The directional speaker is an amazing useful invent technology. It will help our future to reduce the noise pollution. Imagine that you stand in-front of Mona Lisa in the Louvre art gallery. Just only you can hear some story about this famous picture without any earphone. People surround you cannot hear anything at all. When you move to the other picture, you can heard another story relate to the picture you are watching.
How can they can do that. It is a new directional speaker technology.
How does the normal speaker works.
In order to translate an electrical signal into an audible sound, speakers contain an electromagnet: a metal coil which creates a magnetic field when an electric current flows through it. This coil behaves much like a normal (permanent) magnet,.
Inside a speaker, an electromagnet is placed in front of a permanent magnet. The permanent magnet is fixed firmly into position whereas the electromagnet is mobile.
As pulses of electricity pass through the coil of the electromagnet, the direction of its magnetic field is rapidly changed. This means that it is in turn attracted to and repelled from the permanent magnet, vibrating back and forth.
The electromagnet is attached to a cone made of a flexible material such as paper or plastic which amplifies these vibrations, pumping sound waves into the surrounding air and towards your ears
In this kind of sound waves, we can heard the sound every where even behind of the speaker
How does the directional speaker works
The piezoelectric transducers in the directional speaker produce two different ultrasonic waves. In this image we can see the red and blue wave
Both of which are at frequencies way too high to hear (ultrasonic wave).
When the two waves hit something (your ears), they interfering and producing a new wave (green). This wave has frequency is much lower—equal to the difference in frequencies between the two original waves. This is a wave you can hear.
When there’s no-one standing in the beam. The (red and blue) waves keep on traveling without producing an audible sound wave. Therefore, if there’s no-one standing in front of the speaker, there’s nothing you can hear.
The inventor of directional speaker
The kind of directional-speaker technology was originally developed by naval scientists who were using parametric arrays with sonar systems. One of the first people to perfect the technology for use with audible sound was US inventor Woody Norris. And his system, called HyperSonic Sound (HSS)
Check out this movie to understand how does the directional speaker work. Is is called SRAY. It is a project very success in kickstater.com