Around Halloween of 2022, I wondered if I could focus sound much like a laser, with the idea that I could make it sound like something was crawling around behind a wall. Upon further researching, I learned that this sort of thing does exist, and it’s called a directional speaker. By modulating an audible wave over an ultrasonic wave, I could achieve a “laser-like” focus of sound via the ultrasonic carrier wave that would demodulate into audible sound when it made contact with a surface.
Pictured above is what I currently have built. It functions! Sorta. Its really quiet. You can’t really hear anything unless you put your ear right up to it. Unfortunately, I decided to build this over winter break that year and had none of the resources on campus that I’d usually have, like an oscilloscope, to check my work along the way. Instead, I just built the whole thing hoping it would work, and as most things like that go, it doesn’t. Having come back to campus and checked it out, there are a few issues:
the expected output amplitude is much lower, leading me to believe my voltage regulator isn’t passing enough voltage.
to make this work it also requires getting accuracy down to a couple picofarads, and with what I had at the time it was quite difficult to hit that accuracy.
There is also a large DC offset which I wasn’t expecting, so I imagine I have a short somewhere in this circuit.
Now that I am back on campus, I am going to take it apart and rebuild, this time being a bit more careful with the construction. This project is still in development when I have free time, but it has taken less priority over classes and clubs.
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Directional Speaker
