3D printed waveguides

[Pete Schumacher]

Photobucket sucks

[bwaslo]

In related news, Photobucket soon to go out of relevant existence...

[augerpro]

Progress update! I haven't really looked at the data much yet, so kind of a data dump. I appreciate any eyes to share what they see! First, since photobucket jacked my previous posts, let me repost the results of the two most promising prior waveguides, the .75" and 1" deep, tangent mouth guides with small phase shields. Caveat, these measurements are from my first experiment where whittled the PS down by hand, and reattached. So these won't measure exactly like the following guides where the phase shield is designed in from the start and printed as part of the guide.




First up, the waveguide with the occluded surround. This is based on the 1" deep waveguide above. Now there is a very small gap above teh surround, for the heck of it I filled it with some blue tack putty, and it made a surprising difference. Now the putty job wasn't pretty, and it may have even touched the surround here or there, but given the difference, I'm going to design a guide with it .02" smaller and nail down the difference more reliably. As with most of these, I measured both with and without the phase shield:






I also made a shim for the .75" deep T-mouth waveguide that occluded the surround, here the putty was obviously touching since it killed the lowend, still the top octave is promising as way around using a phase shield:



Next we have a waveguide that has a profile using a horizontal ellipse:




Next one uses a vertical ellipse, in this case it is not a very high index ellipse, almost a circle:




Next I played with some phase shield designs from a few posts back. The tall plug type that was inspired by some woofer phase plugs just didn't measure well at all, so I won't both posting the results. Here are the results for the scalloped, on the .75" deep T-mouth waveguide:





And best for last! This is an elliptical waveguide using the golden ratio, so 5" x 3.09". It is .75" deep, and horizontally uses the same radius wall as the .75" T-mouth.






So not having really pored over the results, I think we can conclude a couple things. The elliptical is very promising, and probably where I will put most of my efforts. The occluded surround has promise as a replacement for the phase shield, but it's damn picky, so it might take a few iterations to nail down. From previous posts, it appears a steepish wall at the throat that flares rapidly is better than shallower throat with larger radius curvature.

[ani_101]

Hi Brandon

quick question without really having gone through all the details in the last few posts and the data (not that i can make much informed inferences) is the oval better than the round shape or are you preferring the oval cause it has as good a performance as the round one while also allowing closer CTC. In other word, is there much performance difference between the round and the oval, barring the advantage of closer CTC?

Also, what is the tweeter you are using for benchmarking?

Regards
Ani

[ani_101]

oh, and you can also use google drive, similar to one drive or upload directly to PE, though this process is pretty cumbersome. you can also link from facebook, instagram if you into those things.....

[TN Allen]

Brandon,

I'm curious about the characteristics of a response curve you would consider "ideal" or suitable, and how the guide producing these characteristics might sound, or affect the sound. Looking at the response curves above, I'm not understanding what you're looking for. In the past there were attempts to raise the response toward the midrange, and to avoid falling off abruptly above10-12KHz. Is this also what you're looking for? I imagine in the earlier pists in this thread you probably discussed suitable response curves, perhaps you'd be good enough to review this.


Thank you.

[augerpro]

Ani> What I like about the elliptical is that it has the sort of response I want out of a waveguide (more below), and doesn't require a phase shield, since with and without looks basically the same. So lower complexity if someone can't print this, but only has a CNC. The reduced CTC wasn't a primary aim, but a welcome property nonetheless! The tweeter is the SB26ADC aluminum dome.

Tim> I'm looking for a few things. First, is the directivity, which eliminates the dip/hump in the power response (off axis) around the crossover point. Next, I want smooth, flat response off axis. Of course the tweeters native response impacts this too. Obviously smooth and flat is good in and off itself, but is also an indication that the waveguide is not causing a lot of diffraction. You can also look at the IR for this (I haven't yet until I settle on some good designs). Offset acoustic center is also a big plus! Combining the above, you can see that off axis response will make for a smooth, flat line sloping gently down. Harman has shown that its highest rated speakers power response falls at roughly 6dB from 100hz to 10khz (I find 40 degrees off axis to be a good proxy for power response when I don't have time to actually construct it summing a bunch of off axis measurements). Attached are a couple pics to illustrate with a HP filter in place. How it sounds is a whole 'nother deal. I've only ever compared wg vs non-wg side by side once using the Vifa NE19 and Dave P's waveguide. Very interesting. At first flipping back and forth the waveguide seemed closed in and quiet. Now Dave's wg was pretty deep so directivity was high, so I bumped up the level a little bit until I subjectively thought it matched the non-wg version. Started flipping back and forth again and my preference for the waveguide grew steadily. After a few hours of listening my opinion was the the non-wg version sounded much more sizzly and splashy, while the wg sounded clear, calm, focused, and dynamic. That's my only experience comparing, who knows if it will hold up in more tests?

[TN Allen]

Thank you, I understand your objectives, and the correlation to the resonse curves better. I hope you'll have more opportunities to listen to the guides in cabinets with woofers. Having left and right channels is important to a comprehensive evaluation, particularly given the effect of toe-in on the sound.

I think you're on to a good testing regime, and will be happy to help expand it to integrate listening.

I'll mill you a set you can easily assemble with a suitable opening for your waveguides. Either cabinet could hold a flat baffle, or a WG to provide multiple listening options. These would be free.

[augerpro]

Generous offer Tim, thank you!

I have a couple more designs to send out this week. Going to investigate the occluded surround more, and different wall radius on the elliptical guide.

[ani_101]

Perfect Brandon, not having the phase shield reduces complexity. I was also going to look in to the SB26ADC, now that the RS28 is NLA for the time being.

Are you removing the faceplate / grill of the SB26ADC, as it comes with a built in Phase shield?

[augerpro]

Yeah the faceplate just unscrews from the motor.

[smith59]

A little late to the party, but count me in as another person with a 3D printer and a desire to make some waveguides. I'm only on page 2 of the thread, but working my way through it.

Being a home gamer, my guides are going to have to max out at about 7" in diameter, but I don't think that'll be a huge hindrance. I think it'll be enough for the OC19 and a conservative crossover.

[augerpro]

What machine do you use? What's the build volume?

Update: more guides at with the printer. Hope to see them soon. Someone posted this on another thread, now I see Revel is not immune to the on-axis treble dip:

[TN Allen]

smith59,

Glad you're trying one of the OC19 in a WG. This, the OX20 and OC25 make a lot of practical sense in WGs, given they are easily mounted requiring less space than many larger tweeters. I have a few baffles underway using these 3 tweeters, though in milled guides. It will be interesting to compare results.

[bwaslo]

A little late to the party, but count me in as another person with a 3D printer and a desire to make some waveguides. I'm only on page 2 of the thread, but working my way through it.

Being a home gamer, my guides are going to have to max out at about 7" in diameter, but I don't think that'll be a huge hindrance. I think it'll be enough for the OC19 and a conservative crossover.

Don't know what the build size of your printer is, but you can make waveguides bigger than your build size by doing them in sections. PLA glues together pretty nicely with epoxy, cyanoacrylic or hot melt. I've been doing near 20" wide waveguides on a 12x12 build surface, it's actually easier than if I had a larger bed printer -- when something goes wrong, you don't have as much time or plastic invested in the part