Have you ever wondered what sound waves would look like. Yes, we all know what a wave looks like.
But if you asked me what a 400Hz looks like, I would probably draw a sine wave on a piece of paper and that would be it. I might calculate the length of the wave and tell you that it is 850mm. The velocity of the wave divided by the frequency.
For sound waves of 400Hz in air that would be 343 meter/second divided by 400 = 0.85 meter.
Time for some visuals.
In the past I experimented a lot with slow shutter speed photography and arduino's. Those two could be the answer to my quest. Showing a sound wave with the correct length.
Another similar project on Instructables: Imprint invisible sound and radio waves onto your retina: Augmented reality with perfect alignment by Steve Mann
I did some test with an arduino uno, M0. But finally settled on a teensy 3.x, because it gave me the fasted ADC sound wave sample speed.
What you need to build the SoundWave Printer:
330 Ohm resistor