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SD215 X 2 / RS125 / SD1.1 first test - great success!

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  • SD215 X 2 / RS125 / SD1.1 first test - great success!

    So this was originally under the "mini-***-laude" moniker - a speaker designed to be similar to the "magna-***-laude" project but smaller in size and a lot cheaper to build. The original used the PA130 in place of the RS125 as the midrange, but this RS125 version sounds MUCH better - and for just a few bucks more you can't complain. So much better in fact that I don't want to call it a "party speaker" anymore - so the "mini-***-laude" name needs to go. I'm open to suggestions!

    This is a three way with a transmission-line midrange using two SD215 subwoofers (coils in series, drivers in parallel for 8-ohm total load), an RS125-8, and the SD1.1 tweeter. The box I am testing with is 36"x11.5x16.25 deep, all made of 3/4" high grade (but not baltic) birch ply. I have determined that the box needs to be taller to raise the tweeter height to 36", so the final box dimensions will be 39"x12x16"
    Also, I have determines that the entire box need not be made of birch plywood, so a hybrid method will be used in the final version. A single 4x8 sheet of birch ply is used for the tops, bottoms, sides, and front baffle. A half-sheet of 3/4" MDF (two 2x4 sheets would work too) is used for the rear panel, internal braces, midrange tunnel, and under-baffle. The way the box works is that there is a two-stage baffle. The first 3/4" layer of MDF is glued to the box and the internal braces. This ensures that the box itself is structurally complete. The driver holes should be slightly larger than those of the actual baffle. Into this "under baffle" bolts on the "real" baffle containing the drivers, via hurricane nuts. This allows a thicker baffle to be used (1.5" overall), while still allowing rigid structural adhesion to the box thanks to the permanent under-layer. The under-layer and true baffle should be separated by a thin later of Peal-and-stick cork sheet for sealing and damping purposes.

    This test box of mine is not the final box - in fact the front baffle isn't even attached - just resting on the main box - and it STILL sounds fantastic. Really Really good. Even my mom says she can easily tell the difference between these and the modula MTs I built her a while back. "The drums sound so much better! The guitar sound great!" were her exact words. ANd the silly part is these three ways with dual woofers actually cost about the same as a set of modula MTs - these can be built for about $225 a pair for drivers and crossover components. Likely about $300 including cabinet materials.

    The modeled crossover I first tried was close but still needs some adjustment. By ear, I padded the midrange down a tad more, and removed a response shaping tweeter network because it sounds fine without it. Also, there are two shunt inductors acting as notch filters on the woofers and mid - these need to be changed to series C-R networks across the low-pass inductors to save a few bucks. The tweeter-mid crossover sound great - no need to fiddle with that. Instead, I'd like to push the woofer-mid crossover a bit lower in frequency because the RS125 sounds so good, and as it's currently crossed at about 430hz it's barely moving. I'd like to move this down to 325hz to let the rs125 cover a larger bandwidth, and this will require a bit of change to the L and C values in the woofer low pass and midrange high pass filter section. I'd like to keep each inductor at 5.6mh, as this will keep things simple and allow a price break by ordering four of the same. So the capacitor values will need to be changed, Likely a larger value in series with the midrange to push the cutoff for the midrange a bit lower, as well as relaxing the slope on the woofer a bit. Changing the value of the resistor following the shunt inductor on the midrange will adjust the slope of the midrange falloff. It sounds good as it, but could be cleaned up a bit. Overall, bass extends deep, is clean, and at the right level to match the midrange - it's just the transition point that needs some fine tuning.

    So I'm, very happy with the way this is turning out so far - most surprising is the benefits offered by the transmission line midrange. This really almost gives the speaker an omni effect - you can walk all around it and really not hear much of a dead zone. I've only built one side and by itself, it sounds better than most stereo sets I've heard because of the wide dispersion. No matter where I sit in the house it still sounds good - which was what I had hoped to achieve with the TL midrange and am rather surprised worked so well.

    These have a 4" port which for the first test I did front mounted, but it should really be rear mounted to save space on the front baffle.

    I will measure as soon as I can find my ECM8000, which is hidden somewhere in a moving box in the garage...

    Here's the original crossover design with my annotations added after a few days of auditioning and tweaking with parts on hand:


    Here's my test crossover (don't ask):


    The test baffle (final version will be 3" taller, rear ported, and the subs will be spread out from each other and lowered a bit):


    And here's the TL mid opening at the rear, stuffed with some damping. THis would be a good place to mount the crossover for easy access:

  • #2
    Re: SD215 X 2 / RS125 / SD1.1 first test - great success!

    Max, I'm glad to see you're back working on this project. I always thought the idea behind it was quite good. Interesting that you upgraded the mid. Hopefully, you won't get too caught up in upgrade-itis, or next thing you know it'll be another all-RS project;)

    But seriously, what caught my attention about it was that the drivers you chose were really great values for the money, and overall very robust. Two of those SD215 means some wicked power handling; and those things can dig really deep in a relatively small box. It's still by no means a small speaker, but that's a lot of power for one box!

    Keep it up. I look forward to seeing how it goes.
    Isn't it about time we started answering rhetorical questions?

    Paul Carmody's DIY Audio Projects
    Twitter: @undefinition1

    Comment


    • #3
      Re: SD215 X 2 / RS125 / SD1.1 first test - great success!

      I notice that you're using the P-Core inductors for your large values. I'd be interested in your thoughts about them.

      Comment


      • #4
        Re: SD215 X 2 / RS125 / SD1.1 first test - great success!

        Originally posted by undefinition View Post
        But seriously, what caught my attention about it was that the drivers you chose were really great values for the money, and overall very robust. Two of those SD215 means some wicked power handling; and those things can dig really deep in a relatively small box. It's still by no means a small speaker, but that's a lot of power for one box!
        Keep it up. I look forward to seeing how it goes.
        Thanks for the encouragement Paul! Yes this project was designed from the beginning to be a high value "party speaker" that would be great in a college environment, but I'm frankly just blown away by how good these drivers sound together for the cost. I think a lot of it has to do with the TL midrange - vocals are absolutely crystal clear with none of that dreaded cabinet resonance - but hell you're no stranger to dipolar designs so I don't need to preach to the choir The PA130 version sounded pretty decent, but nowhere near this good - so the driver upgrade in this case is definitely worth it. And considering the RS125 is only $6 more than the PA130, there's just no reason not to.

        I wish I had built some crummier boxes for the first run - these birch ply ones are built like tanks, were expensive and a real PITA to build and haul around when I did them a few months ago in NYC. And now I'm not even going to use them - ha! So it goes...

        I have no idea where my ecm8000 mic went off too. It may very well be in Africa, New York, Seattle, sequoia national park, any number of vehicles used to transport my belongings between these places, and either of two garages. I'll probably end up having to get a new one :/

        As for the P-core inductors, I like them just fine! They are a good value for the performance - perfect for a woofer circuit where low dcr and high inductance without breaking the bank is desired. My only gripe is that there are no mounting holes or anything, so they have to be glued to the board when done, which can be a bit of a pain. But performance wise, no complaints here.

        Comment


        • #5
          Re: SD215 X 2 / RS125 / SD1.1 first test - great success!

          Originally posted by Paul Ebert View Post
          I notice that you're using the P-Core inductors for your large values. I'd be interested in your thoughts about them.
          I've used them many times, and like them quite a bit! You get 15AWG coils, in a rugged and heavy construction, that handle boatloads of power. I accidently dropped one once, and I was afraid it would shatter, but it survived the fall onto carpet without a scratch. The core is powdered ferrous material, and you get a low DCR for the cost and mH value. They are typically cheaper than the 18AWG Air-Cores, so what's the downside?? They seem to sound very good, or I have not found anything to be lacking in projects where I've used them, that is not attributed to the drivers or xover alignment. I usually strap them down on the peg-board sideways, and they don't move. If you need to unwind a coil, that would be fairly easy to do.
          Later,
          Wolf
          "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
          "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
          "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
          "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

          *InDIYana event website*

          Photobucket pages:
          http://photobucket.com/Wolf-Speakers_and_more

          My blog/writeups/thoughts here at PE:
          http://techtalk.parts-express.com/blog.php?u=4102

          Comment


          • #6
            No they don't, Max!

            Originally posted by Max_Andrews View Post
            As for the P-core inductors, I like them just fine! They are a good value for the performance - perfect for a woofer circuit where low dcr and high inductance without breaking the bank is desired. My only gripe is that there are no mounting holes or anything, so they have to be glued to the board when done, which can be a bit of a pain. But performance wise, no complaints here.
            Just strap those suckers down! :D (I'm sure you could strap them vertically as well, with a pair of zips pulling like an eyelid closing on it....)



            Later,
            Wolf
            "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
            "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
            "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
            "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

            *InDIYana event website*

            Photobucket pages:
            http://photobucket.com/Wolf-Speakers_and_more

            My blog/writeups/thoughts here at PE:
            http://techtalk.parts-express.com/blog.php?u=4102

            Comment


            • #7
              Re: SD215 X 2 / RS125 / SD1.1 first test - great success!

              Originally posted by Wolf View Post
              I've used them many times, and like them quite a bit! You get 15AWG coils, in a rugged and heavy construction, that handle boatloads of power. I accidently dropped one once, and I was afraid it would shatter, but it survived the fall onto carpet without a scratch. The core is powdered ferrous material, and you get a low DCR for the cost and mH value. They are typically cheaper than the 18AWG Air-Cores, so what's the downside?? They seem to sound very good, or I have not found anything to be lacking in projects where I've used them, that is not attributed to the drivers or xover alignment. I usually strap them down on the peg-board sideways, and they don't move. If you need to unwind a coil, that would be fairly easy to do.
              Later,
              Wolf
              I agree Wolf. I have used these on my last 5 projects and found them very cost effective, with no reduction in SQ that I could detect and I have compared them to 15-20g air cores in the same speaker. I think they are a real value item.
              Dan N.

              Comment

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