I have made a comparison of a deep and shallow version of my current best attempt at a rectangular guide trying to keep the outer dimensions as close as possible (400mm x 308mm). So not quite what you asked for but as the ABEC sims are already done maybe it is useful.Now I wonder what the radiation impedance of the same waveguide with a bigger mouth would look like, but I don't want to burden mabat with yet another time consuming sim.
One thing I didn't stress explicitly - these simulations are still calculated for a constant acceleration of the driving elements, there's no electroacoustical model of any driver connected. This is a different situation to a compression driver being driven with a constant voltage. Maybe this would be the right moment for incorporating such a model as ABEC allows for that. I just never tried and would need some help here.
This lumped element model, coupled to what I already have, should allow to predict real SPL for a given voltage and also the corresponding excursion. I'd be most interested in these quantities.
fluid, thanks for posting these sims!
As for the ripple, it seems that there is very little difference between the horns.
The short horn seems to exhibit even marginally more pronounced ripple.
Anyway, as far as I'm concerned, there's no sensible explanation.
There was a request for a bigger version of one of my better designs. Here it is, 484 x 418 x 155 mm.
(It begins to be boring I guess... )