Acoustic Horn Design – The Easy Way (Ath4)

[mabat]

BTW, to view a pressure field, simply add this to the "observation.txt" file:

Nodes "FieldNodes"
  Scale=1m
  1  -0.2 0.3
  2  0.4 0.3
  
Field "F1"
  RefNodes="FieldNodes"
  EdgeLength=10mm
  BodeType=LeveldB; StepSize=3
  Range=60
  1 1 2

You will probably want to reduce the number of frequencies however, otherwise it will take quite a long time.

To see the throat in detail you can easily increase the resolution and limit the field area:

Nodes "FieldNodes"
  Scale=1m
[b]  1  0.0 0.2
  2  0.15 0.2[/b]
  
Field "F1"
  RefNodes="FieldNodes"
  [b]EdgeLength=3mm[/b]
  BodeType=LeveldB; StepSize=3
  Range=60
  1 1 2

 

[mabat]

I just realized there are several options for the field type (BodeType):
"LeveldB, Ampl, Real, Imag, Phase, LeveldB_Phase, Ampl_Phase, Complex"

I've never experimented with this. Maybe it could show something interesting.

 

[Arnandsway]

As some start to print and measure the ST260, maybe it's useful to collect (again) the results so far - this is a courtesy of Pet007 who measured virtually the same WG before (maybe there was a tiny difference, I don't really remember), with three different drivers -

Just a note - the DI as shown is calculated from the front polars only (the only measured). The "real" DI will be closer to the simulations, where it is full-space.

What crossover frequency would one want to use with this WG? My guess would be around 1200 hz to keep a smooth DI?

 

[mabat]

What crossover frequency would one want to use with this WG?

This depends mainly on the compression driver used - what it can handle. Generally you want the lowest XO frequency possible with what you have. Then you simply choose a woofer size that makes a smooth overall DI. If we assume that most of the 1" drivers can handle 900 - 1000 Hz with ease, what should be the right woofer size for this, looking at the DI around this frequency (around 7 dB)? I don't know off the top of my head - maybe 12", maybe 10"... There is some freedom anyway.

 

[JSS]

Now it would be great to have this measued to see if it's real to that extent. If it was, the whole system would "ring", i.e. there would be strong peak(s) in the frequency response and accompanying ringing in the time domain. Correctable with EQ but somewhat troublesome. What's interesting is that it has virtually no effect on radiation pattern.

I'll print and measure to see if it's a real problem and report back. It's printing now hopefully it doesn't crap out. It's 9hrs to print half. Hoping to have something to report soon...

 

[Arnandsway]

This is what I get from a simulation in Vituixcad. I simulated the diffraction-response from two 8" woofers on a 25x90 cm baffle. I SPl-traced the measurements of the ST260 + B&C DE502. And then I did some EQ'ing to get the responses flat.
Crossover is at 1000 hz LR4, this gave the smoothest DI. Note that the SPL-traced tweeter response only goes to 90 degrees, while the diffraction simulation goes 360 degrees.

Here is the dashboard from Vituixcad and below that the diffraction-tool.