Acoustic Horn Design – The Easy Way (Ath4)


Two plane waves are traveling along a straight wall. All of a sudden the wall becomes circular and the wave starts diffracting. As both waves and boundaries are just rotates versions of the other, the amount of diffraction is the same.

The second derivative, however, is quite different at both point where the wave starts diffracting. The curvature is constant though.

So, shouldn't we minimize the (maximum) curvature?
I have been playing around with improving the wave guides I have successfully used with a mid range AMT driver. I have been using a simple OS horn with a simple mouth radius. Using the OSSE profiles as guide curves for my own approach. See -

The question is what’s the best approach for modelling a rectangular AMT diaphragm in AKAbak?

I know some believe that adding a waveguide to AMT, doe not have any benefit. I have done a significant amount listening with and without guides, and to mine and others that have heard them, the waveguide improves the dynamics and benefits room interaction.
btw. here is another profile from yesterday, quite similar performance with very different parameters.
hf10ak-kapone-27.png hf10ak-kapone-27_polar_fall.png

Curvature is also different, so real world compatibility to a particular compression driver would differ. I have no idea which one would work better on which driver, although the BEM result is about the same.

Tom's version makes better back side with tmax, less interference around the onion :) I would guess its the smoother curvature when t gets closer to 1 and beyond, mine droops.
Last edited:
Yeah, smoothing the curvature further seems to reduce diffraction, DI is smoother without extra "boost", increased DI around 2kHz in the above sim labeled #27.

Whether this is a good or bad thing I don't know, little diffraction there helps increase DI to lower frequency with same diameter device which makes for more constant directivity. This is same profile as above other than few parameters tuned to smoothen the blue and red curvature lines in Desmos. DI ruler straight, but not constant of course. edit. added #27 graphs for easy comparison.
hf10ak-kapone-27.png hf10ak-kapone-30.png hf10ak-kapone-30_polar_fall.png 30-curvature.png
Last edited:
There's always quite strong diffraction at the very end of the R-OSSE contour that helps to increase the DI at lower frequencies, i.e. at those frequencies which make it to the end of the profile, i.e. only those with large-enough wavelengths. Higher frequencies "leave the contour" soon enough to not to meet the edge very strongly. That's why I still don't see much merit in adding a rear side, except very wide-directivity designs where more higher frequencies ever "see the edge".
  • Like
Reactions: 1 user
I have found something I quite like for the T34A, it is harder to get right than the B version. The simulation conditions seem to matter much more than I found previously.

View attachment 1176180 View attachment 1176181
Just curious - what software are you guys using to generate the images above?

As I try to learn, I've been generating FRD files via ATH, and then importing them into VCAD to view performance. I was just curious if the above app is a faster process.
Last edited: