Walt, I didn't know you had Sten's paper!
Bret - you can read it at Walt's, and I'll stall my letter for now.
Klas.
At 17:46 2004-02-21 -0500, you wrote:
>From: Bret <>
>
>> I have demonstrated above that the the ratio of dish diameter to
>> wavelength in common audio dishes are equal or greater than this ratio
>> for common rf dishes.
>>
>> Please show me another more complicated formula for parabolic gain. I
>> am all ears
>
>One of the major differences is that rf is moving at the speed of light
>essentially massless movement. But, sound is moving particles of
>significant mass that are all but standing still by comparison. Treating
>it as a transverse wave is what gets things not agreeing with actual
>field experience. Sound is movement of particles of significant mass
>along the line of travel, which is a type of wave but has other
>characteristics. Which is why a parabolic much smaller than the
>wavelength still reflects the sound. With all that goes along with that.
>
>Read Sten's paper for starters lots of formula to play with.
>http://naturerecordist.home.mindspring.com/Parabolic.pdf
>
> Parabolics start to have gain at a point where their size is 1/64th of
>the wavelength according to Sten's paper. Let's see, for a 22" Telinga
>that's a wavelength of about 117 feet, my that's a low frequency. Now,
>that's the point where the gain starts to increase, it's still 1:1 at
>that point. But from there on up you do get rapidly increasing gain.
>Especially with something like the Telinga, with it's depth/focal length
>greater than 1 it avoids most of the standing wave problem. What I get
>in the field agrees quite well with Sten.
>
>The 1/1 wavelength to diameter point is just the starting point where
>the already quite significant gain goes to being straight 6dB/octave.
>It's not the start of gain by any means. For the Telinga theoretically
>at the 1/1 point the gain is about 20dB. It passes 6dB gain at a
>wavelength of about 15'.
>
>Note within the limitations of the mic mounted in the parabolic there is
>no frequency point where the sound is suddenly cut off. Below the 1/64th
>point it's just as if the reflector was not there, ie the mic picks up
>the sound like it was a bare mic (though the reflector may act as a
>sound barrier from behind). No sudden transition.
>
>Walt
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>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
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Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
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