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 Multi-Way Conventional loudspeakers with crossovers

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 7th September 2015, 12:29 PM #1 Patrick Bateman   diyAudio Member     Join Date: Oct 2006 Location: San Diego 3D Modeling Tips and Tricks I've been building a ton of loudspeakers and waveguides in 3D, and thought it might be worthwhile to post some of the shortcuts I've figured out. It took me a while to figure out how to quickly make some of these shapes, so maybe this will save people some time. First, here is how I print: 1) I use Autodesk 123D Design to model the speakers (\$0) 2) I use Repetier and Slic3r to 'cut up' the model into something that can be printed (\$0) 3) I use a Printrbot Simple Metal to print the designs (\$599) It is true that you can have things printed by Shapeways. I prefer printing it myself because you can get results in about twelve hours instead of a few days. And filament is so cheap, I can print a nice waveguide for about five bucks.
 7th September 2015, 01:07 PM #2 Patrick Bateman   diyAudio Member     Join Date: Oct 2006 Location: San Diego Object one : an elliptical waveguide The first step in making an elliptical waveguide is to draw an ellipse. In this case, I am using the golden ratio. The ellipse has a width of 12.7mm and a height of 20.5mm. When we're finished this will give us a 1" wide entrance to the waveguide. Step two is to make the waveguide walls. I'm making a progressive transition waveguide. According to JBL, "Progressive Transition waveguides are unique because a single mathematically-continuous surface defines the waveguide from transducer- throat to waveguide-mouth. The distinctive feature is the lack of a traditional diffraction slot. Instead the sidewalls transition smoothly from the driver throat through to the square or rectangular mounting flange." Translated into English, what we have is a curve that slooooooooowly transitions from the angle at the entrance (90 degrees) to the angle at the exit (180 degrees.) here's the real deal, for comparison Note that we're not limited to an entrance of 90 and an exit of 180. We can use any angle we want. For instance, if you were using a compression driver instead of a dome, you might use a narrower entrance angle. IE, if your compression driver had an exit of twelve degrees, you could match the exit angle of the compression driver to the entrance angle of the waveguide to reduce diffraction. The angle that you'll get in your waveguide is determined by the tangent on that circle that I cut out there. Again, I picked 45 degrees, because it works for me. You could pick any angle you want. Once we have that curve, we need to 'scale it up' to whatever size we want in the real world. In my case, I wanted a baffle width of 8". That means that I have to scale up the width of that curve to 3.5". (3.5" for the waveguide walls, times two, plus the width of the entrance, gives us 8" total.) Once the curve is scaled up to size, we move the curve so it's adjacent to our ellipse that we made in step one. Then we "sweep" the waveguide wall around the ellipse. Basically the "sweep" tool lets us take one shape (the wall) and "sweep" it around another shape (the ellipse, which will be our throat.) The last step in making the waveguide is to 'squash' one dimension. Basically we take the whole waveguide and squash it down to 61.7% of it's original dimension. What this does is it gives us a nice elliptical mouth, with a golden ratio of height to width. This isn't just for cosmetics; it improves the frequency response by reducing the on-axis 'hole' that you get with a round waveguide. (A round waveguide has a dip on axis, due to everything being equidistant from the throat; by making the waveguide elliptical we fix that.) A couple of other advantages of an elliptical waveguide is that it allows for tighter spacing between the midrange and tweeter, which improves the vertical polars. And studies from Harman indicate that people prefer wide horizontal directivity and narrow vertical directivity. (I should really provide a citation for that, but I can't find it right now.) Last edited by Patrick Bateman; 7th September 2015 at 01:16 PM.
 7th September 2015, 01:27 PM #3 Patrick Bateman   diyAudio Member     Join Date: Oct 2006 Location: San Diego elliptical cutouts are difficult to cut, so here's how to make a baffle. First, we make a rectangular solid. Then we 'snap' the waveguide to the rectangular solid. Using the 'snap' tool is fast way to line up a couple of shapes; it's way more accurate and easy than trying to do it with a mouse. Once they're 'snapped' together, we use the 'ungroup' tool to unglue them from each other. Then we merge the two shapes on top of each other. I've made an extra copy of both shapes because I'll need the copy in a minute... In this pic, I've 'subtracted' the waveguide shape from the rectangular solid. This gives me an inverse copy of the waveguide, basically a solid that's comprised of the empty space inside of the waveguide. In the pic, you can see how perfectly smooooooth the transition is from the throat to the mouth. Then I use that inverted shape from the last step to 'slice' a shape out of the rectangular solid. I wind up with a baffled waveguide that's 200mm x 129mm x 36mm, or 7.87" x 5.07" x 1.4" These dimensions are just about perfect for a nice two way with a 7" woofer. The waveguide will control directivity down to 1687hz, where you can 'hand off' to the woofer. The depth of the waveguide will give us a bit of horn loading down to around 2700hz. (Check with hornresp to get the exact figure.) If you wanted to load the tweeter lower, just use a deeper waveguide.
 7th September 2015, 02:28 PM #4 Patrick Bateman   diyAudio Member     Join Date: Oct 2006 Location: San Diego Object Two : A Lecleach Horn Here's a LeCleach horn, built using the same methods as the waveguide from the original post in the thread. To get the curve, I modeled the loudspeaker in Hornresp, then used the 'export' function to generate the width of each step in the LeCleach curve. For me, the easiest way to plot the curve in 123D was to use the 'Polyline' tool. The Polyline tool lets you input an angle for your line. And Hornresp lists that angle when you export the horn curve. So you just take the number from Hornresp and plug it into 123D.
 7th September 2015, 03:52 PM #5 xrk971   Got Foam? diyAudio Member     Join Date: Oct 2012 Location: Metro DC area Nice work! Can you please share the STL files? Thanks
Patrick Bateman
diyAudio Member

Join Date: Oct 2006
Location: San Diego
Quote:
 Originally Posted by xrk971 Nice work! Can you please share the STL files? Thanks
I need to set up a file sharing site, I don't have an easy to share anything at the moment.

 15th July 2018, 07:20 PM #8 Patrick Bateman   diyAudio Member     Join Date: Oct 2006 Location: San Diego In a discussion on Facebook, someone asked me to share my T/S params that I use for modeling high frequency waveguides in Hornresp. To be honest, though I've designed a LOT of waveguides, I generally don't model the waveguides in Hornresp. The reason is because waveguides are fairly predictable in my experience. The process of making a waveguide is simple: 1) determine the vertical beamwidth 2) determine the horizontal beamwidth 3) determine whether you want a circular or rectangular mouth 4) pick a profile (conical, oblate spheroidal, tractrix, spherical, etc) 5) Match the exit angle of the compression driver to the entrance angle of the waveguide 6) Add an appropriate roundover at the mouth And you're done! I don't see any real need to model it in hornresp because what would that accomplish? I know that the depth of the waveguide needs to be sufficient to load the driver down to about an octave below the xover frequency, but I can do that math in my head. (speed of sound / depth of waveguide / 4) Occasionally I'll fire up axidriver to run a sim; axidriver can show you the polar response and the frequency response of a horn. But generally I only do that if I'm including some type of phase plug in the waveguide design. And even in THAT case, I'll frequently just design, build and print the phase plug without simulating it. (You can design a phase plug in about 30 minutes.)
philpope
diyAudio Member

Join Date: Jul 2007
diffraction slot throat distortion

Quote:
using a difraction slot with a lower flare rate will hugely increase throat distortion due to adiabatic air compression. one of the main benefits of the synergy horn is that using a conical horn means a very high flare rate where the compression driver is mounted - allowing the compression driver to operate at full output without the usual distortion levels found with other horns.

Patrick Bateman
diyAudio Member

Join Date: Oct 2006
Location: San Diego
Quote:
 Originally Posted by philpope using a difraction slot with a lower flare rate will hugely increase throat distortion due to adiabatic air compression. one of the main benefits of the synergy horn is that using a conical horn means a very high flare rate where the compression driver is mounted - allowing the compression driver to operate at full output without the usual distortion levels found with other horns.
True, but I still like diffraction slots.

They're useful if you're trying to 'have your cake and eat it too', basically allowing wide beamwidth while still loading the tweeter.

My waveguides are for home use and my midranges are two inches in diameter; throat distortion isn't a huge concern.

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