Hey guys...we need a little rallying here... - Page 2

Ponoko now offer 3d printing services: http://www.ponoko.com/
I once made a script for Google sketchup to draw OS waveguides – unfortunately I no longer have it or I would check the pricing of the 3d printing for you folks who lack waveguides.

PE is going to look into both the QSC option, and also doing a clone if QSC does not want to play ball. Hopefully they will get this done.

Thank you Craig!

It's good to know they are aware of this and working on it for us....

If someone wanted to get crazy, they could build a asymmetric oblate spheroid 90x60 about 17" wide. I'd buy a bunch of those. It shouldn't be too hard to model with some math.

I definitely would too!

LTD, that pic is along the lines of what I'm thinking although I prefer a baffle mounted version.

Directly copying the QSC is a little questionable ethically IMO. At least if it is done for more than your own use. I think it would be more appropriate to do something similar or improved. Something similar to the 152 horn but with more width would be great, but I think a asymmetric OS WG would be the best.

This is what I'm thinking:

1. Develop the mathematical model to create a graphic representation of the profile.
2. Take that model and create an actual 3D model with the appropriate material thickness, baffle mounting area, and driver mounting area
3. Send it to a 3D printing/rapid prototyping shop for a 1-off
4. Make some casting molds using the 1-off
5. Cast horns using a rigid urethane plastic

Doable?

Sounds like a plan....what kind of funding is needed?

Yes, doable, but the transition between a round compression driver exit and elliptical flare is critical; that's where the action is, and I think it's also going to vary depending upon the driver exit angle, as well. Doing a two-piece design, throat adapter plus flare, may comprise the most rational course, at least at the prototype stage, until the variable detail is defined....

If you guys come up with a definitive design, I'd love to take a crack at making a one piece complete baffle. The easier setup would be a bolt on compression driver.

In simple terms this is what I'm thinking:

You determine a specific ellipse shape that is the mouth of the horn. At its tallest and widest extents it is a 90x60 (or whatever flavor you want) horn.

The profile at the widest extent can be calculated as a 90 deg flare at a certain radius plugged into the OS profile formula.

The profile at the tallest extent is similar but with a 60 deg flare and smaller radius.

For all points between the tallest and widest, you can calculate the flare and radius to be used. It will terminate to a circle at the throat because the same throat diameter value is always used.

I could easily be mistaken in my assessment as I haven't tested it thoroughly. Please point out where it is more complex.

Edit: Forgot to address driver exit angle. I agree, each OS profile, in order to be optimal is setup for a specific CD exit angle. IMO, the DE250 is the best exit to go with because I believe it is documented, the driver is readily available, moderately priced and well accepted as a top notch CD.

Someone (mabye edlafontaine on PE) posted a decent list of CDs with exit angles. I will have to look. Its either on PE or DIYaudio.com

I believe this is what you're looking for:

Here are the exit angles I've collected, but can't vouch for the accuracy. I believe all are overall angles (/2 per side).

18sound:
NSD1095N, ND1090 = 27°
NSD1480N = 10°


B&C

1"
DE250 14.6°
DE10 7.7°
DE12 24°
DE400TN 20.7°
DE400 31°
DE500 17°
DE200 9.9°

2"
DE85TN 34.5°
DE750TN 22°
DE950TN 17°

BEYMA:

CP750Nd - 24º
CP850Nd - 7º
CP755Nd - 12º60'
SMC65Nd - 15º
CP385Nd - 16º30'
SMC225Nd - 13º1'


jbl 2450 10+°
radian 950 20+°

Here's a spreadsheet for an elliptical OS to get you started with the math. As usual with my (in)famous spreadsheets, it works but it's butt ugly.

About matching the CD exit angle to the horn, I don't think it's a big deal. You can build the horn for a 0 degree exit angle and a few strokes with a piece of sandpaper wrapped around your finger will smooth the transition well enough for guvment work. Even Earl uses modeling clay at the transition to smooth things out.

 

Elliptical Geddes.zip 52.1787109375k . file

Yeah, that was just an experiment in getting the math right when Earl was saying it was so hard. You'd need much thinner slices for a CNC machine and you'd need to deal with the round-over at the mouth too. But it's a start....

Thanks!

There was a discussion about the DE250 angle being different but I couldnt find out the answer.

I should try to measure the angles of my CDs, I have to figure out how to measure them first some have screens over the mouth.

Great work Dennis. I'm going to try to implement a Sketchup script that will give us a 3D model for elliptical horns. I might try to implement it with the option of superellipses as well. I'm new to Ruby scripts so don't expect something right away.

Concerning driver exit angles, the two most popular CDs, the DE250 and CP385ND within 1.5deg of each other. Manufacturing margin of error would likely be greater than that. IMO, we could target 15deg and it will perform admirably.

I just don't see multiple molds or plugs being feasible, let along multiple production runs for different drivers. These won't be $15 horns either when you account for tooling cost so you might as well splurge on nice CDs. This isn't frugal DIY, IMO.

I think the project might be feasible.

What kind of price target? $100?

I agree with setting one throat angle and I like your opinion on doing it for the best CDs ( DE250 and CP385ND ), I should be buying the CP385ND in a bit.

Im not sure. I did just ask which one Augerpro was using because I should be buying the one he built a Passive XO for. I now think that is the CP380/TD12M design.

I was really disappointed to hear the news about the QSC waveguides. I had planned to used them for a first DIY build, but this project sounds very interesting. Why 90x60 instead of round (vertical dispersion control)? And about 17" wide, what horn length/flare rate and what low frequency cut off are you thinking about?

There has been discussion about the 17" veritcal distance creating a larger CTC which creates a null in the vertical listening angle.

Of course as you go larger you can go much lower in the XO frequencies and you can use steeper sloped XOs to mitigate that null issue.

I always say pick your compromises

If someone can generate an accurate prototype, working in fiberglass is not that difficult.....

JSS

put a smiley on that please ....Doing my NOT802D project with fiberglass has convinced me that doing fibreglass is NASTY business.

I think the problem really is getting an accurate prototype.

Couldn't using a MTM arrangement (like the photos above) move the vertical null further away from the center and make the on axis lobe larger?

Fiberglass work with polyester and polyurethane resins is NASTY. With epoxies, much nicer. You just have to pick the right resin system....it is still messy, but will not drive you out of the house/shop/garage with the fumes.

The accurate proto will the the butt-kicker. It will not be easy if home-made (need an ellipse generator router jig at the very least to do a laminated version that has to be smoothed BY HAND, then sealed and waxed in order to generate a female mold that will then be used to generate a male mold that will be used to make the horns), and custom fabricating of the proto will be $$$$$.

JSS

Definitely, I used HD stuff originally. Now Im spending more $$$ on stuff from online sources like Jamestown distributors. The latest Epoxy I have is ultra clear and orderless, much better!

As for molding using silicone stuff from a source like smooth-on is turning out to be awesome. I just finished using Rebound 25 to create my silicone rubber molding, that stuff is AWESOME. Creating the hardshell around it was not awesome with fibreglass/epoxy because it just does not stick to the silicone

Anyways, sorry about the OT stuff.

FWIW, I do not mind adding funds to a project to get a prototype. I may not have the skills necessary but I can always provide some $$$.




Good question, I can not answer that one.

I see two potential routes:

1. Homemade version from wood used as a plug for a mold. Frankly I don't see this as feasible with an ellipse, but I'm not a woodworker.

2. Build a 3D model and have a plug machined. This would be more expensive and would require a production run to make financial sense. I'd imagine using Smooth-On Urethane Plastic in silicone molds would be best. I have to believe this would need to be treated like a business albeit a small one.

I wouldn't mess with fiberglass cloth and resin. I'd rather do a urethane pour into a mold. I'm playing with Ruby scripts in Sketchup right now.

Are there any opinions on the ellipse shape? We could do a superellipse if that was deemed better. I haven't given the ellipse shape much thought.

Soho, any interest in modeling an elliptical OS in Akabak or Hornresp?

Edit: And the reason I mentioned the CP385ND is because it was in that list. I'd probably go with the ferrite version because I'm not building for portability and I doubt anyone else here is either.