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Wavefront DIY OB Dipole Speaker

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  • Wavefront DIY OB Dipole Speaker

    Ok, so I've been wanted to try my hand at an OB speaker and I've spent hours pouring over dipole threads, and making my thumbs bleed in spreadsheets, and looking to cut costs by using cost effective drivers and even reusing some drivers I already have on hand ;) So here is what I have, and I'm posting for open critical advice and general comments.

    The design is a three-way meant to operate 100 hz to 20khz, and my goal was at least 86db /W @ 1M sensitivity. So far it looks like a 90db / 2.83V @ 1M 4 ohm speaker, giving me +1db watt sensitivity over budget (yay).

    It uses a compliment of 2x DA270-8 10" Dayton Audio Aluminum woofers, RS150-4 midrange, and <insert tweeter here>. The tweeter I'm designing against here is the SB sale tweeter at Madisound, TWD25. The thing is, with the 2.5khz LR4 slope, most tweeters would work if they are >90db at 2.83V @1 1M. I picked the RS150-4 because I already own it and well, its damn fine for the price, excepting the breakup which I notched out heavily as you'll see in the PCD results.

    I played around with many many options for the woofer. The design started with the TB W6-789E because of pure efficiency, but eventually I had to cave for a driver with more surface area and xmax. The DA270-8 fits this nicely, and its cost-effective to boot! The distortion plots on this board show it to be a competent if not superior driver, and I'm only asking 2 octaves of it anyway. Plugging its values into the SPL spreadsheet from Linkwitz gives me these SPL limits at xmax:



    So that 100 db at 60 hz, 107 at 80 hz, and 112 at 100. Nice, that'll fit the bill. I won't even show the 2x TB version, its ugly!

    I ended up picking a BW2 filter at just below 500 for the woofer to mid because that cancelled out the dipole gain of the baffle cleanly, cutting back on needed XO parts. That might be pushing the DA270 up farther than I should, listening tests will confirm one way or the other.

    The LR4 at 2.5 khz came about because when I used the RS150-4 in my bento's I think it can go higher than the 1800 I used and I'd like to try. I have a stiff parallel notch on it too for the breakup, as you can see in the filter function on the PCD below. Another nice choice of 2.5 is frankly, I can use almost any tweeter I want ;) I plan on setting it up with a 104 standard tweeter hole so that I can try other tweets in place.

    Without any further talk, here is the current draft XO with 16 parts as PCD simulates on the OB:



    The gray line is the midrange reversed. The smooth power response is promising I think, for a nice in-room balanced sound.

    The baffle is 18" wide and 43" tall. I will likely construct it from 3/4" or 1" mdf. I'm currently thinking about a hammered copper steampunk finish with gold edging, it sounds crazy but neat! I'm unsure about the feet yet, I was thinking two 12" pieces going 4" forward and 7" back and using cabinet spikes on them to make it settle well. Here is a simple scale mockup of the design I modeled for PCD with no rounding on the edges:



    Well, so far things look solid. This design should be capable of serious output when driven by a 250 or 300 watt into 4 ohm amp, though obvious not a speaker for extended high-power use like parties since I'd wager you could melt the RS150 voice coil easily enough. Regardless, I think I'm ready to move to the build step? I am getting measuring mic shortly too, which will help too no end.
    Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
    Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

  • #2
    Re: Wavefront DIY OB Dipole Speaker

    You should look into H framing the 10's, you'll get a lot more low end out of the woofers. Instead of hoping for 100 Hz it'll prolly get down into the 40s or 50 Hz.
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    • #3
      Re: Wavefront DIY OB Dipole Speaker

      I would put the mid on a 7 on 8 inch wide, long (20 to 30 inch ) baffle centered with the tweeter above and offset for minimum diffraction with the Edge baffle modeling. I have the Vifa NEW123s mounted like this and they sound wonderful.

      I think the Daton 10" aluminum driver you mentioned is great driver for the bucks and I have one in a sealed box and like it fine. I think the baffle below would work well with no changes except the driver cut out diameter.

      http://www.gr-research.com/pdf/supervbox.pdf or

      http://www.gr-research.com/pdf/obsub.pdf

      I'll step out of sight and wait for the bricks to fly at me now:eek:

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      • #4
        Re: Wavefront DIY OB Dipole Speaker

        fdieck, no bricks yet! ;) *whew*

        Ok, so looking at adapting my design vs. reinventing it totally, I've come up with this below. I'm starting to model it now, but it looks like it'll be -6 db at 45 hz or so. This will let me push the subwoofer XO further down if I don't mind trading a bit of total output SPL loss in return.

        The design:


        What the woofers see acoustically:


        So I'm using a model as if the woofers are on a 28" high and 34" wide baffle now, though an actual measurement would of course be better. Linkwitz mentions a curved sides design like this on his pages to approximate a circular baffle, so I don't think I'm too far off base by simulating this way. I'll post again when I have a PCD simulation of this version.
        Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
        Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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        • #5
          Re: Wavefront DIY OB Dipole Speaker

          Ok, so after reflecting on the design, and feeling like I'm treading into unknown waters with the OB dipole design, I scaled back.

          Its currently got on DA270-8 10" woofer, the amazingly cost-effective SB15NRXC30-8 5" midwoofer used as a midrange, and the SB TWD25 budget tweeter from madisound.

          I feel pretty good about this, and it looks like I only lost a bit of low end extension (doesn't matter in this application) and sensitivity as it comes in now at 87db 2.83V @1M. Also, leaving the bottom part of the baffle open means designing an active box sub for it later means I can integrate it

          Boxes of parts came today, but I'm still waiting on the paint and some other stuff I ordered. Those SB15NRXC30-8 are kind of plain looking in front, but man when you look at the suspension and motor you can tell they are built well. Cone feels furry on the back, its odd. I hope that won't have any humidity issues with aging.
          Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
          Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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          • #6
            Re: Wavefront DIY OB Dipole Speaker

            Ok, so I'm get more and more excited about this build. I'm hoping that when I trimmed 200$ off the cost it will be an increase in cost-effectiveness. If the baffle design works well, you'll see me build many more versions of this speaker with different drivers. Since this one will have a copper metallic paint baffle with gold paint gilding, I'm calling it "Gilded" ;) Here is the final design for the baffle:



            I don't have a good pic of the TWD25 tweeter, so I just put a rectangle that describes its outline in the design. I centered everything and went back to the full wide baffle. Reason: It was easier to compensate for the baffle peak in the XO if both the woofer and mid saw the same boost. The woofer and mid distance is a function of the width of the baffle too, they are exactly 50% further apart than the baffle is wide. This had an noticeable effect on the crossover slopes and overall response. Of course, this is all just modeling, so who knows.

            The real problem I'm facing is the woofer. Its not really seeing a 43" x 18" baffle, or a 28" x 32" (like it would if the 8" deep wings/legs were extended) and I don't think it counts as a U-frame because its missing a top. So I modeled the driver both ways, and plugged them into PCD and tried to model an XO that looked good for both. Eventually I settled on this:



            Which I think looks smashing, look at that phase! The electrical and acoustic is just damn smooth. The crossover is a 400 hz LR2 and 2800 hz LR4, and the reverse null is quite solid too. I think I hit the LR4 on the money, because there are nulls at +/- 30 degrees vertical. The response +/- 15 degress is damn nice though, with just a small drop across the 200 to 2000 range.

            Here is what the XO looks like, and I'm going to build it up for listening in the next few days.



            I made the the woofer XO elliptical, but I don't even know if that is needed. However, at like, +1$ to the cost, why not? The parallel notch on the mid takes care of that nasty peaking at the top of the SB15RNXC's response nicely. I'll post more here as I progress.

            Oh, and there will be a 12 x 12 modular cutout at the bottom of the baffle for an expansion: small sealed box subwoofer, probably dayton reference 8 or 10" dunno. :D
            Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
            Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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            • #7
              Re: Wavefront DIY OB Dipole Speaker

              I had the chance today to sit down and rest after makes all the cuts for the boards that will become the speaker (+ matching subwoofer) and I took some time to examine the SB Acoustics SB15NRXC30-8 visually. All I can say is:

              damn.

              I mean, it's an impressive looking driver. I was floored by the fact that it isn't even wearing any underwear - you can look right down into the voice coil. Wild. Let me share some speaker porn, each image leads to a full-size (huge perhaps?) version if you click on it.





              Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
              Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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              • #8
                Re: Wavefront DIY OB Dipole Speaker

                Prototype build thread started here: http://techtalk.parts-express.com/sh....php?p=1828413
                Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
                Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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                • #9
                  Re: Wavefront DIY OB Dipole Speaker

                  Prototype build thread updated: http://techtalk.parts-express.com/sh....php?p=1828413

                  Limiting voicing time so far, as I'm about to do much more of that this week. I'm really glad that I didn't worry about 2 10" midbass drivers, as with just one they can really crank out the volume and its barely moving. I had kind of wondered about that, otherwise how could Linkwitz have a single Seas 8" crossed about as low in the Orion. I can't image it being a low output speaker. I imagine the XO is rolling it off enough to impact the excursion requirements, even if its a 24 db / octave digital, which should have a sharp curve right near the XO point right? I have them crossed at 80 Hz to the subwoofer right now, and with it between them it seems to blend cleanly.

                  Since the DA270 isn't putting out (efficiency) what the model says, I'm left to either: tone down the mid and tweet, or find a 10" driver with a nice motor that is 90db 2.83V/1M. I'm unsure which I want to do at the moment. Any drivers immediately come to mind that fit the bill?
                  Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
                  Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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                  • #10
                    Re: Wavefront DIY OB Dipole Speaker

                    More details to follow, but I'm on crossover 2 now. I hadn't properly compensated for the baffle gain which was quite audible. After that, I still had this painful ear hurting quality from behavior about 1 to 2 khz with any volume. I tried various models, various designs, and various thoughts. However it turned out to be my own stupidity. I never routed out the back of the holes for the midrange to let them breath. When I would just walk behind the speaker at any volume, you could hear the offending sound from the back. I imagine that works as a loaded chamber at those frequencies if its not chamfered to open the back? I'd be interested in the acoustic science of that issue, maybe I'll start another thread.

                    All I can say right now, is that man they sound natural. They are so clean and power hungry I find myself using the output meter on my ASUS sound card so that I don't overload my amp :eek:
                    Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
                    Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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                    • #11
                      Re: Wavefront DIY OB Dipole Speaker

                      "Since the DA270 isn't putting out (efficiency) what the model says" Oh man. Let me laugh sickly for a moment.

                      Hahahahahahaha. *sigh*

                      Ok, so during assembly, I made one major misstep. In the model the midrange and tweeter are reverse polarity :/ I give you one guess what I forgot during hookup.

                      Alright, so the DA270 is putting out as promised <.< Now that its not getting canceled by the phase issues in the 200-400 ranger >.>

                      I tell you what, hammering the midrange into shape in a dipole design passively is a challenge. Even more so when you are fighting peaking right outside the pass range in the same XO. Oh my.

                      However, I think I have it now. Everything has come together, and I just spent yesterday voicing tweeter level and adjusting the 3 khz crossover to relax the sound.



                      That is the result of days of music listening covering everything from acoustic live to JPop with the help if the equalizer in Foobar2000. Yes, there are TWO damn parallel notches on the mid, one for the baffle and one for the breakup. I tried to use a 3rd order low-pass without the notch to simplify but then phase wouldn't work.

                      I'll post screen caps from PCD 7 with the final XO next. My impressions of this final version are: wow. These are the best small room speakers I've ever heard, even at volume they don't scream or overload the room (the reason I built dipoles). They really and truly impressed me most with movies. I've never felt the impression of a theater at home before, and these do that awesomely.

                      Oh, I should note that L2, L3, and L5 are all solid core inductors to keep the DCR low and the expense reasonable, ERSE IQ in this case.
                      Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
                      Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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                      • #12
                        Re: Wavefront DIY OB Dipole Speaker

                        Ok so the current model in PCD:



                        This seems to be the best solution I could come up with that is pleasing to the ear. You can see that the mid/tweeter XO moved down to 2.7 khz and the slopes improved, the phase is nearly perfect slightly off-axis (since you listen above the tweeter, which is 32" up from the floor). There is only a single cap on the mid, and so there is a huge peak in response at 45 hz or so from the resonance. The thing is, I'm filtering at 80 hz to a sub, so I don't care. If you did, you could put a shunt 10 mh coil right after the 40 uf cap and it'll take care of that.

                        To show you the nightmare I was dealing with in regards to the mid, here is the baffle response and the final response:



                        Now to get the baffles finished, XO boxes or such built, and so on!

                        Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
                        Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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                        • #13
                          Re: Wavefront DIY OB Dipole Speaker

                          Ok, ECM8000 and mic mate arrived today, I have no idea what I'm doing, but fumbling through the guides on this forum, I ended up with this:



                          I ended setting the gating so that it crossed the impulse at 2MS, just before that second wave of garbage appeared. The response has N=6 smoothing, and I'm unsure I can trust the THD with this setup. The measurement is on tweeter axis at 2 meters in their normal position near the walls.
                          Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
                          Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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                          • #14
                            Re: Wavefront DIY OB Dipole Speaker

                            Looks alright, I'll be the 2 spikes in THD are caused by panels rattling, try bracing the wings a bit more.

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                            • #15
                              Re: Wavefront DIY OB Dipole Speaker

                              Thanks for looking it over. I'll see what I can see about panel resonances, and also I noticed that all these type of designs I see online have a brace running on the back to better support the drivers. I wonder if that would help. The peaks are 2nd order, when I show higher order distortion they go away.
                              Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
                              Sites: Jupiter Audioworks - Flicker Stream - Proud Member of Midwest Audio Club

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