Parametric audio system for operation in a saturated air medium

• US 20050281413A1
• Filed: 07/13/2005
• Published: 12/22/2005
• Est. Priority Date: 08/26/1999
• Status: Active Grant

• Current Assignee: Turtle Beach Corporation
• Original Assignee: American Technology Incorporated (Emerson Electric Company)
• Inventors: Croft, James J. III
• Granted Patent: US 7,596,229 B2
• Time in Patent Office: Days
• US Class Current: 381/77
• CPC Class Codes: H04B 5/00 Near-field transmission systems, e.g. inductive or capacitive transmission systems
• CPC Class Codes: H04B 5/0006 using a receiver structurally associated with a loudspeaker or an earphone
• 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 3/00 Circuits for transducers , loudspeakers or microphones

Abstract

A parametric loudspeaker system and method for reducing distortion in a decoupled audio wave by creating a double sideband parametric ultrasonic signal that substantially approximates a non-square-rooted modulation envelope and emitting a parametric ultrasonic wave that corresponds to the double sideband parametric ultrasonic signal from a parametric loudspeaker at a sufficient amplitude to drive the surrounding air into saturation.

Claims

1. ) A method for reducing distortion in a decoupled audio wave, comprising:

a) creating a double sideband parametric ultrasonic signal that substantially approximates a non-square-rooted modulation envelope; and

b) emitting a parametric ultrasonic wave that corresponds to the double sideband parametric ultrasonic signal from a parametric loudspeaker at a sufficient amplitude to drive the surrounding air into saturation.

19. ) The parametric loudspeaker system of claim 1, wherein the parametric modulator preprocessor creates a single sideband parametric ultrasonic signal.

2. ) A method of minimizing audio distortion by operating a parametric loudspeaker system in a saturated air medium to produce a decoupled audio wave, the method comprising:

a) generating a parametric ultrasonic signal having at least one sideband signal containing audio information;

b) establishing amplitudes of the ultrasonic carrier signal and the at least one sideband signal so that when emitted into a surrounding air medium as a parametric ultrasonic wave, an amplitude of the parametric ultrasonic wave is sufficient to continuously maintain the surrounding air medium in a saturated state; and

c) emitting into the surrounding air medium the parametric ultrasonic wave, comprising an ultrasonic carrier wave and at least one sideband wave, wherein the ultrasonic carrier wave and the at least one sideband wave decouple in air to form the decoupled audio wave.

3. ) The method of claim 2, comprising the more specific step of establishing the amplitude of the ultrasonic carrier signal at a constant level sufficient to continuously maintain the surrounding air medium in the saturated state.

4. ) The method of claim 2, comprising the more specific step of establishing amplitudes of the ultrasonic carrier signal and the at least one sideband signal so that upon a change in input program level signal, a ratio of the amplitudes of the ultrasonic carrier signal and the at least one sideband signal is altered so that the overall amplitude of the parametric ultrasonic wave maintains saturation of the surrounding air medium.

5. ) The method of claim 2, comprising the more specific step of establishing amplitudes of the ultrasonic carrier signal and the at least one sideband signal so that when the maximum input signal is received, the parametric ultrasonic wave is propagated having an optimized modulation index.

6. ) The method of claim 5, comprising the more specific step of establishing amplitudes of the ultrasonic carrier signal and the at least one sideband signal so that when a maximum input signal is received, the parametric ultrasonic wave is propagated having an optimized modulation index of approximately one.

7. ) The method of claim 5, comprising the additional step of further adjusting linear parameters of the parametric ultrasonic signal to compensate for errors in a linear response of the parametric loudspeaker system such that when the parametric ultrasonic signal is emitted, the parametric ultrasonic wave is propagated, having an acoustic modulation index that is optimized.

8. ) The method of claim 2, comprising the additional step of further adjusting linear parameters of the parametric ultrasonic signal to compensate for errors in a linear response of the parametric loudspeaker system such that when the parametric ultrasonic signal is emitted from the parametric loudspeaker system, the parametric ultrasonic wave is propagated, having sidebands that are more closely matched at least at a predefined point in space over at least one sideband frequency range.

9. ) The method according to claim 7 or 8, wherein the linear response of the acoustic output is a function of physical characteristics of the parametric loudspeaker system and an environmental medium wherein the parametric ultrasonic wave is propagated.

10. ) The method according to claim 2, wherein the linear parameters are selected from the group consisting of amplitude, directivity, time delay, and phase.

11. ) The method of claim 2, comprising the more specific step of generating a double sideband parametric ultrasonic signal having a modulation envelope that substantially matches an amplitude modulated version of a non-square-rooted audio input signal.

12. ) A parametric loudspeaker system for operating in a saturated air medium, comprising:

a) ultrasonic carrier and audio input signal sources for providing an ultrasonic carrier signal and an audio input signal; and

b) a parametric modulator preprocessor coupled to the ultrasonic carrier and audio input signal sources, for parametrically modulating the ultrasonic carrier signal with the audio input signal to produce a parametric ultrasonic signal having an amplitude sufficient to continuously maintain operation of the parametric loudspeaker system in the saturated medium; and

c) an electro-acoustical emitter coupled to the parametric modulator preprocessor for emitting a parametric ultrasonic wave at an amplitude sufficient to continuously maintain operation of the parametric loudspeaker system in the saturated medium.

13. ) The parametric loudspeaker system of claim 12, wherein the parametric modulator preprocessor creates the parametric ultrasonic signal having an ultrasonic carrier signal at a constant amplitude sufficient to continuously maintain the surrounding air medium in the saturated state.

14. ) The parametric loudspeaker system of claim 12, wherein the parametric modulator preprocessor is configured to create the parametric ultrasonic signal having at least one sideband signal that increases in amplitude upon an increase in the audio input signal, and decreases in amplitude upon a decrease in the audio input signal, wherein the parametric modulator preprocess is further configured to establish an overall amplitude of the parametric ultrasonic wave to maintain saturation of the surrounding air medium.

15. ) The parametric loudspeaker system of claim 14, wherein the parametric modulator preprocessor is further configured to create the parametric ultrasonic signal having an ultrasonic carrier signal that decreases in amplitude as the audio input signal increases, and increases in amplitude as the audio input signal decreases, wherein the parametric modulator preprocess is further configured to establish the overall amplitude of the parametric ultrasonic wave to maintain saturation of the surrounding air medium.

16. ) The parametric loudspeaker system of claim 12, wherein the parametric modulator preprocessor is further configured to create the parametric ultrasonic signal having an ultrasonic carrier signal having an amplitude so that when the maximum audio input signal is received, the parametric ultrasonic signal has an optimized modulation index.

17. ) The parametric loudspeaker system of claim 16, wherein the optimized modulation index is a modulation index of one.

18. ) The parametric loudspeaker system of claim 12, wherein the parametric modulator preprocessor creates a double sideband parametric ultrasonic signal.

20. ) A method for operating a parametric loudspeaker system in both a non-saturated air medium and a saturated air medium, comprising:

a) receiving at least one audio input signal;

b) generating an ultrasonic carrier signal;

c) parametrically modulating the audio input signal and ultrasonic carrier signal to produce a parametric ultrasonic signal;

d) operating a signal processor in a first predetermined signal processing mode when the parametric loudspeaker is operating in the non-saturated air medium;

e) operating the signal processor in a second predetermined signal processing mode that is distinct from the first predetermined signal processing mode when the parametric loudspeaker is operating in the saturated air medium to create a double sideband parametric ultrasonic signal; and

f) emitting a parametric ultrasonic wave into the air medium to produce a decoupled audio wave.

21. ) The method of claim 20, including the more specific step of receiving at least one complex audio input signal.

22. ) The method of claim 20, including the more specific steps of:

a) operating the signal processor in the first predetermined signal processing mode when the parametric loudspeaker is operating in the non-saturated air medium to create a double sideband parametric ultrasonic signal having a low modulation index; and

b) operating the signal processor in the second predetermined signal processing mode when the parametric loudspeaker is operating in the saturated air medium to create the double sideband parametric ultrasonic signal having a higher modulation index than that of the first predetermined signal processing mode.

23. ) The method of claim 22, further comprising the step of artificially increasing the modulation index of the double sideband parametric ultrasonic signal when the parametric loudspeaker system operates in the saturated air medium.

24. ) The method of claim 22, further comprising the step of gradually increasing the modulation index of the double sideband parametric ultrasonic signal in a transition region between the non-saturated air medium and the saturated air medium.

25. ) The method of claim 23 comprising the more specific step correlating the artificial increase in the modulation index of the double sideband parametric ultrasonic signal with an increase in amplitude of the audio input signal that results in a decrease in distortion level of the decoupled audio wave.

26. ) The method of claim 20, more specifically comprising:

a) operating the signal processor in the first predetermined signal processing mode when the parametric loudspeaker is operating in the non-saturated air medium to create a double sideband parametric ultrasonic signal, wherein a modulation envelope of the double sideband parametric ultrasonic signal substantially matches an amplitude modulated version of a square-rooted audio input signal; and

b) operating the signal processor in the second predetermined signal processing mode when the parametric loudspeaker is operating in the saturated air medium to create the double sideband parametric ultrasonic signal, wherein the modulation envelope substantially matches an amplitude modulated version of a non-square-rooted audio input signal.

27. ) The method of claim 26, wherein the step of operating the signal processor in the first predetermined signal processing mode further includes recursively adjusting the modulation envelope until the modulation envelope substantially matches an amplitude modulated version of a square-rooted audio input signal.

28. ) The method of claim 20, more specifically comprising:

a) operating the signal processor in the first predetermined signal processing mode when the parametric loudspeaker is operating in the non-saturated air medium to create a double sideband parametric ultrasonic signal from a preprocessed square-rooted audio input signal; and

b) operating the signal processor in the second predetermined signal processing mode when the parametric loudspeaker is operating in the saturated air medium to create the double sideband parametric ultrasonic signal from a non-square-rooted audio input signal.

29. ) The method of claim 26 or 28, further comprising changing gradually from the first predetermined signal processing mode to the second predetermined signal processing mode as the parametric loudspeaker transitions from operating in the non-saturated air medium to operating in the saturated air medium.

30. ) A parametric loudspeaker system for operating in both a non-saturated air medium and a saturated air medium, comprising:

a) ultrasonic carrier and audio input signal sources for providing an ultrasonic carrier signal and an audio input signal;

b) a signal processor coupled to the ultrasonic carrier and audio input signal sources, operating in a first predetermined signal processing mode when the parametric loudspeaker is operating in the non-saturated air medium configurable to reduce distortion introduced in a decoupled audio wave in the non-saturated air medium, and operating in a second predetermined signal processing mode when the parametric loudspeaker is operating in the saturated air medium for creating a double sideband parametric ultrasonic signal; and

c) an electro-acoustical emitter coupled to the signal processor for emitting a parametric ultrasonic wave.

31. ) The system of claim 30, further comprising a parametric modulator coupled to the ultrasonic carrier and audio input signal sources, for parametrically modulating the ultrasonic carrier signal with the audio input signal to produce a parametric ultrasonic signal.

32. ) The system of claim 30, wherein the first predetermined signal processing mode is configured to create the double sideband parametric ultrasonic signal having a low modulation index, and the second predetermined signal processing mode is configured to create the double sideband parametric ultrasonic signal having a higher modulation index than that of the first predetermined signal processing mode.

33. ) The system of claim 32, wherein the modulation index of the double sideband parametric ultrasonic signal is artificially increased when the parametric loudspeaker system operates in the saturated air medium.

34. ) The system of claim 32, wherein the modulation index is gradually artificially increased in a transition region between the non-saturated air medium and the saturated air medium.

35. ) The system of claim 33, wherein the artificial increase of the modulation index of the double sideband parametric ultrasonic signal corresponds to an increase in amplitude of the audio input signal that results in a decrease in distortion level of the decoupled audio wave.

36. ) The system of claim 30, wherein the first predetermined signal processing mode is configured to create a double sideband parametric ultrasonic signal having a modulation envelope that substantially matches an amplitude modulated version of a square-rooted audio input signal, and the second predetermined signal processing mode is configured to produce the double sideband parametric ultrasonic signal wherein the double sideband parametric ultrasonic signal having a modulation envelope that substantially matches an amplitude modulated version of a non-square-rooted audio input signal.

37. ) The system of claim 30, wherein the first predetermined signal processing mode is configured to create the double sideband parametric ultrasonic signal from a preprocessed square-rooted audio input signal, and the second predetermined signal processing mode is configured to create the double sideband parametric ultrasonic signal from a non-square-rooted audio input signal.

38. ) The system of claim 30, wherein the parametric modulator and the signal processor are integrated into a single device.

39. ) A parametric loudspeaker system for operating in both a non-saturated air medium and a saturated air medium, comprising:

a) ultrasonic carrier and audio input signal sources for providing an ultrasonic carrier signal and an audio input signal;

b) a parametric modulator coupled to the ultrasonic carrier and audio input signal sources, for parametrically modulating the ultrasonic carrier signal with the audio input signal to produce a double sideband parametric ultrasonic signal having a modulation index;

c) a parametric ultrasonic signal processor coupled to the parametric modulator, configured to artificially increase the modulation index when the audio input signal exceeds a predetermined level; and

d) an electro-acoustical emitter coupled to the parametric ultrasonic signal processor for emitting a parametric ultrasonic wave into a surrounding air medium.

40. ) The parametric loudspeaker system of claim 39, wherein the predetermined level of the audio input signal corresponds to an audio input signal level causing the surrounding air medium to enter into saturation.

41. ) The parametric loudspeaker system of claim 40, wherein the audio input signal level causing the surrounding air medium to enter into saturation corresponds to a decrease in a distortion level of the decoupled audio wave.

42. ) The parametric loudspeaker system of claim 41, wherein the system is configured to maintain the distortion level of the decoupled audio below a predetermined maximum level for all audio input signal levels.

43. ) The parametric loudspeaker system of claim 42, wherein a predetermined maximum distortion level is 5%.

44. ) The parametric loudspeaker system of claim 42, wherein the predetermined maximum distortion level is 3%.