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-   -   Open source Waveguides for CNC & 3D printing! (https://www.diyaudio.com/forums/multi-way/318190-source-waveguides-cnc-3d-printing.html)

Gaga 25th August 2018 10:09 PM

Quote:

In fact, this image does not resize properly, where as the earlier one does. Which browser are you using?
I'm using Firefox 61.0.2 under OSX. May be I re-read how to implement imgages properly and and re-size before posting accordingly. Sorry for the trouble...

augerpro 25th August 2018 10:41 PM

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Last update! Moving now to the 8" waveguides. (note: 8" is the width, as these are all elliptical mouths based on the golden ellipse, the height will be .618 x width).

First up is the SB26ADC. W/ and w/o phase shield, and w/ and w/o throat shim:

Attachment 699839 Attachment 699840 Attachment 699841 Attachment 699842

RST28F on 8" waveguide:
Attachment 699843

RST28A on 8" waveguide:
Attachment 699844

Can't weight to redesign with the smaller throat and no faceplate...

Next are the 6" waveguides. Starting to get enough variation to identify trends accross size. SB26 first, in .75" and 1" depth:

Attachment 699855 Attachment 699856 Attachment 699857 Attachment 699858

augerpro 25th August 2018 10:47 PM

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Attachment 699859 Attachment 699860 Attachment 699861 Attachment 699862

And finally RST28's on 6" waveguide:
Attachment 699863 Attachment 699864

Going forward I need to get my Presonus 22VSL working to get measurements out to 48khz. These plots hint that some subtle tweaking of the phase shield may allow us to notch out the dome resonance of the metal tweeters. That would benefit both linear and non-linear distortion!

augerpro 26th August 2018 03:17 AM

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To get an idea of what these could look like after simple crossover/eq is implemented, I've taken the SB26 on the 8" waveguide C above and applied a HP and high shelf. Shown is on axis, and 40 degrees off-axis which I've found is a good proxy for the "early reflections" as defined by Olive @ Harman:

augerpro 26th August 2018 06:12 PM

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I want to take a moment to demonstrate how different measurement techniques impact the results. I use a 7ms gate that is FREE of reflections, and no smoothing. The gate itself actually has a smoothing effect once you see what is going on in the math. For example, at 7ms, the cutoff frequency is 143hz. This is also the first valid data point. The next valid data point is double that: 286hz. Each following data point is 143hz from the last and everything in between is interpolated. So if the valid data points are wider apart, with everything in between interpolated, you can see that effectively you lose resolution, or "smooth" the response. How would the data points be further apart? A smaller gate. For example at 3ms the first valid data point is 333hz, and all of the next data points are simply every 333hz after that.

The reason I bring this up is that I want people to understand that my plots show as close to reality as practical. Because of that, some people may say, oh look at that dip, or that peak, I don't want to use that driver, speaker, etc. I'll use that one over their that is oh so smooth. But the smooth plot is probably not realistic. If it looks like it was drawn by a child with a crayon, I have my doubts on the accuracy :) Below is a plot where I play with gate and smoothing to give you an idea of the effects. This is why knowing the measurement conditions is critical when evaluating, and especially comparing, different plots.

augerpro 26th August 2018 06:16 PM

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Quick summary on the designs that I'm really liking at this point. I also need to do some additional analysis, like CSD, waterfall, etc. Any preferences?

augerpro 26th August 2018 07:16 PM

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When I first started this project, I didn't want to make generically sized waveguides, but ones driven by application. The first application was: crossing to a 12-15cm woofer at 2.5khz. So let's pick that apart. First, we want the directivity to be about the same at the crossover point. Looking at some manufacturers' plots of the 0 and 60 degree responses, they were typically 2.5-5dB apart at 2.5khz, with a sweet spot of 3.5dB. So this is the first criteria: 0/60 degree plots 3.5dB apart at 2.5khz. Second, I wanted to match the acoustic center of the woofer, typically about .75" - 1" deep for 12 - 15cm woofers. I picked .75" and moved on. I should mention though that now that I have some good designs, I need to verify this assumption. Some plots to illustrate:
Attachment 699850 Attachment 699851 Attachment 699852 Attachment 699853

Regarding directivity, I think this design hits its target, in fact it might even be able to be a bit smaller. Acoustic center is an assumption to be verified, but should be pretty close.

So what are some other applications? I think matching to a 18 - 22cm is an obvious one and one reason why I jumped from 5" to 8" waveguides. I still have to define directivity @ XO, and acoustic center targets. So work continues there. Any thoughts here appreciated.

Now most of the time people are wanting to use a waveguide to push lower, because you now have control of dispersion. But I can also see value in using it to push higher. Think a small 3" midrange where the designer wants it to carry most of the vocal range, so no crossover until 3-4khz. Like this Scan Disco 10F:

Attachment 699854

The waveguide allows us to push higher because now, even though we have some roll off of the 3" driver response, we can now match that response for the tweeter. So the off axis response will be falling, but still smooth. So we could define that application as -3.5dB at 3.5khz, and maybe .5" - .75" deep to match the acoustic center.

Anyway, that's how I'm approaching this. What typical apps would you guys like to see?

andy19191 26th August 2018 08:11 PM

Quote:

Originally Posted by augerpro (https://www.diyaudio.com/forums/multi-way/318190-source-waveguides-cnc-3d-printing-post5527129.html#post5527129)
Anyway, that's how I'm approaching this. What typical apps would you guys like to see?

If I can drum up enough interest in a group project we will be considering a waveguide for the tweeter of a 3 way tower (1" tweeter, 4-5" midrange and 2 x 8" woofers). The midrange is likely to be 5.25" but more like the Discovery 15M rather than 15W because of the sensitivity. The drivers will follow from the design and so a 4" is possible but a 6.5" unlikely. The tweeter will need to be from a standard range in order to fit the budget but otherwise whatever performs best in the waveguide. Suggestions?

ScottG 26th August 2018 08:43 PM

Quote:

Originally Posted by augerpro (https://www.diyaudio.com/forums/multi-way/318190-source-waveguides-cnc-3d-printing-post5527129.html#post5527129)
..I jumped from 5" to 8" waveguides. I still have to define directivity @ XO, and acoustic center targets. So work continues there. Any thoughts here appreciated.

Now most of the time people are wanting to use a waveguide to push lower, because you now have control of dispersion. But I can also see value in using it to push higher.

Don't forget inter-driver spacing vertically in relation to about an octave above the crossover freq. +. (..at least relative to the type of crossover).

One thing (besides a steeper filter) that you can do without much penalty is effectively "cutting into" (or designing "into") the waveguide to get the vertical midrange/midwoofer closer to the tweeter in the waveguide. While it might show a slightly "rougher" result (even done well), it's often an overall audible improvement. (..and typically the smaller the midrange, the better the result.)

I think this is an area where designing it yourself pays dividends (..as opposed to cutting into a pre-made waveguide).

Also,
-the deeper the waveguide, the greater the effect of cancellation/reduction in freq.s in the upper treble on (and near)-axis. (..it also tends to sound less realistic as well where the rest of the speaker is effectively omni.) In this respect then I wouldn't push much past 1.25" in depth.

-results look good so far! :up:

augerpro 26th August 2018 08:50 PM

Quote:

Originally Posted by andy19191 (https://www.diyaudio.com/forums/multi-way/318190-source-waveguides-cnc-3d-printing-post5527189.html#post5527189)
If I can drum up enough interest in a group project we will be considering a waveguide for the tweeter of a 3 way tower (1" tweeter, 4-5" midrange and 2 x 8" woofers). The midrange is likely to be 5.25" but more like the Discovery 15M rather than 15W because of the sensitivity. The drivers will follow from the design and so a 4" is possible but a 6.5" unlikely. The tweeter will need to be from a standard range in order to fit the budget but otherwise whatever performs best in the waveguide. Suggestions?

Well, so far the SB26ADC or SB21SDC on a 5" wg are easy choices. But I'm not sure how the sensitivity matches up as the SB26ADC is somewhat low. You'll need to figure that out. Then you'll need to define the crossover point and likely slope. Then match the directivity of the mid used at that point. That Disco 15M is super cool.


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