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Home/Pro 8" 2-way: RS28A and B&C 8BG51

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  • #61
    Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

    A waveguide done right will improve coherence as there is less room interference. Here is a great graphic that is relevant too.

    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche

    http://www.diy-ny.com/

    Comment


    • #62
      Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

      I just don't see what you do there Mike. Have a look at Dave's flat baffle vs. guide on the same display.



      There are no more "ripples" in the response with the guide than there are on the flat baffle.

      And what tweeter doesn't lose off axis energy up high as you move off axis? The difference with the guide is that the entire band falls off more uniformly than it does without the guide. The advantage of that characteristic is that power response is actually smoother with the guide than without it, depending on the woofer you're crossing to. With the 8" woofer, the off axis response of a flat baffle tweeter system will show a gradual dip in the region of the crossover due to the woofer "beaming" while the tweeter doesn't, until much higher up in frequency. Some members here call it a "midrange mushroom cloud" power response, with an increased energy in the 2KHz - 8KHz region relative to the 800Hz-2000Hz range.

      As for imaging and sound stage, I think the enclosure can have as much to do with that as the driver implementation. An enclosure that talks during the program just ruins the presentation.
      Were are the off-axis and polars? Again we are trying to justify an answer with a single measurement of comparison. You know what I am talking about. I am not going to scan pages from a book and submit them. Here is something I dug up quick. It discusses rooms a bui, however the same issues take place inside a WG http://www.physicsclassroom.com/class/sound/u11l3d.cfm


      I am unsure what midrange mushroom cloud you are referring too. Done right in any format, in any speaker, the power responce should be smooth through the 800-2K range. Yes, it is known that an enclosure ringing can ruin imaging. That is not the question though. I am talking about power responce beyond 5K though, not in the mid-bands.

      The image Face posted appears to assume perfect phase as well. It is not as linear as the drawing states and there is a point where the room is still reactive, just less reactive than a flat baffle.

      Like I already said: The reasons you went WG for this design makes sence. However you did sacrifice in some areas which were less important to the design to gain in others. when it is implied that there is nothing but upside using a WG, I think it is a bit misleading. I do not want to argue what is better, flat baffle or waveguide. Just was looking for acknowldgement that yes, here is why I chose a WG, because these benefits outweight anything given up: here's why. At this point I am thinking I should have stuck to my orignal post and just acknowldge this is going to be a very cool speaker and leave it at that.
      .

      Comment


      • #63
        Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

        Originally posted by mzisserson View Post
        Were are the off-axis and polars? Again we are trying to justify an answer with a single measurement of comparison. You know what I am talking about. I am not going to scan pages from a book and submit them. Here is something I dug up quick. It discusses rooms a bui, however the same issues take place inside a WG http://www.physicsclassroom.com/class/sound/u11l3d.cfm


        I am unsure what midrange mushroom cloud you are referring too. Done right in any format, in any speaker, the power responce should be smooth through the 800-2K range. Yes, it is known that an enclosure ringing can ruin imaging. That is not the question though. I am talking about power responce beyond 5K though, not in the mid-bands.

        The image Face posted appears to assume perfect phase as well. It is not as linear as the drawing states and there is a point where the room is still reactive, just less reactive than a flat baffle.

        Like I already said: The reasons you went WG for this design makes sence. However you did sacrifice in some areas which were less important to the design to gain in others. when it is implied that there is nothing but upside using a WG, I think it is a bit misleading. I do not want to argue what is better, flat baffle or waveguide. Just was looking for acknowldgement that yes, here is why I chose a WG, because these benefits outweight anything given up: here's why. At this point I am thinking I should have stuck to my orignal post and just acknowldge this is going to be a very cool speaker and leave it at that.
        Here is both the flat baffle and waveguide out to 90 degrees Dave posted on the ND25FN, if that helps.

        Flat: Click image for larger version

Name:	0-90_+_Polar flat.jpg
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ID:	1153981

        WG: Click image for larger version

Name:	0-90_+_Polar WG.jpg
Views:	1
Size:	113.1 KB
ID:	1153982
        -Kerry

        Comment


        • #64
          Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

          Originally posted by Navy Guy View Post
          Here is both the flat baffle and waveguide out to 90 degrees Dave posted on the ND25FN, if that helps.

          Flat: [ATTACH=CONFIG]41990[/ATTACH]

          WG: [ATTACH=CONFIG]41991[/ATTACH]
          It most definately does.. and doesn't... I am unsure I see what I was seeing when I took my measurements a while ago. I may need to dig up the information. Weather the mic is capturing it or not, it's there. CSD maybe? Ugh. It was 3 computors ago and 4 external back up drives. Ill look tonight. See if I can dig it up.
          .

          Comment


          • #65
            Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

            Originally posted by mzisserson View Post
            It most definately does.. and doesn't... I am unsure I see what I was seeing when I took my measurements a while ago. I may need to dig up the information. Weather the mic is capturing it or not, it's there. CSD maybe? Ugh. It was 3 computors ago and 4 external back up drives. Ill look tonight. See if I can dig it up.
            If you have only tested the one waveguide, it might be possible that you didn't have everything sealed up properly. There is a post Dave did on putting a ScanSpeak tweeter in one of his waveguides, and it was getting leaks from under the faceplate or something. It ended up causing a ragged response and had some odd distortion peaks. It might also have just been the guide you were using. I haven't measured any waveguides myself to know enough even if you posted it though.
            -Kerry

            Comment


            • #66
              Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

              The SS tweeter was leaking between the cup and motor causing a double hump like a vented cabinet. It depends on the tweeter whether it needs sealed or not.

              I was thinking about putting the ND25 on the flat baffle and EQing it to flat then putting the waveguide in the same size baffle with same edge treatment and EQ it to the same response. Then take polar plots, measure distortion and also CSD and tone burst measurements to see what the differences are. Also post the impulse response of each.

              Dave
              http://www.pellegreneacoustics.com/

              Trench Seam Method for MDF
              https://picasaweb.google.com/101632266659473725850

              Comment


              • #67
                Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                Originally posted by davepellegrene View Post
                The SS tweeter was leaking between the cup and motor causing a double hump like a vented cabinet. It depends on the tweeter whether it needs sealed or not.

                I was thinking about putting the ND25 on the flat baffle and EQing it to flat then putting the waveguide in the same size baffle with same edge treatment and EQ it to the same response. Then take polar plots, measure distortion and also CSD and tone burst measurements to see what the differences are. Also post the impulse response of each.

                Dave
                What are you showing if you EQ them? Just wondering the value. If you boost frequencies, you can easily increase distortion. I think next summer I will design a speaker with the same drivers, one WG, one not. The x-over will be different however the goal will be flat on axis response. Then do some blind testing somehow. No, it will not be perfect... However it may be interesting. I discussed this with TN allen a while back.
                .

                Comment


                • #68
                  Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                  Originally posted by mzisserson View Post
                  What are you showing if you EQ them? Just wondering the value. If you boost frequencies, you can easily increase distortion. I think next summer I will design a speaker with the same drivers, one WG, one not. The x-over will be different however the goal will be flat on axis response. Then do some blind testing somehow. No, it will not be perfect... However it may be interesting. I discussed this with TN allen a while back.
                  I wasn't thinking boosting. I was thinking more like what a passive crossover would do EQing down to flat. I just thought it might be an interesting comparison. I personally don't see a down side to a guide. I'm not saying there isn't one. I just do to know what it is. I thought this type of comparison might show one.

                  Dave
                  http://www.pellegreneacoustics.com/

                  Trench Seam Method for MDF
                  https://picasaweb.google.com/101632266659473725850

                  Comment


                  • #69
                    Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                    Originally posted by davepellegrene View Post
                    I wasn't thinking boosting. I was thinking more like what a passive crossover would do EQing down to flat. I just thought it might be an interesting comparison. I personally don't see a down side to a guide. I'm not saying there isn't one. I just do to know what it is. I thought this type of comparison might show one.

                    Dave
                    Eq-ing down would have the same effect. If you had the time it would be worth it. And we can stop hijacking pete's build lol.
                    .

                    Comment


                    • #70
                      Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                      Originally posted by mzisserson View Post
                      Eq-ing down would have the same effect. If you had the time it would be worth it. And we can stop hijacking pete's build lol.
                      I don't consider any of this hijacking at all. It's a great discussion about the benefits/drawbacks of waveguides, which is central to the build here.

                      Keep it up.
                      R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                      Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                      95% of Climate Models Agree: The Observations Must be Wrong
                      "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

                      Comment


                      • #71
                        Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                        I put my results in the Dayton ND25FN-4 Thread
                        Starting at post #17

                        http://techtalk.parts-express.com/sh...08#post1951508

                        Dave
                        http://www.pellegreneacoustics.com/

                        Trench Seam Method for MDF
                        https://picasaweb.google.com/101632266659473725850

                        Comment


                        • #72
                          Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                          Oh boy, I got a box full of crossover parts and a bunch of wires and alligator clips. :D

                          Tonight I get to listen to the "Marksmen" as speakers for the first time.

                          I'll post my impressions as soon as I get some time on them.
                          R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                          Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                          95% of Climate Models Agree: The Observations Must be Wrong
                          "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

                          Comment


                          • #73
                            Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                            Cool speaker project Pete and an excellent name!
                            Craig

                            The lowest possible F3 box alignment is not always the best alignment.

                            Designing and building speaker projects are like playing with adult Lego Blocks for me.

                            Comment


                            • #74
                              Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                              I thought I'd go ahead and post a room response of the stereo pair at the listening position, room warts and all.

                              I can definitely hear the bloom at 100Hz, but that changes as I move around. Overall, sounds pretty good so far.

                              Gotta move them around to better positions in the room since they're still in the test location away from their normal listening positions.

                              They certainly don't sound lacking on the high end even though they fall off after 15KHz. Once the woofers are really broken in, I'll get a better idea of their bass performance relative to the midrange.

                              Attached Files
                              R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                              Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                              95% of Climate Models Agree: The Observations Must be Wrong
                              "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

                              Comment


                              • #75
                                Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                                I thought I'd go ahead and post a room response of the stereo pair at the listening position, room warts and all.

                                I can definitely hear the bloom at 100Hz, but that changes as I move around. Overall, sounds pretty good so far.

                                Gotta move them around to better positions in the room since they're still in the test location away from their normal listening positions.

                                They certainly don't sound lacking on the high end even though they fall off after 15KHz. Once the woofers are really broken in, I'll get a better idea of their bass performance relative to the midrange.

                                Pete earlier in the thread you said you got the last pair of the BC woofers,
                                was P/E just out of stock and will they be available in the near future?

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