Wednesday, September 21, 2005
Using a beam of inaudible ultrasound as a carrier for audible sound has been on the drawing board for a while, but has yet to find a compelling application. But now Seiko Epson
of Tokyo, Japan, proposes using the technique to let a small video projector beam pictures and sounds into a room, without the need for loudspeakers.
Speech or music is amplitude-modulated on ultrasound at over 40 kilohertz ? rather like the way that Medium and Long Wave radio waves carry AM radio. Only a small transducer, a few centimetres wide, is needed to beam the AM ultrasound from the front of the projector. The beam bounces off the screen and back into the room and only those in the beam?s line of fire hear the sound - perfect for keeping sensitive neighbours happy.
Before the show, the projector is put in a test mode that displays a picture on screen which shows where the chairs should be put so people can hear the sound. The listening area can be modified by altering the distance and angle of the ultrasound beam to the screen, while using two beams creates stereo sound.
Read the sound projector patent here