An Alternative design for loudspeakers using the non- linear interaction of sound waves Seminar Ratish J. Punnoose

Basic Idea Ex: An ultrasonic signal at 200kHz and another one at 201kHz will generate a 1kHz tone and a 401kHz signal which is inaudible to the human ear.

Basic Idea (Contd) If an AM signal with a non-zero carrier amplitude is passed through Air, it is self- demodulated

Difficulties Need powerful ultrasonic sources –modulating these without distortion is difficult Need an array of transducers that have to be precisely controlled. Conventional ultrasonic transducer elements introduce too much distortion.

Features Physically small speakers –No need for crossovers, tweeters, woofers, voice coils Power efficient Directionality –Resultant audio retains directionality of ultrasound source –Acoustic Spotlight

Features (Contd) By altering the direction of projection, audio can be made to originate from different locations

History First attempts created a single tone (1975) Audio tone made directive using a transducer array by Ricoh, Japan (1983) Systems developed for audio frequencies at MIT’s Media Labs and at American Technology Corporation (1998). At present, sound quality is a little worse than conventional speakers.

References Yoneyama, M. “The audio spotlight: An application of nonlinear interaction of sound waves to a new type of loudspeaker design”. Journal of the Acoustical Society of America, vol. 73 no.5, p

Question1: Volume range of the ultrasound speaker? –The volume range of the ultrasound speaker is comparable to traditional speakers but the physical size is smaller. The exact amplitude depends upon the amount of power fed in. The speakers can easily take in 50Watts of power. But since their acoustical impedance is better matched to the acoustical impedance of air, they are more efficient and can produce sound several dBs lounder than a traditional speaker with the same power capability.

2. How to use two ultrasounds to create 3D sound from any point? –Currently, the only technology developed is to use the self-demodulation of a single ultrasound signal to create a sound. This wave can be projected onto a surface of the room and then a listener will perceive the wave as originating from that point. The technology as described cannot be used to created 3D sound from any point in space. It can only be used to make sound originate from any surface in a room.