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New Smallish Speaker: BMR-SB19

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  • New Smallish Speaker: BMR-SB19

    I've wanted to try out a tectonics BMR, so I put the TEBM65C20F-8 together with the SB19ST, crossed at 3.5k in a cabinet just over 4L for a low-cost speaker with very wide dispersion. It met the dispersion goal extremely well, and throws stable phantom image across a very wide horizontal stage, covering essentially the entirety of its intended room.

    I built this as a ported speaker, but found it had a pronounced midbass hump across just about every reasonable tuning frequency (it ended up being tuned at 61Hz) so I just made a plug for the port out of closed cell foam which tamed the midbass hump enough to de-emphasize fault and give a pleasant roundness to the comparatively limited bass from a small driver in a small box.

    It has been a long time since I've done a budget build, and quite happy with the results of this one - so I figured I'd post it. The most annoying factor with this project was fitting everyhing in a tiny box, and getting it in and out of a very tiny woofer hole.

    Interestingly enough, it actually measures slightly better with the grill on - the hump in the top octave completely disappears.



  • #2
    Cool build. Another trick for taming a midbass hump is judicious stuffing, like with Acousta-Stuf.
    Francis

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    • #3
      Thanks!

      Polyfill was my first instinct too - I tried different levels of stuffing up to and including full stuffing, and it did help, but didn't bring it down enough - which led me to just plug the port. I left a generous handful in there in the final config.

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      • #4
        Originally posted by Adam_M View Post
        Thanks!

        Polyfill was my first instinct too - I tried different levels of stuffing up to and including full stuffing, and it did help, but didn't bring it down enough - which led me to just plug the port. I left a generous handful in there in the final config.
        Yeah well, I like sealed best when the bass is sufficient. Sounds like all's well that ends well.
        Francis

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        • #5
          I've been wanting to try something smallish but fairly full range with a bmr and small tweeter, like you've done. Maybe mating that with something like a tcp140. You mention imaging, how does the bmr image compared to conventional cones? Anything that sticks out or impresses with the bmr?
          http://techtalk.parts-express.com/fo...khanspires-but
          http://techtalk.parts-express.com/fo...pico-neo-build
          http://techtalk.parts-express.com/fo...ensation-build

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          • #6
            The imaging is reminiscent of well-done open baffle speakers. It's insulting to the LX521's in my main room to compare +-$100 speakers to them (they don't compare...), but they image in much the same way. As you walk, the image doesn't move towards the closer speaker - rather it stays rock solid where it should until you get unreasonably far off axis.

            The trick seems to work better with complex music too - I've listened to Wish You Were Here a couple times through because of it - than it does on something like the Bach Cello suites with less complexity (but no less beautiful). The simpler compositions still sound as they should, albeit more like what you would expect from a conventional M/T box speaker.

            The other thing that really caught me off guard was the bass. There's no way these things should put out the bass they do, especially sealed. There's no cone area! It's tiny! It takes a TON of power to get the bass, and they do have their limits, but they tell you kind of gracefully.

            Also, The BMR doesn't sound 1/2 bad running full range. I bet it could be tamed pretty easily with a notch filter for the hump at 1500Hz and another one to tame a peak in the top octaves.



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            • #7
              Nice!

              Wow, four inductors, including some really large-value ones. What does the x-over board look like? And the raw response of the drivers that you used?
              Brian Steele
              www.diysubwoofers.org

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              • #8
                I really envy your creativity and hands-on ability!

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                • #9
                  i like seeing these builds using the TEBM65, i really like them and think they are underated ****, I think it is worth using a 0.18cuft enclosure personally as i quite like the bass from it. My boombox build using the BMR's as well is around that 4L mark and its good as well.

                  Keep em coming


                  **** this is just my limited experience as i've really only used TEBM's in this size.

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                  • #10
                    Nice build, I like a front port when done well. Looks like a good project.

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                    • #11
                      Originally posted by Brian Steele View Post
                      Nice!

                      Wow, four inductors, including some really large-value ones. What does the x-over board look like? And the raw response of the drivers that you used?
                      I split the woofer and tweeter boards - but unfortunately didn't take pictures of them before I shoved them in the box. They are glued on opposite walls of the box. The boards literally couldn't have been any bigger - or they wouldn't have fit. In hindsight, a removable back may have been in order, but oh well, it worked.

                      As a compromise to space and cost, I sacrificed DCR a bit and went with higher gauge inductors. The woofer board, from left to right, is a .22Mh 18ga with a 50uf NPE about 1" above it (in the air). The 1mH is a laminate core oriented top to bottom. the .4 18ga is glued flat to the top of the speaker (quite heavily I might add) and the XO board butts up against it. The 7.5 uf is shoved on the board somewhere - it had space (barely).

                      The tweeter board wasn't too problematic - everything is more or less parallel to each other. The .5 is a 20ga, so it's actually not too big.

                      Given the proximity of the inductors, and the admittedly non-optimal spacing/layout, I measured everything on the board before mounting to ensure it'd work. Even with placing the inductors so they are perpendicular to each other, I was a bit concerned about the values changing enough to through the XO off. It was fine.

                      I didn't want want to make the woofer XO a 3rd order electrical, and tried quite hard to make a 2nd order work. It almost worked with a tank cap, but the response came back up too high above the tank frequency (making the peak in the top octaves worse) and I couldn't quite get the phase alignment to work. After hours and hours of fussing, this was one of those things were you add the extra component, everything snaps into place, and all is well. I was targeting an XO of under 4K due to the CTC spacing of the drivers, and came in at 3.5K, - the tweeter was still quite happy there.

                      Raw responses and a quick and dirty polar plot are attached. You can see how freakishly broad the radiation pattern on the BMR is, and the SB19 looks about how a 3/4" tweeter should on a box without a huge roundover (diffraction ripples). I also find the suckout of that driver at 1.7K fun. I don't think it's horribly audible - it doesn't bother me. You can also see that the small dips just above the XO point fill in nicely off axis, which explains why this XO sounded right. I put a little more peak in the tweeter XO to fill it in in one revision, and it sounded too hot.

                      I also posted a distortion plot (sorry about the scale, I was looking to see if the tweeter was stressed, and there was no smoke so I didn't take more detailed measurements) from the final XO using parts from the parts bin, not the actual ones that went into the speaker. Not bad! Except for the 2nd order peak at 320 or so. That's definitely audible. And of course the nastiness at 1.7k.
                      Attached Files

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