Method and apparatus for controlling the propagation of acoustic waves on a wall

Abstract

The present invention relates to a method and apparatus for controlling the propagation of acoustic waves in the vicinity of a wall, the method and apparatus implementing a master device for controlling a set Nc of cells (1) consisting mainly of loudspeakers (11), a set of Nm microphones (10) connected to the loudspeakers, and a control unit (12) by means of a control law that determines the intensity of an electrical signal that must be sent to each loudspeaker (11) to obtain a target-determined generalized acoustic impedance of each loudspeaker (11), such that a portion of the acoustic wave is absorbed by the membrane of each loudspeaker (11).

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for controlling the propagation of acoustic waves in the vicinity of a wall. Reducing noise disturbances caused by transportation and human activities has become a major issue. The use of passive coatings in buildings or vehicles has made it possible to limit the acoustic signature of aircraft, but it is not possible to adapt to flight conditions and there is no significant effect over a wide frequency band.

[0002] The techniques used in acoustic processing generally rely on the use of foamed type absorption materials or designed honeycomb materials.

[0003] Therefore, in specific applications in construction or transportation, acoustic liners with distributed Helmholtz resonators are used at low frequencies and foam at high frequencies. The reduction obtained remains less than a few decibels at low frequencies.

[0004] The effectiveness of conventional absorbent treatments is related to the thickness of the material, and therefore, the problems of absorption of water and contaminants into these porous materials go without saying, and are restricted by the increase in volume and weight.

[0005] All of these techniques are passive and do not have the ability to adapt or selectively process noise.

[0006] They also cannot induce emissions.

[0007] In response to these technical problems, active noise control techniques have been developed since the 1980s, and their applications are related to various fields such as consumer audio or transportation, but they rely on non-dispersive strategies.

[0008] As a result of the problems of volume and effectiveness at low frequencies of acoustic processing systems, their effectiveness for many potential applications is limited.

[0009] Therefore, it has been found that there is a need to develop new solutions that can handle problems in particularly wide frequency bands.

[0010] The developed technology makes it possible to ensure an efficient absorption of acoustic disturbances within a reduced thickness range of up to a few centimeters, for complex waves (such as ramp or diffused waves), and for a wide range of frequencies including low frequencies when passive treatment is not effective.

[0011] For this purpose, the present invention proposes implementing a method and an apparatus that make it possible to adaptively control the generalized acoustic impedance of a wall, either locally or non - locally.

[0012] Note that the acoustic impedance is a customary known physical variable corresponding to the ratio between the sound pressure and the speed of sound.

[0013] The apparatus is composed of a first layer of acoustic transducers, each consisting of a microphone and a speaker. The second layer is formed by electronic components for signal conditioning and real - time command / control. The apparatus is cellular, and each cell incorporates a speaker, a microphone, and electronics for computing and signal management.

[0014] Regarding the method, each cell is independent and executes a control law whose parameters can be determined and updated by an integration interface. This makes it possible to manage the matrix of cells and access the inputs and outputs of the entire system.

[0015] Similarly, powering the apparatus is included through all of the elements. The present invention relates more specifically to the distributed and tunable characteristics of the system.

[0016] The present invention relates in particular to a method for controlling the propagation of acoustic waves in the vicinity of a wall, the method comprising Step a) in which Nc cells mainly constituted by a speaker connected to a set of Nm microphones are attached to a wall, where the microphones and the speaker are provided to be driven by a control unit, Step b) in which each microphone of each cell measures the sound pressure of an acoustic wave, where each measurement value is returned to a cell control unit, Step c) in which a control unit estimates the sound pressure at the level of the speaker and / or its spatial derivative, and then defines a control law for setting the number of amperes of the current that must be sent to the speaker to obtain the determined generalized acoustic impedance Z det of the speaker, Step d) in which the control unit transmits an electrical signal to the speaker so that a part of the acoustic wave is absorbed by the membrane of the speaker is included.

[0017] According to the invention, in step c), the control unit estimates the sound pressure at the level of the speaker, or its spatial derivative, or both.

[0018] The use of the spatial derivative of the pressure advantageously makes it possible to take into account the rate of change of the pressure field on the acoustic treatment wall and the effective propagation speed of the noise through the wall.

[0019] The main control device drives all of the control units using a learning loop so as to adjust the determined generalized acoustic impedance Z det of each cell.

[0020] Thus, following an iterative process for each cell, the parameters of the control law are adapted while the value of the insertion loss is less than a predetermined threshold, and then when the threshold is reached, step c) of claim 1 is executed, which is to apply an appropriate control law (defined by the adaptation of the parameters) for the purpose of obtaining the determined (i.e., targeted) generalized acoustic impedance Z det of the speaker.

[0021] Of course, following the iterative process of each cell, it is also possible to adapt the parameters of the control law while the values of the reference physical variables other than the insertion loss (e.g., transmission loss, absorption coefficient, or target impedance) are close enough to a predetermined value.

[0022] Optional features of the present invention are given below, whether additional or alternative. According to a particular feature, the loop includes the following steps.

[0023] BEGIN: Start step A1: Step of loading a general acoustic model A2: Step of assigning a control law to at least one of the cells A3: Step of calculating the parameters associated with the control law A4: Step of applying the control law to the cells A5: Step of generating a calibration signal (e.g., white noise or sine wave sweep) A6: Step of acquiring the signal by a microphone A7: Step of calculating the insertion loss (IL) A8: Comparing the insertion loss (IL) with a predetermined insertion loss value IL0 corresponding to the acquisition of the desired generalized acoustic impedance Z det A9: Step of returning to A3 for adaptation of the parameters of the control law in order to minimize the error of the measured impedance when IL < IL0.

[0024] According to another feature, each cell includes three to five, preferably four, microphones.

[0025] According to a further feature, a part of the acoustic wave absorbed by the diaphragm of the speaker is converted into electrical energy to be supplied to all of the cells.

[0026] According to another feature, the generalized acoustic impedance is modified by a control law defined as follows.

[0027] The desired dynamics of the current in amperes (i) are expressed in the form of a sum of infinite impulse response (IIR) filters with respect to the sound pressure (p) and its gradient (grad(p)), and the dynamics are represented by two transfer functions H loc and H dis which are embodied.

[0028] [Equation 1] [Number]

[0029] H loc and H dis are described in discrete time as polynomial fractions of z.

[0030] [Equation 2] [Number]

[0031] (a i , b i ) are the real coefficients of the equation, and (m, n) are the integers corresponding to the filter order.

[0032] z -1 being a pure delay of the sampling period, it is assumed that an iterative control equation is generated between the output at instant k (y k ) and the input at instant k (x k ).

[0033] [Equation 3] [Number]

[0034] Assuming that the current drive signal in the speaker coil depends on the pressure and its gradient, the complete control equation is described as the sum of two iterative equations of the preceding form: y tot =y loc +y dis .

[0035] y loc depends on the measured pressure, and y dis depends on the estimated pressure gradient.

[0036] Thus, the method consists of imposing a physical power on the system when only the measured values of the physical state of the system (pressure and / or pressure gradient in the vicinity of the speaker membrane) are known.

[0037] Thus, the method does not require the use of a theoretical model of the behavior of technical components (such as speakers).

[0038] According to yet another feature, the control unit is preferably a microcontroller of the ARM type. This type of microcontroller is based on a 32-bit (ARMv1 to ARMv7) and 64-bit (ARMv8) RISC type external architecture developed by ARM Ltd since 1983 and introduced by Acorn Computers since 1990.

[0039] According to yet another feature, the control law is defined at a frequency included between 25 and 150 kHz.

[0040] The present invention further relates to an apparatus for controlling the propagation of acoustic waves in the vicinity of a wall, which mainly comprises a speaker, a set of Nm microphones connected to said speaker, a control unit, and Nc cells composed of a power supply, wherein said microphones and speakers are provided to be driven by said control unit, and a part of the acoustic waves absorbed by the speaker membrane is converted into electrical energy for supplying the set of cells Nc, each microphone of each cell can measure the sound pressure of the acoustic wave, each measured value is returned to the cell control unit, and the control unit estimates the sound pressure at the level of the speaker and / or its tangential spatial derivative, and the determined generalized acoustic impedance Z of the speaker detA control rule for setting the number of amperes of an electrical signal that must be sent to the speaker to be obtained can be applied, and the apparatus also includes a main control device for driving a set of control units in a loop including the following steps.

[0041] BEGIN: Start step A1: Step of loading a general acoustic model A2: Step of assigning a control rule to at least one of the cells A3: Step of calculating parameters associated with the control rule A4: Step of applying the control rule to the cell A5: Step of generating a calibration signal (e.g., white noise or sine wave sweep) A6: Step of acquiring a signal by a microphone A7: Step of calculating the insertion loss (IL) A8: Comparing the insertion loss (IL) with a predetermined insertion loss value IL0 corresponding to the acquisition of the desired generalized acoustic impedance Z det A9: Step of returning to A3 for adaptation of the parameters of the control rule in order to minimize the error of the measured impedance when IL < IL0.

[0042] Optional features of the present invention are given below, either in addition or in the alternative.

[0043] According to a particular feature, each cell of the apparatus includes from 3 to 5, preferably 4, microphones.

[0044] Similarly, supplying power to the apparatus is included via all of the elements. The present invention relates more specifically to the distributed adjustable characteristics of a distributed system.

[0045] The distributed characteristics of the microphones make it possible to reconstruct the spatial differentiation and measure the pressure field in real time.

[0046] The distributed characteristics of the actuator enable it to have a control law that is spatially variable.

[0047] The distributed characteristics of the control unit enable it to have a high level of robustness (even with some malfunctioning elements, the system can function in a degraded mode).

[0048] All control units are independent, but can be reconfigured in real time by a main control device that enables self - learning to adapt to new environmental conditions.

[0049] Finally, the assembly can be attached directly to the wall or embedded in the form of a support mesh, which enables modularity for adapting to various shapes.

[0050] The present invention further relates to an acoustic panel covered by a set of cells Nc mainly composed of speakers, a set of Nm microphones connected to said speakers, and control units, wherein said microphones and speakers are provided to be driven by said control units, a part of the acoustic waves absorbed by the membrane of the speaker is converted into electrical energy for supplying to the set of cells Nc, the generalized acoustic impedance of each speaker is subject to a control law so as to locally define an absorption or reflection behavior on the surface of the panel, and the panel is further connected to a main control device for driving the set of control units in the loop detailed above.

[0051] Other advantages and features of the present invention will become apparent by reading the detailed description of non - limiting embodiments and implementations and from the following attached drawings.

Brief Description of the Drawings

[0052]

Figure 1

Figure 2

[0053] Since the embodiments described below are in no way limiting, variants of the present invention may be considered to include only the selection of the characteristics described, separated from the other characteristics described (even if this selection was separated in the context including these other characteristics), when this selection of characteristics is sufficient to confer a technical advantage of the present invention over the prior art or to differentiate the present invention. This selection includes at least one, preferably functional, characteristic, without structural details or, when only a part of them is sufficient to confer a technical advantage of the present invention over the prior art level or to differentiate the present invention, with only a part of the structural details.

[0054] The device according to the present invention is intended to convert an electroacoustic transducer into a multi-valued electroacoustic resonator and to absorb the sound energy in a space or even to accommodate this energy between two adjacent spaces, without using a detection element to achieve the desired noise reduction.

[0055] Technological innovation includes, in particular, the modification of the internal dynamics of the electroacoustic transducer via the load electrical impedance connected to its terminals, adapted to the electroacoustic transducer used as well as to the acoustic dispersion conditions and the desired acoustic performance.

[0056] The role of this impedance is to adjust the losses and to compensate for the reactive part of the transducer, with the intention of exhibiting a performance that meets the acoustic requirements.

[0057] Thus, the acoustic impedance exhibited by the electroacoustic transducer membrane in the surrounding sound field can be made transmissive, absorptive, or insulating with respect to the incident sound wave, according to the transfer function performed by the load electrical impedance.

[0058] The synthesized electrical impedance constitutes a functional link between the voltage induced by an electroacoustic transducer subjected to an external pressure field and the current that needs to absorb or accommodate the incident sound energy.

[0059] The present invention relates, inter alia, to an electroacoustic system that is permanently controlled in a self - regulating closed loop, the control law of which depends on prior knowledge of the transfer mechanism as well as the dissipation and reaction mechanisms inherent in an internal model, i.e., a transducer attached to an enclosure or baffle.

[0060] Regarding the operating principle, the movable parts of a speaker (e.g., diaphragm, dust cap, and coil) are moved when exposed to an external sound pressure field, vibrate back and forth along the axis of symmetry of the transducer, and are returned to the equilibrium position under the action of the spider and peripheral suspension elements. The movement of the coil itself immersed in the magnetic field generated by a permanent magnet generates an electromotive force, which is represented by the voltage induced at the electrical terminals of the transducer.

[0061] This induced voltage is an image of the acoustic disturbance at the origin of the movement of the movable part, but also depends on the internal dynamics of the speaker system and the conditions of acoustic dispersion (enclosure, indoor position, etc.). This constitutes the input of a regulator that has the role of sending a compensating current calculated to counteract the mechanical forces in the diaphragm adapted to the desired acoustic effect, i.e., sound absorption in a space or sound insulation between two adjacent spaces.

[0062] The control of the generalized acoustic impedance, i.e., the dynamics of the relationship between pressure, pressure gradient, and velocity at the level of the controlled surface, results in a significant reduction in the energy transmitted along the processed surface. This control is carried out by the distribution of speakers acting on the velocity field and the distribution of microphones enabling the measurement of the sound pressure field and its gradient.

[0063] Therefore, it is necessary to apply a current flowing through the coil of the speaker, and the ampere value is preferably calculated by an infinite impulse response filter (IIR) as a function of the measured sound pressure and its gradient.

[0064] The developed device enables simultaneous control of N active cells of the speaker.

[0065] The architecture of the device also enables real-time modification of the dynamics of each filter used.

[0066] Therefore, by programming the generalized acoustic impedance locally applied to the active surface attached to the wall, easy implementation of different control strategies becomes possible.

[0067] Applying the generalized acoustic impedance to the wall will impose the dynamics between the sound pressure, the sound pressure gradient, and the air velocity at the level of this wall.

[0068] Then, with the development of such a control method and such a control device, it is possible to generate a control loop having the signal of the microphone as input and output at the setpoint of the current that must be applied to the coil of the speaker.

[0069] The passband of interest ranges from 20 to 20000 Hertz, specifically from 20 to 1500 Hertz within the context of civil engineering applications.

[0070] To ensure a reduction in volume and enable effective control within the assumed frequency band, the wall can be subdivided into local control zones of 5 centimeters per side.

[0071] As shown in Figures 1 and 2, the device is composed of a speaker 11, Nm microphones 10, an electronic signal conditioning card, a digital computing card, and a power supply, and is represented by a control unit 12 in total, and is composed of Nc = 12 identical and independent cells 1.

[0072] Each cell includes from 3 to 5, preferably 4 microphones 10.

[0073] Each speaker 11 is controlled by a power supply driven by a specially developed digital calculation card. The four microphones 10 of each cell 1 make it possible to estimate the average pressure at the center of the membrane of each speaker. The pressure difference between the left and right boundaries of the cell makes it possible to evaluate the spatial pressure gradient along the wave propagation axis in the duct.

[0074] With regard to the operation, referring to FIG. 2, the device acquires the sound pressure by the microphone 10.

[0075] After being adjusted in the processing unit 13, the signal is digitized by an analog-to-digital converter (ADC).

[0076] Based on the measurements of the microphone, the average pressure at the center of the membrane and / or the spatial derivative of the pressure at the level of the membrane are estimated. Then, the control law is calculated by the calculation unit 12.

[0077] The current setpoint resulting from the calculation is generated by a digital-to-analog converter (DAC).

[0078] Finally, the current source drives the current flowing through the speaker 11.

[0079] More specifically, the control method according to the present invention includes the following steps.

[0080] A step in which Nc cells 1 mainly composed of speakers 11 connected to a set of Nm microphones 10 are attached to the wall, and the microphones and speakers are provided to be driven by a control unit 12.

[0081] A step in which each microphone 10 of each cell 1 measures the sound pressure of the acoustic wave, and each measurement value is returned to the cell control unit 12.

[0082] The control unit 12 estimates the sound pressure at the level of the speaker and / or its spatial derivative, and then determines a control rule for setting the number of amperes of the electrical signal that must be sent to the speaker 11 to obtain the determined acoustic impedance Z of the speaker. det of the electrical signal.

[0083] According to the present invention, in this step, the control unit estimates the sound pressure at the level of the speaker, or its spatial derivative, or both.

[0084] By using the spatial derivative of the pressure, it is advantageously possible to take into account the rate of change of the pressure field on the acoustic treatment wall and the effective propagation speed of the noise through the wall.

[0085] The step in which the control unit 12 transmits an electrical signal to the speaker 11 such that a part of the acoustic wave is absorbed by the membrane of the speaker and the remaining second part is reflected.

[0086] For certain applications, the calculation of the control rule is preferably performed locally at a frequency of 50 kHz by an ARM-type microcontroller.

[0087] Advantageously, a part of the acoustic wave absorbed by the membrane of the speaker 11 is converted into electrical energy for supplying each of the cells.

[0088] The main control device C equipped with the interface card advantageously enables communication with the control unit 12 of each unit cell from the graphical user interface.

[0089] Then, the counting of the formula can be determined and updated in real time, and the cells can be individually activated or stopped.

[0090] This type of architecture makes it possible to implement local control rules that require different dynamics for each cell.

[0091] In addition, the main control device C can drive all of the control units 12 using a learning loop.

[0092] As an example, the loop can include a first step "BEGIN" to start the process.

[0093] Next, a general acoustic model is started in the sense that any acoustic model can be appropriate, and in this case step A1, which is actually defined by Equation [Equation 3], follows.

[0094] Next, at A2, a control law is assigned to at least one of the cells.

[0095] At A3, the parameters associated with the control law are calculated.

[0096] At A4, the control law is applied to the cells.

[0097] To verify the suitability of the device constituted by the set of cells with respect to the generalized impedance, a reference signal is generated at A5. This reference signal is actually the "noise" started by the speaker or an external element, which is collected by the microphone during step A6 to start the control loop.

[0098] Step A6 enables the microphone to collect the signal.

[0099] Next, at A7, the insertion loss (IL) must be calculated.

[0100] Note that the insertion loss is a customary known physical variable corresponding to the reduction in the level of the sound pressure that occurs by inserting an acoustic control device into the duct instead of a section of the duct having a rigid wall.

[0101] At A8, the insertion loss is the desired generalized impedance Z detTo verify whether it is greater than the minimum IL0 value corresponding thereto, the insertion loss (IL) is compared with a predetermined insertion loss value IL0.

[0102] In A9, when IL < IL0, in order to minimize the error of the measured impedance, the main control device C loops back to A3 to conform to the parameters of the control law.

[0103] Otherwise, the loop ends with the command END.

[0104] Therefore, when the insertion loss IL is less than the minimum value, the main control device C resumes the loop to refine the control law.

[0105] This process is repeated until the desired generalized impedance Z det is obtained.

[0106] It is possible to calibrate each cell simultaneously, just as it is possible to calibrate the cells iteratively, i.e., one after another.

[0107] The control law implemented is an infinite impulse response filter (IIR).

[0108] The output of the filter depends on both the state of the input (pressure and pressure gradient) and the output (current setpoint) at the instant t and the preceding instants as a function of the filter order.

[0109] The calculation of the dynamics of the device is performed by a microcontroller. This calculation is performed in discrete time at each sampling interval in an iterative form.

[0110] Therefore, it is necessary to establish this iterative form based on the equation of the transfer function representing the target dynamics.

[0111] The following equivalent relationship d / dt = jω = p is used, by which it is possible to convert from the time domain to the harmonic frequency and Laplace domain. Therefore, the control law can be defined as follows.

[0112] The desired dynamics of the current in amperes (i) are expressed in the form of a sum of infinite impulse response filters (IIR) with respect to the sound pressure (p) and its gradient (grad(p)), and the dynamics are represented by two transfer functions H loc and H dis which are embodied.

[0113] [Equation 1] [Equation] H loc and H dis are described in discrete time as polynomial fractions of z.

[0114] [Equation 2] [Equation]

[0115] (a i , b i ) are the real coefficients of the equation, and (m, n) are integers corresponding to the filter order.

[0116] z -1 being the pure delay of the sampling period generates a recursive control equation between the output at instant k (y k ) and the input at instant k (x k ). [Equation 3]

[0117] [Equation 3] [Equation]

[0118] Since the current drive signal in the speaker coil depends on the pressure and its gradient, the complete control equation is the sum of two recursive equations of the previous form: y tot = y loc + ydis is described as y loc depends on the measured pressure, and y dis depends on the estimated pressure gradient.

[0119] The speaker is controlled by a current source based on an operational amplifier of 150 mA. The form used is a reinforced Howland power supply that is stable in the case of inductive loads such as speakers.

[0120] Therefore, each microphone (10) of each cell (1) measures the sound pressure of the acoustic wave. Based on this, this pressure measurement value and the gradient of this pressure measurement value are in the formula y tot =y loc +y dis and exist in y loc depends on the measured pressure, and y dis depends on the estimated pressure gradient. y loc usually corresponds to the local value of the current at the output, and y dis corresponds to the variance value of the current at the output.

[0121] Similarly, x loc usually corresponds to the local value of the current at the input, and x dis corresponds to the variance value of the current at the input.

[0122] The pressure gradient is a quantity used in mechanics to represent the pressure change in a fluid (here air).

[0123] Equations [Equation 2] and [Equation 3] are equations that are the conventional general definitions of filtering techniques that enable Equation [Equation 1] to represent the desired dynamics of the current amperage (i) with respect to the sound pressure (p) and its gradient (grad(p)) in the form of the sum of infinite impulse response filters.

[0124] Therefore, the method and apparatus for electroacoustic control enable the implementation of a dispersion control law based on the advection equation regarding the attenuation of oblique acoustic waves in a tube.

[0125] Thus, following the iterative procedure for each cell, the parameters of the control law are adapted while the value of the insertion loss is less than a predetermined threshold, and then when the threshold is reached, step c) of claim 1 is executed, which consists in obtaining the determined (i.e. targeted) generalized acoustic impedance Z det of the speaker by applying an appropriate control law (defined by the adaptation of the parameters).

[0126] The advantages of the present invention are as follows.

[0127] The device can be programmed and the priority direction of the processing can be corrected, the device can be programmed in "self-learning" mode so as to locally define in real time the optimal acoustic behavior, the device is adjustable and can take several forms, the device enables the synthesis of an acoustic diode (non-reversible wave propagation) and its 2D extension, the device enables the measurement of the pressure plume of the wall in real time and thus provides source analysis capabilities, the device is more robust than conventional control methods as a result of the distributed nature of the control unit, the device has higher performance than other active systems in terms of pure efficiency and energy consumption.

[0128] It should be noted that the different characteristics, forms, variants, and embodiments of the present invention can be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive.

[0129] Of course, it is also possible to adapt the parameters of the control law while the value of a reference physical variable other than the insertion loss (e.g. transmission loss, absorption coefficient, or target impedance) is sufficiently close to a predetermined value following the iterative process for each cell.

Claims

1. A method for controlling the propagation of acoustic waves in the vicinity of a wall (2), the method comprising: step a) in which Nc cells (1) are attached to the wall, each cell comprising a set of Nm microphones (10), a control unit (12), a power supply, and a speaker (11) connected to the Nm microphones (10), the microphones and the speaker being provided to be driven by the control unit (12); step b) in which each microphone (10) of each cell measures the sound pressure of the acoustic wave and each measurement value is returned to the cell control unit (12); The control unit (12) estimates the sound pressure and / or its tangential spatial derivative at the level of the speaker, and then applies a control rule for setting the number of amperes of the electrical signal that must be sent to the speaker (11) to obtain the determined generalized acoustic impedance Z of the speaker ｄｅｔ of step c), The control unit (12) transmits the electrical signal to the speaker (11) such that a part of the acoustic wave is absorbed by the diaphragm of the speaker (11), and the main control device (C) uses a learning loop to drive all of the control unit (12) so as to adjust the determined generalized acoustic impedance Z of each cell ｄｅｔ step d), which adjusts the comprising the loop comprising BEGIN: a start step; A1: a step of loading a general acoustic model; A2: a step of assigning a control law to at least one of the cells; A3: a step of calculating a parameter associated with the control law; A4: a step of applying the control law to the cell; A5: a step of generating a reference signal; A6: a step of acquiring the reference signal by the microphone; A7: a step of calculating an insertion loss indicated by IL; A8: a step of comparing the calculated insertion loss indicated by IL with a predetermined insertion loss value IL0 corresponding to the acquisition of the determined generalized acoustic impedance Zdet; A9: a step of returning to A3 for adaptation of the parameters of the control law in order to minimize the error of the measured impedance if IL is less than IL0, otherwise the process ends at END A method for controlling the propagation of acoustic waves, characterized by comprising the above.

2. The method for controlling the propagation of acoustic waves according to claim 1, characterized in that each cell comprises 3 to 5 microphones (10).

3. The method for controlling the propagation of acoustic waves according to claim 1 or 2, characterized in that each cell comprises 4 microphones (10).

4. The method for controlling the propagation of acoustic waves according to any one of claims 1 to 3, characterized in that a part of the acoustic wave absorbed by the diaphragm of the speaker (11) is converted into electrical energy specialized for the supply of each of the cells.

5. The generalized acoustic impedance Z_det is modified by the control law for setting the number of amperes of current that must be sent to the speaker, and is defined as follows, a method for controlling the propagation of acoustic waves according to any one of claims 1 to 4: The desired dynamics of the current in amperes (i) are represented in the form of a sum of infinite impulse response filters, indicated by IIRs, with respect to the sound pressure (p) and its gradient (grad(p)), and the dynamics are embodied by two transfer functions H ｌｏｃ and H ｄｉｓ .

6. The control unit (12) is preferably a microcontroller of the ARM type, a method for controlling the propagation of acoustic waves according to any one of claims 1 to 5.

7. The control law is defined at a frequency included between 50 and 150 kHz, a method for controlling the propagation of acoustic waves according to any one of claims 1 to 6.

8. An apparatus for controlling the propagation of acoustic waves in the vicinity of a wall (2), which comprises a set Nc of cells (1) mainly composed of a speaker (11), a set of Nm microphones (10) connected to the speaker, a control unit (12), and a power source, the microphones and the speaker being provided to be driven by the control unit, a part of the acoustic waves absorbed by the membrane of the speaker (11) being converted into electrical energy for supplying the set Nc of cells, each microphone of each cell being able to measure the sound pressure of the acoustic waves, each measured value being returned to the cell control unit, the control unit estimating the sound pressure and / or its tangential spatial derivative at the level of the speaker, and applying a control rule for setting the number of amperes of the electrical signal that must be sent to the speaker so as to obtain the determined generalized acoustic impedance Z ｄｅｔ and the apparatus can also BEGIN: a start step, and A1: a step of loading a general acoustic model, and A2: a step of assigning a control law to at least one of the cells, and A3: a step of calculating a parameter associated with the control law, and A4: a step of applying the control law to the cell, and A5: a step of generating a reference signal, and A6: a step of acquiring the reference signal by the microphone, and A7: a step of calculating the insertion loss indicated by IL, and Step of comparing the insertion loss indicated by A8: IL with a predetermined insertion loss value IL0 corresponding to the acquisition of the desired generalized acoustic impedance Z ｄｅｔ and a step of comparing with A9: a step of returning to A3 for adaptation of the parameters of the control law in order to minimize the error of the measured impedance when IL is less than IL0 The main control device (C) for driving the set of the control unit (12) in a loop including is also included, a device.

9. Each cell includes 3 to 5 microphones (10), a device for controlling the propagation of acoustic waves in the vicinity of the wall (2) according to claim 8.

10. Each cell includes 4 microphones (10), a device for controlling the propagation of acoustic waves in the vicinity of the wall (2) according to claim 9.

11. The device according to any one of claims 8 to 10, more specifically, an acoustic panel covered by a set Nc of cells (1), each cell including a speaker (11), a set of Nm microphones (10) connected to the speaker (11), and a control unit (12) The microphone and the speaker are provided to be driven by the control unit. A part of the acoustic wave absorbed by the membrane of the speaker (11) is converted into electrical energy for supplying to the set Nc of the cells. The generalized acoustic impedance of each speaker (11) is subject to a control law so as to locally define an absorption or reflection behavior on the surface of the panel. The panel is an acoustic panel connected to a main control device (C) for driving the set of the control unit.

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