Acoustic Horn Design – The Easy Way (Ath4)

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#13,881
Can't edit anymore.

Perhaps these are more useful:
1697459704543.png
Wide baffle, looking at waves before diffraction occurs


1697459822000.png

Narrow baffle, with diffraction

1697460007211.png

"Cone" on a wide baffle

I have to admit, I find it difficult to interpret these.
 
#13,882
The ripple tank is fine for observing the principles - now as you make the cone angle sharper, there's will be more and more of the secondary radiation. It's apparent even in the first example. The applet has its limitations (slanted walls are not smooth, for one), but it can show the basics.

I still don't see any flaw in the BEM model...
 
#13,885
Yeah, I played around with it some more. I don't see anything funky going on until the cone becomes deep and the angle of incidence becomes small, then comb filtering becomes evident, as my theory would predict. Therefore, unlike mabat I do believe there's something wrong with the BEM simulation I did.

Flat
1697470133556.png

Shallow cone
1697470222904.png


Deep cone
1697470251312.png
 
#13,886
tmuikku said:
One can add infinite baffle to ABEC sim, after you've created ABEC project with ATH, edit solving.txt manually and add something like this:

Code: 
Infinite_Baffle
  Subdomain=1
  Position=x
  IBOffset=-400mm

I think ATH put subdomain 1 for the outside so thats correct, but change Position=x to y or z, depending which plane is behind the waveguide. Use Offset to adjust distance. More info in ABEC help file.
Click to expand...
love this
 
#13,888
keyser said:
Can't edit anymore.

Perhaps these are more useful:
View attachment 1224232Wide baffle, looking at waves before diffraction occurs


View attachment 1224233
Narrow baffle, with diffraction

View attachment 1224236
"Cone" on a wide baffle

I have to admit, I find it difficult to interpret these.
Click to expand...

Hornresp does this way better

Back in the day, I attempted to enhance the 'ripple pool' code that you can find online

I had no luck at it, it was over my head

I mentioned this to David McBean and he generously added my requested enhancements to hornresp

As I understand it, the wavefront simulator and the ripple pool simulator online are based on the same code
 
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#13,889
keyser said:
Any idea why this doesn't work?
Click to expand...
I think it is how the data is presented, rather than the simulation being wrong.

cone.png


There is a relatively strong diffraction from the junction between the infinite baffle and the cone.

I have attatched a VACS project where you can grab the y axis and move it up and down to see the response at that angle in the right pane. Converting it to curves just makes it an overwhelming mess.

Cone Polar.png
 

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#13,890
The interference ripple is roughly 3db and likely audible. ~3db ripple seems to happen when secondary sound is about 17db down. Since this is likely a sound system that should sound great at any angle(?) then you should perhaps reduce the ripple if at all possible.

One could reduce distance to edge to push all the ripple up in frequency, thus reducing bandwidth of the "problem". And change shape to distribute the time delay to the edge reducing the amplitude, so perhaps tall and narrow shape. Further reduce the edge if possible to actually reduce the secondary sound. Easiest would be to use smallest button tweeter you can find, about 1" diameter "disk" would show diffraction on the top octave, likely not that audible as diffraction ripple from 300Hz up 🙂
 
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#13,892
Yeah, and the audibility.. hard to test. Judging from the interference pattern Q of "peaks" and "dips" is so broad around mids it's likely very audible, if I did such EQ moves on mixed song. Perhaps not if staying stationary, but as one moves within the room and the filters would move I think it becomes apparent the sound changes. Sound would change for many reasons, by turning ones head for example, so perhaps it would still be relatively unnoticed in reality.

ps. such circymmetric shape is rather easy to prototype I think, test it.

pps. Happened to have a DAW and a mix open, tried to implement such interference ripple with EQ quickly and of course it's audible but the difference is quite subtle after all, less than I thought. Gotta make listening test with that, ignoring all the time delay associated just implement the interference ripple using EQ filters.
 
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#13,898
keyser said:
I don't think so. Please enter a thought experiment with me. Say the baffle we're simulating is a flat circle with the same 155 mm radius in an infinite baffle. Then the result should be identical to a driver in an infinite baffle, because a flat baffle that's flush with an infinite baffle IS an infinite baffle. Next, we turn the R=155 mm circle into a very short cone, say a height of 1 mm. What has changed acoustically? Pretty much nothing. Yes, there's now a transition between the flat infinite baffle and the cone at the edge of the cone, but the cone is short that it's almost a flat circle. This will still behave like a driver in an infinite baffle.

At what height does the edge really become a source of significant diffraction? It depends on the angle and the wavelength. Is it even diffraction, or should we call this reflection instead?
Click to expand...
It really a is reflection. Well, it could be viewed like one. We can think of a wall like of an acoustic mirror, so shallow cone on a wall is equivalent to a couple of shallow cones joined together at their bases. For a range of wavelengths substantially longer than cone depth, but not substantially longer than cone diameter whole two-cone enclosure can be simplified to a simple disc baffle which diffracts strongly.
OTOH, hemispherical on-wall enclosure equals free space sphere, so half-balls sticking out of the wall are acoustically purest solution.
 
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