3D printed waveguides

[TN Allen]

"...when something goes wrong..."

That seems to come with 3D printing. The first printer I used a few years ago printed most of the files with few problems, but after a week or so a week stepper motor shaft twisted off. It was faulty and later replaced free.

[bwaslo]

"...when something goes wrong..."

That seems to come with 3D printing. The first printer I used a few years ago printed most of the files with few problems, but after a week or so a week stepper motor shaft twisted off. It was faulty and later replaced free.

Yeah! You notice I didn't say "if something goes wrong".

[TN Allen]

I did, and felt it important to point that out so others would take it in and realize that the potential and attractiveness of 3D printed waveguides also includes risks and wasted time, effort and material. It's an exciting technology, and very seductive, but in its infancy.

[bwaslo]

True. But I'd also point out that: the materials are pretty cheap (last filament I bought was 5 rolls of 1kg each, for $11 per, delivered). And the time is the printer's time, you don't have to do anything much yourself during that time other than check on it occasionally (an "Octopi" camera makes that really easy). The biggest and most frustrating time killer is when something goes wrong in the printer and it takes you a while to figure out what it is. Getting better at that with some experience, though.

[bwaslo]

Like, for instance, critter infestations

[TN Allen]

Better in the printer than lurking in the back seat of your car at midnight.

Is this a printer you built? If so, impressive.

[bwaslo]

Well, yes and no. It's a kit printer (Folgertech FT-5, about $450), but with a fair number of mods, mostly printed on the printer itself. Pretty effective setup if you don't mind spending a month or so getting all the bugs out (the one in the photo not included)

[augerpro]

More test results! After seeing the results of the elliptical above, and promise of the occluded surround, combining the two should be the bomb right? Wrong:



So what wrong? Well for one, with a throat that is smaller and .08" above the tweeter faceplate, forces a slightly different wall profile with a shallower radius. So that could be it. And in contravention of good scientific method I changed two things: I also made the throat diameter just a bit smaller than the prior design so it ended up above the edge of the dome where the voice coil attaches. I suppose I'll have to try it with the same as prior designs I posted, but really, I'm not sure following this path matters much, just going to an (golden) elliptical waveguide provided all the benefits already.

I noticed before that it seems like a lower angle throat that widens rapidly (small wall radius) seems to be the best. To test this more directly I made two waveguides that start as conical to set the throat angle, than a roundover (fillet actually) is applied to transition from throat to mouth. One throat angle was set at 80 degrees and the other at 100. Results:




So that does add some good data to support that conclusion. Somewhat along those lines I also made another version of the elliptical from post #303 where I made the vertical wall radius smaller: 1" versus 1.5" of the original. Here are vertical and horizontal measurements, with and without phase shield:






I'll have a lot more to say once I compare that with the original. But I think we're VERY close to an end result!

All of those prior ellipticals were golden ellipses, where the vertical diameter is 61.8% of the horizontal diameter. I thought I would try another variant that wasn't as "squished" but still based on Fibonacci ratios. One ratio would be 23.6%, and subtracting that from 100 leaves 76.4%. I've seen this used in stock trading indicators, but if I understand how Fibs work this isn't a real one, but hey what the heck let's try it anyway:



Very good, though not better than the golden ellipse. Forgot the vertical responses, sorry.

Best so far:

[augerpro]

Here is a direct comparison of the elliptical from post #303 (which I'll call A), and the one above in post #323 (which I'll call C). These are with the phase shield, 0 and 40 degrees:



Both are really good, seems to me splitting the difference would be just right. So I'll have that one printed. Certainly looks better than factory, especially when you consider the baffle diffraction signature is virtually gone with the waveguide:



Take another look at C of just the 0 and 60 degree responses:



Going back to post #26, I think I've met the criteria for this first design: intended to mate with a 12-15cm woofer at @2.5khz, with the difference between 0 and 60 degrees off axis at the crossover being about 3.5dB. Looking just at the on axis response, the tweeter has a natural bump around 5khz, and the waveguide makes the top octave wiggle a bit. Moving off axis the response quickly becomes smooth and straight. The phase shield looks best, but even without it these ellipticals look pretty nice. Thoughts so far? Anything else I should try? If you guys agree I'm going to move on to some 8" waveguides now that it *appears* I have some best practices.

[scottvalentin]

This has been a very informative exercise Brandon - thanks for undertaking this and doubly so for sharing the details in such a clear manner. Your approach has been very scientific so I would agree you have ironed out some best practices/approaches.

[augerpro]

Thanks for kind words! It's been a fun project so far, and I've really just started. I'll be curious to see how these match a woofer in actual usage. For example the -3.5db at crossover matches the intended woofer on paper, but in practice since there is an overlap, that requirement may be relaxed, allowing a smaller waveguide. Or not. I'm also going to do a version that is intended for LR2. It will have to be wider than above for the same crossover, and acoustic center will be more important. If someone wants to mock up a speaker and test this out (I don't have woodworking ability right now) I can send them a waveguide for pretty cheap.

I can also do specific tweaks to the design pretty easily if someone wants to experiment. Prices are cheap right now for the waveguide, might want to take advantage while you can.

I also want to move on to Satori tweeters. They appear to attach the faceplate the same way, so it really makes it easy. If anyone has a loaner out there, let me know!

And again, if anyone finds this useful, a donation would be a huge help. I'm already well over $500 into this, can't keep up that burn rate forever, I'm not Tesla! My paypal is whippersnapper02 at yaho, even $10 here or there helps.

[augerpro]

Here is the C elliptical with LR4 @ 2khz acoustic response, at 0 and 40 degrees, to give you an idea:



Here are some files if anyone wants to play with this a bit. If you're using Fusion 360 the .f3d file is the one you want. Otherwise the others are with and without phase shield, and with and without a circular flange for easier mounting. Probably easier for prototyping work. I'll make a router template when I get a chance, that would make routing the ellipse easy for those who don't know how to make a template directly from the part.

.f3d file: https://www.dropbox.com/s/lxbau322t6...%20v2.f3d?dl=0

Elliptical flange, with phase shield: https://www.dropbox.com/s/oo2w1id8e6...ndard.stl?dl=0

Elliptical flange, no phase shield: https://www.dropbox.com/s/q3wa1byn4f...ndard.stl?dl=0

Circle flange, with phase shield: https://www.dropbox.com/s/rv6jbsvprz...ircle.stl?dl=0

Circle flange, no phase shield: https://www.dropbox.com/s/r2avxyyzxr...ircle.stl?dl=0

[augerpro]

if anyone finds this useful, a donation would be a huge help.

Thanks Ed!

[augerpro]

Here are some pics of the conical 80 and 100 degree waveguides from a few posts back for reference. The seam you see is where the straight cone ends and the fillet begins. They are a little different because I wanted the fillet radius to be similar:

[augerpro]

Here is Kef's Ref 5 measurements. Looking at on-axis and early reflections, looks very similar to my result in post 324 or 327: