Touch gesture control of in-ear electrostatic acoustic devices

Abstract

An earphone assembly includes an electrostatic acoustic device, wherein an acoustic signal is input to the electrostatic acoustic device, a membrane of the electrostatic acoustic device configured to mechanically respond to a variable electric field responsive to the acoustic signal when the acoustic signal is input, and a detector configured to detect a time-dependent displacement of the membrane in response to an external stimulus on the housing and to issue a command in response to the detected time-dependent displacement of the membrane and the external stimulus corresponding to the detected time-dependent displacement of the membrane.

Description

[Technical Field]

[0001] background 1.Technical Field The present invention relates to electrostatic audio devices, including earphones and speakers. [Background technology]

[0002] 2. Description of Related Art In high-fidelity sound reproduction, electrostatic speakers have gained prominence due to their inherently superior sound quality and smooth response across a wide frequency range. In such devices, a flexible, sound-generating membrane is positioned near an electrode, or, in a push-pull configuration, a pair of electrodes are positioned on either side of the membrane. A polarization potential is applied between the membrane and the electrode, and an acoustic signal is superimposed on the electrode, causing the membrane to move in response to the acoustic signal. Because the electrodes are acoustically transparent, sound generated by the membrane's movement is radiated outward through the electrode to the listening area.

[0003] Electrostatic devices are highly efficient, both electrically and mechanically. They have a high electrical impedance that decreases with increasing acoustic frequency. This high electrical impedance results in very low operating currents, minimizing electrical losses. Mechanically, they have no moving parts other than a very lightweight moving membrane. Electrostatic devices are therefore inherently more energy efficient than the electrodynamic acoustic devices currently used in battery-operated electronic devices. Summary of the Invention [Means for solving the problem]

[0004] Disclosed herein are various earphone assemblies and methods of controlling the same, including an electrostatic acoustic device. An acoustic signal is input to the electrostatic acoustic device. A membrane of the electrostatic acoustic device is configured to mechanically respond to a variable electric field responsive to the acoustic signal when input. A housing encloses the electrostatic acoustic device and a detector. The detector is configured to detect a time-dependent displacement of the membrane in response to an external stimulus on the housing. A processor operably attached to the detector may be configured to issue a command selected from a group of previously defined commands. The selected command may be responsive to the detected time-dependent displacement of the membrane and the corresponding external stimulus. The processor may be configured to select an operating mode of the electrostatic acoustic device according to the detected time-dependent displacement of the membrane and the corresponding external stimulus. A housing may enclose the electrostatic acoustic device and the detector. The housing may include a nozzle configured to transmit sound from the membrane to the ear canal during in-ear operation. The processor may be configured to detect a displacement of the membrane in response to an external stimulus, including a touch gesture that applies pressure to the housing toward the ear canal during in-ear operation. The processor may be configured to detect a time-dependent displacement of the membrane during in-ear operation as an impulse response to an external stimulus, including a finger tap gesture on the housing. The processor may be configured to distinguish between a finger tap on the housing with a fingernail and a finger tap on the housing with the pad of a finger. The processor may be configured to detect a time-dependent displacement of the membrane during in-ear operation in response to an external stimulus, including a touch gesture of stroking the surface of the housing. The processor may be configured to distinguish between at least two directions of stroking. The housing may include a surface having a roughness profile configured to produce different time-dependent displacements of the membrane when rubbed in different directions.

[0005] The invention is herein described, by way of example only, with reference to the accompanying drawings. [Brief explanation of the drawings]

[0006] [Figure 1A] 1A and 1B show schematic cross-sectional views of electrostatic devices according to aspects of the present invention; [Figure 1B] 1 is a rear isometric view of an earphone in accordance with aspects of the present invention; FIG. [Figure 1C] 1C shows the earphone as viewed from the back as in FIG. 1B with the back cover removed, according to a further feature of the present invention. [Figure 2] FIG. 1 is an electronic block diagram of a feedback control system for noise cancellation and / or adjustable acoustic transparency in accordance with aspects of the present invention. [Figure 2A] 3 shows an electronic block diagram of the proportional-integral-derivative (PID) controller of FIG. 2 according to the prior art. [Figure 3] FIG. 1 is a system diagram including an electrostatic acoustic device and its driver for simultaneous dual use as a speaker and microphone. [Figure 4A] An electronic block diagram of the electrostatic acoustic device and its driver used in FIGS. 2 and 3 is shown. [Figure 4B] 4 shows an alternative block diagram driver for an electrostatic acoustic device and driver in accordance with aspects of the present invention for use in FIGS. 2 and 3. FIG. [Figure 5] FIG. 1 is a flow diagram of a method illustrating features of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0007] The foregoing and / or other aspects will become apparent from the following detailed description when considered in conjunction with the accompanying drawing figures.

[0008] Detailed Description Reference will now be made in detail to the features of the present invention, examples of which are illustrated in the accompanying drawings, in which like reference numerals refer to like elements throughout. To illustrate the invention with reference to the drawings, features can be described below.

[0009] By way of introduction, different aspects of the present invention may be directed to in-ear electrostatic acoustic devices that can be used in different modes of operation. The in-ear electrostatic acoustic devices can be configured as in-ear earphones, include or interface with an audio player, and can include functions such as play, stop, go forward or backward in a playlist, etc. Alternatively, the in-ear device can be operated as a hearing aid. According to embodiments of the present invention, touch gestures on the housing of the in-ear electrostatic acoustic device during operation in the ear can be detected and used to control the operation of the device.

[0010] A feature of the present invention can include an earphone housing having one or more apertures to provide an acoustically transparent back surface and an integrated power source, e.g., a battery, with power and acoustic circuitry integrated within the in-ear housing. Two primary modes of operation are available: i) a closed-loop control mode, including 1) a noise-cancellation mode in which feedback to the electroacoustic device can be configured to cancel ambient sounds and noises, and / or 2) an adjustable acoustic transparency mode, i.e., a mode in which the range at which a user hears ambient sounds can be adjusted by tuning feedback in the control circuit. The second primary mode of operation is ii) an open-loop mode, which allows for the extraction of a signal responsive to the time-dependent displacement of the membrane of the electrostatic speaker. In mode ii), the electrostatic speaker can be used simultaneously as a microphone and a speaker, and sound can be generated by touch gestures on the housing of the in-ear device to control the operation of the device. In accordance with a feature of the present invention, touch gestures can be used to switch the device between primary modes i) and ii).

[0011] Referring now to the drawings, reference is made to FIG. 1A, which schematically illustrates an electrostatic acoustic device 10 in accordance with aspects of the present invention. A vertical axis Z is shown passing through the center of the acoustic device 10. A tensioned membrane 15 is supported by the edges of electrodes 11 in a plane substantially perpendicular to the vertical axis Z. The membrane 15 may be impregnated with a conductive, resistive, and / or electrostatic material to provide mechanical response to a changing electric field. The central region of the electrode 11 is mounted proximate to the membrane 15, e.g., parallel to the membrane 15, and nominally equidistant therefrom, e.g., at a distance d of 20 to 500 micrometers from the membrane 15. As shown, the electrode 11 may be perforated with an aperture 12 that is transparent to sound waves emanating from the membrane 15 when the electrostatic acoustic device 10 is operating. Alternatively, or additionally, one or more side ports 13 may allow sound waves to pass from the air surrounding the membrane 15 to the exterior of the device 10.

[0012] During operation of the electrostatic acoustic device 10, a constant direct current (DC) bias voltage, e.g., +V DC A non-inverted voltage signal +V can be applied to one of the electrodes 11 using conductive contacts. i and an identical but inverted voltage signal -V i Alternatively, a voltage signal V i is applied to the membrane 15, and the electrode 11 is connected to ±V DC It can also be biased by ±V / 2. i can vary with audio frequencies nominally between 20 and 20,000 Hz. The dotted lines indicate the voltage signals ±V i 1 shows a schematic representation of a membrane 15 that moves in response to a changing voltage according to

[0013] 1B, which is an isometric view from the back of an earphone 101 in accordance with aspects of the present invention. The housing of earphone 101 includes one or more assembled parts: a back housing 17 and a front housing 18. Back housing 17 may include one or more apertures 14 or through-holes that provide acoustic transparency from the surroundings through apertures 14 and through apertures 12 in electrodes 11 to membrane 15 of electro-acoustic device 10.

[0014] Reference is now also made to FIG. 1C, which shows earphone 101 with back housing 17 removed, in accordance with a feature of the present invention. Acoustic seal 19 is removably mountable over nozzle 16. Acoustic seal 19 is intended to fit within the user's ear canal and provide an acoustic seal. Inside nozzle 16 is a channel leading to electrostatic acoustic device 10, which includes membrane 15 (not shown) sealed therein. Circuit board 29 receives a voltage input from battery 280 and a direct current (DC) bias voltage V DC The circuit board 29 may include a DC-DC converter that provides the audio voltage signals ±V. i , and other circuitry disclosed herein or otherwise desired.

[0015] Thus, in embodiments of the present invention including electrostatic acoustic device 10 used as an earphone and sealed within the ear canal, mechanical displacement of the tympanic membrane can be coupled to mechanical displacement of membrane 15. The user's voice can be transmitted to the tympanic membrane by bone conduction and to membrane 15 by internal coupling, allowing membrane 15 to be used as a microphone. When used as a microphone, membrane 15 is sensitive not only to ambient sounds but also to sounds generated by touch gestures on housings 17, 18.

[0016] Reference is now made to Figure 2, which illustrates a control circuit in accordance with an aspect of the present invention. In the forward path, G(s) represents the open loop gain of the control circuit including system 21, where s is the open loop gain of A(e iωt+φ), where A represents the amplitude, ω = 2πf represents the angular frequency, where f represents the frequency in Hertz, and φ represents the phase shift in radians.

[0017] 2A, which illustrates a prior art proportional-integral-derivative (PID) block 24. The feedback loop may include a proportional-integral-derivative (PID) block 24 in the forward path G(s). Block 24 may include a proportional gain, a linear combination of derivatives and / or integrals for the error signal 25, as well as frequency filtering to output a control signal 26.

[0018] Returning to FIG. 2, in the feedback path, block 22 outputs the output voltage signal V o The feedback path output from the feedback block 22 may output a feedback signal 27, which is converted by a comparator 230 into the input signal V i may be subtracted from the output signal V to generate an error signal 25. In response to the error signal 25, the PID controller 24 may o The control signal 26 is output to the controller block 21 so that the voltage output V approaches the set point. o The voltage input V of the controller 21 i Divided by can be modeled by Equation 1:

number

[0019] Input signal V i is nominally zero, feedback signal 27 becomes error signal 25. Alternatively, comparator 23 can be equivalently replaced by signal combiner 23, and feedback block 22 generates voltage output signal V o of 、 A feedback signal 27 is suitably transformed (eg, inverted) and coupled to the error signal 25 .

[0020] The stability of the control system 20 is contingent on the denominator 1 + G(s) · H(2) being sufficiently large and / or non-zero. It is well known that in a resonant system 21 containing an externally driven damped harmonic oscillator, the oscillator response is in phase with the external drive (i.e., φ ≈ 0) at drive frequencies significantly below the resonant frequency, in quadrature (i.e., φ ≈ π / 2) at the resonant frequency, and out of phase (i.e., φ ≈ π) at frequencies significantly above the resonant frequency. When the control system 21 contains a resonant and oscillatory energy source, to maintain stability, the oscillatory energy source operates either below or above the resonant frequency without exceeding the resonant frequency. When the resonant frequency crosses over, a phase-shifting filter can be added to mitigate discontinuities in the phase response.

[0021] 3, which is a simplified electronic system block diagram including electrostatic acoustic device 10 in an open-loop mode of operation for simultaneous operation as a speaker and as a microphone. Block 21 provides a voltage signal V for driving electrostatic acoustic device 10. i The reference signal 28 represents a driver or electronic circuit that receives the input acoustic signal V and causes the movable membrane 15 to emit sound. i is divided or subtracted from and input to a comparator 23. Block 21 detects a signal proportional to or responsive to the mechanical movement of membrane 15 and generates a signal responsive to the movement of membrane 15, e.g., a voltage V o The voltage output signal V o is the second input to the comparator 23. The comparator 23 converts the reference signal 21 into the output voltage signal V o and by suitable signal processing it is possible to extract a microphone signal 250 which is responsive to the vibrations of the membrane caused by ambient sounds or sounds generated by touch gestures on the housing 17, 18 of the in-ear device 101.

[0022] Detection of a signal proportional to or responsive to mechanical movement of membrane 15 can be accomplished by a variety of detection methods known in the art. Herein, detection of changes in electrostatic current or capacitance between membrane 15 and electrode 11 is described. Other detection methods for measuring movement of membrane 15 may be used in accordance with different embodiments of the present invention, including, for example, optical sensors, external field gradient (force) detection such as electrostatic or magnetic field gradients using Hall Effect magnetic sensors.

[0023] For any detection method that responds to the movement of the membrane 15, the microphone signal 250 is i The microphone signal can be extracted by subtracting or comparing the time-dependent behavior of the response of membrane 15 to the signal. Subtraction can be performed in the time domain by digital signal processing with appropriate level adjustments and / or time delays. Alternatively, subtraction can be performed in the frequency domain by performing a signal transform, e.g., a short-time Fourier transform, and then performing the subtraction in the frequency domain and the inverse, e.g., a Fourier transform, back to the time domain to extract the microphone signal.

[0024] Reference is now made to Figure 4A, which shows in more detail and generally illustrates a circuit 21A that is an alternative to the system 21 of Figures 2 and 3, in accordance with an aspect of the present invention. The driver 21A includes an electrostatic acoustic device 10 that receives a high voltage audio input +V at a first electrode 11. i and at the second electrode 11, an inverted high voltage acoustic input -V that varies at an acoustic frequency intended for conversion into sound by the electrostatic acoustic device 10. i can be configured to receive

[0025] A probe signal from a local oscillator (LO) 51 at a radio frequency, for example 0.1 to 20 megahertz, may be coupled across the primary winding P of the transformer T. The acoustic signal +V i and the inverted acoustic signal -V i are supplied to the electrodes 11 via the series-connected secondary windings S1 and S2 of the transformer T. The acoustic signals ±V i may be a high voltage signal. Alternatively, the acoustic signal ±V ican be a low voltage signal up to about ±20V. DC voltage bias +V DC may be applied to membrane 15. The probe signal generates a current whose magnitude is determined by the characteristic reactance (essentially a variable capacitor) of the electrical circuit formed by membrane 15 and electrode 11. The probe signal from local oscillator (LO) 51 may also be combined with the voltage output of amplifier 30 in signal combiner / multiplier 32. Signal combiner / multiplier 32 produces a voltage output signal V that varies at acoustic frequencies. o The signal is output to low pass filter 34, which demodulates and transmits it. System 21B is a homodyne detection circuit that uses local oscillator 51 as a reference that is multiplied with the measurement signal output by amplifier 30 at the same frequency. The baseband or DC component of this multiplication contains a frequency-converted signal from a narrow band around the LO51 frequency that is detected with a very high signal-to-noise ratio.

[0026] The membrane 15 may be mechanically responsive to ambient sound waves such that the device 10 may behave as a microphone. In response to ambient sound, the distance d (FIG. 1) between the membrane 15 and the electrode 11 changes, causing a change in the capacitance C of the electrostatic acoustic device 10. The current i(t), which varies with ambient sound, can be sensed using a transimpedance amplifier 30 and approximated by:

number

[0027] Alternatively, instead of a transimpedance amplifier, a charge amplifier 30 may be considered that integrates the current i(t) to sense the charge Q(t) that varies with the change in capacitance of the electrostatic acoustic device 10, and the sensed charge is then fed to an output voltage signal V o is converted to

[0028] Amplifier 30 can be configured to be inverting or non-inverting and can have a bandpass that includes acoustic frequencies from 20 to 20,000 hertz.

[0029] The advantage of using radio frequencies lies in the fact that radio frequencies do not produce perceptible mechanical motion, but are modulated by electrical capacitance changes associated with mechanical motion that occurs in the presence of acoustic signals and / or ambient sound. Furthermore, radio frequency amplitude modulated signals have a higher signal-to-noise ratio with respect to the total capacitance change of the device when compared to the current induced by the direct capacitance change shown in relationship (2).

[0030] Reference is now made to FIG. 4B, which illustrates schematically another alternative 21B of block 21 of FIGS. 2 and 3, in accordance with a different aspect of the present invention. In controller 21B, the acoustic voltage V i can be applied to the membrane 15. The primary P is connected in parallel with the local oscillator 51 and the secondary S generates an acoustic voltage V i A probe signal from the local oscillator 51 can also be induced at the membrane 15 using a transformer T connected in series between the bias voltage V DC is applied symmetrically to the electrodes 11, and -V DC / 2, and +V to the second electrode 11 DC / 2 is applied. A differential amplifier 31 can be used with inputs that are capacitively coupled to the electrodes 11, respectively. The voltage output of the differential amplifier 31 varies with the capacitance of the device 10. A probe signal from a local oscillator (LO) 51 may also be combined with the voltage output of the differential amplifier 31 in a signal combiner / multiplier 32, which produces a voltage output signal V that varies with the acoustic frequency. o The differential amplifier 31 is a Texas Instruments / Burr-Brown low-pass filter. TM In accordance with a feature of the present invention, the controller 21B receives a single high voltage audio signal V i is used, it has the advantage over controller 21A because only one high voltage input amplifier is needed instead of two.

[0031] Reference is now also made to Figure 5, which is a flow diagram of a method 50 illustrating an aspect of the present invention. Referring again to Figures 2 and 3, a detector circuit 75 is shown connected to a processor 77 configured to monitor (step 52) the time-dependent displacement of membrane 15. The time-dependent displacement results in a time-dependent change in capacitance that can be detected by processing the respective outputs of detector 75 and / or microphone signal 250, as shown in Figure 3.

[0032] The processor 77 can be configured to classify the time-dependent displacement as corresponding to one of a set of previously defined touch gestures (step 53). The processor 77 and detector 75 can be configured to detect a pressure gesture on the housing 17, 18 of the in-ear device 101 during operation (decision block 54). Because the in-ear device 101 is slightly pressed into the ear while both the eardrum and membrane 15 are sealed within the ear canal, and while the aperture 14 in the back housing 17 equalizes the pressure between the membrane and the ambient atmosphere, pressure applied toward the inner ear for, e.g., 100-1000 milliseconds, can result in an average outward displacement of the membrane 15. In accordance with a feature of the present invention, if a pressure gesture is detected (decision block 54), the operating mode of the in-ear device 101 switches between modes (i) noise cancellation / acoustic transparency adjustment (FIG. 2) and (ii) simultaneous operation as a microphone and speaker (FIG. 3) (step 55). During mode (ii), the microphone signals are processed by the processor 77, which can issue respective commands in response to the microphone signals classified from the particular sounds generated by the user by the touch gesture (step 56).

[0033] Referring again to FIG. 1B , which illustrates a further feature of the present invention, the processor 77 can be configured to detect time-dependent displacement of the membrane in response to external stimuli, including touch gestures in which a user strokes the surface of the housing 17 or 18 during inner ear operation. Various touch gestures can include impacts, such as a finger tap gesture on the outer housing 17. The processor 77 may be configured, i.e., pre-trained, to distinguish between finger taps on the housing with a fingernail and finger pads. The housings 17 and / or 18 may include roughness or spatial periodicity 71, 73, which, when stroked, emit a characteristic sound that can be sensed by the detector 75 and cause a characteristic time-dependent displacement of the membrane 15, which can be classified as a control command by the processor 77. As shown in the device 101 of FIG. 1B , the housing 17 is illustrated with two examples of surface roughnesses 71 and 73 having different periodicities and different directions of the periodicity. The amount of periodicity or roughness changes the frequency content of the characteristic sound caused by stroking the housings 17, 18. A user stroking the housing 17, optionally in different directions at different locations 71 and 73, can result in two different commands being issued by the processor 77.

[0034] As used herein, the term "homodyne" refers to a method of detecting / demodulating a signal that is phase and / or frequency modulated onto an oscillator signal by combining it with a reference oscillation.

[0035] As used herein, the term "surroundings" refers to the vicinity of the membrane of an electrostatic acoustic device.

[0036] As used herein, the term "driver" refers to an electronic circuit configured to electrically bias and transmit signals to and / or from an electrostatic acoustic device.

[0037] As used herein, the term "transimpedance amplifier" converts current to voltage. A transimpedance amplifier can be used to process the current output of a sensor into a voltage signal output.

[0038] As used herein, the term "charge amplifier" converts a time-varying charge into a voltage output, typically by integrating a time-varying current signal.

[0039] The terms "acoustic" or "acoustic frequency" refer to an alternating current or voltage in the frequency range 0 to 20,000 hertz, or a magnetic, electric, or electromagnetic field, or the rate of oscillation of a mechanical system.

[0040] As used herein, the terms "acoustic signal," "acoustic output," and "acoustic output signal" refer to an electrical signal that varies essentially at acoustic frequencies.

[0041] The term "radio frequency" (RF) refers to an alternating current or voltage, or a magnetic, electric, or electromagnetic field, or the rate of oscillation of a mechanical system, in the frequency range from about 20,000 times per second (20 kHz) to about 300 billion times per second (300 GHz).

[0042] As used herein, the transitional term "comprising" is synonymous with "including" and is inclusive or open-ended, not excluding additional elements or method steps not expressly recited. The articles "a" and "an" are used herein, such as in "a circuit" or "an electrode," to mean "one or more," i.e., "one or more circuits," "one or more electrodes."

[0043] All optional and preferred features and modifications of the described embodiments and dependent claims can be used in all aspects of the invention taught herein. Furthermore, individual features of the dependent claims, and all optional and preferred features and modifications of the described embodiments, are combinable and interchangeable with each other.

[0044] While selected features of the present invention have been illustrated and described, it will be understood that the invention is not limited to the described features.

Claims

1. An earphone assembly, An electrostatic acoustic device including a film and adjacent electrodes, An acoustic signal input unit configured to receive an acoustic signal input for the electrostatic acoustic device, wherein the voltage difference applied between the film and the adjacent electrode generates an electrostatic force that mechanically moves the film. Detector and A processor operably mounted to the detector, A housing enclosing the electrostatic acoustic device, the processor, and the detector, This is an earphone assembly that includes, The detector is configured to generate a signal indicating time-dependent membrane displacement in response to an external stimulus applied to the housing, in an earphone assembly.

2. The earphone assembly according to claim 1, wherein the processor is configured to issue a command selected from a previously defined set of commands, the selected command corresponding to a detected time-dependent displacement of the membrane.

3. The earphone assembly according to claim 1, wherein the housing further includes a nozzle configured to transmit sound from the membrane to the external auditory canal during intra-ear movement.

4. The earphone assembly according to claim 3, wherein the processor is configured to determine the displacement of the membrane from the signal during the intra-ear operation, and when the external stimulus applies pressure to the housing toward the external auditory canal, the time-dependent displacement includes an average displacement component of the membrane in response to the pressure on the housing.

5. The earphone assembly according to claim 4, wherein the processor is configured to switch the operating mode of the electrostatic acoustic device in response to the average displacement component.

6. The earphone assembly according to claim 4, wherein the processor is configured to detect, during the in-ear operation, a time-dependent displacement of the membrane as an impact response to the external stimulus including a finger tap gesture to the housing.

7. The earphone assembly according to claim 6, wherein the processor is configured to distinguish between a fingertip tap on the housing and a fingertip tap on the housing with the pad of a finger.

8. The earphone assembly according to claim 4, wherein the processor is configured to detect a time-dependent displacement of the membrane in response to the external stimulus including a touch gesture of stroking the surface of the housing during the in-ear operation.

9. The earphone assembly according to claim 8, wherein the processor is configured to distinguish at least two directions of the stroking motion.

10. The earphone assembly according to claim 9, wherein the housing includes a surface having a roughness profile with directional periodicity configured to produce different time-dependent film displacements when rubbed in different directions.

11. A method for enabling control of an earphone assembly including an electrostatic acoustic device, a detector, a processor, and a housing, wherein the electrostatic acoustic device includes a membrane, adjacent electrodes, and an acoustic signal input section, the housing encloses the electrostatic acoustic device, the processor, and the detector, and the method is The acoustic signal input unit inputs an acoustic signal to the electrostatic acoustic device, thereby generating an electrostatic force that mechanically moves the film by applying a voltage difference between the film and the adjacent electrode. To detect the time-dependent displacement of the membrane in response to an external stimulus on the housing, Methods that include...

12. Issuing a command selected from a group of previously defined commands, wherein the selected command corresponds to the detected time-dependent displacement of the membrane and the corresponding external stimulus. The method according to claim 11, further comprising:

13. The housing is provided with a nozzle configured to transmit sound from the membrane to the external auditory canal during intra-ear movement. The method according to claim 11, further comprising:

14. The method according to claim 13, wherein when a touch gesture applies pressure to the housing toward the ear canal, the detected displacement includes an average displacement component of the membrane in response to the pressure on the housing.

15. Switching the operating mode of the electrostatic acoustic device in response to the average displacement component. The method according to claim 14, further comprising:

16. The switching includes switching the electrostatic acoustic device from a closed-loop control mode to an open-loop mode in response to the average displacement component being caused by pressure on the housing toward the ear canal, In the closed-loop control mode, the feedback to the electrostatic acoustic device is configured to cancel ambient sound or noise and / or adjust acoustic transparency. In the open-loop mode, the signal in response to the time-dependent displacement of the membrane is extracted while the electrostatic acoustic device is used simultaneously as a speaker and a microphone. The method according to claim 15.

17. During the aforementioned intra-ear movement, the time-dependent displacement of the membrane is detected as an impact response to an external stimulus, including a finger tap gesture on the housing. The method according to claim 12, further comprising:

18. To distinguish between tapping the housing with a fingernail and tapping the housing with the pad of a finger. The method according to claim 17, further comprising:

19. During the aforementioned intra-ear movement, the time-dependent displacement of the membrane is detected in response to the external stimulus including a touch gesture that strokes the surface of the housing. The method according to claim 12, further comprising:

20. Distinguishing at least two directions of the aforementioned stroking method. The method according to claim 19, further comprising:

21. The method according to claim 20, wherein the housing includes a surface having a directional periodic roughness profile configured to produce different characteristic time-dependent film displacements when rubbed in different directions.

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