Parametric Audio System

• US 20120051556A1
• Filed: 08/24/2011
• Published: 03/01/2012
• Est. Priority Date: 07/16/1998
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Pompei, F. Joseph
• Granted Patent: US 9,036,827 B2
• Time in Patent Office: Days
• US Class Current: 381/77
• CPC Class Codes: G10K 15/02 Synthesis of acoustic waves synthesis of speech G10L13/00
• CPC Class Codes: H04R 2201/401 2D or 3D arrays of transducers
• CPC Class Codes: H04R 2217/03 Parametric transducers where sound is generated or captured by the acoustic demodulation of amplitude modulated ultrasonic waves
• CPC Class Codes: H04R 2430/20 Processing of the output signals of the acoustic transducers of an array for obtaining a desired directivity characteristic H04R2203/12 takes precedence
• CPC Class Codes: H04R 3/04 for correcting frequency response
• CPC Class Codes: H04R 3/12 for distributing signals to two or more loudspeakers specially adapted for hearing aids H04R25/407

Abstract

Ultrasonic signals are used to transmit sounds from a modulated ultrasonic generator to other locations from which the sounds appear to emanate. In particular, an ultrasonic carrier is modulated with an audio signal and demodulated on passage through the atmosphere. The carrier frequencies are substantially higher than those of prior systems, e.g., at least 60 kHz, and the modulation products thus have frequencies which are well above the audible range of humans; as a result, these signals are likely harmless to individuals who are within the ultrasonic fields of the system. The signals may be steered to moving locations, and various measures are taken to minimize distortion and maximize efficiency.

Claims

1. A method of selectively transmitting audio signals to a selected location, the method comprising the steps of:

(a) modulating an ultrasonic carrier with at least one audio signal, the frequency of the carrier being sufficiently high that all of the components of the modulated carrier have frequencies above the range in which the human auditory system responds; and

(b) directing a beam containing the modulated carrier toward the location, whereby the audio signal appears to emanate therefrom or is confined thereto.

2. The method of claim 1 wherein the carrier is generated by at least one capacitive ultrasonic transducer having a mechanical resonance frequency, and further comprising the step of driving the at least one transducer with a driver including an inductor coupled with the transducer capacitance to provide an electrical resonance corresponding to the mechanical resonance of the transducer.

21. The method of claim 1, wherein the amplitude level of the modulated ultrasonic carrier is adjusted in response to a change in the audio signal, and the adjustment to the modulated ultrasonic carrier is temporally asymmetric with the change in the audio signal.

23. The method of claim 1, further comprising enhancing harmonic effects of the emanating audio signal, such that the emanating audio signal is substantially louder for a given ultrasonic intensity.

24. The method of claim 23, wherein enhancing harmonic effects comprises selectively bypassing preconditioning for part of the audio signals or overmodulating the carrier.

25. The method of claim 1, further comprising selectively bypassing preconditioning for part of the audio signals.

26. The method of claim 1, further comprising overmodulating the carrier.

27. The method of claim 1, wherein the carrier is generated by at least one ultrasonic transducer including a PVDF membrane, and the method further comprises employing an electric field to bias the transducer.

28. The method of claim 1, wherein the carrier is generated by at least one ultrasonic transducer, and the transducer has a substantially triangular response centered on the frequency of the carrier, and the method further comprises employing a re-emphasis filter to correct for non-uniform transducer response.

29. The method of claim 1, wherein the location is a listener'"'"'s ear, the method further comprising producing binaural audio.

30. The method of claim 1, wherein the location is a displayed item, a work cubicle, a location near a dangerous area, or a blind person;

or the location is the position of a person to form a personal audio source.

3. -13. (canceled)

14. A method of transmitting audio signals, the method comprising the steps of:

(a) modulating an ultrasonic carrier signal with audio signals;

(b) radiating the modulated carrier as ultrasonic signals at an output level; and

(c) compensating for distortion arising from atmospheric propagation of the radiated ultrasonic signals;

wherein the compensation is based on at least one of (a) an assumed distance, (b) airborne humidity level, and (c) an amplitude of the modulated carrier, or the method further comprises the step of determining a distance to a listener, compensation being based on the determined distance.

15. -16. (canceled)

17. A method of transmitting audio signals, the method comprising the steps of:

(a) modulating an ultrasonic carrier signal with audio signals;

(b) radiating the modulated carrier as ultrasonic signals at an output level; and

(c) controlling ultrasonic signals to as to avoid subjecting listeners to unsafe output levels comprising (i) determining a distance between the transducer and a listener; and

(ii) controlling the output level based on the sensed distance.

18. -20. (canceled)

22. (canceled)