Although "radius" will get you most already, I found the "resonance"-fog interesting.

All but the ellipse form will have a cloud of mixture outside the bellmouth.

The Ellipse has only a very shallow cushion right on the bellmouth.

Interesting if you fire your injectors directly into the bellmouth....

 

TJ

If the horn is attached to a carburetor and the engine is at one of several RPM that generates the standing wave. It is common to see this on a dyno. And is more likely on piston engines, with the long time out between induction events. When the horns are inside a plenum, that alters the tune, and the fuel fog problem is moved to a different RPM, and may be less profound. In carbureted engines the plenum should be stout enough to withstand an explosion from a fuel air mixture that may be close to an ideal ratio.

 

Notice that in street cars those things are thick walled castings and a bit heavy, even in injected engines.

 

Lynn E. Hanover