Most speakers emit sound in all directions because they are relatively small compared to the wavelength. Audible sounds have wavelengths of up to several meters, so an acoustically “large” speaker might not even fit in your house.

Fortunately, strong modulated ultrasound is slowly converted to normal sound as it passes through the air. Ultrasound wavelengths are typically around a centimeter allowing a compact directional speaker.

Maurycy used this to make a “large” directional speaker using an array of ultrasonic transducers.

These transducers can’t be driven from a regular audio amplifier, because they have very different requirements then normal speakers. They are sensitive to charge, and need both high voltage and high current, unlike speakers which need some current but minimal voltage.

The beam also bounces off objects, making it seam like the sound is coming from somewhere else. Strangely, the sound is actually louder when bouncing off a hard object like a wall then when listening to it directly. I’m guessing that the surface creates areas of higher ultrasound intensity, creating more sound then would be created otherwise.

It works quite well for rickrolling, especially if the sound is bounced of a wall to make it harder to track down. This is my only pranking device that has everyone asking how it works.

On the other hand, it’s not really a good speaker. It has virtually no bass response, tends to distort louder audio, and is not all that loud.

See the video below and reead more in the post here. The work is under a Creative Commons Attribution-ShareAlike 4.0 International License.