Actually, GF, your post is exactly on target.

I guess the first thing is I don't get how a horn by itself, basically an inert flared tube, has an "impedance" at all. I understand the impedance of AC current in a circuit, but how does this apply to a horn? I assume it has something to do with sound waves moving in an air medium through a restricted space.

I gather that the lower the frequency, the longer the sound wave so it makes sense to me that the length of a horn could influence frequency efficiency, but length seems to be irrelevant in that shorter horns can still be rated lower than longer horns of a difference shape. I don't get it.

The good news is at this point I don't have to. I have what I have as far as equipment and you gotta dance with who you brung. I'm just trying to figure out what the ramifications are of trying to put 500Hz through an 811B horn. I'm going to try it anyway and see what I hear. It will either sound better to me or worse. It's a luxury to know why, not a necessity.