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  • The Oneness
    replied
    Originally posted by augerpro View Post
    Here are some measurements of the Bliesma T25A, to see how it measures on the waveguides I made for the T25B. The domes are very different, the A version is much taller. Clearly there is an issue here, which is disappointing.


    Ignore my comment on the post, wasn't sure how this forum works.

    Thanks for the reply the other day, missed that you had these posted. Thanks to everyone involved in these projects, massive help to us less knowledgeable/able diy'ers.

    Anyone think they would do decent firing straight back in a car? So I'd be approximately 30° off axis from the drivers side and 45° of axis form the passenger side. Perhaps the null between 0-10° may be beneficial since they would be in the sails panel area firing straight back at the door/window frame.

    Any plans to test the T25S-6? Have a pair I may be able/willing to loan out
    Last edited by The Oneness; 01-08-2022, 11:29 PM.

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  • The Oneness
    commented on 's reply
    Thanks for the reply the other day, missed that you had these posted. Thanks to everyone involved in these projects, massive help to us less knowledgeable/able diy'ers.

    Anyone think they would do decent firing straight back in a car? So I'd be approximately 45° off axis from the drivers side and 30° of axis form the passenger side. Perhaps the null between 0-10° may be beneficial since they would be in the sails panel area firing straight back at the door/window frame.

    Any plans to test the T25S-6? Have a pair I may be able/willing to loan out

  • TNA
    replied
    Originally posted by JRT View Post


    Have you tried any waveguides with planars/ribbons, and or AMT air motion transformers? Any thoughts as what type(s) of curvature(s) and throat angles might be appropriate?
    I've tried a few WGs with planar tweeters that provided adequate, but not outstanding results. I'm curious about others experience.

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  • augerpro
    replied
    I'd really like to get around working with AMTs. Just haven't had time. No idea what contour would work, but I think they might be able to be treated as plane wave sources, which makes design easier to model in something like ABEC. OS or conical would probably work well.

    Leave a comment:


  • JRT
    replied
    Originally posted by augerpro View Post
    So far, my best results are from hard domes. It's the soft domes that are tougher. However, after an early elliptical wall contour didn't measure well, I've stuck with a circular contour with constant radius. This has worked great for hard domes. When I see others post decent results with soft domes, it usually appears to be some sort of OS type contour. Along with my experience with hard domes, I've modeled some contours in ABEC (SB26ADC and T25B) and it has agreed with what I found: hard domes typically do better with a constant radius contour, and OS and conical were not that good. Wish I could do the same soft domes, but those are near impossible to model for a DIYer.

    Have you tried any waveguides with planars/ribbons, and or AMT air motion transformers? Any thoughts as what type(s) of curvature(s) and throat angles might be appropriate?

    Leave a comment:


  • augerpro
    replied
    Here are some measurements of the Bliesma T25A, to see how it measures on the waveguides I made for the T25B. The domes are very different, the A version is much taller. Clearly there is an issue here, which is disappointing.


    Leave a comment:


  • augerpro
    replied
    I removed the screen on the Peerless, and the faceplate on the Scanspeak.

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  • jhollander
    replied
    Did I miss it, are you removing the screens and faceplates on the Scan D3004 and the Peerless DA25TX?

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  • augerpro
    replied
    Refined a couple of the previous designs and measured them today. Also added the first variant for the Peerless DA25TX. I'm surprised by the Peerless, it's a small dome which has worked well for me, but this has a big dip on axis. I would have expected it to measure very close to the SB26ADC given how similar the domes are. I may have to start working in ATH/ABEC for this one to figure out what works.







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  • augerpro
    replied
    Yeah I think our coming to different positions on whether hard domes are easier or harder to work with, was due to the path we took at the beginning. You used off-the-shelf waveguides, which tend to be some form of quasi-OS, so your struggled with hard domes, but soft domes worked well. I started with wanting to 3D print, so I had to learn CAD. With little CAD skill, it was easier for me to model profiles based on a simple circle. Which simply by chance worked well with hard domes, but not soft. I think that itself might be a worthwhile lesson to anyone following along. And I will state with some certainty that hard domes do better with circle-based wall profiles, not just from my own measured results, but also the results of working with ABEC to try different contours, including an actual OS.

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  • dlr
    replied
    That's certainly surprising. I still suspect the difference is the lack of damping in hard domes with more output in the center. Would be interesting to see some tests of each type with a bit of cotton damping close to the dome. My testing was all using soft domes in the PE waveguides. I was using the cheap PE tweeters, the ones small enough to fit into the throat without taking apart, surprisingly good in the right mounting. I used blu-tac around the throat to manually shape it for a near perfect fit with the tweeter faceplate.

    I tested the NB16FA-6 in the 8" waveguide & ND20TB-4 in the 6" waveguide. The smaller one measured better, more due to persistence with the blu-tac shaping on my part, I think. But both were still best with cotton in the throat. I still have them mounted in test baffles, sitting on the shelf. These two are the ND16FA-6 in 8" waveguide.

    dlr

    Click image for larger version  Name:	NB16FA-6  8inch Waveguide Cropped.jpg Views:	0 Size:	649.0 KB ID:	1479677

    Click image for larger version  Name:	NB16FA-6 Closeup Cropped.jpg Views:	0 Size:	468.5 KB ID:	1479675

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  • augerpro
    replied
    Thanks Dave. So far, my best results are from hard domes. It's the soft domes that are tougher. However, after an early elliptical wall contour didn't measure well, I've stuck with a circular contour with constant radius. This has worked great for hard domes. When I see others post decent results with soft domes, it usually appears to be some sort of OS type contour. Along with my experience with hard domes, I've modeled some contours in ABEC (SB26ADC and T25B) and it has agreed with what I found: hard domes typically do better with a constant radius contour, and OS and conical were not that good. Wish I could do the same soft domes, but those are near impossible to model for a DIYer.

    Leave a comment:


  • dlr
    replied
    Originally posted by augerpro View Post
    ...I suspect fabric domes work better in OS contours.
    Likely due to the hard domes radiating far more around the tip of the dome whereas soft domes have damping characteristics that damp more as frequency increases. The result would be that there is more energy from the center that is interference with that which is radiated from the edge that is close to the waveguide. There is a time delta between center and edge that likely results in more "diffraction" with the waveguide. I did a lot of testing some years ago with the PE standard waveguides. I added cotton stuffing (not too dense) deep in the waveguide and got significant improvement in response even for soft domes. It didn't take much. Consider what Geddes did with his horns. He filled them with two densities of foam. Compression drivers he used don't have an exposed dome, yet there was significant diffraction...his description...in the waveguide. The cotton stuffing I used acted similarly.

    Your efforts essentially reduce the diffraction from a non-perfect interface between dome and waveguide. Nearly impossible to achieve fully with hard domes, much improved with soft domes. As I see it.

    dlr

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  • augerpro
    replied
    New waveguides! Bliesma T34B looks pretty good out of the gate. I think I've finally nailed the throat for the Scanspeak ring radiator, so I'll be expanding to other sizes and shapes now. The Scanspeak dome is a bit tougher nut to crack. But I'm going to move to a different contour, I suspect fabric domes work better in OS contours. Unfortunately, my Peerless DA25TX had a resonance at 16khz, must be defective. I have another on order.




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  • augerpro
    replied
    Little teaser of some waveguides I'll be measuring this week:



    I'll also be verifying the T25A works on the waveguides I did for the T25B. And the newest generation of Scanspeak waveguides where I hope to continue the improvement I made last time for the soft domes, which can be a real problem on waveguides.

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