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Re: How to get the most efficiency in horns from the throat design?

The horn MOUTH size is determines the smoothness of the frequency response, NOT the efficiency.

The horn mouth size is related to an antenna suffering reflections due to an impedance mismatch if the mouth is undersized. The idea is to match the mouth to the impedance of the radiation angle it exhausts (or transmits) into.

A mismatch (typically from too small of a mouth) will cause reflections back down the horn to the throat seen by the driver as changes in acoustic impedance (variations in reactance).

A general rule of thumb also described in Keele's paper is the mouth size (Sm) is commonly acepted as mouth CIRCUMFERENCE = WAVELENGTH (Fc). This is for a 1/2 space radiation angle (floor-standing, etc). The mouth can be half of that value for 1/4 space, and one-quarter the 1/2 space mouth size value for corner placement (1/8 space).
Some go even further - the 1980's Gillum/Klipsch MCM patent indicates that the mouthsize can be as small as 1/12th wavelength (Fc) when properly annulled.

This would shorten the horn quite a bit. Should the throat size also be made smaller? Won't work - because other considerations of performance are at play in the throat size.

So the bottom line is that 1/4 wavelength HORN PATHWAYS are not required when other considerations are at play in the horn design. Hopefully, this does not confuse anyone.

DM


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