US-12627933-B2 - Simultaneous dual use of an acoustic device as a loudspeaker and microphone

Abstract

Operating an electrostatic acoustic device simultaneously as a speaker and as a microphone. The electrostatic acoustic device includes a membrane and an electrode disposed proximate to the membrane. An input varying audio signal is input to the electrostatic acoustic device. The membrane is configured to respond mechanically to a varying electric field responsive to the varying audio signal input. A portion of the input varying audio signal is tapped to produce a reference signal. A signal is detected responsive to motion of the membrane, to convert the signal to an output varying voltage signal. The output varying voltage signal is compared to the reference signal to produce a microphone signal. The microphone signal is responsive to motion of the membrane induced by air pressure variations of ambient sound.

Inventors

• Gabriel Zeltzer
• Meir SHAASHUA

Assignees

• WAVES AUDIO LTD.

Dates

Publication Date

20260512

Application Date

20221109

Priority Date

20211117

Claims (20)

1. 1 . A method comprising: configuring an electrostatic acoustic device to operate simultaneously as a speaker and as a microphone, wherein the electrostatic acoustic device includes a membrane and an electrode disposed proximate to the membrane, by enabling: applying an input varying audio signal input to the electrostatic acoustic device, wherein the membrane is configured to respond mechanically to a varying electric field responsive to the varying audio signal input; tapping a portion of the input varying audio signal to produce a reference signal; detecting motion of the membrane thereby receiving a signal responsive to the motion of the membrane, and converting the signal to an output varying voltage signal; and comparing the output varying voltage signal to the reference signal to produce a microphone signal, wherein the microphone signal is responsive to motion of the membrane induced by air pressure variations of ambient sound.
2. 2 . The method of claim 1 , further comprising: inputting the input varying audio signal to the membrane; and connecting the electrode to a high voltage DC bias.
3. 3 . The method of claim 1 , further comprising: inputting the input varying audio signal to the electrode; and connecting the membrane to a high voltage DC bias.
4. 4 . The method of claim 1 , wherein the electrode includes a first electrode disposed on a first side of the membrane and a second electrode disposed on a second side of the membrane opposite the first side, wherein the input varying audio signal includes an inverted varying audio signal input to the first electrode and a non-inverted varying audio signal input to the second electrode and wherein the reference signal is responsive to the inverted varying audio signal input and the non-inverted varying audio signal input.
5. 5 . The method of claim 1 , further comprising: injecting a probe signal varying at radio frequency into an input of the electrostatic acoustic device; said detecting by converting a current or charge signal output to a modulated voltage signal, wherein the current or charge signal includes an audio signal varying at audio frequencies modulating the radio frequency of the probe signal; demodulating the modulated voltage signal to produce the output varying voltage signal varying at audio frequency.
6. 6 . The method of claim 5 , wherein the output varying voltage signal varying at audio frequency is obtained by homodyne detection of the modulated voltage signal at radio frequency.
7. 7 . The method of claim 5 , further comprising: phase and frequency locking the modulated voltage signal at radio frequency and a radio frequency carrier signal responsive to the probe signal varying at radio frequency.
8. 8 . The method of claim 5 further comprising: generating an oscillator signal synchronous with a radio frequency carrier of the modulated voltage signal; outputting the probe signal responsive to the synchronous oscillator signal.
9. 9 . The method of claim 5 , wherein said demodulating the modulated voltage signal is performed by low pass filtering.
10. 10 . The method of claim 5 , further comprising performing said demodulating by rectifying prior to low pass filtering.
11. 11 . A driver of an electrostatic acoustic device including a membrane and an electrode disposed proximate to the membrane, the driver configured to: operate the electrostatic acoustic device simultaneously as a speaker and as a microphone by: applying an input varying audio signal input to the electrostatic acoustic device, wherein the membrane is configured to respond mechanically to a varying electric field responsive to the varying audio signal input; tapping a portion of the input varying audio signal to produce a reference signal; detecting motion of the membrane thereby receiving a signal responsive to the motion of the membrane, and converting the signal to an output varying voltage signal; and comparing the output varying voltage signal to the reference signal to produce a microphone signal, wherein the microphone signal is responsive to motion of the membrane induced by air pressure variations of ambient sound.
12. 12 . The driver of claim 11 , further configured to: input the input varying audio signal to the membrane; and connect the electrode to a high voltage DC bias.
13. 13 . The driver of claim 11 , further configured to: input the input varying audio signal to the electrode; and connect the membrane to a high voltage DC bias.
14. 14 . The driver of claim 11 , wherein the electrostatic acoustic device includes a first electrode disposed on a first side of the membrane and a second electrode disposed on a second side of the membrane opposite the first side, the driver configured to: input an inverted varying audio signal to the first electrode and a non-inverted varying audio signal input to the second electrode and wherein the reference signal is responsive to the inverted varying audio signal input and the non-inverted varying audio signal input.
15. 15 . The driver of claim 11 , further configured to: inject a probe signal varying at radio frequency into an input of the electrostatic acoustic device; convert a current or charge signal output from the electrostatic acoustic device to a modulated voltage signal, wherein the current or charge signal includes an audio signal varying at audio frequencies modulating the radio frequency of the probe signal; and demodulate the modulated voltage signal to produce the output varying voltage signal varying at audio frequency.
16. 16 . The driver of claim 15 , further configured to obtain the output varying voltage signal varying at audio frequency by homodyne detection of the modulated voltage signal at radio frequency.
17. 17 . The driver of claim 15 , further configured to: phase and frequency lock the modulated voltage signal at radio frequency and a radio frequency carrier signal responsive to the probe signal at radio frequency.
18. 18 . The driver of claim 15 , further configured to: generate an oscillator signal synchronous with a radio frequency carrier of the modulated voltage signal; outputting the probe signal responsive to the synchronous oscillator signal.
19. 19 . The driver of claim 15 , further comprising a low-pass filter to demodulating the modulated voltage signal.
20. 20 . The driver of claim 15 further comprising a rectifier configured to demodulate by rectifying prior to low pass filtering.

Description

BACKGROUND 1. Technical Field The present invention relates to electrostatic audio devices, including earphones and loudspeakers. 2. Description of Related Art In the art of high fidelity sound reproduction, the electrostatic loudspeaker has received attention because of inherent excellent sound quality and smooth response over wide frequency ranges. In such devices, a flexible sound producing membrane is positioned near an electrode, or in the case of a push-pull arrangement, a pair of electrodes, one on either side of the membrane. A polarization potential is applied between the membrane and the electrodes, and an audio signal is superimposed on the electrodes, causing the membrane to move in response to the audio signal. Electrodes are acoustically transmissive so that sound produced by the moving membrane radiates outward through the electrode to the listening area. Electrostatic devices are highly efficient both electrically and mechanically. Electrical impedance is high and decreases with increasing acoustic frequency. High electrical impedance results in very low operating currents and minimal electrical losses. Mechanically, there are no moving parts other than the moving membrane which is very light in weight. Electrostatic devices are therefore inherently more energy efficient than electrodynamic acoustic devices currently used in battery operated electronic devices. BRIEF SUMMARY Various methods and drivers are disclosed herein for configuring an electrostatic acoustic device to operate simultaneously as a speaker and as a microphone. The electrostatic acoustic device includes a membrane and an electrode disposed proximate to the membrane. An input varying audio signal is input to the electrostatic acoustic device. The membrane is configured to respond mechanically to a varying electric field responsive to the varying audio signal input. A portion of the input varying audio signal is tapped to produce a reference signal. A signal is detected responsive to motion of the membrane, to convert the signal to an output varying voltage signal. The output varying voltage signal is compared to the reference signal to produce a microphone signal. The microphone signal is responsive to motion of the membrane induced by air pressure variations of ambient sound. The input varying audio signal may be input to the membrane and the electrodes may connect to a high voltage dual DC bias symmetric or asymmetric source. Alternatively, the input varying audio signal may be input to the electrode and the membrane may be connected to a high voltage DC bias. The electrode may include a first electrode disposed on a first side of the membrane and a second electrode disposed on a second side of the membrane opposite the first side. The input varying audio signal may include an inverted varying audio signal input to the first electrode and a non-inverted varying audio signal input to the second electrode. The reference signal may be responsive to the inverted varying audio signal input and the non-inverted varying audio signal input. A probe signal varying at radio frequency may be injected into an input of the electrostatic acoustic device. The detection may be performed by converting a current or charge signal output to a modulated voltage signal. The current or charge signal may include an audio signal varying at audio frequencies modulating the radio frequency of the probe signal. The modulated voltage signal may be demodulated to produce the output varying voltage signal varying at audio frequency. The output varying voltage signal varying at audio frequency may be obtained by homodyne detection of the modulated voltage signal at radio frequency. The homodyne detection of the modulated radio frequency carrier signal may be achieved via a lock-in amplifier detector having the output low pass filter bandwidth higher than the audio frequency range of interest. The modulated voltage signal at radio frequency may be phase and frequency locked and a radio frequency carrier signal responsive to the probe signal may vary at radio frequency. An oscillator signal may be generated synchronous with a radio frequency carrier of the modulated voltage signal. The probe signal may be output responsive to the synchronous oscillator signal. The demodulation of the modulated voltage signal may be performed by low pass filtering or by rectifying prior to low pass filtering. BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: FIG. 1 illustrates schematically a cross-sectional view of an electrostatic device, according to features of the present invention; FIG. 2 is a system diagram including an electrostatic acoustic device and driver thereof for dual use as a loudspeaker and a microphone; FIG. 3A illustrates an electronic block diagram of electrostatic acoustic device and driver thereof; FIG. 3B illustrates further details of the embodiment of