Oblate Spheroid Waveguide - Consolidated Construction Thread

[MEH]

How long ago? Which resin process?

[Variac]

the system involves a lot more, like the woofer, crossover, enclosure, oh and the crossover, and did I mention the crossover?

While the results often aren't perfect, DIY'ers like to experiment with this kind of stuff. we can't help ourselves!!!

By offering the WG and plug I think you are doing a good thing. Lots of very interesting designs will pop up. Not necessarily better , or even as good, but interesting, and who knows? better in some ways?

Mark

[tinitus]

Originally posted by MEH
Has anyone gone so far as to get a price quote on an 18" waveguide done with stereolithography?

I thought I understood that HOM may get worsened with bigger waveguides

At the moment thinking about a smaller one modified with bigger mouth roundings

[gedlee]

No, the HOM get lower in frequency with a wider coverage pattern, but a larger device is only good. Good that is up to a point of diminishing returns. An 18" waveguide may not be perceptably better than a 15" - I just don't know. I do know that costs, etc. go way up with size. You can see this in my pricing. An 18" would have to be around $500 each for me to even consider doing it.

Bigger mouth roundings appears to be a double edged sword. As the mouth gets rounder the waveguide is, in essence, getting shorter- not a good thing.

The stereoliths that we did was about a year ago. I don't know the process, it was in Thailand, and still it was expensive. Here, in that size, well all I can say is that I'm glad I'm not paying for it.

[MEH]

Yes, well, 18" waveguides are going to be expensive regardless of how they are made. The point of the exercise is to question how many would need to be made using fiberglass and associated tooling before the unit cost would be less than creating one using stereolithography. Of course, that all presumes that a waveguide made from something like this would be usable in the first place.

[pooge]

Would stereolithography be a good technique to make a compression driver phase plug using your new ideas on those?

[Ed LaFontaine]

What? You start a party and send no invitations?

Josh, thanks for the revision.

Looking into Josh's latest worksheet, OS WG2, I find a very minor adjustment to be made. Cell C10 contains the throat exit angle for the CD. All is good.
Cell D10 contains the formula which converts the throat angle to radians for further digestion in the worksheet. The formula in D10 is flawed as it contains a hard value of "6" for the throat angle. Changing to a different entry value in cell C10 produces no change in output.
The fix is simple. Select cell D10 and in the fx box above, enter "D10" after the = sign in place of the "6". This makes the worksheet respond to changes in user input for throat angle.
I found this when I changed the value to 6.5 degrees and saw no change in the output. 6.5 is the angle most recently referred to by Earl for the DE250. With other devices YMMV.

Xc is the axis intercept for the point on the OS profile that is tangent to the throat angle.
Yc should be radius at that point &
a1 is the radius of the OS profile where it is parallel to the axis of the throat

Now, with this one should be able to enter a variety of throat radii and view changes in the profile. I have found this doesn't occur. More investigation is necessary into that part of the worksheet.

[gedlee]

That's always the business decision, which is why I would not be one to enter into the 18" realm since I would doubt that one could make any money at it. A large initial investment that has to be amortized over the volume. Unless there is a sufficient volume this will make each piece quite expensive. And the only way that you would know for sure if that material would work is to try it. Gueni (sp?) pigs anyone? I'd love to know, but I wouldn't bet on it.

[gedlee]

Originally posted by pooge
Would stereolithography be a good technique to make a compression driver phase plug using your new ideas on those?

Well it would work, but there would be far less expensive ways to go. And making a phase plug doesn't get the driver made and I can't do that. Prototyping work is very expensive - and then you get one! Has to be a pretty big carrot out there someplace that I'm not seeing.

[Ed LaFontaine]

Looking further into the OS WG 2 worksheet, another small change is necessary.

Select cell C14. In the function box above, type in "=C3" and delete all other entries. This will make the calculated profile conform to user input in cell C3.

Has anyone experienced other unexpected behavior in the worksheet?