Quote Originally Posted by alancohen View Post
...gather the curve of the horn structure is tuned to maximize a certain frequency range, but what would happen if you put a 500Hz signal into an 811b horn, assuming the driver itself could handle it? Of course a sound would come out, but what would be happening to it to make it undesirable? Inquiring minds want to know.
I may have missed the original post about undesireability... so maybe this is not entirely on target.
I think the overall point is that the horn will not load the driver below Fc. This creates an impedance mismatch. So you loose efficiency, perhaps to the point of no sound coming out.

Take the analogy to the next step and think of it this way.

If you strapped a 15" woofer to an 811, would sound come out? Yes.
Would 30hz come out? Probably: 'not really'.