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LCR 2-way Crossover Design Help Needed

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  • LCR 2-way Crossover Design Help Needed

    Hello All.

    This my first real post here even though I've been in the audio game for a long, long while. I've built probably a thousand speaker enclosures (mostly car audio subwoofer systems) over the last 30+ years, but I haven't designed and built custom passive crossovers in at least 15 years. And even though I've been buying from PE on and off for many years, I just found out about this forum. Crazy, I know. In this new project, I intend to use the B&C 8FG51 with the DE250-8 and FaitalPRO STH100 waveguides for my LCR's in half cube ported enclosures tuned to 65Hz. My intention is to keep these enclosures fairly tight to the wall behind an AT fabric wall (<12" baffle to wall). A motorized drop-down AT screen will also be in front of the speakers most of the time. The system will be powered from an NAD receiver with DIRAC. I saw that Wolf had put together something very similar using the FaitalPro midbass, but these extend down a little more and may be a tad better sounding, so I'm pretty sure this is the route I'd like to go unless someone has another suggestion that is at a similar budget.

    The room is not a dedicated theater, but more like a media room. 17' wide by 13' deep and MLP is about 10.5-11' from the baffle. It has poured concrete walls, floor, and ceiling. I'm not really concerned about hitting reference levels, but I am concerned more with having a nice wide stage and (not) having a honky, harsh horn sound. From what I can tell this setup shouldn't be too bad as long as it's crossed over properly. Another thing I'm considering is if I should go with an MTM setup for the center channel. Unfortunately it would have to be a horizontal MTM because I also have a TV and a fireplace on that same wall sharing center space.

    I'd love to hear your suggestions, and if there are other data points I need to fill in, please let me know. Thanks in advance.

  • #2
    If you can take real .frd and .zma measurements of the finished speaker, more than likely someone here would be willing to take a shot at the crossover.

    As far as that goes, some here could sim the entire thing start to finish and be dead nuts on target.
    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

    Comment


    • #3
      Not sure what you mean by "reference levels", but that should be a fairly loud speaker if you plan on using a sub.

      When Kornbread asked if you can take .frd and .zma measurements he's asking if you have the equipment needed to measure the driver responses (frequency response and overall impedence).

      The short version for xover design is... Build your cabinet, then measure the frequency response of each driver, then measure the impedence of each driver. Then import those measurements into the xover design program of our liking and play around until we get a respectable simulated response. From there we assemble that simulated xover, and manipulate components until we're happy.

      Without response measuring equipment (like Omnimic and DATS for example), doing this successfully is very difficult.
      "The ability of any system to produce exceptional sound will be limited mainly by the capability of the speakers" Jim Salk
      "Audio is surely a journey full of revelations as you go" JasonP

      Comment


      • #4
        Might be important that the DE250's claimed flat resonse and ~1.4khz recommended XO point are assuming you're pairing it with an exponential shaped horn that can load it down to ~1khz rather than the waveguide which doesn't reach as low. https://www.parts-express.com/B-C-ME...2-Bolt-294-622
        The lower XO point when pairing with a large, 8" woofer helps avoid beaming and can get a wider soundstage without gaps / lobes at certain frequencies.
        Without the horn's help down low, the tweeter will have to work really hard at its lower frequencies and you might get noticeable distortion or harshness.

        I'm pretty sure you'll ideally want to cross below 2khz, probably as near the 1.4-1.5khz as you can safely get the tweeter to reach (1.2khz would be really cool if it's possible, might be unrealistic to ask though).

        That said, I know very little about horns and there are folks here who ARE brimming with knowledge on the subject. So take what I said with a grain of salt.

        EDIT: that horn attachement in the link isn't the only one of it's kind...just happened to be the exact one the DE250 used in the spec'ed graphs/measurements. There are likely more affordable options like fpitas is showing in the post below.
        Last edited by LOUT; 08-31-2021, 01:19 PM.
        My first 2way build

        Comment


        • #5
          You'll definitely need measurements of each driver in the enclosure, as people described above. You might get by with the published data for the woofer (maybe, sorta), but the DE250 on that waveguide will be a complete unknown until you measure it. I also tend to agree with LOUT about using a bigger waveguide. Here's another appropriate one for a reasonable price: https://www.parts-express.com/Eminen...rew-On-290-555

          although you will need a screw-on adapter. Another nice one is the H290C by Pi Speakers (Google is your friend).
          Francis

          Comment


          • #6
            Thank you all for chiming in. I don't currently have that kind of equipment, but I will order it. What I may do is order those drivers along with some pre-fab eminence 1,600Hz xovers and build everything out. That way I can take my time playing with the xovers and A/B them to the eminence ones as a learning experience. Once I get some true measurements, I'll pop back in with some better data.

            Comment


            • Steve Lee
              Steve Lee commented
              Editing a comment
              Excellent plan.

            • fpitas
              fpitas commented
              Editing a comment
              Be sure to design your CD pad to present 8 ohms to the crossover. You'll have to guess at the CD impedance to design the circuit, but the plane wave tube impedance should be close since you're not using a real horn. If you get DATS, that will measure the CD impedance in situ on whatever waveguide you choose.

          • #7
            The CD padding will be so severe (even w/NO baffle-step - for "on-wall") that to maintain 8n(ohms) the PR would need to be near 1 ohm.
            That CD DOES have F/Z data avail. (when mounted to their ME45 horn). I'll probably play w/an XO for you using THAT data, which should be substantially better than a "generic".

            Comment


            • #8
              Thanks, Chris Roemer . That would be great. I appreciate it!

              Comment


              • #9
                Imagine parts drawn L > R (amp to drivers), as std. convention.
                2nd order HighPass w/ "L-pad" for about -18dB attenuation on CD:
                3uF series cap, 2.5mH shunt coil (to gnd. - DCR can be higher), SeriesResistor = 10n(ohms) / PR = 2n
                2nd order LP (on woofer) w/Zobel-like thingy to shape rolloff:
                2.0mH series coil (low DCR, so iron-core is indicated), 6uF shunt cap, Zobel is 15n + 5uF.

                Crosses near 2k. Essentially no BSC (for on/near wall), runs about 90dB sensitivity. Solid (above) 8 ohm load.

                Used data for B&C ME45 horn. Worst "blip" is driver (woofer) DROP just above 1kHz.
                Have NO idea on tweeter polarity (due to depth of waveguide/horn on CD). Try it both ways and see.

                If you can handle a 4ohm load, AND if you double your box volume and run 2 woofers in parallel (MTM), the CD can be unpadded by 6dB raising the system sensitivity to 96dB (which is pretty good for "near" Hi-Fi).

                Enjoy

                Comment


                • #10
                  Yeah, the z offset is one of the tricky parts about horn speakers. If neither tweeter polarity works real well, I guess you have to go to unsymmetrical slopes.
                  Francis

                  Comment


                  • #11
                    Originally posted by Chris Roemer View Post

                    If you can handle a 4ohm load, AND if you double your box volume and run 2 woofers in parallel (MTM), the CD can be unpadded by 6dB raising the system sensitivity to 96dB (which is pretty good for "near" Hi-Fi).
                    Thanks Chris! I have a couple questions on this:

                    1. Is it okay that it would have to be a horizontal MTM configuration for my center channel (I have a TV and fireplace limiting my available vertical space).
                    2. If I can run the center MTM horizontally, would it be possible to send me the crossover specs for that configuration?
                    Last edited by SubNRG; 09-02-2021, 03:49 PM.

                    Comment


                    • #12
                      Yeah, the horn (tweeter) makes a CC (horizontal MtM) a bit messy, since the horn (7" wide?) pushes the 2 midbasses an unusually large distance apart (and that affects horizontal lobing/comb-filtering).

                      Could you run the basses (nearly) tight to each other w/the horn centered above them (so THAT baffle might be 18"w by 16"-17"h)?

                      Comment


                      • #13
                        Originally posted by Chris Roemer View Post
                        Yeah, the horn (tweeter) makes a CC (horizontal MtM) a bit messy, since the horn (7" wide?) pushes the 2 midbasses an unusually large distance apart (and that affects horizontal lobing/comb-filtering).

                        Could you run the basses (nearly) tight to each other w/the horn centered above them (so THAT baffle might be 18"w by 16"-17"h)?
                        It looks like a 21" wide by 15" tall baffle will have the drivers about 1.75" apart. The baffle would be pretty much butted against the TV and fireplace with an inch or two gap, max on each side. Seems like that should be close enough, right? If so, any chance you can send me the crossover specs for this? I really appreciate your help!

                        Comment


                        • #14
                          These are the component changes you'd make to an MTM XO to get (roughly) the same response as for the TM - but the sensitivity will go up by about +6dB/v. Of course, the load drops (on the woofer section) to a Zmin of about 3.5ohms near 200Hz.

                          HP: only the padding changes, to SR=9n (was 10) / PR=5n (was 2).
                          Both these L-pads present about a 12n load to the pass filter.

                          LP: since the MTM's impedance halves, the "equivalent" filters sees inductor and resistor values HALVE, and caps double.
                          so, 1mH series coil (was 2), 12uF shunt cap (was 6), Zobel = 8n+10uF (was 15n+5uF).
                          Box volume needs to double, and use 2 ports (or their equivalent) for the same tuning/F3.

                          Comment


                          • SubNRG
                            SubNRG commented
                            Editing a comment
                            Thanks Chris. I'm going to give that a shot. I really appreciate it!
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