Combining the ideas of parabolic microphone/speaker and shotgun microphone, I wonder whether I could project high frequency sound (15 kHz for instance) fairly directionally with a small speaker/transducer at the focus of a parabola with 10 cm diameter, which in turn is attached to one end of a piece of 10 cm diameter pipe.
Normally the beam angle in radians is lambda/D (where lambda = wavelength, D = diameter of parabola), but would attaching it to the pipe help much? And how long does the pipe need to be?
I've found formulas/instructions on the web for building approx. parabolas by marking out a bunch of inversely tapering wedges on paper, cutting them out, and sticking them together. Would paper coated with transparent plastic film work for reflecting sound?
thanks, Bob