From: Bret <>
>
> Great comments, Eric.=20
> Diffraction at the edge of the parabola is yet another problem not
> addressed by any of the papers nor is there a simulation offered.=20
> Regarding accuracy of the parabolic shape, I have read that for RF
> purposes that you want accuracy to 1/10 wavelength.=20
> Regarding dispersal over time, Backman shows this in impulse responses.
> There can be a sort of pre-echo.
Both Sten's paper and the Army one show the diffraction. Sten's in the
measured polar pattern of a real parabolic, the Army in it's calculated
polar pattern's. Though these two differ quite a bit in the polar
pattern shown. I trust Sten's far more at least for the particular
parabolic as it's real measurements.
Remember, sound is working with particles with real mass. Radio and
light work with essentially massless particles. Much easier to diffract
those.
Again, RF accuracy requirements are for radically different purposes
than sound parabolics.
Walt
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