Ultrasonic Audio
Ultrasonics can be used to produce highly directional audible sound beams. This technology is based on physical properties of air, particularly that air becomes a nonlinear medium at high sound pressures. Hence, it is possible to transmit two high-intensity ultrasonic tones, say at 100 kHz and 101 kHz, and produce an audible 1 kHz tone as a result of the intermodulation between the two ultrasonic tones. However, the demodulated signal will be significantly distorted, so the audio must be preprocessed to reduce the distortion after demodulation (Pompei, 1999). Although this technology is impressive, it cannot reproduce low-frequency sounds effectively, and it has lower fidelity than standard loudspeakers.