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  • Rectangular throated waveguide with dome tweeter

    I'm curious if anyone has experimented with a square or rectangular throated waveguide over a dome tweeter. If so, do you have any results or experiences to share?

    I built a rectaungular waveguide out of 4 pieces of cherry for my Mystiques project and it seemed to work quite well, but that was for a Raal 70-10 and fit its normal face plate opening shape. I'm speculating this could work for a dome by using a spacer to offset the throat to reside just above the dome surround. One would perhaps have some flexibility to vary the shape of the throat by adjusting the width or height a bit as long as the dome and surround were free to move within its xmax range and not touch the waveguide. An example might be to make it a bit narrower in width and taller in height to potentially increase horizontal versus vertical dispersion. Varying from a square might vary the throat reflections enough so as to reduce upper octave cancellations.

    At any rate, below is what I did with the Raal tweeter and I'm curious if anyone has messed with a similar approach with a dome.

    Any thoughts?
    Dan N.

  • #2
    Yes. In my Synergy horn I used a square connection to the dome tweeter. I experimented with round to square transitions and fillets in the square opening. My focus was to reduce the deep null on axis around the 10K range and the ripple above.

    The square opening was the better than round and with fillets. I tested a bunch of tweeters with foam board horns. I put blue tape on the tweeters then used yellow glue to glue the tweeter to the horn.

    The tweeter recess below the edge of the tweeter mounting flange and then the closeness of the horn opening edge to the side of the tweeter dome were critical to the performance. I subjectively felt I could dial in the performance of the tweeter by adjusting the size of the square opening. I also subjectively think a rectangular or triangular opening might be better.
    John H

    Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

    Comment


    • #3
      Excellent info, John. Thanks! I had thought that square and even more likely, rectangular, could be better than round simply because they might spread the throat diffraction around a wider range of frequencies, rather than focusing them all at one frequency.

      I'm thinking of trying this in a shallow waveguide implementation matched to a Morel MDM-55 crossed around 3khz or so, primarily intended to improve directivity match, but hopefully with a little distortion reduction if I can get enough boost to equalize out in the XO and drop distortion levels.
      Dan N.

      Comment


      • #4
        What about an oval opening?

        Comment


        • dlneubec
          dlneubec commented
          Editing a comment
          I'm guessing this would offer similar potential benefits to the square or rectaungular approach.

      • #5
        I think that a vertical slot over a dome tweeter might be an interesting experiment, for the reasons that you mentioned. Adjustable width would be a nice touch, it could be optimized that way. I'd be especially interested in seeing what the impedance curves does as the slot becomes more narrow.

        Comment


        • #6
          Originally posted by Billet View Post
          I think that a vertical slot over a dome tweeter might be an interesting experiment, for the reasons that you mentioned. Adjustable width would be a nice touch, it could be optimized that way. I'd be especially interested in seeing what the impedance curves does as the slot becomes more narrow.
          I tested a few throat chamber/ phase plug ideas. I had some chamber resonances that did not improve the top end response. I lost interest because I could not make the chamber and openings small or close enough to the dome to be effective. If you have a 3-D printer this would be easier to experiment with.
          John H

          Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

          Comment


          • #7
            Round vs Square with the XT25
            John H

            Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

            Comment


            • #8
              So at a risk of confusing the issue here is the DC28 tweeter in a Round vs. Square connection to the wave guide. The round opening does not have the huge dip. I was able to change the square connection dip by moving the edges closer to the dome
              John H

              Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

              Comment


              • #9
                Great stuff John, thanks. No doubt each tweeter would probably need to be tweaked for the best response. No doubt the square looks a lot better with the XT25 and that probably could be extrapolated to ring radiators in general, maybe to the dimple domes as well.

                Does the DC28 have a highly protruding dome? I'm curious because I'm wondering if a flatter dome might do better, it propagation being perhaps more similar to a ring radiator and you could possibly cover more of the dome as a result. I know the TL N26C ceramic domes do well in a waveguide and they are quite flat.
                Dan N.

                Comment


                • #10
                  Originally posted by dlneubec View Post
                  Does the DC28 have a highly protruding dome? I'm curious because I'm wondering if a flatter dome might do better, it propagation being perhaps more similar to a ring radiator and you could possibly cover more of the dome as a result. I know the TL N26C ceramic domes do well in a waveguide and they are quite flat.
                  The DC28F dome has a 1/2 recessed in the tweeter flange where the XT25TG30 and XT25SC90 had/ were less recessed. I also tested the Peerless D27TG and it was similar to the DC28F. I think there is some interaction of the dome recessed in the tweeter face plate and the horn. The "moat" or recessed grove between the dome and tweeter is something to be aware of.
                  John H

                  Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                  Comment


                  • #11
                    OK, that makes sense. The waveguides I have implemented before all were with face plate removed. The design of the faceplate could certainly present some serious challenges.
                    Dan N.

                    Comment


                    • #12
                      Here is what I have in mind. I already have a 2-way box that I will repurpose for this project. I will add a 2" base to allow the crossover to go in the bottom, outside of the box. I will add a 3/4" baffle on top of the existing 1" baffle and create the waveguide in this new baffle. The new baffle will probably remain removable so I can get to the tweeter if need be. Attached is a drawing that should help to make sense of my description.

                      For the waveguide base, I cut a slot horizontally across the new baffle. I make the slot about 3/32" shy of all the way through. This 3/32" will provide the recess that the tweeter dome and surround sets in so the waveguide pieces can slide out over the surround and partially over the dome. I will cut the slot wider than the pieces within so I can change the size of the throat. Spacer pieces would be installed in the slots on the top and bottom when testing various sizes and eventually fixed in place when the best solution is found.

                      The waveguide itself would be made of 4 pieces. Two that run all the way across the top and bottom that form the top and bottom sides of the waveguide. These parts are shown as blue. Initially I will probably try these at 60 degrees. The other two pieces form the sides of the waveguide and can slide across it left to right. I will probably try to cut these at around 70 75 degrees initially. It appears that I can change the aspect of the rectange from 13/16" square, to 1-1/4" square and a rectangle of as much as 13/16" x 1-1/4", which is pretty close to the golden mean ratio.

                      Depending on how it goes and what the measurements show, I can try different angles on both sides of the waveguide by cutting new test pieces. Initially everything would be cut out of 3/4" mdf and chances are the final parts would be as well. I would like to use hardwood, like I did on the Mystiques waveguide, but cutting those sharp angles in hardwood to create the waveguide was tough because either way you ran the wood grain, you ran the risk of easily splitting the wood at the narrowest points.

                      Attached Files
                      Dan N.

                      Comment


                      • #13
                        If the pieces are separate do you really need 3/32 thickness of material above the tweeter vs mounting the wave guide pieces on the tweeter face plate? I'd be concerned about the wave guide pieces over hanging the tweeter opening as you move them closer to the dome.
                        John H

                        Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                        Comment


                        • #14
                          Originally posted by jhollander View Post
                          If the pieces are separate do you really need 3/32 thickness of material above the tweeter vs mounting the wave guide pieces on the tweeter face plate? I'd be concerned about the waveguide pieces overhanging the tweeter opening as you move them closer to the dome.
                          Depends on the tweeter and the faceplate. If it has a faceplate that is flat to the edge of the surround, then it might work fine. If it is sculpted, then I will probably want to remove it, unless it can't be removed. Back when Dave Pellegrene and I were working together on some of the waveguides he did for me, we found that covering the surround with the throat, so that the thoat hovered above the surround often resulted in a smoother top end. I want to push that if I can to see the effect of covering part of the dome as well, while making sure I have adequate clearance for excursion.

                          The 3/32" is a guess at this point. I haven't decided what tweeter I will use yet. I do have an old pair of Vifa D26NC55's that have face plates that snap off and that I used in a mini waveguide for a design many moons ago. That tweeter measures very flat and is about perfect for this application, but the drawback is it is NLA. It has a tiny surround and if I'm crossing in the 3000-4000 Hz range, I don't need much excursion.

                          I could also recess the tweeter itself into the underlying baffle to get the offset I'm looking for.

                          Vifa D26NC55
                          Click image for larger version

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                          Dan N.

                          Comment


                          • #15
                            Originally posted by dlneubec View Post
                            Here is what I have in mind. I already have a 2-way box that I will repurpose for this project. I will add a 2" base to allow the crossover to go in the bottom, outside of the box. I will add a 3/4" baffle on top of the existing 1" baffle and create the waveguide in this new baffle. The new baffle will probably remain removable so I can get to the tweeter if need be. Attached is a drawing that should help to make sense of my description.

                            For the waveguide base, I cut a slot horizontally across the new baffle. I make the slot about 3/32" shy of all the way through. This 3/32" will provide the recess that the tweeter dome and surround sets in so the waveguide pieces can slide out over the surround and partially over the dome. I will cut the slot wider than the pieces within so I can change the size of the throat. Spacer pieces would be installed in the slots on the top and bottom when testing various sizes and eventually fixed in place when the best solution is found.

                            The waveguide itself would be made of 4 pieces. Two that run all the way across the top and bottom that form the top and bottom sides of the waveguide. These parts are shown as blue. Initially I will probably try these at 60 degrees. The other two pieces form the sides of the waveguide and can slide across it left to right. I will probably try to cut these at around 70 75 degrees initially. It appears that I can change the aspect of the rectange from 13/16" square, to 1-1/4" square and a rectangle of as much as 13/16" x 1-1/4", which is pretty close to the golden mean ratio.

                            Depending on how it goes and what the measurements show, I can try different angles on both sides of the waveguide by cutting new test pieces. Initially everything would be cut out of 3/4" mdf and chances are the final parts would be as well. I would like to use hardwood, like I did on the Mystiques waveguide, but cutting those sharp angles in hardwood to create the waveguide was tough because either way you ran the wood grain, you ran the risk of easily splitting the wood at the narrowest points.
                            Is this going to be a three way with a dome mid? MDM55?

                            Comment

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