How Do Directional Speakers Work?

1. The emergence of directional speakers

You're walking past the Mona Lisa in the Louvre Museum and you don't even notice it, but, as you pass, the woman in the painting starts to tell you her story - who she is, she how it was drawn, and how she lived a cramped life for nearly 500 years within this simple wooden frame. Under the right circumstances, you walk through the gallery and the same thing happens to the next painting, and the next, and the next!

Sound like a joke? This will happen as museums, galleries and exhibitions begin to take advantage of a new type of museum directional speakers. Directional speakers can position sound in precise locations like a stage spotlight. Directional loudspeakers are used for everything from high-tech megaphones on navy ships to billboards that appeal to your ears and eyes. So how do directional speakers work?

2. How do directional speakers work?

Directional loudspeakers work in a completely different way than traditional speakers. The big difference is that they don't generate ordinary audible sound waves through a single moving solenoid and cone. Instead, they use ultrasonic waves generated by an array of electronic devices called piezoelectric transducers at frequencies too high to be heard by the human ear. Ultrasound is used because its higher frequency waves have correspondingly shorter wavelengths and spread less as they propagate. Also, having an array of many small transducers results in less dispersion of sound than a single large transducer.

Ultrasonic waves are transmitted from the ultrasonic directional speaker in the form of a narrow focused column, like a flashlight beam. But when it hits something, it goes back to the normal sound you can hear. So, in the example of the talking Mona Lisa, there is a hidden directional speaker next to the picture. It emits ultrasonic waves that travel from the front of the screen and gradually dissipate into the room. If someone walked into the beam, the ultrasonic waves would collide, return to normal sound, and magically hear the Mona Lisa.