Method and apparatus for controlling propagation of sound waves on a wall

Abstract

The invention relates to a method and a device for controlling the propagation of sound waves in the vicinity of a wall, the method and the device implementing, by means of a control law, a master device for controlling a set of Nc elementary cells (1) mainly composed of a loudspeaker (11), a set of Nm microphones (10) connected to the loudspeaker and a control unit (12), the control law determining an electrical signal to be sent to each loudspeaker (11) to obtain a target generalized acoustic impedance determined for each loudspeaker, so that a portion of the sound waves is absorbed by the membrane of each loudspeaker (11).

Description

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

[0002] Reducing sound disturbance caused by traffic and human activity has become a major challenge. The use of passive coatings in buildings or vehicles makes it possible to limit the acoustic signature of the aircraft, but does not allow adjustment to flight conditions and does not have a significant effect on a wide frequency band.

[0003] The techniques used for acoustic treatment are generally based on the use of absorbent materials of the foam type or structural honeycomb materials.

[0004] Thus, for certain applications in construction or traffic, at low frequencies, acoustic linings with distributed Helmholtz resonators are used, while at high frequencies, foams are used.

[0005] At low frequencies, the obtained sound attenuation remains below a few decibels.

[0006] The effectiveness of conventional absorbent treatments is related to the thickness of the material, and is therefore limited by the increase in volume and weight, not to mention the problem of water and pollutant absorption into these porous materials.

[0007] All these techniques are passive and do not have the ability to adjust or selectively treat noise.

[0008] All these techniques also no longer have the ability to direct emissions.

[0009] Since the 1980s, in response to these technical challenges, active noise control techniques have been developed and applications involve different fields such as consumer audio or traffic, but rely on non-distributed strategies.

[0010] The problem of the volume and low-frequency effectiveness of acoustic treatment systems leads to their limited effectiveness for many potential applications.

[0011] For this reason, it has been found necessary to develop new solutions that make it possible to treat, in particular, the problem of a wide frequency band.

[0012] The deployed technique makes it possible to ensure, in a thickness reduced to a few centimeters, effective absorption of sound disturbance for complex waves (for example, oblique or diffuse) and for a wide range of frequencies, including low frequencies for which passive treatments are ineffective.

[0013] To this end, the present invention proposes to implement a method and a device that make it possible to locally and non-locally control the generalized acoustic impedance of a wall in an adjustable manner.

[0014] It is noted that the acoustic impedance is a customary and known physical variable corresponding to the ratio between the acoustic pressure and the speed of sound.

[0015] The device is made up of a first layer of acoustic transducers, each acoustic transducer being made up of a microphone and a loudspeaker. A second layer is formed by electronic components for signal conditioning and real-time command / control.

[0016] The device is cellular, each cell integrating a loudspeaker, a microphone, and electronic means for computation and signal management.

[0017] As regards the method, each cell is independent and implements a control law whose parameters can be determined and updated through an integrated interface. It makes it possible to manage the matrix of cells as a whole and to access the inputs and outputs of the system.

[0018] Similarly, the device is powered by all the elements. The invention relates more particularly to the distributed and adjustable character of the system.

[0019] In particular, the invention relates to a method for controlling the propagation of sound waves in the vicinity of a wall, the method comprising:

[0020] - a step a) in which a number Nc of cells, mainly constituted of a loudspeaker connected to a set of Nm microphones, are fixed on the wall, the microphones and loudspeakers being arranged to be driven by a control unit,

[0021] - a step b) in which each microphone of each cell measures the sound pressure of the sound waves, each measurement being returned to the cell control unit,

[0022] - a step c) in which the control unit estimates the sound pressure and / or its spatial derivative at the loudspeaker, then defines a control law of the current amperes that must be sent to the loudspeaker to obtain a determined generalized acoustic impedance Z det for the loudspeaker,

[0023] - a step d) in which the control unit sends an electrical signal to the loudspeaker so that a portion of the sound waves is absorbed by the membrane of the loudspeaker.

[0024] According to the invention, in step c), the control unit estimates the sound pressure at the loudspeaker, or its spatial derivative, or both.

[0025] The use of the spatial derivative of the pressure makes it possible to advantageously take into account the rate of variation of the pressure field on the acoustically treated wall, and the effective propagation speed of the noise through the wall.

[0026] The main control device uses a learning loop to drive all the control units to adjust the determined generalized acoustic impedance Z det for each cell.

[0027] Thereby, according to an iterative procedure for each cell, the parameters of the control law are adjusted while the value of the insertion loss is less than a predetermined threshold, then when the threshold is reached, the step c) of claim 1 is implemented, which applies the control law (defined by the adjustment of the parameters) suitable for obtaining the determined (i.e. target) generalized acoustic impedance Z for the loudspeaker det .

[0028] Of course, according to an iterative procedure for each cell, it is also possible to adjust the parameters of the control law while the value of a reference physical variable (for example the transmission loss, the absorption coefficient or the target impedance) other than the insertion loss is sufficiently close to a predetermined value.

[0029] The following provides optional features (whether additional or alternative) of the application.

[0030] According to certain features, said cycle comprises the following steps:

[0031] BEGIN: start

[0032] A1 : load the general acoustic model

[0033] A2: assign a control law to at least one of the cells

[0034] A3: calculate the parameters associated with the control law

[0035] A4: apply the control law to the cell

[0036] A5: generate a reference signal (for example white noise or a sinusoidal sweep)

[0037] A6: acquire the signal by means of a microphone

[0038] A7: calculate the insertion loss (IL)

[0039] A8: compare the insertion loss (IL) with a predetermined insertion loss value IL0 corresponding to the desired generalized acoustic impedance Z det

[0040] A9: in the case where IL < IL0, return to A3 to adjust the parameters of the control law in order to minimize the error of the measured impedance.

[0041] According to other features, each cell comprises 3 to 5, preferably 4 microphones.

[0042] According to still other features, the portion of the acoustic wave absorbed by the membrane of the loudspeaker is converted into electrical energy for powering all the cells.

[0043] According to still other features, the generalized acoustic impedance is varied by means of a control law defined as follows:

[0044] ​The desired dynamics of the current amperage (i) with respect to the sound pressure (p) and its gradient (grad(p)) are expressed in the form of a sum of infinite impulse response (IIR) filters whose dynamics are given by two transfer functions H loc and H dis are particularized as:

[0045] [Math 1]

[0046]

[0047] where H loc and H dis are written in discrete time as polynomial fractions in z:

[0048] [Math 2]

[0049]

[0050] where (a i ,b i ) are the real coefficients of the equation and (m,n) are integers corresponding to the order of the filter.

[0051] Given that z -1 is a pure delay of the sampling period, the circular control equation between the output at instant k (y k ) and the input at instant k (x k ) is given by:

[0052] [Math 3]

[0053]

[0054] Given that the current drive signal in the coil of a loudspeaker depends on the pressure and its gradient, the complete control equation is written as the sum of two circular equations of the aforementioned form: y tot = y loc + y dis .

[0055] where y loc depends on the measured pressure and y dis depends on the estimated pressure gradient.

[0056] From this, the method consists in imposing the physical dynamics on the system when only the measurements of the physical state of the system (pressure near the membrane of the loudspeaker, and / or pressure gradient) are known.

[0057] Thus, the method does not require the use of a theoretical model of the behavior of the technical means (for example, loudspeaker).

[0058] More still other features, the control unit is a microcontroller, preferably of the ARM type. Microcontrollers of this type are based on the RISC type external architecture of 32 bits (ARMv1 to ARMv7) and 64 bits (ARMv8) developed by ARM Ltd since 1983 and introduced by Acorn Computers from 1990.

[0059] According to still other features, the control law is defined at a frequency of 25 to 150 kHz.

[0060] The application also relates to a device for controlling the propagation of acoustic waves in the vicinity of a wall, characterized in that it comprises a number Nc of cells consisting essentially of a loudspeaker, a set of Nm microphones connected to the loudspeaker, a control unit and a power supply, the microphones and the loudspeaker being arranged to be driven by the control unit, the part of the acoustic wave absorbed by the membrane of the loudspeaker being converted into electrical energy for powering the set of Nc cells, each microphone of each cell being able to measure the sound pressure of the acoustic wave, each measurement being returned to the cell control unit, the control unit being able to estimate the sound pressure and / or its tangential spatial derivative at the loudspeaker and to apply a control law setting the number of amperes of the electrical signal that must be sent to the loudspeaker in order to obtain a determined generalized acoustic impedance Z det , for the loudspeaker

[0061] BEGIN: start

[0062] A1: load a generic acoustic model

[0063] A2: assign a control law to at least one of the cells

[0064] A3: calculate the parameters associated with the control law

[0065] A4: apply the control law to the cell

[0066] A5: generate a reference signal (for example white noise or a sinusoidal sweep)

[0067] A6: acquire the signal by the microphones

[0068] A7: calculate the insertion loss (where IL is the Insertion Loss)

[0069] A8: compare the insertion loss (where IL is the Insertion Loss) with a predetermined insertion loss value IL0 corresponding to obtaining the desired generalized acoustic impedance Z det

[0070] ​A9: in case IL < IL0, return to A3 to adjust the parameters of the control law to minimize the error of the measured impedance.

[0071] The following gives optional features of the application, whether additional or alternative.

[0072] According to certain features, each cell of the device comprises 3 to 5, preferably 4 microphones.

[0073] Similarly, the device is powered by all the elements. The application more particularly relates to the distributed and adjustable features of the distribution system.

[0074] The distributed features of the microphones enable the reconstruction in real time of the spatial derivatives and the measurement of the pressure field.

[0075] The distributed features of the actuators enable having a control law variable in space.

[0076] The distributed features of the control units enable having a high level of robustness (the system can still operate in degraded mode even with multiple elements out of order).

[0077] All the control units are independent but can be reconfigured in real time by a master control device allowing self-learning to adjust to new environmental conditions.

[0078] Finally, the assembly can be directly mounted on the wall or in a built-in form on a supporting grid, which allows modularity to adjust to various geometries.

[0079] The application also relates to an acoustic panel covered with a set of Nc cells consisting essentially of a loudspeaker, a set of Nm microphones connected to the loudspeaker and a control unit, the microphones and the loudspeaker being arranged to be driven by the control unit, the part of the sound wave absorbed by the membrane of the loudspeaker being converted into electrical energy for powering the set of Nc cells, the generalized acoustic impedance of each loudspeaker being constrained by a control law to locally define at the surface of the panel an absorption or reflection behavior, the panel being also connected to a master control device for driving the set of control units in a cycle as described above.

[0080] Other advantages and features of the application will become apparent upon reading of the detailed description of the implementation and embodiments, which are in no way limiting, and upon reading of the following drawings:

[0081] [ Figure 1 ] This figure shows details of an acoustic control device according to the application.

[0082] [ Figure 2 ] This figure shows details of an acoustic cell according to the application.

[0083] Since the embodiments described hereinafter are in no way limiting, variants of the application can be considered in particular which include only a selection of the features described, isolated from the other features described (even if this selection is in a sentence which includes these other features), as long as this selection of features is sufficient to confer a technical advantage or to distinguish the application over the prior art. This selection includes at least one, preferably functional, feature without structural details, or only with part of the structural details, if only this part is sufficient to confer a technical advantage or to distinguish the application over the prior art.

[0084] The device according to the application aims to transform an electroacoustic transducer into a multi-valent electroacoustic resonator, making it possible to absorb the acoustic energy in a space, or even to contain this energy between two adjacent spaces, without using a detection element, in order to achieve the desired noise reduction.

[0085] The technical innovation consists in particular in modifying the internal dynamics of the electroacoustic transducer by means of a load impedance connected to its terminals, which is adjusted to the electroacoustic transducer used, as well as to the acoustic diffusion conditions and the desired acoustic performance.

[0086] The role of this impedance is to adjust the losses, and to compensate for the reactive components of the transducer, with the aim of allowing it to exhibit a performance which meets the acoustic requirements.

[0087] According to the transfer function implemented by the load impedance, the membrane of the electroacoustic transducer exhibits an acoustic impedance to the surrounding sound field which can thus be transparent, absorptive, or isolating with respect to the incident sound waves.

[0088] The synthetic impedance constitutes a functional link between the voltage induced by the electroacoustic transducer subjected to an exogenous pressure field, and the current which absorbs or contains the incident acoustic energy.

[0089] The application relates, among other things, to an electroacoustic system controlled continuously in a self-regulating closed loop, the control law of which relies on prior knowledge of the internal model, i.e. the dissipative and reactive mechanisms inherent in the transduction mechanism and the transducer mounted on a housing or baffle.

[0090] For the operating principle, the movable parts of the loudspeaker, such as the membrane, the dust cap and the coil, move when they are subjected to an exogenous sound pressure field, oscillate back and forth along the axis of symmetry of the transducer, and return to the equilibrium position under the action of the peripheral suspension elements of the spider type. The movement of the coil, which is itself immersed in the magnetic field generated by the permanent magnets, generates an electromotive force, which is expressed by the voltage induced at the electrical terminals of the transducer.

[0091] The resulting voltage is the image of the acoustic disturbance causing the mobile part to move from its origin, but also depends on the internal dynamics of the loudspeaker system and on the conditions of acoustic diffusion (enclosure, position in the room, etc.). It constitutes the input of a regulator whose role is to send a compensation current calculated as a function of the mechanical force at the membrane, which is adjusted to the desired acoustic effect: sound absorption in the space, or soundproofing between two adjacent spaces.

[0092] The control of the generalized acoustic impedance (i.e. the dynamics of the relationship between the pressure, the pressure gradient and the velocity at the controlled surface) leads to a significant reduction in the energy transmitted along the treated surface.

[0093] This control is implemented by the distribution of loudspeakers acting on the velocity field, and of microphones allowing the measurement of the sound pressure field and of its gradient.

[0094] It is thus necessary to be able to impose a current flowing in the coil of the loudspeaker, the value in amperes being calculated by an infinite impulse response (IIR) filter as a function of the measured sound pressure and of its gradient.

[0095] The device developed makes it possible to control simultaneously N active elementary cells of loudspeakers.

[0096] The architecture of the device also makes it possible to change in real time the dynamics of each filter used.

[0097] The programming of the generalized acoustic impedance locally imposed on the active surface fixed on the wall thus allows different control strategies to be easily implemented.

[0098] The imposition of the generalized acoustic impedance on the wall constitutes the imposition of the dynamics between the sound pressure, the sound pressure gradient and the air velocity at this wall.

[0099] The development of such a control method and such a control device makes it possible to produce a control loop, the input of which is the microphone signals and the output of which is the current set point that must be imposed in the coil of the loudspeaker.

[0100] The passband of interest is 20 to 20 000 Hertz, and in particular 20 to 1 500 Hertz in the case of civil engineering applications.

[0101] In order to ensure a reduced volume and to allow effective control in the considered frequency band, the wall can be divided into local control zones of 5 centimeters per side.

[0102] As shown in Figure 1 and 2 The device is composed of Nc=12 identical independent elementary cells 1, composed of a loudspeaker 11, Nm microphones 10, an electronic signal conditioning card, a digital calculation card and a power supply, which as a whole represents a control unit 12.

[0103] Each cell comprises 3 to 5, preferably 4 microphones 10.

[0104] Each loudspeaker 11 is controlled by a power supply driven by a specifically developed digital computing 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 loudspeaker. The pressure difference between the left and right boundaries of the cell makes it possible to evaluate the spatial pressure gradient along the propagation axis of the wave in the tube.

[0105] In terms of operation, with reference to Figure 2 , the device acquires the sound pressure by means of the microphones 10.

[0106] After conditioning in the processing unit 13, the signal is digitized by an analog-digital converter (ADC).

[0107] Based on the measurements of the microphones, the average pressure at the center of the membrane and / or the spatial derivative of the pressure at the membrane are estimated. The control law is then calculated by the calculation unit 12.

[0108] The calculated current setpoint is generated by a digital-analog converter (DAC).

[0109] Finally, the current source drives the current that flows in the loudspeaker 11.

[0110] In more detail, the control method according to the present application comprises the following steps:

[0111] - a step in which a number Nc of cells 1, mainly consisting of loudspeakers 11 connected with a set of Nm microphones 10, are fixed to the wall, said microphones and loudspeakers being arranged to be driven by a control unit 12,

[0112] - a step in which each microphone 10 of each cell 1 measures the sound pressure of the sound wave, each measurement being returned to the cell control unit 12,

[0113] - a step in which the control unit 12 estimates the sound pressure at the loudspeaker and / or its spatial derivative, then determines the control law that sets the number of amperes of the electrical signal that must be sent to the loudspeaker 11 to obtain a determined acoustic impedance Z for the loudspeaker det .

[0114] According to the present application, the control unit estimates the sound pressure at the loudspeaker, or its spatial derivative, or both.

[0115] The use of the spatial derivative of the pressure advantageously makes it possible to take into account the rate of variation of the pressure field on the acoustically treated wall and the effective speed of propagation of the noise through the wall.

[0116] - a step in which the control unit 12 sends an electrical signal to the loudspeaker 11 so that a portion of the acoustic wave is absorbed by the membrane of the loudspeaker and a second remaining portion is reflected.

[0117] In some applications, the calculation control law is implemented locally at a frequency of 50 kHz by a microcontroller, preferably of the ARM type.

[0118] Advantageously, the portion of the acoustic wave absorbed by the membrane of the loudspeaker 11 is converted into electrical energy used to power each of the cells.

[0119] The master control device C is equipped with an interface card which advantageously enables communication from a graphic user interface with the control unit 12 of each cell.

[0120] The coefficients of the equation can then be determined and updated in real time and the cells can be activated or deactivated respectively.

[0121] This type of architecture enables the implementation of control laws requiring dynamics that are different from each other between the cells.

[0122] In addition, the master control device C is able to drive all the control units 12 using a learning cycle.

[0123] By way of example, the cycle can comprise a first step "BEGIN" to initiate the process.

[0124] This is then followed by a step Al in which a generic acoustic model is initiated, i.e. any acoustic model can be suitable and in the present example is in fact defined by the equation [Math3].

[0125] Then, in A2, a control law is assigned for at least one of the cells.

[0126] In A3, the parameters associated with the control law are calculated.

[0127] In A4, the control law is applied to the cell.

[0128] In order to verify the suitability of the device made up of the set of cells for the generalized impedance, in A5 a reference signal is generated. This reference signal is in fact a "noise" initiated by the loudspeaker or an external element which is captured by the microphone during step A6 to initiate the control cycle.

[0129] Step A6 allows the microphone to capture the signal.

[0130] Then, in A7, the insertion loss (IL) must be calculated.

[0131] It is noted that the insertion loss is a generally known physical variable corresponding to the decrease in sound pressure level resulting from the insertion in the duct of the acoustic control device instead of the duct segment having rigid walls.

[0132] In A8, the insertion loss (IL) is compared to a predetermined insertion loss value IL0to verify whether the insertion loss is greater than the minimum value IL0corresponding to the desired generalized impedance Z det .

[0133] In A9, in case IL < IL0, the main control device C loops back to A3 to adjust the parameters of the control law to minimize the error of the measured impedance.

[0134] Otherwise, the loop ends with the command END.

[0135] Thus, in case the insertion loss IL is less than the minimum value, the main control device C reinitiates the loop to fine-tune the control law.

[0136] The process is repeated until the desired generalized impedance Z det is obtained.

[0137] It is possible to calibrate each of the cells simultaneously, as it is also possible to calibrate the cells iteratively, i.e. one after the other.

[0138] The implemented control law is an Infinite Impulse Response (IIR) filter.

[0139] The output of the filter depends on both the input (pressure and pressure gradient) and the output (current setpoint) at time t and at previous times according to the filter order.

[0140] The computation of the device dynamics is implemented by the microcontroller. This computation occurs at each sampling interval in the form of a loop equation in discrete time.

[0141] It is thus necessary to establish this loop equation based on an expression representing the transfer function of the target dynamics.

[0142] The following equivalence is used: d / dt = jco = p, which makes it possible to convert from the time representation to the harmonic frequency and Laplace representation.

[0143] Thus, it is possible to define the control law as follows:

[0144] The desired dynamics of the current amperes (i) with respect to the sound pressure (p) and its gradient (grad(p)) are expressed in the form of a sum of Infinite Impulse Response (IIR) filters, the dynamics of which are particularized by two transfer functions H loc and H dis :

[0145] [Math 1]

[0146]

[0147] where H loc and H dis are the polynomials in discrete time written as fractions of polynomials in z:

[0148] [Math 2]

[0149]

[0150] where (a i ,b i ) are the real coefficients of the equation and (m,n) are integers corresponding to the filter order.

[0151] z -1 is a pure delay of the sampling period, the characteristic that produces the recurrent equation between the output at time k (y k ) and the input at time k (x k ):

[0152] [Math 3]

[0153]

[0154] Since the current in the coil of the loudspeaker depends on the pressure and its gradient, the complete control equation is written as the sum of the two recurrent equations in the form presented above: y tot = y loc + y dis .

[0155] where y loc depends on the measured pressure and y dis depends on the estimated pressure gradient.

[0156] The loudspeaker is controlled by a current source based on an operational amplifier of 150 mA. The form used is the enhanced Howland source, which is stable in the case of inductive loads such as the loudspeaker.

[0157] Thus, each microphone (10) of each cell (1) measures the acoustic pressure of the acoustic wave. Based on this, the pressure measurement and the gradient of this pressure measurement exist in the equation y tot = y loc + y dis ,

[0158] where y loc depends on the measured pressure and y dis depends on the estimated pressure gradient.

[0159] y loc corresponds to the local value of the current at the output, while y disThis corresponds to the current distribution at the output.

[0160] Similarly, x loc This typically corresponds to the local value of the current at the input, while x dis The distribution value corresponding to the current at the input.

[0161] The pressure gradient is a quantity used in mechanics to represent the change in pressure in a fluid (air in this case).

[0162] Equations [Math 2] and [Math 3] are the conventionally defined equations for filter techniques that enable the desired dynamics of the current ampere number (i) to be expressed in the form of the sum of the sound pressure (p) and its gradient (grad(p)) of an infinite impulse response filter using equation [Math 1].

[0163] Therefore, the method and apparatus for electroacoustic control allow for the implementation of distributed control based on the advection equation concerning the attenuation of oblique acoustic waves in a tube.

[0164] Therefore, after iterating over each cell, while the insertion loss is less than a predetermined threshold, the parameters of the control law are adjusted. Then, when the threshold is reached, step c) of claim 1 is executed, which applies a suitable control law (limited by parameter adjustment) to obtain a definite (i.e., target) generalized acoustic impedance Z for the loudspeaker. det .

[0165] The advantages of this invention are as follows:

[0166] - The device can be programmed, and the processing priority can be changed.

[0167] - The device can be programmed in a "self-learning" mode to locally and in real-time optimize acoustic performance.

[0168] - The device is adjustable and can be used in various geometries.

[0169] -The device allows for the synthesis of acoustic diodes (non-reciprocal wave propagation) and potentially their two-dimensional extension.

[0170] - The device allows for real-time measurement of the pressure field of the wall, thus providing source analysis capabilities.

[0171] Due to the distributed nature of the control units, the device is more robust than conventional control methods.

[0172] - In terms of pure efficiency and energy consumption, the device outperforms other active systems.

[0173] It is pointed out that the various features, forms, variants and embodiments of the application can be combined together in various combinations, within the limits that they are not mutually exclusive or incompatible.

[0174] Of course, after the iteration process for each cell, it is also possible to adjust the parameters of the control law while the value of a reference physical variable other than the insertion loss (for example the transmission loss, the absorption coefficient or the target impedance) is sufficiently close to the predetermined value.

Claims

1. A method for controlling the propagation of acoustic waves in the vicinity of a wall (2), the method comprising: - a step a) in which a number Nc of cells (1) is fixed to the wall, each cell being mainly composed of a set of Nm microphones (10), a control unit (12), a power supply and a loudspeaker (11) connected to the set of Nm microphones (10), the microphones and the loudspeaker being arranged to be driven by the control unit (12), - a step b) in which each microphone (10) of each cell (1) measures the sound pressure of the acoustic waves, each measurement being returned to the control unit (12) of the cell, - step c) in which the control unit (12) estimates the sound pressure and / or its tangential spatial derivative at the loudspeaker and then applies a control law that sets the number of amperes of the electrical signal that must be sent to the loudspeaker (11) in order to obtain a determined generalized acoustic impedance Z for the loudspeaker det , - step d) in which the control unit (12) sends the electrical signal to the loudspeaker (11) so that a portion of the acoustic wave is absorbed by the membrane of the loudspeaker (11), the master control device (C) using a learning cycle to drive all the control units (12) to adjust the determined generalized acoustic impedance Z for each cell det , the loop comprising the following steps: BEGIN: start A1: load a general 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 reference signal A6: acquire a signal by the microphones A7: calculate the insertion loss IL A8: comparing the computed insertion loss IL with a predetermined insertion loss value IL0 corresponding to obtaining the determined generalized acoustic impedance Z det ​ A9: in case IL is less than IL0, return to A3 to adjust the parameters of the control law to minimize the error on the measured impedance, otherwise the process ends with END.

2. The method for controlling the propagation of sound waves according to claim 1, wherein, Each cell comprises 3 to 5 microphones (10).

3. The method for controlling the propagation of sound waves according to claim 1 or 2, characterized in that, The part of the acoustic waves absorbed by the membrane of the loudspeaker (11) is converted into electrical energy used to power each of the cells.

4. The method for controlling propagation of sound waves according to claim 1 or 2, characterized by, varying the generalized acoustic impedance Z by the control law det , the control law setting the number of amperes of current that must be sent to the loudspeaker and defined as follows: The desired dynamics of the current amperage (i) with respect to the sound pressure (p) and its gradient (grad(p)) are expressed in the form of a sum of infinite impulse response (IIR) filters whose dynamics are given by two transfer functions H loc and H dis are particularized as: [Math 1] where H loc and H dis Polynomial fraction in z written as discrete time: [Math 2] where (a i ,b i ) are real coefficients of the equation, (m,n) are integers corresponding to the filter order, Given z -1 is a pure delay of the sampling period, the output (y k ) at time instant k is related to the input (x k ) at time instant k by the circular control equation: [Math 3] The current drive signal in the coil of the loudspeaker given the pressure and its gradient, the complete control equation writes as the sum of the two loop equations in the preceding form: y tot = y loc + y dis where y loc depends on the measured pressure, y dis depends on the estimated pressure gradient.

5. The method for controlling the propagation of sound waves according to claim 1 or 2, characterized in that, The control unit (12) is a microcontroller.

6. The method for controlling propagation of sound waves according to claim 1 or 2, characterized by, The control law is defined for a frequency of 50 to 150 kHz.

7. The method for controlling the propagation of acoustic waves according to claim 2, each cell comprising 4 microphones.

8. The method for controlling the propagation of acoustic waves according to claim 5, the microcontroller being an ARM type microcontroller.

9. A device for controlling the propagation of sound waves in the vicinity of a wall (2), characterized in that, The device comprises a set of Nc cells (1), each cell consisting essentially of a loudspeaker (11), a set of Nm microphones (10) connected to the loudspeaker, a control unit (12) and a power supply, the microphones and loudspeaker being arranged to be driven by the control unit, the part of the acoustic wave absorbed by the membrane of the loudspeaker (11) being converted into electrical energy for powering the set of Nc cells, each microphone of each cell being able to measure the sound pressure of the acoustic wave, each measurement being returned to the control unit of the cell, the control unit being able to estimate the sound pressure and / or its tangential spatial derivative at the loudspeaker and to apply a control law setting the number of amperes of the electrical signal that must be sent to the loudspeaker in order to obtain a determined generalized acoustic impedance Z for the loudspeaker det The device also comprises a main control device (C) for driving the set of control units (12) in a loop comprising the following steps: BEGIN: start A1: load a general 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 reference signal A6: acquire a signal by the microphones A7: calculate the insertion loss IL A8: comparing the insertion loss IL with a predetermined insertion loss value IL0 corresponding to obtaining a desired generalized acoustic impedance Z det of the ear canal A9: in case IL is less than IL0, return to A3 to adjust the parameters of the control law to minimize the error on the measured impedance.

10. Device for controlling the propagation of acoustic waves in the vicinity of a wall (2) according to claim 9, characterized in that, Each cell comprises 3 to 5 microphones (10).

11. The device for controlling the propagation of acoustic waves in the vicinity of a wall (2) according to claim 10, each cell comprising 4 microphones (10).

12. An acoustic panel comprising the device of any one of claims 9 to 11, covered with a set of Nc cells (1), each cell consisting mainly of a loudspeaker (11), a set of Nm microphones (10) connected to the loudspeaker and a control unit (12), the microphones and loudspeaker being arranged to be driven by the control unit, the portion of the acoustic wave absorbed by the membrane of the loudspeaker (11) being converted into electrical energy for powering the set of Nc cells, the generalized acoustic impedance of each loudspeaker (11) being constrained by a control law to locally define an absorption or reflection behavior at the surface of the panel, the panel being further connected to a master control device (C) for driving the set of control units.

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