Acoustic Horn Design – The Easy Way (Ath4)

I somehow fail to have the throat extension generated for simulation.
That's some pretty old syntax used. The last Ath version provided (available on my website) should process the following better.
It's a strictly conical part connected to a R-OSSE termination.

1707462215692.png
1707462229489.png


Code:
R-OSSE = {
  R = 200
  r0 = 100
  a0 = 40
  a = 40
  
  k = 1
  r = 0.3
  b = 0.2
  m = 0.75
  q = 3.8
}

; conical part
Throat.Ext.Length = 100
Throat.Ext.Angle = 40

Source.Shape = 2      ; force flat-wavefront source (?)

Mesh.ThroatExtSegments = 30
Mesh.LengthSegments = 30
Mesh.AngularSegments = 8
Mesh.SubdomainSlices =
Mesh.WallThickness = 5

ABEC.SimType = 2            ; free air
ABEC.SimProfile = 0         ; axisymmetric mode
ABEC.f1 = 200               ; [Hz]
ABEC.f2 = 20000             ; [Hz]
ABEC.NumFrequencies = 80
ABEC.MeshFrequency = 36000  ; [Hz]
ABEC.Abscissa = 1

ABEC.Polars:SPL = {
  MapAngleRange = 0,180,37    ; [from_deg,to_deg,N]
  NormAngle = 20  ; [deg]
  Offset = 0      ; [mm]
  Distance = 2    ; [m]
}

Output.ABECProject = 1
Output.STL = 0

Report = {
  Title = "Conical/R-OSSE"
  Width = 1400
  Height = 900
  NormAngle = 20
}

This is the result, BTW:
1707462373812.png


If you remove or comment the line ABEC.SimProfile (and reduce ABEC.MeshFrequency=1000), you can simulate an octagonal version as well (as a 3D model):
1707462525835.png
 
  • Like
Reactions: 1 user
ATH330EX will be next. Now it's really fast when I have the unified mounting.
This one will just fit a 250x250 mm print bed in two halves.

ATH330EX-6.jpg
ATH330EX-5.jpg


BTW, it's amazing how clean can an axisymmetric horn actually be. If I only had known this before, I would have spared a great deal of effort on all the various ways how to make it something else. What a waste of time :)
 
Last edited:
  • Like
Reactions: 3 users
This is for ⌀450 mm, which really "only" shifts the DI knee, where it start to decrease (for decreasing frequency).
(5 deg step)

1707574583417.png


It gets ridiculously big if it's to be below ~1kHz (which is about the knee here), there's probably nothing that can be done about this.
 

Attachments

  • 1707574647746.png
    1707574647746.png
    17 KB · Views: 38
Last edited:
  • Like
Reactions: 1 user
I get strange results:

Info : Running 'C:\gmsh\gmsh.exe bem_mesh.geo -' [Gmsh 4.8.4, 1 node, max. 1 thread]
Info : Started on Mon Feb 12 16:56:50 2024
Info : Reading 'bem_mesh.geo'...
Error : Unknown curve 0
Error : 'bem_mesh.geo', line 62: Could not add plane surface
Error : Unknown curve 0
Error : 'bem_mesh.geo', line 138: Could not add plane surface
error: gmsh call status = 1

Screenshot 2024-02-12 165743.png
 
I found a bug:

I'm using ath beta 4.9

I found that ath wouldn't make an ABEC project that worked, but it also didn't throw an error

After investing some time in troubleshooting, I found that the issue was that my filename has spaces in it

IE, if you have a config file named "my waveguide.cfg" it doesn't seem to produce a working ABEC file (everything else works fine) but if you change the name to remove spaces, like "my_waveguide.cfg", ATH produces the project properly
 
  • Like
Reactions: 1 user