Audible frequency amplitude modulation of 20kHz carrier for diffraction demo.
I am attempting to build an audio projector that takes advantage of the low diffraction of high frequency audio waves. Audible range frequencies diffract more than, say 20kHz, so I want to modulate a 20kHz carrier wave by an audible range source, hoping that the carrier wave will be maintained for longer distances (like a beam of sound), and that my ear will ultimately perceive the audible input being delivered on the carrier wave.
My question is: Should I be aiming to produce an AM Radio type modulation that has an envelope of the input both above and below, mirrored across the x axis? Or should I try to make it so the final signal has the same shape as the source wave, just filled in with 20kHz carrier?
Also, is a square wave carrier sufficient, or will it need to be a sine wave?