A Laser and a Few Scraps Create Speakers Anyone Can Build

Patients within MRI scanners have a difficult time to begin with. You have the continuous thump of the machine while they lie still for what seems like an eternity. Headphones are supposed to help pass the time and block out some of the noise, but standard issue designs just don’t cut it. The common restriction is no magnets or cables near the equipment, so technicians simply pipe the audio through plastic tubes, resulting in a faint and muffled sound.

One inventor decided to do something about it. He came up with a solution based on a principle discovered in 1880 by Alexander Graham Bell. The concept is that if you shine a really bright beam of light onto particular materials, it will heat them up sufficiently to produce sound waves. There is no need for speakers, magnets, or coils; simply a laser beam to carry the communication.

The setup begins with one of those five-watt laser engraver modules that you can purchase online for a cheap price. All you have to do is connect it to an audio source, and your music or speech will regulate the laser power. Most of these modules can accept a pulse signal that replicates the audio waveform, so pulsing the beam a thousand times per second produces a clear 1000-hz tone or a complete song with all the notes.

Gold leaf is actually a fantastic starting point because it absorbs blue light well while remaining light enough to allow heat to travel through it and into the surrounding air. If you point the modulated beam to a small portion of it, the quick heating expands the air in sync with the music, allowing you to distinguish individual tracks.

You can also utilize soot, which is easy to obtain. Simply hold a glass slide or the interior of a small glass pipe over a flame for a few seconds to produce a thin black covering. The soot will then absorb the laser energy and transfer the heat swiftly. Place the coated glass in the beam path, and music will begin to play again. The results with a pipe were a little mixed because it spread the sound too much, but a simple glass slide worked perfectly.

Certain gases absorb light immediately, without first passing through a solid surface. Nitrogen dioxide, the orange gas used in certain laboratory procedures, is an excellent example. Direct the laser into a tiny container of it, and the sound will be clearer than with solids. Be careful with this thing; it’s not without risk, but the payout is worthwhile.

You can create a personal listening device by printing a small earphone shape on a 3D printer. Then just line the interior cavity with gold leaf and send the laser through a fiber-optic wire directly into it. The light will strike the gold with no stray rays in the way, and the sound will travel directly to your ear. One builder tried it and could hear his own speech echoing back at him through the device.
[Source]