Thanks Mike....
Bigger is always better, is it ???
The resonance issue - its not so much the Q but where it is in this case. With the LAB its around 30Hz so its not that critical, at those frequencies its more about energy than defining the timbre of an instrument, but if it was at 80Hz then it would be an issue.
FWIW I did actually model (I had to pay for it) my 18 inch version of the LAB with a program that I guess you could say is like a finite element acoustic model – is capable of predicting a lot of things including directivity at various frequencies and will take into account anomalies in the horn - The poor computer has to think for about an hour or so per run, anyway it agreed with what McBean simpler model had predicted.
BTW that nice power point presentation with all that math assumes plane waves propagating down the horn, which is what you would expect from the second order differential equation that describes the wave propagation in a horn – the problem is they’re not quite ... hence the problems with models.