As far as I have been able to determine, these one piece cast H-811 horns were only produced for a year or less in about 1952 or '53. They replaced the earlier H-808 800Hz. eight cell multicellular horn which had been made in several versions dating back to 1937. Radial horns, an invention of RCA engineer John Volkmann, were all the rage in the early 1950s after the introduction of RCA's new radial horn designed for theatre, PA and monitoring. The radial horn combined the excellent directivity of the conical horn in the horizontal, while sacrificing directivity in the vertical but maintaining exponential loading with the heavily curved upper and lower walls. This and later 811 horns would be classed as modified radial horns due to the narrower angle of the initial throat section, which concentrated high frequencies and made for a nice looking on axis response curve. Most of the RCA horns had a narrow throat as well.
Anyway, these H-811s are quite scarce. I've never owned one, though a friend has managed to collect a half dozen.
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