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Multi-Way Conventional loudspeakers with crossovers

Transmission line Omni speakers? Duevel Planets clone with transmission line?
Transmission line Omni speakers? Duevel Planets clone with transmission line?
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Old 4th October 2018, 12:54 PM   #11
DonVK is offline DonVK  Canada
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It certainly looks like a CD and a waveguide that's under the sphere/reflector. That's definitely better than a dome tweeter for this application. I tried lots of shape adjustments through ABEC models. I'll check if I kept some relevant spherical ones. I would suspect that a smallish sphere would still allow most the MF-HF waves to wrap around and continue in the same direction to diffuse off the ceiling.

To get the wavefront to exit perpendicular to the driver I needed physical boundaries (inner and outer walls). So I ended up with nested waveguides like the Duevel Bella Luna. I also found that, at higher freq I would get reflections from anything above the driver, so I have a narrow pointy tip above the CD to reduce this. The cone above the woofer in my Omni helps direct MF and reduce the MF reflections because I XO@1800Hz.

The basis (sim & calc) for what I did is at this post OmniDirectional - work in progress and the subsequent post.
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Old 5th October 2018, 09:39 AM   #12
DeeLuxx is offline DeeLuxx  New Zealand
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Thanks for the response.

I had a look through your thread, the ABEC software looks interesting, will give it a go.

Had another question - What would be the best way to measure the phase inside the TL for tuning purposes?

I assume I could get a usb audio interface (focusrite or similar) and plug in twin measurement mics, one at the driver cone and another at the exit of the TL port, and analyse using REM? Again, no idea as i've never done this before.

At work we use a vector network analyzer (VNA) to tune RF antennas, so im curious as to what the acoustic equivalent is. Will start a new thread with the measurement question, but thought i'd post here as well.

Thanks!
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Old 6th October 2018, 03:09 AM   #13
DonVK is offline DonVK  Canada
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You should only need a single mic and REW to measure the phase. REW will align to its swept sine and you can extract phase (unwrap and generate min phase) for near field measurements of both driver and port exit.

I could not find all the older trial reflector shapes I tried. So I just removed the top of my Omni ABEC model and added a sphere based on the Planet's images. I used my 8" Silverflute whereas the Planet has a 6" so I scaled the sphere to match. This should give a good idea of what happens.

I'm going to post the result images in 2 separate posts so that the unobstructed woofer is viewed over top of the sphere images. You can see the woofer starting to beam and narrow.
Attached Images
File Type: jpg woofer only@100hz.jpg (21.6 KB, 153 views)
File Type: jpg woofer only@500hz.jpg (23.3 KB, 160 views)
File Type: jpg woofer only@1200hz.jpg (24.8 KB, 155 views)
File Type: jpg woofer only@2000hz.jpg (26.3 KB, 132 views)
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Old 6th October 2018, 03:10 AM   #14
DonVK is offline DonVK  Canada
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Now the sphere.
Attached Images
File Type: jpg sphere h2@100hz.jpg (21.1 KB, 136 views)
File Type: jpg sphere h2@500hz.jpg (23.1 KB, 32 views)
File Type: jpg sphere h2@1200hz.jpg (25.3 KB, 36 views)
File Type: jpg sphere h2@2000hz.jpg (26.6 KB, 37 views)
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Old 6th October 2018, 03:56 AM   #15
DeeLuxx is offline DeeLuxx  New Zealand
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Thanks so much for this! Helps explain things a lot.

I see you still tend to get the upper lobe with the sphere. Will have a play around and talk to the other engineer.

Seems like a sphere is not the greatest reflector, but they are so easy to get hold of compared to fabricating a more ideal shape.
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Old 6th October 2018, 04:20 AM   #16
DonVK is offline DonVK  Canada
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That's very true, spheres are easy to get.

Yes, its not ideal, but it could still work for a woofer with a reasonably low XO (<2Khz) and high order filter (4th order). In the images above, the last pic has the woofer dia, sphere dia and freq wavelength about equal.

The more difficult problem is the HF. If I get some spare cycles I'll post a sphere in front of a short waveguide like the Planets. I don't remember trying that combo in my earlier attempts. It might not be ideal but maybe workable in order for you to try an Omni.

Last edited by DonVK; 6th October 2018 at 04:21 AM. Reason: typo
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Old 9th October 2018, 10:38 AM   #17
DeeLuxx is offline DeeLuxx  New Zealand
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I tried ABEC, quite the learning curve haha, but i'll stick at it.

And looking for other things I can use as reflectors but nothing i can find with a hyperbolic shape in the correct size that is readily available.

I think it might just be easier to 3D print if i wanted to go down that route. I was thinking i could possibly 3D print an OK ish hyperbolic cone with a shaft attachment, and then smooth out the shape on a lathe and polish it off
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Old 10th October 2018, 05:15 AM   #18
DeeLuxx is offline DeeLuxx  New Zealand
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Duevel Bella Luna - Weibchen CNC

Just saw this as well, didn't realise that was how they made them (I thought they were turned).

I have access to a 3 axis CNC that is more than capable of this, but the toolpath programming would be a pain.

Would this horn design be significantly better for high frequency performance? I know its all subjective, but just wondering whether its worth it or not.

Thanks!
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Old 10th October 2018, 01:21 PM   #19
DonVK is offline DonVK  Canada
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ABEC is a very steep climb and desperately needs better tutorials & help & error parsing to understand what its doing. It's an amazing tool and I'm still learning it.

Yeah, I would have thought lathe then a CNC touch up. Good video though, and this other one is of the inner shape that forms the radial horn Duevel Bella Luna - male CNC

I do think its more effective to have inner/outer surfaces for the HF to direct the wavefront. You can get close by nesting 2 circular horns like the Dayton 8 or 10" models and add a tip to the inner one. I did find the spacing and tip shape did make a difference. I still need to post a horn + sphere,.. probably later today.
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Old 10th October 2018, 05:55 PM   #20
DonVK is offline DonVK  Canada
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Sooner than expected. It seems I had some partial work when I was playing with the HF sections. So it was easy to drop a sphere in front. I use a 10" Dayton circular model which is larger than the Planet, so I scaled the sphere dia and offset just to get a picture of whats happening.

Again, 2 posts so you can compare top and bottom.
Attached Images
File Type: jpg horn @2Khz.jpg (37.6 KB, 22 views)
File Type: jpg horn @3.4Khz.jpg (40.7 KB, 16 views)
File Type: jpg horn @4Khz.jpg (41.9 KB, 12 views)
File Type: jpg horn @7Khz.jpg (46.0 KB, 15 views)
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