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

Abstract

The present invention relates to a method and a device for controlling the propagation of acoustic waves in the vicinity of a wall, the method and device implementing a master device for controlling a set Nc of cells (1) primarily made up of a speaker (11), a set of Nm microphones (10) connected to the speaker, and a control unit (12), by means of control laws that determine the intensity of the electrical signal that must be sent to each speaker (11) so as to obtain a target determined generalized acoustic impedance for each speaker, such that a fraction of the acoustic waves is absorbed by the membrane of each speaker (11).

Description

[0001] The present invention relates to a method and device for controlling the propagation of acoustic waves in the vicinity of a wall.

[0002] Reducing noise pollution from transport and human activity has become a major challenge. The use of passive coatings in buildings and vehicles has helped to limit the acoustic signature of aircraft, but it does not adapt to flight conditions and is not significantly effective in the broad frequency band.

[0003] The techniques used for acoustic treatment are generally based on the use of absorbent materials such as foam or architecturally structured cellular materials.

[0004] Thus, for certain applications in building or transport, acoustic liners are used which feature a distribution of Helmholtz resonators at low frequencies and foam at high frequencies.

[0005] The reduction achieved remains less than a few decibels in low frequencies.

[0006] The effectiveness of conventional absorbent treatments is linked to the thickness of materials, therefore constrained by bulk and added mass, not to mention the problems of water and pollutant absorption in these porous materials.

[0007] All these techniques are passive and do not offer any capacity for adaptation or selective noise processing.

[0008] They also do not offer the ability to direct emissions.

[0009] Active noise control techniques were developed as early as the 1980s to address these technological challenges, and applications cover areas as varied as consumer audio or transport, but remain on non-distributed strategies.

[0010] The size and low-frequency efficiency problems of acoustic treatment systems limit their effectiveness for many potential applications.

[0011] Therefore, it became necessary to develop new solutions, particularly to address the issue of broad frequency bands. Document WO 2016 / 083970 A1 describes an active technique for controlling the propagation of acoustic waves using an arrangement of microphones, processing and control units, and one or two cells, each comprising a loudspeaker.

[0012] The technique deployed here makes it possible, in a thickness reduced to a few centimeters, to guarantee good efficiency in absorbing acoustic nuisances for complex waves (grazing or diffuse for example) and for a wide range of frequencies including low frequencies where passive treatments are ineffective.

[0013] The invention proposes to implement a method and a device enabling local and non-local control and adaptive control of the generalized acoustic impedance of a wall.

[0014] We remind you that acoustic impedance is a common and well-known physical quantity which corresponds to the ratio between acoustic pressure and acoustic velocity.

[0015] The device consists of a first layer of acoustic transducers, each made up of microphones and a loudspeaker. A second layer is formed by the electronic part for signal conditioning and real-time control.

[0016] The device is cellular, with each cell integrating a loudspeaker, microphones, and the electronics for processing and signal management. Regarding the process, each cell is autonomous and executes a control law whose parameters can be determined and updated via an integrated interface. This interface manages the network of cells and provides access to the inputs and outputs of the entire system.

[0017] Similarly, the power supply to the device is distributed throughout all the components. The invention relates more specifically to the distributed and modular nature of the system.

[0018] The invention relates in particular to a method for controlling the propagation of acoustic waves in the vicinity of a wall according to claim 1, the method comprising: a step a) in which a number Nc of cells are affixed to the wall, consisting mainly of a loudspeaker connected to an array of Nm microphones, said microphones and loudspeaker being intended to be controlled by a control unit, a step b) in which each microphone of each cell measures the acoustic pressure of the acoustic waves, each measurement being returned to the control unit of the cell, a step c) in which the control unit estimates the acoustic pressure and / or its spatial derivative at the loudspeaker, then defines the control law which fixes the intensity of the electric current which must be sent to the loudspeaker in order to obtain a determined generalized acoustic impedance Z det for the loudspeaker, a step d) in which the control unit sends the electrical signal to the loudspeaker, so that a fraction of the acoustic waves is absorbed by the loudspeaker diaphragm.

[0019] According to the invention, the control unit, in step c) estimates either the sound pressure at the loudspeaker, or its spatial derivative, or both.

[0020] Using spatial derivatives of pressure makes it advantageous to take into account the rates of variation of the pressure field on the wall of the acoustic treatment and to take into account the effective speeds of the wall propagation of the noise.

[0021] A master device controls all the control units following a learning loop in order to adjust the generalized acoustic impedance determined Z det for each cell.

[0022] Thus, according to an iterative process and for each cell, the parameters of the control law are adapted as long as the value of the insertion loss is less than a predetermined threshold, then when the threshold is reached, step c) of claim 1 is carried out, which applies the appropriate control law (defined by the adaptation of the parameters) in order to obtain the determined (i.e. targeted) generalized acoustic impedance Zdet for the loudspeaker.

[0023] Of course, according to an iterative process and for each cell, we could also adapt the parameters of the control law as long as the value of a reference physical quantity, other than the insertion loss (for example the transmission loss, an absorption coefficient or a target impedance), is sufficiently close to a predetermined value.

[0024] Optional features of the invention, complementary or alternative, are set out below.

[0025] Depending on certain characteristics, the loop includes the following steps: BEGIN: start A1: load a generic acoustic model A2: assign a control law to at least one of the cells A3: calculate the parameters associated with the control law A4: apply the control law to the cell A5: generate a calibrated signal (white noise or swept sine wave, for example) A6: acquire the signal by the microphones A7: calculate the insertion loss (or IL = Insertion Loss ) A8: Comparison of insertion loss (or IL = Insertion Loss) with a predetermined insertion loss value IL0 corresponding to obtaining the desired generalized acoustic impedance Z det A9: return to A3 to adapt the parameters of the control law to minimize the error on the measured impedance, in the case where IL < IL0.

[0026] Depending on other characteristics, each cell has between 3 and 5 microphones, preferably 4.

[0027] According to other characteristics, the fraction of acoustic waves absorbed by the speaker diaphragm is converted into electrical energy to power all the cells.

[0028] According to other characteristics, the generalized acoustic impedance is modified by means of the control law defined as follows:

[0029] The desired dynamics of the current intensity (i) with respect to the acoustic pressure (p) and its gradient (grad(p)) are expressed as a sum of infinite impulse response (IIR) filters. Infinite Impulse Response (in English) whose dynamics are represented by two transfer functions H loc and H dis:

[0030] With Hloc and Hdis, which can be written in discrete time as a fraction of polynomials in z: H z = a 0 + a 1 z − 1 + … + a n z − n b 0 + b 1 z − 1 + … + b m z − m

[0031] With (ai, bi) the real coefficients of the equation and (m, n) the integers corresponding to the order of the filter.

[0032] Given that the property that z -1< is a pure delay of one sampling period gives the recurrent control equation between an output at time k (yk ) and an input at time k (xk ): y k = 1 a 0 ∑ i = 1 m b i . x k − i − ∑ j = 1 n a j . y k − j

[0033] Knowing that the current control signal in the speaker coil depends on the pressure and its gradient, the complete control equation can be written as the sum of two recursive equations of the previous form: y tot = y loc + y dis.

[0034] With y loc depending on the measured pressure and y dis depending on the estimated pressure gradient.

[0035] Thus the process consists of imposing a physical dynamic on the system based solely on knowledge of the measurement of the physical state of the system (pressure, and / or pressure gradient in the vicinity of the speaker diaphragm).

[0036] The process therefore does not require the use of a theoretical model of the behavior of technological components (for example the loudspeaker).

[0037] According to other characteristics, the control unit is a microcontroller, preferably of the ARM type. This type of microcontroller falls under an external architecture of the 32-bit (ARMv1 to ARMv7) and 64-bit (ARMv8) type RISC1 developed by ARM Ltd since 1983 and introduced from 1990 by Acorn Computers.

[0038] According to other characteristics, the control law is defined at a frequency between 25 and 150 kHz.

[0039] The invention also relates to a device for controlling the propagation of acoustic waves in the vicinity of a wall according to claim 8, characterized in that it comprises a number Nc of cells consisting mainly of a loudspeaker, an array of Nm microphones connected to said loudspeaker, a control unit, and a power supply, said microphones and loudspeaker being intended to be controlled by said control unit, a fraction of the acoustic waves absorbed by the loudspeaker diaphragm being converted into electrical energy to power the array Nc of cells, each microphone of each cell being capable of measuring the acoustic pressure of the acoustic waves, each measurement being returned to the cell's control unit, the control unit being capable of estimating the acoustic pressure and / or its tangential spatial derivatives at the loudspeaker,and capable of applying the control law that determines the intensity of the electrical signal to be sent to the loudspeaker in order to obtain a determined generalized acoustic impedance Zdet for the loudspeaker, the device further comprising a master device to control all the control units according to a loop comprising the following steps: BEGIN: start A1: loading of a generic acoustic model A2: assignment of a control law to at least one of the cells A3: calculation of the parameters associated with the control law A4: application of the control law to the cell A5: generation of a calibrated signal (white noise or swept sine wave for example) A6: acquisition of the signal by the microphones A7: calculation of the insertion loss (or , IL = Insertion Loss ) A8: Comparison of insertion loss (or IL = Insertion Loss) with a predetermined insertion loss value IL0 corresponding to obtaining the desired generalized acoustic impedance Z det A9: return to A3 to adapt the parameters of the control law to minimize the error on the measured impedance, in the case where IL < IL0.

[0040] Optional features of the invention, complementary or alternative, are listed below

[0041] Depending on certain characteristics, each cell of the device contains between 3 and 5 microphones, preferably 4.

[0042] Similarly, the power supply to the device is distributed throughout all the components. The invention relates more specifically to the distributed and modular nature of the distributed system.

[0043] The distributed nature of the microphones makes it possible to reconstruct spatial derivatives and to measure a pressure field in real time.

[0044] The distributed nature of the actuators allows for a control law that varies in space.

[0045] The distributed nature of the control units allows for a high level of robustness (the system can operate in degraded mode, even with several malfunctioning elements).

[0046] All control units are autonomous, but can be reconfigured in real time by a master device which allows self-learning to adapt to new ambient conditions.

[0047] Finally, the assembly can be mounted directly on the wall or as an interlocking piece on a support grid, allowing for modularity to adapt to various geometries.

[0048] The invention also relates to an acoustic panel coated with an array Nc of cells consisting mainly of a loudspeaker, an array of Nm microphones connected to said loudspeaker, and a control unit, said microphones and loudspeaker being intended to be controlled by said control unit, a fraction of the acoustic waves absorbed by the loudspeaker membrane being converted into electrical energy to power the array Nc of cells, the generalized acoustic impedance of each loudspeaker being subjected to a control law, so as to define locally on the surface of said panel an absorbing or reflecting behavior, the panel being further connected to a master device to control the array of control units following a loop such as that detailed above.

[0049] Other advantages and features of the invention will become apparent upon reading the detailed description of implementations and embodiments, which are by no means limiting, and the following attached drawings: [ Fig.1 This figure represents a schematic view of an acoustic control device according to the invention. Fig.2 This figure represents a detail of an acoustic cell according to the invention.

[0050] The embodiments described below are not exhaustive; variants of the invention may include, in particular, a selection of the described features, isolated from the other described features (even if this selection is isolated within a sentence containing these other features), provided that this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one feature, preferably a functional feature without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0051] The device according to the invention aims to transform an electroacoustic transducer into a versatile electroacoustic resonator capable of absorbing sound energy in a space or containing this energy between two adjacent spaces without using sensors in order to achieve the desired noise reduction.

[0052] The technological innovation includes, in particular, a modification of the internal dynamics of the electroacoustic transducer by means of an electrical load impedance connected to its terminals, adapted to the electroacoustic transducer used as well as to the acoustic radiation conditions and the desired acoustic performance.

[0053] The role of this impedance is to adjust losses and compensate for reactive parts of the transducer, in order to enable it to deliver performance that meets acoustic requirements.

[0054] The acoustic impedance presented by the membrane of the electroacoustic transducer to the surrounding sound field can thus be made transparent, absorbing or insulating to incident sound waves, depending on the transfer function performed by the electrical load impedance.

[0055] The synthesized electrical impedance constitutes the functional link between the voltage induced by the electroacoustic transducer subjected to an exogenous pressure field and the current required to absorb or contain the incident sound energy.

[0056] The object of the invention relates among other things to an electroacoustic system regulated in closed loop and continuously according to a self-adjustment whose control laws are based on prior knowledge of the internal model, that is to say of the transduction mechanisms and the dissipative and reactive mechanisms inherent in the transducer mounted on a speaker or baffle.

[0057] In terms of operating principle, a moving part of the loudspeaker (for example, the diaphragm, dust cover, and voice coil) is set in motion when subjected to an external acoustic pressure field. It oscillates back and forth along the transducer's axis of symmetry and is returned to an equilibrium position by the action of a spider and peripheral suspensions. The movement of the voice coil, itself immersed in a magnetic field generated by a permanent magnet, creates an electromotive force, which is translated into an induced voltage across the transducer's electrical terminals.

[0058] This induced voltage mirrors the acoustic disturbance that causes the movement of the moving part, but it also depends on the internal dynamics of the loudspeaker system and the acoustic radiation conditions (enclosure, position in a room, etc.). It constitutes the input to the regulator, whose role is to send back a calculated compensating electrical current to apply a mechanical force to the diaphragm adapted to the desired acoustic effect: sound absorption in a space or sound insulation between two adjacent spaces.

[0059] Controlling the generalized acoustic impedance, that is, the dynamics of the relationship between pressure, pressure gradient and velocity at the controlled surface, results in a significant reduction of the energy transmitted along the treated surface.

[0060] This control is achieved by a distribution of loudspeakers, which act on the velocity field, as well as by a distribution of microphones which allow the measurement of the acoustic pressure field and its gradient.

[0061] It is therefore necessary to be able to impose the electric current flowing in the speaker coil, the value of the intensity being preferably calculated by an infinite impulse response (IIR) filter, as a function of the measured acoustic pressure and its gradient.

[0062] The developed device allows for the simultaneous control of N active loudspeaker cells.

[0063] The architecture of the device also allows for real-time modification of the dynamics of each implemented filter.

[0064] Programming the generalized acoustic impedance imposed locally on the active surface affixed to the wall thus allows for the easy implementation of different control strategies.

[0065] Imposing a generalized acoustic impedance on a wall is equivalent to imposing the dynamics between acoustic pressure, the acoustic pressure gradient, and the air velocity at the level of that wall.

[0066] The development of such a process and such a control device then makes it possible to create a regulation loop having as input the signals from the microphones and as output the setpoint of the current to be imposed in the speaker coil.

[0067] The bandwidth of interest extends from 20 to 20000 Hertz, and in particular in the context of civil engineering applications from 20 to 1500 Hertz.

[0068] To ensure a reduced footprint and allow effective control in the target frequency band, the wall can be subdivided into local control zones of five centimeters on each side.

[0069] As represented in figures 1 et 2 , the device consists of Nc = 12 identical and autonomous cells 1 composed of a loudspeaker 11, Nm microphones 10, an electronic signal conditioning board, a digital calculation board and a power supply, the whole representing the control unit 12.

[0070] Each cell contains between 3 and 5 microphones, preferably 4.

[0071] Each loudspeaker 11 is controlled by a power supply managed by a specifically developed digital processing board. The four microphones 10 of each cell 1 allow for the estimation of the average pressure at the center of the diaphragm of each loudspeaker. The pressure difference between the right and left boundaries of the cell allows for the evaluation of the spatial pressure gradient along the wave propagation axis in the duct.

[0072] In terms of operation and in relation to the figure 2 The device captures acoustic pressure using 10 microphones.

[0073] After conditioning in a processing unit 13, the signals are digitized by an analog-to-digital converter (ADC).

[0074] The average pressure at the center of the membrane and / or the spatial derivative of the pressure at the membrane level is estimated from the microphone measurements. The control law is then calculated by the computing unit 12.

[0075] The current setpoint from the previous calculation is generated by a digital-to-analog converter (DAC).

[0076] Finally, a current source drives the current flowing through Speaker 11.

[0077] In more detail, the control method according to the invention comprises the following steps: a step in which a number Nc of cells 1 are affixed to the wall, consisting mainly of a loudspeaker 11 connected to a set of Nm microphones 10, said microphones and loudspeaker being intended to be controlled by a control unit 12, a step in which each microphone 10 of each cell 1 measures the acoustic pressure of the acoustic waves, each measurement being returned to the control unit 12 of the cell, a step in which the control unit 12 estimates the acoustic pressure at the level of the loudspeaker and / or its spatial derivative, then determines the control law which fixes the intensity of the electrical signal which must be sent to the loudspeaker 11 in order to obtain a determined acoustic impedance Z det for the loudspeaker,

[0078] According to the invention, the control unit, in this step, estimates either the acoustic pressure at the loudspeaker, or its spatial derivative, or both.

[0079] Using spatial derivatives of pressure makes it advantageous to take into account the rates of variation of the pressure field on the wall of the acoustic treatment and to take into account the effective speeds of the wall propagation of the noise. a step in which the control unit 12 sends the electrical signal to the loudspeaker 11, so that a fraction of the acoustic waves is absorbed by the loudspeaker diaphragm, the remaining second fraction being reflected.

[0080] In some applications, the calculation of control laws is performed locally at a frequency of 50 kHz by a microcontroller, preferably of the ARM type.

[0081] Advantageously, the fraction of acoustic waves absorbed by the speaker diaphragm 11 is converted into electrical energy to power each of the cells.

[0082] A master device C equipped with an interface card allows advantageous communication with the control unit 12 of each unit cell from a graphical user interface.

[0083] The coefficients of the equations can then be determined and updated in real time, and the cells can be activated or deactivated separately.

[0084] This type of architecture allows for the local implementation of control laws requiring different dynamics from one cell to another.

[0085] Furthermore, the master device C can control all the control units 12 following a learning loop.

[0086] As an example, the loop may include a first "BEGIN" step to initiate the process.

[0087] Then follows a step A1 in which a generic acoustic model is initiated, in the sense that any acoustic model can be suitable and in this case, it is in fact defined by the equation [Math3].

[0088] Next, in A2, we assign a control law for at least one of the cells.

[0089] In A3, we calculate the parameters associated with the control laws.

[0090] In A4, the control law is applied to the cell.

[0091] To verify the suitability of the device consisting of all the cells in terms of generalized impedance, a reference signal is generated in A5. This reference signal is actually "noise" initiated by the loudspeaker or an external component, which is collected during step A6 by the microphones to initiate the control loop.

[0092] Step A6 allows the microphones to collect the signal.

[0093] Next, the insertion loss (or) must be calculated in cell A7. IL = Insertion Loss).

[0094] We remind you that insertion loss is a common and known physical quantity which corresponds to the reduction in the acoustic power level, caused by the insertion of an acoustic control device in a duct in place of a rigid walled duct section.

[0095] In A8, we compare the insertion loss (or IL = Insertion Loss) with a predetermined insertion loss value IL0, to check if the insertion loss is greater than the minimum value IL0 corresponding to the desired generalized impedance Z det.

[0096] In A9, the master device C loops back to A3 to adapt the parameters of the control law to minimize the error on the measured impedance, in the case where IL < IL0.

[0097] Otherwise, the loop ends with the END command.

[0098] Thus, in the case where the insertion loss IL is less than a minimum value, the master device C restarts the loop in order to refine the control laws.

[0099] This process is repeated until the desired generalized impedance Z det is obtained.

[0100] It is possible to calibrate each of the cells at the same time, just as it is possible to calibrate the cells iteratively, that is, one after the other.

[0101] The implemented control laws are infinite impulse response (IIR) filters.

[0102] The filter output depends on both the state of the inputs (pressure and pressure gradient) and outputs (current setpoint) at time t and at previous times as a function of the filter order.

[0103] The device dynamics are calculated by a microcontroller. This calculation takes place in discrete time, at all sampling periods, in the form of a recurrent equation.

[0104] It is therefore necessary to establish this recursive equation from the expression of the transfer function representing the targeted dynamics.

[0105] We use the following equivalence relation d / dt = jω = p which allows us to go from the time representation to the harmonic and Laplace frequency representation.

[0106] The control law can therefore be defined as follows:

[0107] The desired dynamics of the current intensity (i) with respect to the acoustic pressure (p) and its gradient (grad(p)) are expressed as a sum of infinite impulse response (IIR) filters. Infinite Impulse Response (in English) whose dynamics are represented by two transfer functions H loc and H dis:

[0108] With Hloc and Hdis, which can be written in discrete time as a fraction of polynomials in z: H z = a 0 + a 1 z − 1 + … + a n z − n b 0 + b 1 z − 1 + … + b m z − m

[0109] With (ai, bi) the real coefficients of the equation and (m, n) the integers corresponding to the order of the filter.

[0110] The property that z -1< is a pure delay of one sampling period gives the recurrent control equation between an output at time k (yk ) and an input at time k (xk ): y k = 1 a 0 ∑ i = 1 m b i . x k − i − ∑ j = 1 n a j . y k − j

[0111] Since the current control signal in the speaker coil depends on the pressure and its gradient, the complete control equation is written as the sum of two recursive equations of the previous form: y tot = y loc + y dis.

[0112] With y loc depending on the measured pressure and y dis depending on the estimated pressure gradient.

[0113] The loudspeakers are controlled by a current source based on 150mA operational amplifiers. The chosen form is an improved Howland source, stable in the case of inductive loads such as loudspeakers.

[0114] Thus, each microphone (10) of each cell (1) measures the acoustic pressure of the acoustic waves. Therefore, this pressure measurement and the gradient of this pressure measurement are found in the equation y tot = y loc + y dis, with y loc depending on the measured pressure and y dis depending on the estimated pressure gradient.

[0115] y loc usually corresponds to the local value of the output current while y dis corresponds to the distributed value of the output current.

[0116] Similarly, x loc usually corresponds to the local value of the input current while x dis corresponds to the distributed value of the input current.

[0117] The pressure gradient is the quantity used in mechanics to represent the variation of pressure in a fluid (here, air).

[0118] Equations [Math 2] and [Math 3] are equations which are classic generic definitions of filtering techniques which allow to express with equation [Math 1] the desired dynamics of the current intensity (i) with respect to the acoustic pressure (p) and its gradient (grad(p)), in the form of a sum of filters with infinite impulse response.

[0119] Thus, the electroacoustic control process and device allow the implementation of a distributed control law based on an advection equation aimed at attenuating grazing acoustic waves in a tube.

[0120] Thus, according to an iterative process and for each cell, the parameters of the control law are adapted as long as the value of the insertion loss is less than a predetermined threshold, then when the threshold is reached, step c) of claim 1 is carried out, which applies the appropriate control law (defined by the adaptation of the parameters) in order to obtain the determined (i.e. targeted) generalized acoustic impedance Zdet for the loudspeaker.

[0121] The advantages of the invention are as follows: The device can be programmed and the preferred direction of processing can be modified; the device can be programmed in "self-learning" mode so as to define locally and in real time the optimal acoustic behavior; the device is modular and can adopt several geometries; the device allows the synthesis of an acoustic diode (non-reciprocal propagation of waves) and potentially its 2D extension; the device allows the measurement of wall pressure fields in real time and therefore offers a source analysis capability; the device is more robust than classical control approaches due to the distributed nature of the control units; the device is more efficient than other active systems, in terms of pure efficiency and energy consumption.

[0122] Note that the different characteristics, forms, variants and embodiments of the invention can be associated with each other, according to various combinations insofar as they are not incompatible or exclusive of each other.

[0123] Of course, according to an iterative process and for each cell, we could also adapt the parameters of the control law as long as the value of a reference physical quantity, other than the insertion loss (for example the transmission loss, an absorption coefficient or a target impedance), is sufficiently close to a predetermined value.

Claims

1. Method for controlling the propagation of the acoustic waves in the vicinity of a wall (2), the method comprising: - a step a) in which a number Nc of cells (1), Nc>1, each comprising a set of Nm microphones (10), a control unit (12), a power supply, a speaker (11) linked to said set of Nm microphones (10) is affixed on the wall, said microphones and speaker being provided to be driven by said control unit (12), - a step b) in which each microphone (10) of each cell (1) measures the acoustic pressure of the acoustic waves. each measurement being returned to said cell control unit (12), - a step c) in which the control unit (12) of said cell estimates the acoustic pressure and / or its tangential spatial derivatives at the level of the speaker of said cell, then applies the control law that sets the amperage of the electrical signal that must be sent to said speaker (11) so as to obtain a determined generalized acoustic impedance Zdet for said speaker, - a step d) in which the control unit (12) of said cell sends the electrical signal to the speaker (11), so that a fraction of the acoustic waves is absorbed by the membrane of the speaker (11), a main control device (C) driving all of the control units (12), using a learning loop so as to adjust the determined generalized acoustic impedance Zdet for each cell.

2. Method for controlling the propagation of acoustic waves according to claim 1, characterized in that the loop includes the following steps: BEGIN: start A1: loading a generic acoustic model A2: assigning a control law to at least one of the cells A3: calculating the parameters associated with the control law A4: applying the control law to the cell A5: generating a reference signal A6: acquiring the signal by the microphones A7: calculating the insertion loss denoted IL A8: comparing the calculated insertion loss denoted IL with a predetermined insertion loss value IL0 corresponding to obtaining the determined generalized acoustic impedance Zdet A9: return to A3 for adaptation of the parameters of the control law in order to minimize the error on the measured impedance, in the event that IL is less than IL0, otherwise, the process finishes with END.

3. Method for controlling the propagation of acoustic waves according to any one of the preceding claims, characterized in that each cell includes between 3 and 5 microphones (10), preferably 4.

4. Method for controlling the propagation of acoustic waves according to any one of the preceding claims, characterized in that the fraction of the acoustic waves absorbed by the membrane of the speaker (11) is converted into electrical energy dedicated to supplying each of the cells.

5. Method for controlling the propagation of acoustic waves according to any one of the preceding claims, characterized in that the generalized acoustic impedance Zdet is modified by means of the control law that sets the amperage of the electric current that must be sent to the speaker, defined as follows: The desired dynamics of the current amperage (i) is expressed with respect to the acoustic pressure (p) and its gradient (grad(p)), in the form of a summation of infinite impulse response filters denoted IIR, the dynamics of which is materialized by two transfer functions Hloc and Hdis.

6. Method for controlling the propagation of acoustic waves according to any one of the preceding claims, characterized in that the control unit (12) is a microcontroller, preferably of the ARM type.

7. Method for controlling the propagation of acoustic waves according to any one of the preceding claims, characterized in that the control law is defined at a frequency comprised between 50 and 150 kHz.

8. Device for controlling the propagation of acoustic waves in the vicinity of a wall (2), characterized in that it comprises a set Nc of cells (1), Nc>1, each comprising a speaker (11), a set of Nm microphones (10) linked to said speaker, a control unit (12), and a power supply, said microphones and speaker being provided to be driven by said control unit, a fraction of the acoustic waves absorbed by the membrane of the speaker (11) being converted into electrical energy to supply the set Nc of cells, each microphone of each cell being capable of measuring the acoustic pressure of the acoustic waves, each measurement being returned to the cell control unit, the control unit being capable of estimating the acoustic pressure and / or its tangential spatial derivatives at the level of the speaker, and capable of applying the control law that sets the amperage of the electrical signal that must be sent to the speaker so as to obtain a determined generalized acoustic impedance Zdet for the speaker, the device also including a main control device (C) for driving the set of control units (12) in a loop including the following steps: BEGIN: start A1: loading a generic acoustic model A2: assigning a control law to at least one of the cells A3: calculating the parameters associated with the control law A4: applying the control law to the cell A5: generating a reference signal A6: acquiring the signal by the microphones A7: calculating the insertion loss denoted IL A8: comparing the insertion loss denoted IL with a predetermined insertion loss value IL0 corresponding to obtaining the desired generalized acoustic impedance Zdet A9: return to A3 for adaptation of the parameters of the control law in order to minimize the error on the measured impedance, in the event that IL is less than IL0.

9. Device for controlling the propagation of acoustic waves in the vicinity of a wall (2) according to claim 8, characterized in that each cell includes between 3 and 5 microphones (10), preferably 4.

10. Acoustic panel incorporating a device according to one of claims 8 to 9, more particularly covered with a set Nc of cells (1), Nc>1, comprising a speaker (11), a set of Nm microphones (10) linked to said speaker, and a control unit (12), said microphones and speaker being provided to be driven by said control unit, a fraction of the acoustic waves absorbed by the membrane of the speaker (11) being converted into electrical energy to supply the set Nc of cells, the generalized acoustic impedance of each speaker (11) being subject to a control law, so as to define locally to the surface of said panel the absorbing or reflecting behaviour, the panel being connected to a main control device (C) for driving the set of control units.

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