3D printed waveguides

[TNA]

Brandon,

This is Tim Allen, using a different User Name. I've been using the larger version of the tweeter. The face plates I've had were not concentric with the surround. Removing the faceplate solves the problem, but there is adhesive that pulls the connecting wires, risking disconnection and a tricky reconnection. I do like these tweeters, they produce a very nice sound combined with the Peerless NE225W-04 in T/L cabinets.

[jhollander]

Removing the face plate on my DA25TX00 caused the edge of the dome to lift. Not completely detached so I was able to reassemble without issues.

[augerpro]

Good to hear from you Tim!

Yeah I wish you could remove the faceplate, but that's a sketchy business as John found. But at least it is flat so not a huge issue to design around. And it's thin. So the throat of the waveguide should be pretty similar to others I've done as far as how the dome "sees" it.

[TNA]

Brandon,

I did remove the plate, and resolder the broken wires. But, also thought of turning a very thin throat section to make up directly to the surround, just clearing the FP. The section could have been ~.015" in section, no more.

Depending upon the concentricity of the tweeter you receive, you may be able to print a thin ring at the throat to clear the FP and make up to the surround, but the print resolution will need to be quite accurate, otherwise, you'll need to live with the manufacturer's FP bevel as part of the throat.

It all worked out well, and the sound is just what I wanted. However, for a few cents more, the manufacturer could have done better, especially given the cost of these tweeters.

[augerpro]

Brandon,

But, also thought of turning a very thin throat section to make up directly to the surround, just clearing the FP. The section could have been ~.015" in section, no more.

Yes that is exactly the feature the next design will have. My printer should print it just fine.

[TNA]

Here is what I had in mind, black is the FP, blue the turned, printed, or milled lip that allows the WG throat to make up to the surround. This allows the WG contour to remain consistent to the surround.

[hex168]

I do not have a Peerless BC25TG around now - can anyone supply a picture with the faceplate off? If not, I'll do it next time I get one.

[augerpro]

Going forward I'm thinking about posting .3MF instead of .STL files. They have the units included so there is no confusion if the design is in inches or mm. Also this format apparently reduces the weird intersecting manifold problems that some printers' websites choke on when you upload a .stl file. Anyone see any issue with this? I think most slicers can handle .3MF just fine?

[Mandroid]

Have you printed waveguides with phase shield using your Ender 3? If so, How did they turn out?

[augerpro]

They turn out fine but filament selection is critical because how well support material breaks off is pretty different among brands. I like eSun PLA+. Sunlu is pretty close. Hatchbox doesn't work for these. A little finesse helps. Use a knife to slip into the support grooves and give them a little twist and they break free pretty well.

[augerpro]

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.

[augerpro]

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.

[dlr]

...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

[augerpro]

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.

[dlr]

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