audible resultant from two supersonic frequencies?

[Nathan Bower]

> >What
> > would be the point of experimenting with sounds we can't hear?
>
> The question is,  are there AUDIBLE resultants, which is a sound
> we CAN HEAR, that is produced from two frequencies we can't hear
> such as 20,440 - 20,000 hz which gives on paper 440 hz  or A440
> which certainly we can hear.   An experiment has to be conducted
> to determine if this is true.   I am wondering if this has ever
> been done, and if not how might it be done?   I need two audio
> frequency generators?   Can the computer give hz over 20,000?
> How bout tune lab? Would I need two?     ---rm   (the "r" stands
> for 'ric' and the "m" stands for "M")

I for one can't hear above 16Khz anymore, at almost any SPL.

I think this study shows that audible resultants can be made by ultrasound
frequencies, but whether this is a beat frequency phenomenon or not is
anyones guess.

http://www.spie.org/web/oer/october/oct00/indfocus.html

"Ultrasound has the advantage of being highly directional (compared to
audible sound) because of its relatively short wavelength. Decades ago,
researchers realized they could exploit this property to create directional
sound beams by using intermodulation of ultrasound beams in air. This is
possible because at high enough intensity (above 125 dB </snip>"

N