message to Curt, as he may have system measurements that he could send you. Glenn.

          • Geoff Millar
            Geoff Millar commented
            Editing a comment
            According to the description on RAD, the FR was 40Hz to 20KHz plus or minus 2dB, but the FR graph wasn't on the website.

            They certainly sound smooth and accurate, and I think the paper/kevlar/fibreglass cone would be pretty rigid. I couldn't compare them directly but I auditioned the RS621 kit (RS150, RS28A) and I find the Slapshots work better with our music collection; I used the same audition CDs with both speakers.

            Compared to our other DIY projects- the Tritrix and Classix II- for example - they bring out much more detail in the sound but are not quite so tolerant of poor recordings as the Classix. I wouldn't worry about the measurements, they sound great and that's what matters!

            I'm sure you will enjoy them, kudos to Mr Campbell!
            Last edited by Geoff Millar; 10-17-2020, 01:37 AM.