3D printed waveguides

[ani_101]

another question - is there something that we can use to generate the profile for a given throat, mouth and throat angle? or it's drawing directly in CAD?

[augerpro]

I'm drawing it directly in CAD. Well sort of, I do a set of curves that are then used as "guide rails" for the Loft operation in F360. I would love to learn how to use some app that can generate say, an OS curve that can then be imported into F360 and used as the new guide rails.

[dkalsi]

I'm drawing it directly in CAD. Well sort of, I do a set of curves that are then used as "guide rails" for the Loft operation in F360. I would love to learn how to use some app that can generate say, an OS curve that can then be imported into F360 and used as the new guide rails.

Doesn't this application offer this option: https://www.diyaudio.com/forums/mult...easy-ath4.html

[augerpro]

Doesn't this application offer this option: https://www.diyaudio.com/forums/mult...easy-ath4.html

I believe so, but just don't have the time to delve into it. If someone can post a demo on how to generate a curve in that software and pull it into F360 that would be awesome.

[TN Allen]

One of the advantages of designing an entire wg is the flexibility to use specific dimensions, and then modify the design to compare the sound from similar but slightly different guides. Another is the ability to design complex guide surfaces, for example combining a midrange guide and tweeter guide with a transition surface blending the two. Guides for ribbon tweeters are another possibility.

Given the range of tweeter surround diameters, guide depths, mouth diameters and shapes, for example oval, round, square & and various other unconventional shapes, it seems unlikely to me there would be a program to accommodate all of these possibilities in whatever individual users might want to try.

It is probably best to find a general CAD program and put the effort into learning it. Fusion 360 may still be free, Solidworks has a student version around $100 if a person wants parametric design tools. Key Creator had a free student version a few years ago, and may still. Rhino may have a student version as well. Enrolling in an adult ed. program might qualify for a free or student version.

I don't know if Solid Works or Fusion 360 have a way to import coordinates generated in Excel. I suspect both do, and that it is probably fairly easy to do. The real initial work would be working through the math to define the surface, and then extracting the 2D curve files needed to generate the CAD surface or solid. It may also be possible to import the 3D Excel coodinates and translate these directly to a surface file, however, I don't know if it is.

I have however generated coodinates for 2D curves in Excel, and then imported these into KeyCreator to delineate the curves, which are then used to generate surfaces. The G-code tool paths are then produced based upon thode surfaces for milling. The files for 3D printing are also generated from the surfaces. Solid model surfaces also work for both G-code or 3D print files. The surface or solid model is essential to either milling or printing, and the CAD model is where most of the design work is.

[augerpro]

I've started a gofundme for this project now that I'll have to depend on commercial printers. Initial goal is for finalizing designs for the SB21 and SB26 families, and continuing development for the Bliesma T25B. Fundraiser: Waveguides for CNC and 3D printing!

[augerpro]

Might be making big jump forward in waveguide design. I started using mabat's ATH program to generate the files that ABEC uses to simulate waveguides, including a representation of the tweeter diaphragm itself as acoustic source! Here are the simulated results of the T25B in ABEC, followed by my actual measurements:




BTW: I believe the off axis hump @ 15khz is the natural response of the tweeter itself, so not captured by the ABEC sim. I've measured the domes of the T25B, SB26ADC/CDC, SB21SBC, and Dayton RST28A. If all works out well, it might be nothing more than sim once, print once.

[augerpro]

SB26ADC on my 5" x .75" deep vH waveguide, simmed vs measured:

[dlr]

Excellent correlation. Years ago I tested the PE horns with various small tweeters. One thing that helped significantly (in those at least) was to put some damping close to the tweeter dome, cotton and wool (not needled felt). A piece of acoustic foam would probably do well, too. The area from 10-20K was improved. Somewhat similar to what Geddes did with his, though he used two layers, IIRC, with one layer density different that's close to the compression driver exit and he totally filled the horn. But yours don't look like they need so much.

My belief is that the small amount I used largely damped the internal reflections near to the dome. Beyond that the wavelengths made reflections less of an issue for the 10-20K range. The new model software you're using must significantly reduce those reflections.

Nice work.

dlr

[tvrgeek]

I am missing something here? Just scanning through all 41 pages, it seems the results are a huge coupling efficiency mid-range and an overall ragged response that needs considerable crossover correction to what are otherwise decent tweeters.

[augerpro]

If that's how you see the results, then they aren't for you. Maybe this will give you a better perspective: http://techtalk.parts-express.com/fo...91#post1386191

[scottvalentin]

I am missing something here? Just scanning through all 41 pages, it seems the results are a huge coupling efficiency mid-range and an overall ragged response that needs considerable crossover correction to what are otherwise decent tweeters.

What graphs are you looking at?

[augerpro]

What graphs are you looking at?

To be fair, probably one of my ten thousand lightbulbs that didn't work

[DanP]

I am missing something here? Just scanning through all 41 pages, it seems the results are a huge coupling efficiency mid-range and an overall ragged response that needs considerable crossover correction to what are otherwise decent tweeters.

I'd say you're missing several things. In all the WG examples posted here, there are very few with ragged response below 20kHz. An acoustic boost in the midrange right as distortion is starting to rise is extremely beneficial and this type of broad hump response is very easy to shape into a predictable and stable rolloff. Add the facts that diffraction peaks/dips are minimized in situ, directivity mismatch to the woofer is minimized, and acoustic centers are better aligned and you'll find these tweeters in waveguides usually require less correction to integrate well with the woofer.

[augerpro]

More Bliesma T25B and SB26 results! Reminder these are 7ms of clean signal, no smoothing. Depending on waveguide size, baffle diffraction starts to show up @ 3-4khz. Basically if you see the responses getting wavy and crossing each other as you move off axis, baffle diffraction is showing up and the waveguide is losing pattern control.