Parametric audio system

• US 20080285777A1
• Filed: 06/20/2008
• Published: 11/20/2008
• Est. Priority Date: 01/14/2000
• Status: Active Grant

• Current Assignee: Frank Joseph Pompei
• Original Assignee: Frank Joseph Pompei
• Inventors: Pompei, Frank Joseph
• Granted Patent: US 8,953,821 B2
• Time in Patent Office: Days
• US Class Current: 381/116
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: B06B 1/0622 on one surface
• CPC Class Codes: B06B 1/0692 with a continuous electrode on one side and a plurality of electrodes on the other side
• CPC Class Codes: G10K 15/02 Synthesis of acoustic waves synthesis of speech G10L13/00
• 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: H04S 2400/09 Electronic reduction of distortion of stereophonic sound systems

Abstract

A parametric audio system having increased bandwidth for generating airborne audio signals with reduced distortion. The parametric audio system includes a modulator for modulating an ultrasonic carrier signal with a processed audio signal, a driver amplifier for amplifying the modulated carrier signal, and an array of acoustic transducers for projecting the modulated and amplified carrier signal through the air along a selected projection path to regenerate the audio signal. The acoustic transducer array includes a backplate having a succession of depressions formed thereon with at least one varying feature and/or dimension, and a membrane disposed along the backplate. The feature and/or dimension of the respective depressions vary so that the center frequencies of the respective acoustic transducers span a desired frequency range, thereby broadening the frequency response of the acoustic transducer array.

Claims

1. A parametric audio system for generating at least one airborne audio beam, comprising:

at least one audio signal source operative to provide at least one audio signal;

a modulator operative to receive a signal representative of the audio signal, and to convert the signal representative of the audio signal into ultrasonic frequencies; and

an acoustic transducer array including at least one acoustic transducer, the acoustic transducer array being operative to receive the converted signal, and to project the converted signal through the air along a selected path, thereby regenerating the audio signal along at least a portion of the selected path, the acoustic transducer array having an associated frequency response,

wherein the acoustic transducer array further includes;

a backplate having a surface and a succession of depressions formed on the surface, the respective depressions having at least one varying dimension; and

a membrane with at least one conductive surface adjacently disposed along the backplate,

wherein the membrane and the succession of depressions define the plurality of acoustic transducers, each of the plurality of acoustic transducers having an associated center frequency determined at least in part by the at least one varying dimension of a respective depression, and

wherein the at least one varying dimension of the respective depressions are configured to vary so that the center frequencies of the respective acoustic transducers span a predetermined frequency range, thereby broadening the frequency response of the acoustic transducer array.

2. The parametric audio system of claim 1 wherein each acoustic transducer is a Sell-type electrostatic transducer.

3. The parametric audio system of claim 1 wherein each acoustic transducer is a Sell-type electrostatic transducer including the membrane, an electrode, and an insulative backplate disposed between the membrane and the electrode.

4. The parametric audio system of claim 1 wherein each acoustic transducer is a Sell-type electrostatic transducer including the membrane, an electrode, and a spacer disposed between the membrane and the electrode.

5. The parametric audio system of claim 1 wherein each acoustic transducer includes the membrane, an electrode, and a DC bias source disposed between the membrane and the electrode.

6. The parametric audio system of claim 5 further including:

at least one driver amplifier coupled between the modulator and the acoustic transducer array, the driver amplifier being operative to receive the converted signal, and to generate an amplified signal representative of the converted signal; and

a blocking capacitor coupled between the driver amplifier and the acoustic transducer array, the blocking capacitor being configured to block the DC bias from the driver amplifier.

7. The parametric audio system of claim 5 wherein the DC bias source is provided by an embedded charge.

8. The parametric audio system of claim 1 further including:

at least one driver amplifier coupled between the modulator and the acoustic transducer array, the driver amplifier being operative to receive the converted signal, and to generate an amplified signal representative of the converted signal; and

a matching filter operative to compensate for a frequency response of a combination of the acoustic transducer array and the driver amplifier.

9. The parametric audio system of claim 1 further including:

at least one driver amplifier operative to receive the modulated carrier signal, and to generate an amplified signal representative of the modulated carrier signal;

wherein the acoustic transducer array has a mechanical-acoustic resonance; and

wherein the driver amplifier includes an inductor coupled to the acoustic transducer array to form a resonant circuit having a resonance frequency approximating both the frequency of the mechanical-acoustic resonance and the frequency of the ultrasonic carrier signal.

10. The parametric audio system of claim 9 wherein both the frequency of the mechanical-acoustic resonance and the frequency of the ultrasonic carrier signal are greater than or equal to 45 kHz.

11. The parametric audio system of claim 9 wherein both the frequency of the mechanical-acoustic resonance and the frequency of the ultrasonic carrier signal are greater than or equal to 55 kHz.

12. The parametric audio system of claim 9 wherein the driver amplifier further includes a damping resistor coupled between the inductor and a capacitive load of the acoustic transducer array.

13. The parametric audio system of claim 9 wherein the driver amplifier further includes a step-up transformer, and the inductor is provided by the step-up transformer.

14. An adaptive parametric audio system for generating at least one airborne audio beam, comprising:

at least one audio signal source operative to provide at least one audio signal;

a peak level detector operative to receive the audio signal, and to generate a first output signal;

a signal conditioner operative to receive a sum of the audio signal and the first output signal generated by the peak level detector, and to generate a second output signal, the second output signal being representative of a non-linear inversion of the audio signal;

a modulator operative to receive the second output signal generated by the signal conditioner, and to convert the second output signal into ultrasonic frequencies, the converted signal having an associated modulation depth; and

an acoustic transducer array including at least one acoustic transducer, the acoustic transducer array being operative to receive the converted signal, and to project a primary ultrasonic beam through the air along a selected path, thereby generating an audible secondary beam along at least a portion of the selected path, the primary ultrasonic beam having an associated amplitude,

wherein the modulator is operative to control the modulation depth of the converted signal to maximize the modulation depth, while maintaining the modulation depth below a predetermined maximum value, and

wherein one or more of the peak level detector and the signal conditioner are operative to control the amplitude of the primary ultrasonic beam to maintain an audible level of the secondary beam, and to minimize generation of ultrasound in the absence of an audio signal.

15. The adaptive parametric audio system of claim 14 wherein the primary ultrasonic beam is defined as

p₁(t)=P₁E(t)sin(ω

_ct),

wherein “

P₁”

is a carrier amplitude, and “

ω

_c”

is a carrier frequency, and “

E(t)”

is defined as

E(t)=(1+∫

∫

mg(t)dt²)^1/2,

wherein “

m”

is the modulation depth and “

g(t)”

corresponds to the audio signal, g(t) being normalized to a peak value of unity.