Patent EA-001423-B1 (EA)
Title: Acoustic heterodyne device and method
Inventor: NORRIS ELWOOD G
IPC: H04R3/02
Filed: 1997-07-16
Abstract: 1. A system for indirectly generating and enhancing at least one audible frequency from within a resonant cavity by interaction between at least two ultrasonic frequency signals of different frequency, said system comprising: a resonant cavity which enables interacting ultrasonic signals to interfere in accordance with acoustic heterodyning to generate an audible sound output within air contained within the resonant cavity, said resonant cavity including an opening for permitting entry of the ultrasonic signals; an ultrasonic frequency emitter contained within one of a stereo headphone, a hearing aid, or an audio headset, said emitter being directed toward the opening of the resonant cavity for transmitting first and second ultrasonic signals along a common axis into the resonant cavity without indirect reflection from other sources; modulating means coupled to the ultrasonic frequency emitter for generating the second ultrasonic frequency having a difference in value relative to the first ultrasonic frequency which is equal to the at least one audible frequency; means for concurrently operating the ultrasonic frequency emitter and the modulating means to generate the first and second ultrasonic signals, and  means for directing the first and second ultrasonic signals into the resonant cavity. 2. A method for indirectly generating and enhancing at least one audible frequency from within a resonant cavity using at least two ultrasonic signals of different frequency, the method comprising the steps of: 1) transmitting a first ultrasonic signal into the resonant cavity using an emitter contained within one of a stereo headphone, a hearing aid, or an audio headset; 2) concurrently transmitting a second ultrasonic signal from said emitter into the resonant cavity along a common axis with the first ultrasonic signal, wherein the second ultrasonic signal has a frequency which differs from the first ultrasonic signal by a value generally equal to the at least one audible frequency, and wherein the resonant cavity amplifies the interference between the first and the second ultrasonic signals; 3) whereby at least one audible frequency arises from the interference of the first and the second ultrasonic signals within the resonant cavity. 3. A method for indirectly generating omni-directional sound as part of an audio sound system for entertainment use by a listener and having a remote virtual source distant from the listener, the method comprising the steps of: 1) emitting a first ultrasonic wave train including a base frequency into a region of air from a transducer means; 2) concurrently emitting a second ultrasonic wave train from said transducer means into the region to thereby interact with the first ultrasonic wave train, wherein the second ultrasonic wave train has a base frequency equal to the base frequency of the first ultrasonic wave train and is projected along a common axis for both the first ultrasonic wave train and second ultrasonic wave train, which common axis is the only transmission path between said transducer means and a reflective surface of an object which is distant from the listener; 3) varying the base frequency of the second ultrasonic wave train through a frequency range corresponding to a sum of the base frequency and the new audible sound wave train; and 4) reflecting the first and second ultrasonic wave trains from said reflective surface to generate omni-directional dispersion of audible sound leaving a virtual, localized sound source at the reflective surface. 4. The method as defined in claim 3 wherein the method comprises the additional step of generating both the (i) first ultrasonic frequency and (ii) the second ultrasonic frequency from a single ultrasonic generating means, thereby eliminating frequency drift between the first and the second ultrasonic frequencies. 5. A method as defined in claim 3, further comprising the step of controlling the movement and orientation of the wave train with a computer driver.