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

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

    Originally posted by cjd View Post
    You can force a crossover at any point you think reasonable, but you're not getting the same boost at that frequency. The RS28A has been crossed at 1k (I think? Or was it 1.2?) without a waveguide, but it's tricky to get right. It also depends on the mid-woofer - not all 8" can cross that high, or need extra care to do so.

    That said, I don't quite understand your question. You want to know if a horn will cross with a horn? It's about the tweeter you use IN the horn, and you'll get less low end the smaller the waveguide/horn.
    As I understand it, this build assumes a 1kHz crossover point.

    Both the RS28 and DNA 360 driver can be made to crossover nicely at 1kHz in the right horn/waveguide.

    My question assumes one of two things may happen:

    1. The RS28 is loaded into a different waveguide than is spec'ed in the build,

    2. A compression driver and horn are used in place of the RS28, but with the same crossover section to the 8BG51.

    Is that more clear?
    https://www.facebook.com/lowecustomguitar

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

      It's not that simple to switch parts without a completely reworked crossover. Change the width of the enclosure....new crossover. Change the depth of one of the components....new crossover. Change the woofer or tweeter....new crossover.

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

        I have the B&C 8PS21 mentioned earlier by Erich and I have it paired with the JBL 6x6 waveguide and loaded with JBL 2408H but I would love to try a larger waveguide for my Seas 27TDFC, does anyone make an 8" waveguide that could work with that Seas tweeter?

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

          Originally posted by Erich H View Post
          It's not that simple to switch parts without a completely reworked crossover. Change the width of the enclosure....new crossover. Change the depth of one of the components....new crossover. Change the woofer or tweeter....new crossover.
          I understand completely.

          I've been talking with Pete offline about a separate project with the 8BG51 as the woofer.

          I'd like to use a DNA/DIYSG horn and waveguide for the top end.

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

            Trying another crossover now . . . LR2 instead of LR4.

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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
            "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

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

              Pete, here's some photos of the EOS-6 with the other B&C to give you an idea on it's overall size:

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              Ideally it would be a little bigger. But stepping up to a custom EOS-8 might be too big for some smaller woofer designs later. Another thing is how easy the EOS-6 can be recessed into the baffle.

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              You mentioned the SEOS-10 above the B&C. I already had a baffle cut for that, so I took a photo. It looks just a bit too wide on just a MT version. That's the white fiberglass model with the standard 1" throat because I didn't have my modified model with me.

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

                Originally posted by Erich H View Post
                Pete, here's some photos of the EOS-6 with the other B&C to give you an idea on it's overall size:

                [ATTACH=CONFIG]42816[/ATTACH]

                [ATTACH=CONFIG]42817[/ATTACH]

                Ideally it would be a little bigger. But stepping up to a custom EOS-8 might be too big for some smaller woofer designs later. Another thing is how easy the EOS-6 can be recessed into the baffle.

                [ATTACH=CONFIG]42818[/ATTACH]

                You mentioned the SEOS-10 above the B&C. I already had a baffle cut for that, so I took a photo. It looks just a bit too wide on just a MT version. That's the white fiberglass model with the standard 1" throat because I didn't have my modified model with me.

                [ATTACH=CONFIG]42819[/ATTACH]
                Seeing the EOS6 on that baffle makes me think that the EOS8 would be an almost perfect match to the guide I'm currently using.

                By the way, what is the profile on those guides? Is it conical up to the point where it rounds over to the baffle?
                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.

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

                  I think we might be pretty close with the EOS-6. I drew a line where I think the waveguide portion ends on both designs versus the side of the woofer flange. They're probably about .5" different. I'll try to find a photo showing the inner curve of the EOS.

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                  The 8" model is a decent amount wider. Some of that is just because of the outer mounting flange in bigger.

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

                    Originally posted by Erich H View Post
                    I think we might be pretty close with the EOS-6. I drew a line where I think the waveguide portion ends on both designs versus the side of the woofer flange. They're probably about .5" different. I'll try to find a photo showing the inner curve of the EOS.

                    [ATTACH=CONFIG]42820[/ATTACH]
                    [ATTACH=CONFIG]42821[/ATTACH]

                    The 8" model is a decent amount wider. Some of that is just because of the outer mounting flange in bigger.

                    [ATTACH=CONFIG]42822[/ATTACH]
                    How deep is the EOS6? I'm getting almost 15dB boost around 1200Hz with the guide on that baffle.

                    By the way, the 2nd order XO just doesn't cut it. That woofer NEEDS to be crossed at no higher than 1200Hz LR4.
                    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.

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

                      By the way, the 2nd order XO just doesn't cut it. That woofer NEEDS to be crossed at no higher than 1200Hz LR4.
                      Not that 2/3 of an octave will make much difference probably, but would lowering the crossover point keep the woofer in check w/ a 2nd order slope? I thought you'd ran this tweeter down to 800Hz in a 'guide before?
                      Thanks,
                      Aaron

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

                        Originally posted by aarond View Post
                        Not that 2/3 of an octave will make much difference probably, but would lowering the crossover point keep the woofer in check w/ a 2nd order slope? I thought you'd ran this tweeter down to 800Hz in a 'guide before?
                        The guide for the 800Hz cross was a little larger than this one. The guide cutoff is about 1200Hz (where the peak occurs) which allows me a 1000Hz XO point.

                        The main reason the woofer needs to cross LR4 is that there are some cone/surround resonance issues that cause a couple of spikes in the distortion spectrum. Whether it's audible or not is debatable, but after hearing the lower ordered slopes, the clarity I was hearing by letting the tweeter reach lower on its own became quite apparent. I'm back to the LR4 XO and I'm liking it much better.
                        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


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

                          Boy, that looks really elegant!

                          https://www.facebook.com/lowecustomguitar

                          www.lowecustomguitars.com

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

                            That looks like a variation of the new JBL M2 waveguide. Missing the vertical nodes to match the horizontal.

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

                              double post..

                              Greg Jensen

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

                                I think the M2 resemblance is just light reflections and not physical shape...? Anyways, I don't get the SEOS 6 or 8 when Pete seems to be on to a good woofer and crossover point from 1-1.2 kHz. To maintain boost and pattern control down to that point you need the SEOS 10. Maybe a little boost from the SEOS 8, but definitely not good pattern control down that low (though maybe there is a real difference in this area between domes and compression drivers as I have only seen measurements of the latter in these SEOS guides...).

                                I think a real contender for ultimate home theatre DIY speaker would be an MTM with B&C 8BG51 and RS28A on a custom SEOS 10 (throat cut to be shallow/zero, mounting plate). Even better yet, a fairly large MTM tower with ML-TL on the woofers at slightly different tuning in separate chambers. If the woofer runs out of steam before the tweeter in waveguide, then double down on the woofers, do a little more baffle step compensation in the crossover so that you have a bit stronger bass, couple that with the ML-TL and a tweeter that definitely has a wave guide big enough to provide support well down into the danger zone... you get the idea. Not taking anything away from Pete's MT design here, which I am personally very interested in.

                                But the waveguide dilemma seems to still be a very real thing for those of us not wanting to do the pro compression driver route. Between CNC baffles and cutting up existing designs it still seems like a bit of a mess. I like what Mr Pellegrene is doing, and hoping that he can cover more ground and find favor with those still compelled to look elsewhere as his prices seem reasonable and quality seems good. Even better yet, knowing that the RS28A works well down to a certain point and that DIY crowd is very interested in waveguides...when will PE offer an integrated tweeter waveguide design that is designed to mount/work perfectly together? To me that is the frustrating part... that the makers of good dome tweeters aren't getting involved in mating them to good waveguides in an optimal fashion.

                                Regards,

                                Greg Jensen
                                Last edited by Greggo; 12-17-2013, 02:09 PM.

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