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Acoustic Horn Design - The Practical Way
Acoustic Horn Design - The Practical Way
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Old 20th May 2020, 05:29 AM   #1
mabat is offline mabat  Czech Republic
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Default Acoustic Horn Design - The Practical Way

It was suggested to me to start a thread regarding the actual practical builds of horns and waveguides, mainly designed with the Ath. So here it is, for everyone to share their own way of converting their design into something real and listenable. Show off!

So far the tool can generate:
- STL file,
- coordinates files to be imported into Autodesk Fusion 360 as splines and/or smooth surfaces.

There may be other useful features implemented in to tool to enhance the practical possibilities - just let me know.
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Old 20th May 2020, 06:31 AM   #2
mabat is offline mabat  Czech Republic
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First, let me summarize how to import the shape into Fusion 360 since it is still not properly documented in the User Guide.


Definition file parameters (4.5.0 and above)

Output.Coords = true
Output.Coords.NumProfiles = 8 ; Number of exported curves in "_profiles.csv" file (default = 4)

Notes

Two files are created in the project folder:

<project_name>_slices.csv
<project_name>_profiles.csv

Now there are two Add-Ins for Autodesk Fusion 360 included in the Ath package:

Ath4_CurvesImport - used for spline-only import, can be used either with the "slices" or the "profiles" file
Ath4_SurfaceImport - used for lofted surface creation from the "slices" file.

The number of curves in the "slices" file is controlled by Mesh.DepthSegments parameter.


Installation of the Add-Ins in Fusion 360

1) Tools -> ADD-INS -> Scripts and Add-Ins
2) Click "+" in "My Scripts"
3) Select the folder "CurvesImport", part of Ath package
4) Repeat steps 2-3 for the "SurfaceImport" folder, part of Ath package
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Old 20th May 2020, 06:52 AM   #3
mabat is offline mabat  Czech Republic
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In this post I show how the z-coordinates of the exported slices can be customized if needed.
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Old 20th May 2020, 09:36 AM   #4
mabat is offline mabat  Czech Republic
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I guess that another output from the program could be a paper model to be cut out and glued together. It could give the basic shape structure to be worked with further, if not used as the final horn
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Old 20th May 2020, 10:09 AM   #5
mabat is offline mabat  Czech Republic
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Or to print templates of ribs that could be covered by a cloth and laminated. Then the final horn could be made out of a paper mache quite easily - paper horn.
Let the ribs cut out of plywood or balsa on CNC and the rest you could do in your living room...
Attached Images
File Type: png ribs.PNG (39.0 KB, 486 views)
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Last edited by mabat; 20th May 2020 at 10:14 AM.
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Old 20th May 2020, 02:54 PM   #6
ani101 is offline ani101  United States
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thanks for posting this. Looks quite interesting. Will give it a try!
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Old 20th May 2020, 08:44 PM   #7
Ro808 is offline Ro808  Netherlands
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It probably wouldn't hurt to (re)post an example of a 3d printed ATH4 here (courtesy of Pet007).
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File Type: jpg ath8_3D_proto_done.jpg (38.5 KB, 425 views)
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Old 20th May 2020, 11:12 PM   #8
wesayso is offline wesayso  Netherlands
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Quote:
Originally Posted by mabat View Post
Or to print templates of ribs that could be covered by a cloth and laminated. Then the final horn could be made out of a paper mache quite easily - paper horn.
Let the ribs cut out of plywood or balsa on CNC and the rest you could do in your living room...
One could try this:

Quote:
Originally Posted by Nissep View Post
If you start messing with fiberglass, take a look at what can be done with stretched fabric over a frame. The entire horn could potentially be made by making a box with shelves that one cut the desired shapes in. Then you stretch the fabric over the top and press down with a 1” rod or 3D-printed horn throat shape of choice. The fabric will take the shape of the cuts in the shelves and the pushrod.

Then cover the fabric in epoxy and let it cure. The hardened horn is not rigid enough but holds the desired shape. To increase the rigidity put fiberglass on the inside. To increase damping of an all fiberglass horn one can experiment with constrained layer damping. Looking from the outside we have the epoxy/fabric then fiberglass then fabric with soft polyurethane rubber brushed on it, and the last layer is fiberglass. Hard skin, soft viscoelastic center.
Or as Nissep posted after that:

Quote:
Originally Posted by Nissep View Post
To support my claim it’s always a good idea to quote Danley..
Quote:
Originally Posted by Tom Danley
Hi guys

For what its worth, the every first one of these below was made using burlap to make the “waveguide”.
Perhaps you can use spandex to do the same thing.
Stretch the fabric across a framework, uniformly stretched a bit.
With something round, the size you need, press in the fabric to the depth you need and clamp in position.
Get some thin epoxy resin from the hobby shop and brush on a few coats until the fabric is ridged enough to deal with. Fill in the rear area with “great stuff” or equivalent polyurethane expanding foam.
Be sure to drill a number of big holes on the back side to let the excess out as it expands.
Figure it will take a couple trys until you get the hang of it but then it will be easy once you figure out what you need for your application.
Good luck

Tom Danley

Danley Sound Labs, Inc.
Source: synergy.....Take #7
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Old 21st May 2020, 05:08 AM   #9
mabat is offline mabat  Czech Republic
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Stretching fabric seems a good idea (very clever actually) but has its limitations. It is extremely easy to do but is fine only if you actually don't care about the shape too much since the shape is determined by what the fabric will do and not what you want it to do. This may not always be the optimum, you would need at least a proper mouth flare template. I couldn't make the shape I want by stretching a fabric - it wouldn't do what I want.

So the task remains to make the desired/designed shape, not just some shape.
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Last edited by mabat; 21st May 2020 at 05:22 AM.
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Old 21st May 2020, 06:47 AM   #10
mabat is offline mabat  Czech Republic
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BTW, for anyone used to a different CAD, the imported model can be exported from Fusion 360 to IGES or STEP format. I tried to export IGES file and open it in Gmsh and mesh it, it works smoothly (this shape goes from circle to circle through an ellipse) -

This mould could be milled on CNC from styrofoam (XPS) easily and quite cheaply I guess. Then laminated with a thin layer of fine fiberglass for a smooth surface.
Attached Images
File Type: png iges-0.PNG (11.9 KB, 355 views)
File Type: png iges-0m.PNG (113.8 KB, 348 views)
File Type: png mouls-4.PNG (154.8 KB, 353 views)
File Type: png mould.PNG (582.4 KB, 46 views)
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Last edited by mabat; 21st May 2020 at 06:54 AM.
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