Using a C.A.T. Scanner to Photograph Sound

Think about how useful it would be if you could see sound. Or, better yet, if you could photograph sound. The scientific and practical potential would be immense. But that’s impossible, because soundwaves are invisible, right? Not so fast! You can see soundwaves under specific conditions and can capture images of them with the right equipment. To achieve that for the purpose of designing a volumetric display, PlasmatronX developed this C.A.T. Scanner.

To understand how this works, first consider that soundwaves are just vibrations traveling through a physical medium—anything other than a vacuum. For our ears, that usually means vibrations moving through air. Because you can’t see the air, you can’t see the soundwaves.

But then consider what might change if you made the air visible. For example, if you put some light smoke in the local area, you could see some minor disturbances caused by the soundwaves.

To approach that in a practical way, PlasmatronX takes photographs through a small slit. That has the effect of “magnifying” the ripples in the air caused by the soundwaves, which are visible — but nearly imperceptible — as tiny changes in refraction, without any smoke needed. That is, however, just a 2D image and it isn’t very useful for seeing the volume of the soundwaves and their location in 3D space.

To reach that next step, PlasmatronX build his C.A.T. (Computerized Acoustical Tomography) Scanner. It is a 3D-printed, stepper-actuated rig to rotate the subject in front of the camera, similar to how a photogrammetry 3D scanner works. As it the subject turns, a Raspberry Pi 4 Model B triggers the shutter and captures those slit images.

The result from a scan is a pile of images that really just look like noisy garbage at first glance. But with a lot of mathematical processing that I can’t even begin to understand, those are translatable to data that ultimately becomes something like a 3D point cloud of air disturbances caused by soundwaves.

Scanning an acoustic levitator, PlasmatronX can see exactly where the soundwaves are in space. And he’ll be able to use that information to development a volumetric display based on the same principles, as he can gather empirical data to supplement the theoretical projections.