Old sorta like exciter speakers. June 1955 Radio Electronics p30

[ChrisABC]

FYI
or more like a big cone

https://www.americanradiohistory.co...ronics/50s/1955/Radio-Electronics-1955-06.pdf

 

[Squeak]

So a resonant waveguide? The explanation in the article isn’t very good.
It could work. But it all hinges on the exact construction, dampening and weighing of the waveguide/resonator, which was/is not an exact science.

 

[turk 182]

it would be interesting to see if this sort of "clothoid horn" construction could be used in conjunction with the new family of exciters...