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

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

    This thread is to document a build using the RS28A in a waveguide teamed up with the B&C 8BG51 Neo motor pro-sound mid-woofer.

    Tom Jones (takitaj) provided the baffle. He fashioned a waveguide to fit the opening of the RS28, 2" deep, 7" overall width, with a smooth curve that ends tangential to the baffle. I'm unsure yet as to how well it will work but I have high hopes. It follows fairly closely the profile of the larger guide made by DanP with a 3D printer a couple years back. That guide was wider, with a larger radius profile. This one features the same throat opening, and same depth. Exit angle is a bit smaller at about 90 degrees.

    Tom's baffle is made to replace the baffle on the .75 cf TM Parts Express cabinet, using the same mounting screws, so it will be removable to allow mounting the tweeter onto the rear of the baffle.

    I expect the baffle to be here tomorrow so hopefully I can get things mounted and start testing. I want to bring this to the KYDIY this weekend, so I probably won't have time to get any paint on the baffle. Hopefully, I'll have enough time to get a crossover built along with getting some voicing time in.

    This will be an 8 Ohm system, and I'm guessing at around 87dB overall sensitivity after baffle step, with F3 about 47Hz, and should be able to produce over 110dB from 50Hz on up. Not too shabby for a stand mount monitor. I'm going to try a 2.5" port which will have 38m/s port velocity with 100W input. It's a compromise for sure, but the smaller port pushes the port resonance up above 1KHz. And for normal listening levels, port velocity will be low enough to not cause problems.

    More to come as progress continues.

    Click image for larger version

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    Attached Files
    Last edited by Pete Schumacher ; 12-14-2013, 04:51 AM. Reason: corrected exit angle
    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

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

    Looks like a very cool project Pete. Can't wait to see how it turns out.

    Originally posted by Pete Schumacher View Post
    This thread is to document a build using the RS28A in a waveguide teamed up with the B&C 8BG51 Neo motor pro-sound mid-woofer.

    Tom Jones (takitaj) provided the baffle. He fashioned a waveguide to fit the opening of the RS28, 2" deep, 7" overall width, with a smooth curve that ends tangential to the baffle. I'm unsure yet as to how well it will work but I have high hopes. It follows fairly closely the profile of the larger guide made by DanP with a 3D printer a couple years back. That guide was wider, with a larger radius profile. This one features the same throat opening, exit angle (120 degrees) and same depth.

    Tom's baffle is made to replace the baffle on the .75 cf TM Parts Express cabinet, using the same mounting screws, so it will be removable to allow mounting the tweeter onto the rear of the baffle.

    I expect the baffle to be here tomorrow so hopefully I can get things mounted and start testing. I want to bring this to the KYDIY this weekend, so I probably won't have time to get any paint on the baffle. Hopefully, I'll have enough time to get a crossover built along with getting some voicing time in.

    This will be an 8 Ohm system, and I'm guessing at around 87dB overall sensitivity after baffle step, with F3 about 47Hz, and should be able to produce over 110dB from 50Hz on up. Not too shabby for a stand mount monitor. I'm going to try a 2.5" port which will have 38m/s port velocity with 100W input. It's a compromise for sure, but the smaller port pushes the port resonance up above 1KHz. And for normal listening levels, port velocity will be low enough to not cause problems.

    More to come as progress continues.

    [ATTACH=CONFIG]41806[/ATTACH]
    Loren Jones

    http://techtalk.parts-express.com/sh...-sound-drivers

    http://techtalk.parts-express.com/sh...for-live-sound

    Comment


    • #3
      Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

      Ran a sweep of the 8BG51 nearfield, mic about 3" from the dust cap, just outside the front of the woofer flange. I'm guessing about 1W input. Ungated, no smoothing. This looks close to the manufacturer's data. Clean performance up to 1K. I hope the RS28A/guide can meet up with this without too much trouble.

      Click image for larger version

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      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

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      • #4
        Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

        So what's the major "diameter" on that woofer?
        Thanks,
        Aaron

        Comment


        • #5
          Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

          Originally posted by aarond View Post
          So what's the major "diameter" on that woofer?
          From the PE product page:

          Overall Outside Diameter 8.8"
          Baffle Cutout Diameter 7.4"
          Depth 3.50"
          Bolt Circle Diameter 8.3"
          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

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          • #6
            Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

            Ha, I looked there but didn't scroll down to see it. I'm still not used to the (not so) new site format. I didn't see an "A" dimension in the description and assumed they left it out because of the odd shape.

            So practically speaking it's the same OD as the RS225, which is what I was really wanting to know.

            Following along, enjoying the ride.
            Thanks,
            Aaron

            Comment


            • #7
              Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

              cool Pete. Eager to see how the WG works out.
              " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

              Quote Originally Posted by hongrn. Oct 2014
              Do you realize that being an American is like winning the biggest jackpot ever??

              http://www.midwestaudioclub.com/spot...owell-simpson/
              http://s413.photobucket.com/albums/pp216/arlis/

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

                Pete, looks really interesting. I have been eyeballing that 8" BC for a while.
                Facebook Page - Ocean State Acoustics

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                • #9
                  Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                  Well, getting this to KYDIY is going to be tough. The baffles need to be modified on the back side in order to fit into the cabinets. It'll take some creative router or table saw work but the mod shouldn't be more than time consuming.

                  In the meanwhile, I got the RS28A mounted and ran a sweep. I'm liking the looks of this guide. Should be a perfect match for the cutoff knee of the woofer.



                  Click image for larger version

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                  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

                  Comment


                  • #10
                    Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                    Well I couldn't get the baffle all the way onto the enclosure, but it did fit well enough to get a measurement of both woofer and tweeter together without the dipole cancellation on the woofer. I really wanted to start on a crossover design.

                    So far,so good. 8 components yields this system response. LR4 at 1200Hz.



                    Click image for larger version

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Views:	1
Size:	59.1 KB
ID:	1153916
                    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

                    Comment


                    • #11
                      Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                      Pete, is this wg the same as the LOKI or is it slightly smaller? Speaking about the LOKI, is that design dead? I hope not!
                      "It is only Scrooge McDuck and others with a personality disorder who have money as their goal"

                      Comment


                      • #12
                        Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                        That should be an excellent HT speaker for folks that want high output levels from a standmount form factor. I'm sure it will ne nice for music too, but reasonable sensitivity and extension in a standmount box with pretty high output levels is a nice combination.

                        Originally posted by Pete Schumacher View Post
                        Well I couldn't get the baffle all the way onto the enclosure, but it did fit well enough to get a measurement of both woofer and tweeter together without the dipole cancellation on the woofer. I really wanted to start on a crossover design.

                        So far,so good. 8 components yields this system response. LR4 at 1200Hz.



                        [ATTACH=CONFIG]41875[/ATTACH]
                        Loren Jones

                        http://techtalk.parts-express.com/sh...-sound-drivers

                        http://techtalk.parts-express.com/sh...for-live-sound

                        Comment


                        • #13
                          Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                          Originally posted by jonasz View Post
                          Pete, is this wg the same as the LOKI or is it slightly smaller? Speaking about the LOKI, is that design dead? I hope not!
                          L.O.K.I. will resume when the new reference drivers come out. The 8" composite cone should be around in February (or there about) according to Rory.

                          This particular guide is slightly smaller than the original and from the looks of it, doesn't extend quite as deep before cut off. Otherwise, it still produces the same smooth transfer function.
                          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

                          Comment


                          • #14
                            Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                            Originally posted by Pete Schumacher View Post
                            In the meanwhile, I got the RS28A mounted and ran a sweep. I'm liking the looks of this guide. Should be a perfect match for the cutoff knee of the woofer.
                            Distortion looks excellent all the way down to 1 khz, and that is impressive. Most of the response slope is nice and smooth, great work. I'm not sure I like that massive early roll-off though. I wonder how audible that will be in the end.
                            Audio: Media PC -> Sabre ESS 9023 DAC -> Behringer EP2500 -> (insert speakers of the moment)
                            Sites: Jupiter Speakerworks - SpeakChat 2.0 - Flicker Stream - FRD Consortium Archive - Proud Member of Midwest Audio Club

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                            • #15
                              Re: Home/Pro 8" 2-way: RS28A and B&C 8BG51

                              Originally posted by JasonP View Post
                              Distortion looks excellent all the way down to 1 khz, and that is impressive. Most of the response slope is nice and smooth, great work. I'm not sure I like that massive early roll-off though. I wonder how audible that will be in the end.

                              Good point. I'm not sure how much of it is really there. These were all far less than optimal measurement conditions. Once I get the baffle into the cabinet properly, I'll get a new set of data.

                              But it looks like this will not make it to KYDIY. Just not enough time. And now, my traveling partner has come down with a bad chest cold, so I'll likely be staying home to baby sit her.
                              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

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