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Acoustic Horn Design - The Practical Way
Acoustic Horn Design - The Practical Way
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Old 25th May 2020, 10:23 AM   #31
thunk303 is offline thunk303  Australia
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Hey team.

I am designing my own version of a 3D printed stubby I first saw made by bwaslo.

I am using different drivers so it's a complete redesign. I am hoping to have the plywood attached on the inside so I can simply use spacers to get the ply perfectly aligned with the 3D printed section.

So the question is, can and how do I tell ATH to transition fully from the round throat to a rectangle at 180mm up the wall, then continue (fully flattened) from 180mm to 250mm?

Hope what I am asking is clear.

Cheers
Dean
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Old 26th May 2020, 07:36 PM   #32
mabat is offline mabat  Czech Republic
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I don't follow this part: "...continue (fully flattened) from 180mm to 250mm". Why the extra segment? Maybe a sketch would help.

I could also add an option of a true rectangle for the guiding curve, without any corner radius, if that's what you want. You would be limited to STL output but that should not be an issue if created with high enough resolution.

Without the terminating term (Term.s = 0) it could be connected to a straight-wall extension like that.
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Last edited by mabat; 26th May 2020 at 07:46 PM.
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Old 26th May 2020, 08:53 PM   #33
toulou is offline toulou  Greece
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Quote:
Originally Posted by mabat View Post
BTW, what bmc0 has shown will be hard to beat because of its relative simplicity (being still an axisymmetric device), yet the performance is stellar. This is the way to go.
It's some time I have been thinking of switching to high sensitivity, plus narrow well controlled directivity speakers, following exactly bmc0's method of construction! --> building the suitable tool to shape some easy to work with material, via rotation.
Yet, being a complete newbie to this wave-guide thing, I am concerned with tolerances: Not sure of the precision I can achieve by such a method, so how off can you go without audibly compromising performance? Is it possible to model some slightly flawed shapes to get a general idea?
What I really need is some expert's opinion to how tolerable the flawed shape is - when does it start to be audibly flawed?


Thanks in advance, t

Last edited by toulou; 26th May 2020 at 09:00 PM.
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Old 27th May 2020, 07:09 AM   #34
mabat is offline mabat  Czech Republic
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That's a good question. I don't know what precision has bmc0 achieved but it is definitely good enough. I wouldn't be too worried.

I can try to add some artificial deviations into a mesh and do some analysis altough it may be difficult to actually simulate the possible practical imperfections (that may be far from random). Also, some imperfections can even help eventually. It may be an interesting exercise.
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Old 27th May 2020, 08:09 AM   #35
bmc0 is offline bmc0  United States
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As long as you can make an accurate template, the result should be very good. My waveguides followed the template pretty much exactly.



I did a few simulations of minor axisymmetric defects a while ago and from what I remember, discernible differences started to show up when they were on the order of a couple tenths of a millimeter when near the throat. I doubt anyone really knows what the audibility threshold is. It would depend on the nature of the error as well.



I'd hazard a guess that if the final product is visually smooth and within a few tenths of a millimeter near the throat, there'd be little or no audible improvement with greater accuracy.
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Old 27th May 2020, 09:34 AM   #36
thunk303 is offline thunk303  Australia
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Quote:
Originally Posted by mabat View Post
I don't follow this part: "...continue (fully flattened) from 180mm to 250mm". Why the extra segment? Maybe a sketch would help.

I could also add an option of a true rectangle for the guiding curve, without any corner radius, if that's what you want. You would be limited to STL output but that should not be an issue if created with high enough resolution.

Without the terminating term (Term.s = 0) it could be connected to a straight-wall extension like that.
Ok so I need to make sure the lower section of approx 180mm is fully transitioned from a circle to a straight sided rectangle before I can do the cutout for the ply in the second upper section.

Hope this makes it clearer.

Cheers
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Old 28th May 2020, 04:45 AM   #37
mabat is offline mabat  Czech Republic
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I'm still not sure I understand. Anyway, you can't make a flat wall with OS profile. It flattens with distance from the throat but is never exactly flat. There's no way how to do that with Ath at the moment. The best you could probably do is just to connect the "almost flat" OS segment to the plywood.
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Old 28th May 2020, 09:55 AM   #38
thunk303 is offline thunk303  Australia
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Ahhh got you... It is the current os profile I have tried that has some curvature in the horizontal plane, which is intended for os, I just need the last 50mm to be dead flat towards the mouth.

Ta for input. Will post the stl if I get to to work.
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Old 9th June 2020, 09:53 PM   #39
danibosn is offline danibosn  Croatia
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Acoustic Horn Design - The Practical Way
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Hi guys


it is nice to see some practical implementations after long theoretical thread. Kudos to mabat for excellent software tool and to bmc0 for very clever and successful design of tools and horn as well.
My plan is to made male mold from polyurethane foam on homemade lathe machine, make a layer from fiberglass and finally smoothed out as much as possible.

It is planned to make horn from fiberglass as well or maybe, from already mentioned, paper mache as described here
DIY Paper Mache Horn - The Paper Horn by Inlow Sound


To complete this I need template of WG/horn profile and even though I've red al thread it is not completely clear to me how to get it. So please little help.

What is the easiest way to get WH/horn profile in 1:1 size from all those nice software's?


regards Danijel
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Old 10th June 2020, 05:53 AM   #40
mabat is offline mabat  Czech Republic
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To sum up, following your case:

1) In your script file, enable coords output:

Output.Coords = 1

2) Execute the calculator. In the horn project directory you will find a file called *_profiles.csv

This file contains the coordinates of the profile curves (4 of them by default, all the same in a case of axisymmetric design). It is just a text file with X;Y;Z coordinates, each curve separated by a blank line.

Now you either have some other means how to process this file (can be imported into a spreadsheet etc.) or you can import these curves into Fusion 360. For Fusion you have to install the add-ins (see post #2). In Fusion you can export the curve as DXF, etc.


PS. Number of points of the curve is defined via "Mesh.DepthSegments". In general you may want to have two different settings - for ABEC output and for the CAD output.
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Last edited by mabat; 10th June 2020 at 06:16 AM.
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