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New project: RSX

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  • New project: RSX

    It will be a while before these come to be as I need to complete our basement project, but I had completed some measurements and sims, and have been listening to some crossover versions while working on the basement, so far I’m happy enough with the concept.

    The project will be a large floor standing two-way with two rs270p 10” woofers per tower and side firing passive radiators. The top woofer is converted to a coax, fitted with a nd28 with the flange cut off.

    Two woofers is overkill but should reduce cone movement and therefore thd and am distortion on the coax.

    The tweeter puts up with this surprisingly quite well. Being so close to fs, I notched it. Current version is acoustically 4th Bessel on both sides. Third order electrically.

    Based on sims and testing this setup should produce 105db / 1m from 30-20k -3db below xmax, with an f10 of 20hz.

    in testing with just the coax driver so far it had no problem with extended playback at over 100db. No noticeable distortion and no heat issues in either the crossover or drivers.

    Of course this level is unreasonable and dangerous, but sometimes it’s cool knowing you have the horsepower even though you’ll never use it. Like an old man with a 700hp vette.

    The large woofer made a nice waveguide for the tweeter. It of course has various significant suckouts depending on listening angle, but I can live with those; peaks I cannot.

    Anyway I will likely resume this build quite a while from now, but wanted to throw it out there. I want to claim the first Rs270p coax (I think).

  • #2
    Here some pics.


    • #3
      Here is the current crossover. I initially notched the breakup, but found it lifeless. I removed the notches to find the breakup to not be a bother. Sorry for screenshots being camera shots.. it’s what worked better at the time than uploading from the computer.


      • #4
        Here are distortion measurements at 95db. This is with a previous crossover version however (lower frequency and woofer notches).


        • #5
          Nice! How did you cut the tweeter flange?


          • #6
            Thanks. It actually surprised me how easy it was to cut. I used the bandsaw. I put some masking tape down on the table to not scuff up the tweeter and ease movement and then put the tweeter face down on the table. Worked great.

            I love your Master Shake avatar btw!


            • #7
              Dynamo, this is a very cool project. Do you have any pics of the tweet and wood modifications, and installation procedure? I really like the rs225 paper, and I bet this bad boy will pack a nice punch. Glenn.


              • #8
                Thanks, I didn’t take pics when I first modded the tweeter and it might be a bit before I could get around to pulling the driver and taking the tweeter out, but I will when I can.

                to mount the tweeter, I used JB Weld two part epoxy to glue a quarter inch nut to the back of the tweeter. I used a stack of 5 or so large washers to space it out to where it needed to be (also epoxied together) I cut a quarter or so out of several of the washers with a bolt snips to allow room for the tweeter terminals and wire routing. Wires then just run down the pole like any other coax. I used a 1/4” brass bolt to mount the tweeter from the back of the magnet.

                I used mostly copper washers for spacing as they are non magnetic and also have good thermal properties.

                The woofers “phase plug” is easily removed by putting a large punch into the back of the magnet and applying a good tap of a hammer.


                • #9
                  The tweeter looks like it was made for that woofer. Very nice!


                  • #10
                    Thanks! I thought so too, I was happy with how the tweeter guide profile led to the woofer cone. I could have done a better job with the cut for a smaller gap, but I suppose this bigger gap cools better and is quieter.


                    • #11
                      I tried removing the tweeter fs notch and put it back after listening. I also tried a series notch in parallel to the tweeter to reduce the size of the cap needed but far preferred the sound of the parallel notch so I stuck with that. The series notch messed with the roll off. I’m pretty happy with this crossover for a single 8 ohm woofer. Not shown is a 0.05mH series inductor on the tweeter as well. On-axis the tweeter top end tips up and its flat off-axis. The inductor brings it flat on axis and a touch down off axis, which I prefer. These seem to make fairly good rock speakers. They sound good to me overall but are perhaps not the last word in clarity and fine detail.


                      • #12
                        Just an FYI...
                        The ND28 faceplate can unscrew and separate from the main body. This will lend well for cutting the flange off.

                        Nicely done!
                        "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
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                        • #13
                          Originally posted by Wolf View Post
                          Just an FYI...
                          The ND28 faceplate can unscrew and separate from the main body. This will lend well for cutting the flange off.

                          Nicely done!
                          Thanks Ben! I saw the screws but wasn’t sure if it was glued on as well so I left it. Good to know.


                          • #14
                            I’m chillin on the couch working on box sizes. Gotta love box calculator apps for your phone.

                            Looks like for a single rs270p coax a 2 ft3 box tuned to 29hz will yield an f3 of 30 and a f10 of around 24. This is nice and flat as well. It stays within Xmax from 24 on up at 128w. This outputs 108db before bsc, so figure on 102-104db, which I was getting without issue in testing. Dual woofers would be looking at 108-110db within xmax, tweeter being the weak link of course. As mentioned the bigger goal to me with dual woofers is lower distortion, particularly am. Seems one driver is plenty fine though.

                            If you wanted to save space, 1.75 ft3 moves the f3 up a touch to 32.

                            If you want refrigerators, 3 ft3 will give you an ebs to an f3 of 26 and the f10 around 20. My original design goals were along these lines but you give up power handling and a lot of size. Doesn’t seem worth it to me I guess. I think I’m going in the middle at 2 ft3 per driver or even the smaller version. Depends on what the cabinet design ends up looking like.


                            • #15
                              So I’ve been making some progress on these. I opted to go open baffle three way (woofer enclosed). The large diameter of the 10” as an open baffle midbass allowed me to cross at 400hz on a 13” baffle, first order.

                              Ive never done an open baffle mid before and was pleasantly surprised at how cool they can sound.

                              I mocked up a test enclosure and have been playing with voicing, and am now building the actual enclosures.