Device for processing a signal, audio system, loudspeakers, acoustic resonator, and vehicle door, equipped for sound, associated therewith

Abstract

The invention relates to a processing device (30a) for processing an input signal (Si), generating an output signal (So) intended to be fed to a loudspeaker (13), said device comprising a processing line (Lt) comprising: an estimation module (31) for estimating expected movements (Da) of the loudspeaker (13) based on the input signal (Si); a determination module (32) for determining an adaptive control signal (CmdA) to be transmitted to the loudspeaker (13) in order to get as close as possible to the expected movements (Da) while correcting the nonlinearities of the loudspeaker (13); at least one transmission line (L1, L2) for the input signal (Si), delivering at least one non-adaptive control signal (Cmd1); and a summer (14), delivering the output signal (So) by summing the adaptive control signal (CmdA) and the at least one non-adaptive control signal (Cmd1).

Description

Technical field

[0001] The invention relates to the field of sound processing devices, i.e. devices generating an analog or digital output signal, designed to power a loudspeaker from an analog or digital input signal.

[0002] In particular, the invention relates to a device for processing an analog or digital signal making it possible to limit the non-linearities of the loudspeaker with which it is associated. More precisely, the invention advantageously makes it possible to reduce the sound distortions of the loudspeaker while maintaining a large amplitude of sound intensity.

[0003] The invention integrates the acoustic load seen by the loudspeaker and finds a multitude of applications, including the use of the loudspeaker in simple or complex acoustic enclosures and resonators. The invention finds, for example, a particularly advantageous application for sound reinforcement in a vehicle door requiring ever smaller and lighter loudspeakers. Prior art

[0004] By definition, a loudspeaker is a device that converts an electrical signal into acoustic waves. To do this, a loudspeaker's motor typically consists of a permanent magnet and a coil that moves within the magnet's field. The electrical signal at the speaker's terminals is converted into an electric current that flows through the coil. This current sets the coil in motion, transmitting this driving force to a membrane that, in turn, generates a compression wave in the surrounding air.

[0005] In a linear regime, for a given frequency, the acceleration of the coil is proportional to the current flowing through it. However, the higher the current flowing through the coil, the more the loudspeaker exhibits non-linearities leading to potentially audible distortions of the sound produced by the loudspeaker.

[0006] Non-linearities can arise in particular from the lack of uniformity of the magnetic field in which the coil is immersed. Indeed, the more intense the electric current circulating in the coil, the greater the amplitude of its displacement, even going so far as to partially leave the zone where the magnetic field of the magnet is uniform.

[0007] Nonlinearities can also arise from the loudspeaker's mechanical suspensions. Indeed, for large displacement amplitudes, the stiffness of these suspensions does not remain constant.

[0008] Nonlinearities can still arise from the acoustic load of the loudspeaker and be due, for example, to the presence of vibrations or acoustic short circuits at the level of the acoustic load seen by the loudspeaker.

[0009] It is possible to delay the appearance of these non-linearities by increasing the dimensions of the loudspeaker. However, there is a real need to miniaturize loudspeakers to provide sound for increasingly lighter and more compact surfaces. For example, car manufacturers want to reduce the size and weight of vehicles as much as possible to minimize fuel consumption. To achieve this, the aim is to integrate small loudspeakers, i.e., loudspeakers with a membrane diameter of less than 10 cm. A compromise is therefore made between sound quality and the space left available for the loudspeaker.

[0010] Furthermore, to obtain quality sound with a small speaker, it is known to limit the analog signal in frequency and / or amplitude through the use of filters or compressors and / or limiters. This solution has the effect of limiting the maximum sound level emitted by the speaker.

[0011] There are also systems that can act on the analog loudspeaker control signal to compensate for sound distortions related to loudspeaker non-linearities. Such systems require determining the characteristics of the loudspeaker and its operating environment in order to create a mathematical model to estimate the distortions that may appear on the loudspeaker depending on the analog signal applied to the loudspeaker.

[0012] For example, document US 2017 / 0019732 describes a processing device 300 schematized on the figure 1of the state of the art. This processing device 300 receives an analog input signal If and provides an analog output signal So to power a speaker 13 through an amplifier 18. The processing device 300 includes an estimation module 310 expected trips From of the speaker membrane 13 depending on the input analog signal If. From these expected movements Yes, a module 320 determines the signal So to transmit to the speaker 13 to obtain the expected movements Yes, taking into account the non-linearities of the loudspeaker 13.

[0013] To do this, the module 320uses a mathematical model that takes into account the non-linearities of a loudspeaker and allows the analog signal driving the loudspeaker to be modified in real time to produce sound with reduced distortion by limiting the frequency and / or intensity of the analog signal only when the mathematical model indicates that distortions may appear on the loudspeaker.

[0014] This control system effectively limits distortions of the loudspeaker and maintains the sound volume as long as the electrical signals sent to the loudspeaker do not risk damaging it. On the other hand, when the mathematical model detects a risk of damage of electrical and / or mechanical origin to the loudspeaker, the electrical signal sent to the loudspeaker is restricted and has an upper limit of sound amplitude, beyond which the user can no longer increase the sound volume, even by applying a larger command. Document US1010473 B2 describes a device for processing an input signal, generating an output signal designed to power a loudspeaker via an amplifier, said device comprising a processing line comprising: a module for estimating the expected movements of the loudspeaker as a function of the input signal;and a module for determining an adaptive control signal to be transmitted to the loudspeaker, i.e. a signal determined digitally from an expected displacement of the membrane; at least one input signal transmission line delivering at least one non-adaptive control signal, i.e. a signal originating directly or indirectly from the input signal; and a summer delivering the output signal by summing the adaptive control signal and the at least one non-adaptive control signal, the determination module being configured to solve a system of coupled differential equations aimed at determining the signal to be transmitted to the loudspeaker to obtain the expected displacement of the membrane, the system of coupled differential equations representing the loudspeaker, considered as a non-linear transducer.;

[0015] The technical problem that the invention proposes to solve is to implement a loudspeaker control system that makes it possible to limit distortions while maintaining greater freedom of control by the user. Summary of the invention

[0016] To address this technical problem, the invention proposes, according to claim 1, to process only part of the input signal, using a module for estimating the expected movements and a module for determining the control signal to be applied to obtain movements close to the expected movements, and not to process the remaining part of the input signal.

[0017] To drive the speaker, the unprocessed part is added to the processed part to form the output signal.

[0018] Thus, if the determination module detects that the loudspeaker is likely to cause distortion for a given input signal, the portion of the signal passing through the determination module will potentially be restricted, but the user will still be able to increase the volume because at least a portion of the amplified signal will not be restricted.

[0019] The invention therefore increases the user's freedom of control, as the user will be able to enjoy distortion-free sound as long as the sound level is kept below the limit imposed by the determination module, but he will also have the possibility of continuing to increase the sound level if he wishes. To do this, however, the user will have to accept a risk of higher distortion, as the signal will then come from the unprocessed portion of the signal.

[0020] In other words, according to a first aspect, the invention relates to a device for processing an input signal, generating an output signal designed to power a loudspeaker directly or indirectly via an amplifier, said device comprising a processing line comprising: a module for estimating the expected displacements of the loudspeaker as a function of the input signal; and a module for determining an adaptive control signal to be transmitted to the loudspeaker, i.e. a signal determined digitally from an expected displacement of the membrane.

[0021] The invention is characterized in that the treatment device further comprises: at least one input signal transmission line delivering at least one non-adaptive control signal, i.e. a signal originating directly or indirectly from the input signal; and a summer delivering the output signal by summing the adaptive control signal and the at least one non-adaptive control signal.

[0022] The determination module is for example configured to solve a system of coupled differential equations aimed at determining the signal to be transmitted to the loudspeaker to obtain the expected displacement of the membrane, the system of coupled differential equations representing the loudspeaker, considered as a non-linear transducer, and the environment of the loudspeaker.

[0023] For the purposes of the invention, a loudspeaker has characteristics and geometry. Characteristics are physical quantities such as the mass of the moving part, the mechanical strength or the compliance of the loudspeaker suspensions. The geometry of the loudspeaker may correspond to the mechanical dimensions, such as the radiating surface of its membrane. Depending on the characteristics and geometry taken into account, the resulting equations may be linear or non-linear.

[0024] The coupled differential equations are solved as a function of the expected displacements of the membrane of the loudspeaker associated with the device of the invention. To do this, the estimation module determines the expected displacement of the membrane as a function of the input signal. For a very simplified example, if the input signal corresponds to a sinusoidal signal with a frequency of 440 Hz, the expected displacement of the membrane is sinusoidal, of the same frequency, and the expected sound signal created by the loudspeaker corresponds to the musical note "A", free of distortion. Depending on the desired amplitude of this sound response, the non-linearities of the loudspeaker can degrade the quality of the sound response.

[0025] To limit this phenomenon, the resolution of the system of coupled differential equations aims to determine what real electrical signal must be transmitted to the loudspeaker to obtain the expected displacement of the membrane, and therefore the expected sound response.

[0026] The adaptive control signal is thus generated following the resolution of the coupled differential equation system by the determination module. If the expected control signal is analog, this control signal is conventionally obtained by a digital / analog converter after a digital resolution of the coupled differential equation system.

[0027] Preferably, the sampling frequency for generating the adaptive control signal is chosen to be as high as possible while remaining calibrated to the resolution speed of the coupled differential equations, so as to limit the distortions introduced by the digital / analog conversion.

[0028] Furthermore, to obtain an accurate modeling of the loudspeaker in its environment, the system of coupled differential equations preferentially integrates parameters representing the loudspeaker, considered as a nonlinear transducer, and the parameters of the loudspeaker's environment, typically its acoustic load. To take into account the nonlinear parameters of the loudspeaker, the system of coupled differential equations preferentially integrates the geometric definition and the linear and nonlinear characteristics of the loudspeaker. To take into account the parameters of the loudspeaker's environment, the system of coupled differential equations preferentially integrates the geometric definition and the characteristics of the environment, possibly estimated from hypotheses on the variations of air flow at the loudspeaker and in its environment.

[0029] In a first example, the loudspeaker is integrated into an acoustic enclosure comprising a rear box, the determination module can be configured to solve a system of coupled differential equations representing: the geometric definition and characteristics of the loudspeaker; and the dimensions of the enclosure.

[0030] Typically, the acoustic enclosure may include a box whose volume is closed, the box is then mounted at the rear of a loudspeaker so as to form its acoustic load.

[0031] In a second example, the loudspeaker is integrated into an acoustic enclosure comprising a rear box and at least one vent, the determination module can then be configured to solve a system of coupled differential equations representing: the geometric definition and characteristics of the loudspeaker; the dimensions of the enclosure; and the characteristics of at least one vent.

[0032] In a third example, the loudspeaker is integrated into an acoustic enclosure comprising a rear box and at least one radiator, the determination module can then be configured to solve a system of coupled differential equations representing: the geometric definition and characteristics of the loudspeaker; the dimensions of the enclosure; and the characteristics of at least one radiator.

[0033] In a fourth example, the loudspeaker is integrated into an acoustic resonator comprising at least two boxes communicating via at least one vent and / or at least one acoustic bridge. The determination module can then be configured to solve a system of coupled differential equations representing: the geometric definition and characteristics of the loudspeaker; the dimensions of each box; and the characteristics of at least one vent and / or at least one acoustic bridge.

[0034] In a fifth example, the loudspeaker is integrated into a vehicle door, the determination module can be configured to solve a system of coupled differential equations representing: the geometric definition and characteristics of the loudspeaker; the characteristics of the door panel; the dimensions of the different volumes of the door: the volume of the box integrating the loudspeaker and the peripheral volume formed between a front face of said box and the door panel; and the characteristics of the acoustic bridges between these volumes of the door, the acoustic bridges being constituted by at least one sealing sheet and possible acoustic short circuits.

[0035] In addition, the determination module preferentially receives measurements of operating parameters of the loudspeaker, so that the system of coupled differential equations of the determination module also integrates the evolution of the loudspeaker parameters over time. Indeed, the loudspeaker parameters are likely to evolve over the time of use of the loudspeaker. For example, the impedance increases with the heating of the coil, as does the flexibility of the suspensions. In order to take this evolution into account, the device includes, for example, a feedback loop with sampling of voltage and current information at the loudspeaker and the system of coupled differential equations can be solved in real time by taking this information into account so as to improve the generation accuracy of the adaptive control signal.

[0036] Although the adaptive control signal is digitally designed and tailored, digital and / or analog processing may be performed in the processing line. Similarly, the input signal may undergo pre-processing operations before providing the non-adaptive control signal.

[0037] According to one embodiment, the processing line comprises a low-pass filter and a transmission line of the input signal comprises a high-pass filter. In other words, the input signal can be separated into two frequency components: high frequencies, which are not modified, and low frequencies which are modified by the device.

[0038] This implementation is based on the observation that low frequencies are most distorted. Therefore, focusing processing on low frequencies reduces processing time and memory usage, as processing high-frequency signals requires a much higher sampling rate and processing time.

[0039] Preferably, the processing device comprises two input signal transmission lines delivering two non-adaptive control signals: a first transmission line comprising the high-pass filter; and a second transmission line comprising a low-pass filter.

[0040] This embodiment also allows an unprocessed part to be transmitted at low frequency.

[0041] The distribution of the input signal between the different lines can be modulated according to requirements. To do this, the processing line and the at least one transmission line preferably include a weighter to control the fraction of the signal addressed.

[0042] Furthermore, although the transmission lines allow the user to increase the volume beyond the limiting conditions imposed by the determination module to limit loudspeaker distortion, increasing the volume by the user may drive the loudspeaker into an operating region that may degrade it.

[0043] To protect the loudspeaker, the at least one transmission line and / or said processing line comprise a compressor and / or limiter configured to restrict the control signal if it exceeds a loudspeaker degradation threshold.

[0044] In addition, a compressor and / or limiter can also be placed on the processing line to filter out unrealistic solutions on which said determination module can converge.

[0045] Furthermore, there are several possible implementations of the processing device in which the loudspeaker can be voltage or current controlled without modifying the subject of the invention. Preferably, the estimation module is voltage controlled to estimate the expected displacements. Thus, when the output signal corresponds to a current signal, the estimation module is connected to the voltage of the input signal while the at least one transmission line is connected to a model of the current flowing through the coil, the determination module being configured to determine an adaptive current control signal.

[0046] Estimating the current through the coil is based on linear modeling of the loudspeaker and knowledge of the input voltage.

[0047] In a particular embodiment, the input signal and / or the output signal is an analog signal. Alternatively, the input signal and / or the output signal is a digital signal.

[0048] According to a second aspect, the invention also relates to an audio system integrating a processing device according to the first aspect of the invention, generating an output signal from an input signal, and a loudspeaker connected to the output signal via an amplifier.

[0049] According to a third aspect, the invention relates to the processing of voltage information at the terminals of the loudspeaker and current information flowing in the coil. This makes it possible to integrate into the loudspeaker processing device the evolution of its electrical and / or mechanical characteristics during operation.

[0050] According to a fourth aspect, the invention relates to an acoustic enclosure integrating an audio system according to the second aspect of the invention. The acoustic enclosure may comprise at least one vent and / or at least one radiator.

[0051] According to a fifth aspect, the invention relates to an acoustic resonator comprising at least two boxes communicating via at least one vent and / or at least one acoustic bridge, said resonator integrating an audio system according to the second aspect of the invention.

[0052] According to a sixth aspect, the invention relates to a sound-proofed vehicle door incorporating an audio system according to the second aspect of the invention. Summary description of the figures

[0053] Other advantages and characteristics of the invention will appear on reading the following description, given by way of illustrative and non-limiting example with reference to the following appended figures. [ Fig1 ] There figure 1 is a schematic representation of an audio system incorporating a state-of-the-art processing device; [ Fig2 ] There figure 2 is a schematic representation of an audio system integrating a processing device according to a first embodiment of the invention; [ Fig3 ] There figure 3 is a schematic representation of an audio system integrating a processing device according to a second embodiment of the invention; [ Fig4 ] There figure 4is a schematic representation of an audio system integrating a processing device according to a third embodiment of the invention; [ Fig5 ] There Figure 5 is a schematic representation of an audio system integrating a processing device according to a fourth embodiment of the invention; [ Fig6 ] There figure 6 is a schematic representation of an audio system integrating a processing device according to a fifth embodiment of the invention; [ Fig7 ] There figure 7 is a schematic representation of an audio system integrating a processing device according to a sixth embodiment of the invention; [ Fig8 ] There figure 8 is a schematic representation of the operations carried out by the module for taking into account the loudspeaker parameters in real time according to the sixth embodiment of the invention; [ Fig9 ] There figure 9is a schematic representation of an acoustic enclosure having a closed box including a loudspeaker according to one embodiment of the invention; [ Fig10 ] There figure 10 is a schematic representation of an acoustic enclosure comprising a vent and including a loudspeaker according to one embodiment of the invention; [ Fig11 ] There figure 11 is a schematic representation of an acoustic enclosure comprising a radiator and including a loudspeaker according to one embodiment of the invention; [ Fig. 12 ] There figure 12 is a schematic representation of an acoustic resonator formed of several boxes communicating by vents and / or acoustic bridges and including a loudspeaker according to an embodiment of the invention; [ Fig13 ] There figure 13 is a schematic representation of a vehicle door including a loudspeaker; and [ Fig14 ] There figure 14illustrates comparative curves of the evolution of the displacements of the loudspeaker membrane of the figure 1 in the presence or absence of the treatment device of the invention. Possible ways of carrying out the invention

[0054] Throughout the following description and in the absence of further details, a signal may correspond to an analog or digital signal. An example is notably presented with an analog input signal.

[0055] As illustrated on the figure 2 , the invention relates to a treatment device 30a in which an input signal If is divided between two separate lines: a transmission line L1 and a treatment line Lt. The treatment line Lt includes an estimation module 31 expected trips From of the membrane of a loudspeaker 13 depending on the input signal If, as well as a determination module32 of the adaptive control signal CmdA to transmit to the speaker 13 to best approach the expected movements Yes, while taking into account the non-linearities of the loudspeaker 13.

[0056] The treatment line Lt thus allows to obtain an adaptive control signal CmdA while the transmission line L1 allows to obtain a control signal Cmd1 non-adaptive. These two control signals Cmd1 and CmdA are associated with an adder 14 so as to obtain the output signal So. Typically, this output signal So is designed to power the speaker 13, for example through an amplifier 18.

[0057] Preferably, to limit the constraints of calculating the adaptive control signal CmdA, a low-pass filter 16is applied on the treatment line Lt so that only the low frequencies of the input signal If be processed by the processing line Lt. In this embodiment, the transmission line L1 has a high-pass filter 15, to transmit only high frequencies without processing. Thus, in the example of the figure 2 , the output signal So consists of the high part of the frequency spectrum of the input signal If, which does not involve any processing and the lower part of the frequency spectrum, entirely created by the determination module 32 to limit speaker non-linearity defects 13 in the low frequencies.

[0058] Alternatively, as illustrated in the figure 3 , part of the low frequencies can also be transmitted by a second transmission line L2. So the second transmission lineL2 delivers a non-adaptive control signal Cmd2 passing through a low-pass filter 17. Preferably, the different transmission lines L1-L2 and treatment Lt include weights α, β Or γ of the input signal If. For example, each of these weightings α, β Or γ can be between 0 and 1.

[0059] As illustrated on the figure 3 , the weighter γ as well as the low-pass filter 16 of the treatment line Lt can be placed before the estimation module 31 expected trips Yes. Alternatively, as illustrated in the figure 4 , it is possible to estimate the expected movements From before applying the y-weighting and low-pass filter 16 of the treatment line Lt.

[0060] In addition, at least one transmission line L1-L2 can integrate a compressor and / or limiter 21 so as to restrict the corresponding control signal if it exceeds a threshold value for loudspeaker degradation. Similarly, the processing line Lt can also integrate a compressor and / or limiter 11 so as to limit movements to realistic values, as illustrated in the figure 4 .

[0061] In addition, the determination module 32 may eventually lead to delivering electrical signals exceeding a threshold value for loudspeaker degradation 13 and a compressor and / or limiter 10 can be arranged to restrict the electrical signal from the determination module 32.

[0062] On the figures 3 And 4 , the transmission line L2 as well as the treatment line Lt have low-pass filters 16 And 17and compressors and / or limiters 11 And 21. To limit the number of components, it is possible to share the low-pass filters 16 And 17 into a low-pass filter 17' as well as compressors and / or limiters 11 And 21 into a compressor and / or limiter 21'. So after the low pass filter 17' and the compressor and / or limiter 21' of the Figure 5 , the processing device 30d has a transmission line L2' integrating only the weighting regulating the gain β and, in parallel with this transmission line L2', the treatment line Lt. As previously described with reference to other embodiments, this processing line Lt includes: the weighter adjusting the gain γ, then the estimation module 31, another compressor and / or limiter 11, the determination module32 as well as the limiter compressor 10 configured to electrically protect the speaker 13.

[0063] Furthermore, the speaker 13 can be controlled by current or voltage, so that the processing devices 30a-30e of the figures 2 to 6 can be used to deliver an output signal So in current or voltage.

[0064] Preferably when an output signal is expected So running, the estimation module 31 is still connected to the voltage information of the input signal Si. Indeed, such an estimation module 31 is simpler to perform based on the voltage estimate.

[0065] Whatever the input of the estimation module 31, expected movements From are classically expressed in units of distance and the determination module 32can also be configured to provide an adaptive control signal CmdA in current or voltage.

[0066] In the example of the figure 6 , the input signal If injected is a voltage If(t) for the treatment line Lt and a current If(c) for both transmission lines L1 And L2. The determination module 32 is configured to provide an adaptive control signal CmdA(c) running. To do this, the signal If(t) can be directly taken from the input signal and the signal If(c) can be derived from a model and calculated by the expected current estimation module 34.

[0067] There figure 7 represents the real-time consideration of changes in the electrical and / or mechanical parameters of the loudspeaker 13during operation. To do this, the instantaneous voltage values UHP to the speaker and current terminals Ihp circulating in the coil are addressed to the module 35 adjustment of the electrical and / or mechanical parameters of the loudspeaker. These are manipulated by the determination block 32 adaptive signal control CmdA(c).

[0068] Of course, it is possible to combine these different embodiments depending on the needs of the application. For example, it is possible to combine the embodiments of figures 5 And 6 , that is to say by pooling the two low-pass filters 16 And 17 as well as the compressor and / or limiter 11 And 21 of the figure 6 , as realized on the Figure 5 , while using an estimation module 31 taking into account the input signal voltage If(t)while the transmission lines L1-L2' take into account a modeling of the current flowing through the coil If(c). In fact, the transformation carried out in the estimation module 31 allows you to free yourself from the type of unit used for the processing line Lt.

[0069] Likewise, on the figures 2 to 6 , it is possible to integrate the module 35 adjustment of the electrical and / or mechanical parameters of the loudspeaker 13 between the speaker 13 and the module 32 determination of adaptive control signals CmdA, CmdA(c), as illustrated on the figure 7 .

[0070] Regardless of the topology of the processing device 30a-30f, the determination module 32 is configured to solve a system of coupled differential equations representing the loudspeaker nonlinearities 13 and the characteristics of the speaker environment13.

[0071] There figure 8 details the principle of processing by the module 35 instantaneous voltage values UHP and current Ihp at the speaker level 13. In practice, the instantaneous voltage values UHP and current Ihp are collected during a given observation period. Preferably, the number of points collected is equal to a power of 2, typically 2 11 < = 2048 points. A time weighting, typically a Hanning weighting, can be applied.

[0072] The module 35 then carries out a first step 100 for calculating the frequency spectrum of instantaneous voltage values UHP and current Ihp.In practice, the algorithm known as the "fast fourier transform" can be used to calculate these spectra. For example, for updating the loudspeaker parameters every 15 seconds, the "fast fourier transform" algorithm can be configured with a sampling rate of 44100Hz and a capture of 2048 points. Thus, 323 pairs of voltage spectra UHP and current Ihp are obtained.

[0073] Usually, the obtained spectra contain noise. To solve this problem, the second step 101 is a statistical exploitation of the spectra obtained, aiming in particular to eliminate unusable spectra and to eliminate noise by averaging over several measurements. This exploitation can, for example, be based on the analysis of the histogram of the spectra.

[0074] The stage 102then performs the calculation of the dynamic impedance, defined from the ratio of the voltage spectra UHP and current Ihp From the dynamic electrical impedance curve, it is possible: to analyze the module in the step 103, and to analyze the phase in the step 104.

[0075] From the dynamic electrical impedance curve module, the step 105 dynamic continuous resistance calculation D is realized.

[0076] From the phase of the dynamic electrical impedance curve, the dynamic resonant frequency fs, is calculated in step 106, then the dynamic mechanical compliance CMS (x) speaker suspensions 13 is estimated from the dynamic resonance frequency fs in the step 107.

[0077] The value of the continuous dynamic resistance D of the loudspeaker corresponds to the limit of the impedance module for frequencies tending towards zero and the value of the dynamic resonance frequency fs of the loudspeaker corresponds to the first non-zero frequency of phase cancellation according to increasing frequencies.

[0078] Dynamic mechanical compliance Cms (x) suspensions is estimated from the following relationship: Cms x / Cms 0 x = h fs 0 / fs 2 in which: fs0 is the nominal resonant frequency of the loudspeaker in its environment; fs is the dynamic resonant frequency of the loudspeaker in its environment; Cms0 (x) is the nominal mechanical compliance of the loudspeaker suspensions; Cms (x) is the dynamic mechanical compliance of the loudspeaker suspensions; h is a function connecting CMS ( x ) / CMS 0( x ) And ( fs 0 / fs) 2< . This function is determined experimentally. In particular, h is the “identity” function in the case of a free-air loudspeaker.

[0079] So the module 35 adjustment of electrical and / or acoustic parameters allows to estimate the variations during the operation of the loudspeaker 13 of the two parameters D And Cms (x) manipulated by the module 32 determination of adaptive control signals CmdA, CmdA(c).

[0080] THE figures 9 to 13 illustrate concrete examples of a loudspeaker environment 13 positioned respectively: in a closed acoustic enclosure, in an acoustic enclosure with a vent, in an acoustic enclosure with a radiator, in an acoustic resonator formed of boxes in series connected by vents and / or acoustic bridges, and in a car door.

[0081] Generally speaking and in each of these examples, the vibrating parts of the assembly consisting of the loudspeaker and its acoustic load are identified.

[0082] For the purposes of the invention, the vibrating parts designate all the parts of the loudspeaker and its environment whose vibrations are directly or indirectly linked to the movement of the membrane.

[0083] The vibrating parts are respectively: for the figure 9 : the speaker membrane 13, for the figure 10 : the speaker membrane 13 and the air in the vent 90, for the figure 11 : the speaker membrane 13 and the radiator membrane 91, for the figure 12 : the speaker membrane 13 and the air in each of the vents and / or acoustic bridges 93 1 -93 (p-1) , and for the figure 13 : the speaker membrane 13,air at the acoustic short circuit 84, the sealing sheet 83 and the door panel 85.

[0084] These vibrating parts form a partition, in the mathematical sense, of all the vibrating parts of the loudspeaker and its environment, due to a coupling, in the mechanical and / or acoustic sense, with the loudspeaker membrane.

[0085] The movements, assumed to be uniform, of each of these vibrating parts, to which is added the current flowing through the loudspeaker's moving coil 13, constitute the variables of the system of coupled differential equations.

[0086] Thus, if n vibrating parts, other than the speaker membrane 13, are identified, the number of coupled differential equations is equal to ( n +2).

[0087] The general formulation of the system of coupled differential equations is then as follows: S u t = Re × i t + ∂ ∂ t Le x t × i t + BL x × ∂ ∂ t x t 1 BL x × i t = Mms × ∂ 2 x t ∂ t 2 + Rms × ∂ x t ∂ t + 1 Cms x × x t + 1 2 × ∂ Le x ∂ x × i 2 t + f x t , x 1 t , … xn t 2 g 1 x t , x 1 t , … xn t = 0 3 − 1 g 2 x t , x 1 t , … xn t = 0 3 − 2 … … g n x t , x 1 t , … xn t = 0 3 − n

[0088] In this formulation, equation (1) is the electrical differential equation of the loudspeaker 13, describing the current i(t) running through its coil, and equation (2) is the mechanical differential equation of the loudspeaker 13, describing the movement x ( t ) of its membrane. The coupled differential equations (3-1) has (3-n) link the membrane displacement to the displacements x 1 ( t )- xn ( t ) of the n other vibrating parts, functions f, g 1 - gn establishing mechanical or acoustic links between variables x(t), x 1 ( t )- xn ( t ) .

[0089] There figure 9 illustrates a concrete example of a loudspeaker environment 13 positioned in a closed acoustic enclosure.

[0090] In this case, the variables of the system of coupled differential equations are: the current through the loudspeaker coil 13and the displacement of its membrane. The system is then written: Sa u t = Re . i t + ∂ ∂ t Le x t . i t + BL x . ∂ ∂ t x t 1 a BL x . i t = Mms . ∂ 2 x t ∂ t 2 + Rms . ∂ x t ∂ t + 1 Cms x . x t + P 0 . Sd . 1 − V 1 V 1 + Sd . x t γ + 1 2 . ∂ Le x ∂ x . i t 2 2 a

[0091] In these coupled differential equations: x(t) corresponds to the displacement of the speaker coil 13 ; V1 is the volume of the box 89 ; Sd is the radiating surface of the loudspeaker membrane 13 ; P0 is the atmospheric static pressure; and γ = 1,4 is the ratio of the specific heats of air at constant pressure and volume.

[0092] There figure 10 illustrates a concrete example of a loudspeaker environment 13 positioned in an acoustic enclosure with a vent 90.

[0093] In this case, the variables of the system of coupled differential equations are: the current through the loudspeaker coil 13, the movement of its membrane and the movement of air in the vent 90.The system is then written: Sb u t = Re . i t + ∂ ∂ t Le x t . i t + BL x . ∂ ∂ t x t 1 b BL x . i t = Mms . ∂ 2 x t ∂ t 2 + Rms . ∂ x t ∂ t + 1 Cms x . x t + P 0 . Sd 1 − V 1 V 1 + Sd . x t + S 1 . x 1 t γ + 1 2 . ∂ Le x ∂ x . i t 2 2 b 0 = M 1 . ∂ 2 x 1 t ∂ t 3 + P 0 . S 1 1 − V 1 V 1 + Sd . x t + S 1 . x 1 t γ 3 b − 1

[0094] In these equations: x(t) corresponds to the displacement of the speaker coil 13 ; x1(t) corresponds to the movement of air in the vent 90 ; V1 is the volume of the box 89 ; Sd is the radiating surface of the loudspeaker membrane 13 ; S1 is the radiating surface of the vent 90 ; P0 is the atmospheric static pressure; M1 is homogeneous to a mechanical mass; and γ = 1,4 is the ratio of the specific heats of air at constant pressure and volume.

[0095] There figure 11 illustrates a concrete example of a loudspeaker environment 13 positioned in an acoustic enclosure comprising a radiator 91.

[0096] In this case, the variables of the system of coupled differential equations are: the current through the loudspeaker coil 13, the movement of its membrane and the movement of the radiator 91. The system is then written: Sc u t = Re . i t + ∂ ∂ t Le x t . i t + BL x . ∂ ∂ t x t 1 c BL x . i t = Mms . ∂ 2 x t ∂ t 2 + Rms . ∂ x t ∂ t + 1 Cms x . x t + P 0 . Sd 1 − V 1 V 1 + Sd . x t + S 1 . x 1 t γ + 1 2 . ∂ Le x ∂ x . i t 2 2 c 0 = M 1 . ∂ 2 x 1 t ∂ t 2 + R 1 . ∂ x 1 t ∂ t + 1 C 1 . x 1 t + P 0 . S 1 1 − V 1 V 1 + Sd . x t + S 1 . x 1 t γ 3 c − 1

[0097] In these equations: x(t) corresponds to the displacement of the speaker coil 13 ; x1(t) corresponds to the movement of the radiator 91 ; V1 is the volume of the box 89 ; Sd is the radiating surface of the loudspeaker membrane 13 ; S1 is the radiating surface of the radiator 91 ; P0 is the atmospheric static pressure; M1 is homogeneous to a mechanical mass; R1 is homogeneous to a mechanical resistance; C1 is homogeneous to a mechanical compliance; and γ = 1,4 is the ratio of the specific heats of air at constant pressure and volume.

[0098] There figure 12 illustrates a concrete example of a loudspeaker environment 13 positioned in an acoustic resonator formed of p boxes 93 1 -93 (p-1) in series communicating by ( p- 1) vents and / or acoustic bridges.

[0099] In this case, the variables of the system of coupled differential equations are: the current through the loudspeaker coil 13, the movement of its membrane and the movement of air in the p -1 vents and / or acoustic bridges. The system is then written: Sd u t = Re . i t + ∂ ∂ t Le x t . i t + BL x , ∂ ∂ τ x t 1 d BL x , i t = Mms . ∂ 2 x t ∂ r 3 + Rms . ∂ t t ∂ t + 1 Cms x . x t + P 0 . Sd 1 − V 1 V 1 + Sd . x t − S 1 . x 1 t γ + 1 2 . ∂ Le x ∂ x . i t 2 2 d 0 = M 1 . ∂ 2 x 1 t ∂ t 2 + R 1 . ∂ x 1 t ∂ t + 1 C 1 x 1 t + P 0 . S 1 1 − V 1 V 1 + S 1 . x 1 t − Sd . x t γ + P 0 . S 1 1 − V 2 V 2 + S 1 . x 1 t − S 2 . x 2 t γ 3 d − 1 0 = M 2 . ∂ 2 x 2 t ∂ t 2 + R 2 . ∂ x 2 t ∂ t + 1 C 2 x 2 t + P 0 . S 2 1 − V 2 V 2 + S 2 . x 2 t − S 1 . x 1 t γ + P 0 . S 2 1 − V 3 V 3 + S 2 . x 2 t − S 3 . x 3 t γ 3 d − 2 … 0 = M p − 2 . ∂ 2 N p − 2 t ∂ t 2 + R ρ − 2 . ∂ x p − z t ∂ t + 1 C p − 2 x p − 2 t + P 0 . S p − 2 1 − V p − 2 V p − 2 + S p − 2 . x p − 2 t − S p − 2 x p − 2 t γ + P 0 . S p − 2 1 − V p − 2 V p − 2 + S p − 2 . x p − 2 t − S p − 1 . x p − 1 t γ 3 d − p − 2 0 = M p − 1 . ∂ 2 N p − 1 t ∂ t 2 + R ρ − 1 . ∂ x p − 1 t ∂ t + 1 C p − 1 x p − 1 t + P 0 . S p − 1 1 − V p − 1 V p − 1 + S p − 1 . x p − 2 t − S p − 2 x p − 2 t γ + P 0 . S p − 1 1 − V p V p + S p − 1 . x p − 1 t γ 3 d − p − 1

[0100] In these equations: x(t) corresponds to the displacement of the speaker coil 13 ; x 1 ( t ) -x p -1 ( t ) correspond to the movements of air in the vents and / or acoustic bridges 93 1 -93 (p-1) ; V 1 - V p are the volumes of the boxes 92 1 -92 (p) ; Sd is the radiating surface of the loudspeaker membrane 13 ; S 1 - S p -1 are the surfaces of the vents and / or acoustic bridges 93 1 -93 (p-1) ; P0 is the atmospheric static pressure; M 1 -M p -1 are homogeneous to mechanical masses; R 1 -R p -1 are homogeneous to mechanical resistances; C 1 - C p- 1 are homogeneous to mechanical compliances; and γ = 1.4 is the ratio of the specific heats of air at constant pressure and volume.

[0101] Finally, the figure 13 illustrates a concrete example of a loudspeaker environment 13 positioned in a vehicle door.

[0102] A vehicle door is represented, in a simplified manner, by a loudspeaker 13 mounted on a front face 81 of a box. This box is closed by a rear face 82, thus delimiting a volume 88. A door panel 85 is also fixed on the front face 81 of the box. To integrate the speaker 13, a peripheral volume86 is formed between the front face 81 of the box and the door panel 85.

[0103] These volumes 86, 88 are typically filled with air. Furthermore, these air volumes 88 And 86 are connected by acoustic bridges potentially comprising a clear acoustic short circuit 84 and at least one sealing sheet 83 comparable to a membrane. The loudspeaker 13 radiates into the cabin and can be covered with open-cell foam or a grid 87 to improve the aesthetics of the door. However, given the significant acoustic transparency of this foam or grille, this organ 87 will not be taken into consideration in this diagram. The door panel 85 is acoustically comparable to a membrane also radiating into the passenger compartment.

[0104] In this case, the variables of the system of differential equations are: the current through the speaker coil 13, the displacement of its membrane, the displacement of air at the level of the acoustic short circuit 84, the displacement of the sealing sheet 83 and the movement of the door panel 85. The system is then written: Se u t = Re . i t + ∂ ∂ t Le x t . i t + BL x ∂ ∂ t x t 1 e BL x . i t = Mms . ∂ 2 x t ∂ t 2 + Rms . ∂ x t ∂ t + 2 Cms x . x t + P 0 . Sd 1 − V 2 V 2 + S 1 x 1 t + S 2 x 2 t − S 3 x 3 t γ + 1 2 ⋅ ∂ Le x ∂ x ⋅ i t 2 2 e 0 = M 1 . ∂ 2 x 2 t ∂ t 3 + P 0 . S 1 1 − V 1 V 1 + Sd . x t + V 2 . x 1 t + S 2 . x 2 t γ + P 0 . S 1 1 − V 2 V 2 + S 1 . x 1 t + V 3 . x 2 t − S 3 . x 3 t γ 3 e − 1 0 = M 2 . ∂ 2 x 2 t ∂ t 2 + R 2 . ∂ x 2 t ∂ t + 1 C 2 x 2 t + P 0 . S 2 1 − V 1 V 1 + Xd . x t + S 1 . rl t + S 2 . x 2 t γ + P 0 . S 2 1 − V 2 V 2 + S 1 . x 1 t + V 3 . x 2 t − S 3 . x 3 t γ 3 e − 2 0 = M 3 . ∂ 2 x 3 t ∂ t 2 + R 3 . ∂ x 3 t ∂ t + 1 C 3 x 3 t + P 0 . S 3 1 − V 2 V 1 + Xd . x t − S 1 . rl t + S 2 . x 2 t γ 3 e − 3

[0105] In these equations: x(t) corresponds to the displacement of the speaker coil 13 ; x1(t) is the air displacement at the acoustic short circuit 84 ; x2(t) is the displacement of the sealing sheet 83 ; x3(t) is the displacement of the door panel 85 ; V1 is the volume of the box 88 ; V2 is the peripheral volume 86 ; Sd is the radiating surface of the loudspeaker membrane 13 ; S1 is the section of the acoustic short circuit 84 ; S2 is the surface area of the sealing sheet 83 ; S3 is the radiating surface of the door panel 85 ; P0 is the atmospheric static pressure; M1 , M2, M3 are homogeneous to mechanical masses; R2, R3 are homogeneous to mechanical resistances; C2, C3 are homogeneous to mechanical compliances; and γ = 1.4 is the ratio of the specific heats of air at constant pressure and volume.

[0106] The parameters M 1 -M p -1 , R 1 - R p- 1 , C 1 - C p -1 appearing in the systems of equations [Math4] to [Math7], and therefore implicitly in the functions f, g 1 -gn of [Math2], can for example be determined experimentally from electrical impedance measurements carried out at the loudspeaker terminals at different frequencies, the number of which is greater than or equal to the number of parameters to be determined.

[0107] Typically, if M denotes the number of parameters to be determined and if N denotes the number of frequencies considered, with N ≥ M, the game P of sought parameters can be estimated by the least squares technique, seeking to minimize the function σ ( P ) defined as follows: σ P = ∑ n = 1 N Z m f i − Z t f i P 2

[0108] In this expression, Z m ( fi ) denotes the complex electrical impedance measured at frequency f i , Z t ( f i , P ) denotes the theoretical complex electrical impedance at frequency f i deduced from the electrical equation of the model with the parameter set P , | Z m ( f i ) - Z t ( f i , P )| denotes the modulus of the difference between the complex impedances Z m ( f i ) And Z t ( f i , P ), And σ ( P ) denotes the sum of the squares of these modules | Z m ( f i ) - Z t ( f i ,P )|

[0109] In order to optimize the efficiency of the determination, and therefore the convergence towards the parameter set P sought, it is desirable to choose frequencies f 1 -f N for which the moduli of the electrical impedance differences between the loudspeaker mounted in its environment and the loudspeaker in free air are as large as possible.

[0110] In addition, the time-dependent evolution of the direct current resistance Re and the mechanical compliance of the loudspeaker suspensions Cms (x) can be estimated from the voltage Uhp and current Ihp measured on the loudspeaker. The device can therefore include a feedback port for the current and voltage transmitted to the loudspeaker 13 to transmit these values to the processing module 35, said module 35 delivering the values of Re And Cms (x) to the module 32determination of the adaptive control signal CmdA.

[0111] This system of coupled differential equations thus makes it possible to faithfully model the behavior of the loudspeaker 13 in its real environment. Preferably, the determination module 32 receives measurements of loudspeaker operating parameters 13, so that the system of coupled differential equations of the determination module 32 also integrates the evolution of speaker parameters 13 over time.

[0112] To conclude, the invention allows for more efficient modeling than existing systems since the loudspeaker is modeled in its real environment. For example, the figure 14 illustrates the evolution of the movements of the loudspeaker membrane 13 with the processing device Di and without the processing device Dsi of the invention for a sinusoidal voltage sweep of amplitude 10Vrms imposed on the analog input signal Si. As illustrated on the figure 14 , the distortions present without the processing device Dsi of the invention are practically all eliminated by the processing device 30a-30f of the invention.

[0113] Furthermore, the invention also allows for improved user control over the entire audio system incorporating the processing device. 30a-30f since the user can choose to continue to increase the volume without being restricted when the determination module 32 detects the threshold of appearance of non-linearities.

Claims

1. A device (30a-30f) for processing an input signal (Si), generating an output signal (So) designed to feed a loudspeaker (13), directly or indirectly, through an amplifier (18), wherein said device includes a processing line (Lt) comprising: a module (31) for estimating the expected movements (Da) of the loudspeaker (13) as a function of the input signal (Si); and a module (32) for determining an adaptive control signal (CmdA) to be transmitted to the loudspeaker (13), i.e., a signal determined digitally from an expected displacement of the membrane; and the processing device (30a-30f) further comprises: at least one transmission line (L1, L2, L2') of the input signal (Si) delivering at least one non-adaptive control signal (Cmdl, Cmd2), i.e., a signal originating, directly or indirectly, from the input signal (Si); and an adder (14) delivering the output signal (So) by summing the adaptive control signal (CmdA) and the at least one non-adaptive control signal (Cmd1, Cmd2), wherein the determination module (32) is configured to solve a system of coupled differential equations aimed at determining the signal to be transmitted to the loudspeaker (13) in order to obtain the expected displacement of the membrane, the system of coupled differential equations representing the loudspeaker (13), considered as a nonlinear transducer, characterized in that the coupled differential equations also represents the environment of the loudspeaker (13).

2. The processing device according to claim 1, wherein the processing line (Lt) comprises a low-pass filter (16) and a transmission line (L1) of the input signal (Si) comprises a high-pass filter (15).

3. The processing device according to claim 2, characterized in that the processing device (30a-30f) comprises two transmission lines (L1, L2, L2') of the input signal (Si) delivering two non-adaptive control signals (Cmd1, Cmd2): a first transmission line (L1) comprising the high-pass filter (15); and a second transmission line (L2, L2') comprising a low-pass filter (17, 17').

4. The processing device according to one of claims 1 to 3, wherein the processing line (Lt) and the at least one transmission line (L1, L2, L2') comprise a weigher applying a weighting (α, β, γ).

5. The processing device according to one of claims 1 to 4, wherein, when the output signal (So) corresponds to a current signal, the estimation module (31) is connected to the voltage of the input signal (Si) while the at least one transmission line (L1, L2, L2') is connected to a model of the current flowing through the coil of the loudspeaker (13), coming from the input signal (Si), the determination module (32) being configured to determine an adaptive control signal (CmdA) in current.

6. The processing device according to one of claims 1 to 5, wherein the at least one transmission line (L1, L2, L2 ') and / or said processing line (Lt) comprise a compressor and / or limiter (21, 21') configured to restrict the control signal (Cmd2, CmdA) if it exceeds a degradation threshold of the loudspeaker (13) and a compressor and / or limiter (11) for filtering out unrealistic solutions on which said determination module (32) may converge.

7. The processing device according to one of claims 1 to 6, wherein said processing line (Lt) comprises a compressor and / or limiter (10) configured to restrict the control signal (CmdA) if it exceeds a degradation threshold of the loudspeaker (13).

8. The processing device according to one of claims 1 to 7, wherein the determination module (32) receives measurements of operating parameters of the loudspeaker (13) so that the system of coupled differential equations of the determination module (32) also integrates the evolution of the parameters of the loudspeaker (13) over time.

9. The device according to one of claims 1 to 8, wherein the input signal (Si) and / or the output signal (So) is an analog signal.

10. An audio system incorporating a processing device (30a-30f) according to one of claims 1 to 8, generating the output signal (So) from the input signal (Si), and a loudspeaker (13) connected to the output signal (So) through an amplifier (18).

11. An acoustic enclosure comprising a box (89) and an audio system according to claim 10; the coupled differential equations representing: - the geometric definition and the characteristics of the loudspeaker (13); and - the dimensions of the box (89).

12. The acoustic enclosure according to claim 11, characterized in that it comprises at least one vent (90); the coupled differential equations representing furthermore: - the characteristics of the at least one vent (90).

13. The acoustic enclosure according to claim 11, characterized in that it comprises at least one radiator (91); the coupled differential equations representing furthermore: - the characteristics of the at least one radiator (91).

14. An acoustic resonator comprising at least two boxes (921-92p) communicating through at least one vent and / or at least one acoustic bridge and incorporating an audio system according to claim 10; the coupled differential equations representing: - the geometric definition and the characteristics of the loudspeaker (13); - the dimensions of each box (921-92p); and - the characteristics of the at least one vent and / or the at least one acoustic bridge (931-93p-1)15. A vehicle door equipped for sound incorporating an audio system according to claim 10.

16. The vehicle door equipped for sound according to claim 15, characterized in that the coupled differential equations represent: - the geometric definition and the characteristics of the loudspeaker (13); - the characteristics of the door panel (85); - the dimensions of the different volumes (86, 88) of the door: the volume of the box (88) incorporating the loudspeaker (13) and the peripheral volume (86) formed between a front face (81) of said box and the panel door (85); and - the characteristics of the acoustic bridges between these door volumes (86, 88), the acoustic bridges being constituted by at least one sealing sheet (83) and optional short-circuits (84).

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