811 Fins

[GM]

Hi GM, group,

I have to confess to being a dyed-in-the-wool conical horn enthusiast.........

I have seen some data for the on-axis hole in h.f. response.........

I am not sure what the mechanism of the problematic response would be........... What is neat about conical horns IMO is the degree to which the off axis response mirrors the on axis response.

It is freaky to listen to an LC-9A while standing waaaay off axis, virtually beside the speaker, and hearing very nearly the same response as on axis.

Greets!

Me too up to a point, but I found out early on that without a proper throat/mouth termination that it too left something to be desired. In my experiments I never went as far as Dr. Geddes did though, his and others ovoid shape was more than I wanted to mess with and not sure it's an audible or even perceived improvement over the same design as the round variant I empirically arrived at. Indeed, even with the best HF hearing person I've ever known could barely perceive a difference between my round and ~1.00:1.273 aspect ratio radial variant.

Right, the 'hole in the middle' on a conic expansion is due to its HF naturally falling on axis power response being distributed over a wider (flatter) arc than expo, etc. as you measured and why the 511/811 has more HF roll-off on axis with no vanes, i.e. they're more than just stiffeners.

WRT a conic expansion's intrinsic aberrations, look to telescope design for a ~complete tutorial on optimizing them along with Dr. Geddes's various papers, especially WRT compression driver filter chamber/initial expansion design.

I agree, it was a lone LC9A used for live entertainment that filled Hotlanta's first Shakey's Pizza Parlor in '67 that got me motivated to experiment outside the WE/Altec 'box' I'd been pursuing as the 'Holy Grail' of high performance sound reproduction. It sounded enough 'different' overall WRT my DIY A7-500s that were already somewhat optimized with what I'd already learned about cab construction, horn damping, polar response, etc. that it became an obsession to figure out empirically when I couldn't find much in the way of design theory. I've often wondered why it wasn't included in Cohen's book or any of its revisions.

GM