Possibly a sound idea

Now that I have a 3D printer at home, I realize that I can do something I’ve been wanting to do for a very long time, but never had a good way to do — audio holography. The basic idea is to create a surface with just the right pattern of little bumps and valleys in it (all calculated on a computer, of course). If you design these bumps and valleys just right, the surface acts as an audio hologram.

It works like this: Once you have this surface, you send a pulse of sound that has a very high frequency, say around 300Khz, toward the bumpy surface. At that frequency the wavelength of sound through air is around one millimeter. Because of the little bumps and valleys, the sound reaching the surface bounces off a little sooner in some places (the hills) and a little later in other places (the valleys).

These slight variations kick the reflected sound out of phase in interesting ways. Using computer software, you can arrange the bumps and valleys so that the sound comes back into phase at just the points in space where you want it to.

None of this would be all that interesting to me if there were no way to create a visual display out of this. Fortunately, you can do various optical tricks to convert fine vibrations of air into something that people can see, such as virtual objects that appear to float in mid-air.

The part of all of this that I was always missing was how to create an accurately contoured surface. I knew how to write the computer program to make the right little bumps and valleys, but I didn’t know how to print out the 3D shape in the real world.

Well, now I do. 🙂

Of course it will take a more advanced technology to do what we really want — to create an animated audio hologram. That’s the true long term goal, but the technology needed for that is way beyond my budget.

Meanwhile, I can print out one of these audio-holographic plates with my handy dandy 3D printer. And that’s all I need to get started.