Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R3/00—Circuits for transducers, loudspeakers or microphones
  • H04R3/04—Circuits for transducers, loudspeakers or microphones for correcting frequency response
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R3/00—Circuits for transducers, loudspeakers or microphones
  • H04R3/12—Circuits for transducers, loudspeakers or microphones for distributing signals to two or more loudspeakers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R7/00—Diaphragms for electromechanical transducers; Cones
  • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
  • H04R7/04—Plane diaphragms
  • H04R7/045—Plane diaphragms using the distributed mode principle, i.e. whereby the acoustic radiation is emanated from uniformly distributed free bending wave vibration induced in a stiff panel and not from pistonic motion
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R2440/00—Bending wave transducers covered by H04R, not provided for in its groups
  • H04R2440/01—Acoustic transducers using travelling bending waves to generate or detect sound
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
  • H04R2499/10—General applications
  • H04R2499/11—Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
  • H04R2499/10—General applications
  • H04R2499/15—Transducers incorporated in visual displaying devices, e.g. televisions, computer displays, laptops

Definitions

• the present invention relates to an acoustic device, for example a loudspeaker, generating an improved sound.
• acoustic devices generating sound by using flat surfaces, three-dimensional surfaces, for example complex surfaces which are vibrated, for example for producing large surface devices or devices integrated into devices having already have another function, such as partitions, door trim in a vehicle, screens for example of a touch pad or smartphone-type smart phone.
• these devices do not generate a sound of very good quality compared to that emitted by traditional speakers, because the surface vibrated is not dedicated to the generation of sound.
• the surface can have a particular shape with areas for which the control of the generated sound is complex, fixing areas for which it is also difficult to control the sound emitted, stiffeners, more or less flexible parts. As a result, a homogeneous vibration over the entire surface cannot be generated, which affects the sound quality.
• the document US2018 / 0249248 describes a surface loudspeaker comprising a plurality of actuators controlled by a controller which is configured to improve the phases and the amplitudes between the signals for each of the actuators.
• the principle is based on the resolution of the eigenvalues of the laws of behavior in mechanics of continuous media. On a symmetrical surface there are simple solutions. But for complex structures, the controller implements a relatively complex variational method.
• an acoustic device comprising a surface intended to be vibrated in order to generate a sound and one or more actuators so as to vibrate said surface, means for controlling the actuator (s) ), comprising means for calculating the control signals implementing a reverse filtering operation, and sending control signals to the actuator or actuators.
• Reverse filtering locally treats acoustic distortions that can deteriorate sound quality.
• the actuator or actuators are controlled to cancel the vibrations in these zones by means of reverse filtering.
• the actuator (s) are to be controlled to cancel vibrations in these areas thanks to reverse filtering.
• an active control of the surface vibration field is carried out by controlling one or more actuators which is or are used, some of them both for producing vibrations intended to generate the desired sound and for cancel vibrations that could deteriorate the desired sound quality.
• the invention does not prevent the transmission or propagation of waves throughout the surface but cancels, thanks to the actuators, the vibrations at certain points of the plate.
• the invention therefore makes it possible to compensate for the reverberation of the waves and their propagation which cause an interference phenomenon, that is to say pollution of the desired vibration at a given point by the signal sent to another actuator at another. point of the surface.
• the use of this reverse filter therefore makes it possible to obtain, on different areas of the plate, a vibration corrected for the effects of dispersion and reverberations.
• the plate of the device can for example be a glass plate, a plastic plate, a plate with aesthetic function, a plate forming a partition and comprising stiffening elements, a plate in contact with elements which modify the vibrations of the plate ...
• the device according to the invention can be used to generate a spatialized sound, said to be in three dimensions, by generating several sound sources on the same surface.
• the zones for which vibrations are controlled may or may not be perpendicular to the actuators.
• the actuators are for example piezoelectric actuators, advantageously mechanically amplified, electromagnetic actuators, in particular electrodynamic ...
• the present invention therefore relates to an acoustic device comprising a structure comprising a surface capable of being vibrated at at least one control point so as to emit a sound, and at least one actuator capable of causing deformation on the surface at level of the control point so as to set it in vibration, means for controlling said at least one actuator configured to send control signals to said actuator, comprising means for calculating said control signals, said calculation means implementing a reverse filtering operation, so as to emit, from a sound to be generated, control signals to said at least one actuator, so as to set said at least one control point vibration and emit the given sound, and at least partially compensate for distortion, reverberation and wave propagation.
• the device comprises several actuators distributed over the surface so as to be able to generate the given sound and to control the vibrations in several control points on the surface.
• the actuator (s) are arranged directly above the one or more control points.
• At least part of the control points is distant from the actuator (s) in the plane of the surface and the distance between each actuator and the control point that it controls, in a direction contained in the surface, is less or equal to the greatest distance among the dimension of the sensor in a direction contained in the surface or to the wavelength of the vibrations generated by the actuator.
• the actuator (s) can be one or more piezoelectric actuators or one or more electromagnetic actuators, advantageously electrodynamic.
• the control means are for example such that they generate signals so that at least some of the actuators emit the given sound simultaneously or successively.
• the present invention also relates to an acoustic system comprising at least one device according to the invention, and at least one element and zones of mechanical interaction between the surface of the structure and the element, said structure comprising control points. covering the interaction zones and the calculation means generating control signals such that said control points have reduced vibrations or are not set in vibration.
• the present invention also relates to a method of operating an acoustic device in order to generate a given sound, said device comprising a structure comprising a surface capable of being vibrated at at least one control point so as to emit a given sound, and at least one actuator capable of causing deformation on the surface at the interaction control point so as to set it into vibration and to emit the given sound, comprising: - the generation of a control signal by an inverse filtering operation from the given sound to be generated,
• the method may include the steps:
• the operating method may comprise, prior to the generation of the control signals, for each frequency in the operating frequency range,
• control signals can be such that said control points are miss in vibration to generate said given sound successively.
• said method may include the step of integration in the reverse filtering operation of generation of the control signals to the actuator or actuators so as to reduce vibrations in areas vibrating in phase opposition.
• the method can allow adaptation of the transfer functions.
• FIG. 1A is a schematic representation of a top view of an example of an acoustic device implementing several actuators
• FIG. 1B is a sectional view of the device of FIG. 1A according to the plane A-A,
• FIG. 2 is a side view shown diagrammatically of a plate vibrated by actuators which are not controlled by signals obtained by reverse filtering,
• FIG. 3 is a side view represented diagrammatically of a plate vibrated by actuators which are controlled by signals obtained by reverse filtering,
• FIG. 4 is a schematic representation of a top view of another example of an acoustic device, the structure of which includes stiffeners,
• FIG. 5 is a schematic representation of a top view of an example of an acoustic device using several actuators, in which the control points are not vertically aligned with the actuators,
• FIG. 6 is a schematic representation of a top view of an example of an acoustic system in which the acoustic device is in mechanical interaction with an element.
• FIG. 7 is a schematic representation of an acoustic device with four actuators and four control points
• FIG. 8 is a matrix of transfer functions connecting each actuator to each control point
• FIGS. 9 and 10 represent the amplitudes of the reverse transfer functions for the matrix of FIG. 8 and the phases of the reverse transfer functions for the matrix of FIG. 8 respectively
• FIG. 11 represents the sum of the vibrations between 100 Hz and 1 kHz for an acoustic device according to the invention controlled to vibrate at point P4 and implementing a spatio-temporal inverse filtering by means of IIR filters,
• FIG. 12 represents the sums of the vibrations between 100 Hz and 1 kHz for an acoustic device not employing space-time inverse filtering.
• FIGS. IA and IB an example of an acoustic device shown diagrammatically can be seen comprising an acoustic structure 1, actuators A1, A2, A3, A4, A5 in contact with one face of the acoustic structure so as to be able to set it in vibration.
• the touch interface also includes means 6 for controlling each of the actuators comprising means 8 for calculating control signals.
• acoustic structure means any structure comprising a surface capable of being vibrated under the action of one or more actuators and of emitting an audible sound, for example for humans to generate vibrations. frequencies for example between 20 Hz and 20 kHz.
• the surface can be flexible or rigid and have a two-dimensional shape, for example a plate, or a three-dimensional shape, for example a cylinder or a sphere.
• the material can be a flexible or rigid material, composite or not.
• the surface can be made for example of plastic, metal, glass, ceramic.
• the dimensions of the structure can be very variable, for example between a few centimeters and several meters.
• the thicknesses of the structure can range from less than one millimeter to ten millimeters depending on the materials used.
• the acoustic structure can form a partition within a building, a surface inside a vehicle, a screen of a telephone, a tablet, a television set or the wall of a piece of furniture.
• the acoustic structure is in the form of a flat plate and will be designated by “plate”.
• the actuators are such that they are capable, when activated, of exerting a force on the plate in an out-of-plane direction, ie orthogonal to the plane of the plate, sufficient to put at least part of the plate into vibration
• the plate of the plate is the plane extending parallel to its largest surface.
• the actuators are capable of exerting an upward and / or downward force in the representation of FIG. IA.
• the surface of the actuator (s) is for example between 1 cm 2 and a few cm 2 .
• the actuators are for example piezoelectric actuators, for example comprising a piezoelectric ceramic pellet, such as PZT (Titano-Zirconate of Lead) or GAIN (Aluminum Nitride) fixed on the plate, for example by bonding or by deposit in thin layers.
• a piezoelectric ceramic pellet such as PZT (Titano-Zirconate of Lead) or GAIN (Aluminum Nitride) fixed on the plate, for example by bonding or by deposit in thin layers.
• the piezoelectric actuators comprise means for amplifying the displacement generated by the excitation of the piezoelectric material.
• the amplification means are of the lever type, of the elliptical type also called “moonie amplifier” or of the circular type also called “cymbal amplifier”.
• the actuators are electromagnetic actuators of the electrodynamic exciter type. They use a moving coil connected to a ground to vibrate a surface by inertial effect. The control signal is sent to the coils.
• one end of the actuator is fixed to the surface to be excited and a mass is fixed to the other end of the actuator. The mass is then only in contact with the actuator.
• a second so-called “reactive” integration mode one end of the actuator is fixed to the surface to be excited and the other end of the actuator is fixed to the solid frame.
• the actuator is secured directly to the surface, for example by gluing and deforms the surface, for example when the actuator is a piezoelectric pellet.
• the actuators are placed on the least recessed areas in order to maximize the movement and therefore the vibration.
• the calculation means 8 implement a reverse filtering operation to determine the actuator control signals.
• the calculation means also implement a vibration synthesis algorithm determining the desired signal in an area, as a function of the desired vibration in this area. This type of algorithm is well known to those skilled in the art and will not be described in detail.
• the controller 8 is connected to the actuator or to the actuators for it or transmit the control signals to them.
• all the actuators participate in the generation of the sound.
• the actuators participating in the generation of the sound are designated main actuators.
• one or more actuators participate in the generation of sound, and one or more other actuators serve to reduce, or even eliminate vibrations liable to deteriorate the quality of the sound emitted by the structure, these actuators are designated corrective actuators.
• the main actuator or the main actuators are arranged on areas of the plate making it possible to actuate a maximum section of this plate in order to generate maximum displacement and therefore lower frequencies.
• FIG. 1A several actuators are distributed under the surface of the plate and are connected to the controller 8.
• all the actuators can be main actuators and allow the entire surface of the structure to be vibrated and therefore provide a high intensity sound.
• all the actuators are main actuators.
• the device of FIG. 1A also includes a sensor C for measuring the change in vibrations of the plate due to its initial state. The change may be due to the expansion of the material of the plate following a change in temperature or a change in embedding or the application of pressure on the plate. These phenomena can modify the transfer functions which will be described below.
• the information provided by the sensor advantageously makes it possible to adapt the transfer functions to the new characteristics of the plate.
• the sensor is for example a temperature, stress, vibration sensor.
• the device comprises piezoelectric actuators, they can also serve as sensors, for example stress and / or vibration sensors.
• electrostatic actuators one or more sensors can be used.
• the device comprises three actuators A1 ', A2', A3 'and the control points Z, Z2', Z3 'set in vibration of the plate are those directly to the right of the actuators A, A2', A3 '.
• the controller determines the control signal to be sent to each of the actuators, all the actuators are excited so that they vibrate the plate.
• control points Z, Z2 ', Z3' do not vibrate in the same way. If we consider that the control point Zl 'vibrates in the way desired to generate the desired sound, the control point Z2 'vibrates in phase with the control point Z, but the control point Z3' vibrates in phase opposition with the control point Z1 '. This phase difference results for example from specific constraints applied at the control point Z3 ', for example by fixing means, or due to a structural difference in the plate, for example a variation in thickness or stiffness or in the made of the frequency effect of the plaque, which can appear more particularly at high frequency.
• phase vibrations of the one Z2 'control point can be beneficial to the desired sound generation.
• the vibrations in phase opposition of the control point Z3 ' deteriorate the sound emitted by the control point Zl'.
• FIG. 3 a side view, shown diagrammatically, can be seen, the acoustic device of FIG. IA, the actuators of which are controlled with the controller 8 implementing calculation means applying the reverse filtering operation in an excited state. in order to make a sound.
• control point Z1 and Z2 vibrate in phase, and that the control point Z3 does not vibrate.
• the signals transmitted are such that the control point Z3 does not vibrate and therefore does not participate in deteriorating the quality of the sound.
• the calculation means by applying the reverse filtering operation, take account of the specificities of the different surfaces (shape, fixing point, etc.) to calculate the signals so that the vibrations of the control points participate positively to the generation of the desired sound, which thus makes it possible to obtain a sound of improved quality, cleaned of vibrations liable to deteriorate it.
• An actuator m (having a linear response) capable of vibrating the plate by a signal s m , produces at position j a displacement denoted U j (t) defined by:
• H jm the transfer function between the control point j and the piezoelectric actuator m.
• the displacement U j at the center of an actuator i is therefore not proportional to the signal applied to it, but is filtered by the response of the actuator stuck to the plate and depends, via the terms H jm , on the signals sent to other actuators which produce waves propagating throughout the plate.
• the inverse filter method consists in inverting the matrix H ⁇ ) for each frequency. This matrix will be used to build the signal S ( ⁇ ), which will produce the displacement U (w) desired at the control point, thanks to the following equation:
• the signal S j (t) will be sent to the various actuators to obtain the desired displacement v on the various control points.
• This filter is temporal insofar as it operates a transformation on the amplitude and the phase at all frequencies, and spatial since it takes into account the signals emitted by all of the actuators.
• a database of the behavior of each of the areas of the plate that we wish to vibrate is produced, in order to know the behavior of these areas at the different frequencies at which they can be vibrated. For this, control signals are sent to the actuators so that they vibrate the different zones by varying the vibration frequency over the entire frequency range of the sound that we are likely to want to produce with the plate.
• one of the actuators is chosen, for example the actuator A, and the associated control point Z1, as a reference, and the behavior of the other control points is compared with respect to the behavior of the control point Zl.
• a laser vibrometer to measure the displacement of the different control points.
• the actuators are used to measure the displacement of the various control points, for example in the case of piezoelectric actuators, the variation in current due to the deformation of the pellets made of piezoelectric material is measured.
• the behavior of the control points can vary according to the frequency, a control point vibrating in phase with the reference control point at a first frequency can vary in phase opposition to a second frequency.
• control points vibrating in phase opposition with respect to the control point Z1, that they will not vibrate.
• the signals will be established so that ultimately these control points do not vibrate.
• control points vibrating in phase generally, their vibrations are preserved which will be added in a beneficial way to the vibrations of the control point Z1. Provision may be made to generate control signals so as to amplify the vibrations in the event that these are of lower amplitudes than that of the vibrations of the control point Z1.
• the singular zones of the plate are determined, for example the fixing zones, the zones having complex geometry, the vibrations of which are difficult to control. Preferably, it is also decided that these zones will not vibrate. The signals will therefore be established so that ultimately these zones do not vibrate. Certain zones, which one decides not to vibrate for certain frequencies, can be controlled at other frequencies to participate positively in the emission of sound.
• the frequency response functions H ij (w) are established linking each actuator q to each control point.
• the functions can be calculated, obtained from a response database or interpolated from a reduced response database.
• the matrix H (w) is then assembled from the functions Hij (üj).
• the inversion or pseudo-inversion is then carried out, since the matrix may not be square, of the matrix H (w) for each frequency of the passband.
• control signals of the actuators are then calculated to obtain the desired vibrations using the inverse matrix H (w) 1 .
• the calculation means applying the reverse filtering operation generate signals sq (t) to the different actuators.
• the signal sent to the actuator A3 may be such that it vibrates the point Z3 control point, but this takes into account the propagation effects that the Z3 control point does not vibrate.
• the signal can be such that it amplifies the vibrations of the control point Z2 which will be added to the vibrations of the control point Z1.
• the signal sent to the actuator Al takes into account the vibrations of the other actuators to limit the effects on the vibrations of the control point Zl and to act if necessary on the other zones for example on the point of control one Z3 to cancel vibrations at the control point.
• Reverse filtering generates interdependent control signals and each actuator has effects on its associated control point and on the control points associated with the other actuators.
• the operating mode of the control means is as follows, considering an interface with Q actuators and with P control points capable of being vibrated to produce a sound. First of all the sound to be produced is chosen, ie and therefore the frequency of the vibrations to be generated. The matrix H w is then selected.
• the desired vibrations are filtered by the inverse matrix to obtain the actuation control signals.
• the signals s q (t) for controlling Q actuators are sent and sent to the actuators.
• One or more control points will actually participate positively in the generation of the sound, ie the control points which will effectively vibrate, and possibly one or more other control points will not vibrate.
• the interface comprises a single actuator.
• each actuator is not plumb with a control point, for example the number of actuators and the number of control points are different and / or the actuators are deliberately not at the plumb with checkpoints.
• the filtering is implemented in the same way, with the distinction that the matrix H (w) is not square since the number of points control is different from the number of actuators.
• the matrix H (w) -1 is then a pseudo inverse of the matrix H w).
• control point partly depends on the type of sensor used to measure the response of the plate to vibration.
• the control point In the case of a laser vibrometer, the control point has a diameter of about 20pm.
• the control point In the case of an accelerometer or a piezoelectric pellet, it is the size of the sensor which gives the dimension, at most 4 cm in diameter.
• the potential control points are located in the field close to the actuators.
• the potential control points are located at a distance at most equal to the dimension of the actuators in the plane of the plate or to the wavelength of the controlled vibrations, the greatest distance being considered.
• This exemplary embodiment is particularly suitable for operation at medium and high frequency, for example 200 Hz. This is the minimum wavelength, and therefore the frequency maximum, of the frequency band which limits the maximum distance between the control point and the actuator when the wavelength is greater than the dimension of the actuator.
• This wavelength depends on the speed of the propagation of the wave in the plate and on its frequency.
• the speed of propagation is around 150m / s at 1000Hz. That is, the maximum distance between the center of the control point and the center of the actuator is approximately 15cm (wavelength).
• the propagation speed is around 450m / s and the wavelength is 4.5cm.
• the maximum distance between the center of the control point and the center of the actuator is 20cm.
• an example of an acoustic device can be seen in which the structure comprises a plate and mechanical reinforcements 10 or stiffeners.
• a main actuator A1 is chosen, which is arranged at the intersection of the stiffeners 10 and the correcting actuators A2, A3, A4, A5 are arranged between the stiffeners 10.
• the matrix H w takes into account the presence of stiffeners.
• the control points are level with the actuators.
• the actuator A1 is chosen as the main actuator because, because of its positioning on the stiffeners, it is capable of causing the vibration of at least a large part of the plate, which allows to generate a sound of high intensity .
• the actuators A2 to A5 reduce or even eliminate the effects, for example of the embedding of the stiffeners.
• the actuator A1 is dimensioned to vibrate the plate despite the presence of the stiffeners.
• the main actuators are the actuators A2 to A5, the excitation of an actuator in each zone delimited by the stiffeners makes it possible to use the entire plate to generate the sound, and the actuator Al is used as corrective actuator for reduce or even eliminate vibrations resulting from stiffeners and which may deteriorate the sound.
• FIG. 5 shows schematically an example of an acoustic device in which all the control points Z1 ", Z2", Z4 "are distant from the actuators A1", A2 ", A4 "in the plane of the plate.
• the control points Z3" and Z5 are perpendicular to the actuators A3" and A5 ".
• the actuators A1" to A5 are for example all of the main actuators.
• the spatialization of sound conventionally uses a large number of speakers of the conventional type aligned and controlled by attenuated and delayed signals originating from the same filtered source signal. The vibrations add up to generate the same sound.
• only one part of the control points of the plate is excited to emit a sound, and by controlling the actuators so as to move the control points emitting a sound, the source of the sound can be moved and generate a moving sound and thus form a home theater type acoustic device.
• FIG. 6 an example of an acoustic device can be seen, the plate of which is in interaction with a mechanical element 14.
• the device comprises a main actuator A1 located in the center of the plate and correcting actuators A2, A3, A4 distributed around the actuator A1, the actuators A2 and A3 being at the control points Z2, Z3 of the plate in mechanical interaction with the mechanical element 14, to reduce or cancel the vibrations at these control points and avoid vibrations can deteriorate the sound generated with the main actuator A1.
• this device can be integrated into a door of a motor vehicle, the mechanical element being for example the sheet metal of the bodywork and the interaction points Z2, Z3 are fixing points.
• the actuators A2 and A3 can be located at a distance from the points in mechanical interaction with the mechanical element at a distance at most equal to the dimension of the actuators in the plane or to the wavelength of the controlled vibrations.
• a spatio-temporal inverse filtering also makes it possible to significantly reduce the number of transfer functions required for the operation of the acoustic device according to the invention, and therefore the number of filters to be used. Reducing the number of filters reduces the complexity of the calculations and the cost of an acoustic device.
• calculation means can be configured to use the same transfer function to control several actuators.
• FIG. 7 We consider an acoustic device such as that shown in FIG. 7 comprising four actuators A1 to A4 and the control points, designated PI to P4, are positioned on the actuators.
• the matrix of transfer functions for each point PI to P4 (line) is represented as a function of the actuator actuated A1 to A4 (column) for frequencies up to 1 kHz.
• FIGS. 9 and 10 the amplitudes and the phases of the inverse transfer functions of the matrix of FIG. 8 are shown respectively.
• the similar or identical transfer functions are grouped by dashed ellipses. We can then use one transfer function instead of two. The pairs of filters implementing these transfer functions can be combined. In this example, the number of filters can be reduced to 10. Without losing quality of filtering.
• Either only one of the transfer functions is chosen, or the transfer function results from a combination of similar transfer functions, for example n performs an average of the transfer functions.
• the number of similar functions replaced by a single transfer function can be greater than 2.
• a reduction in the number of transfer functions and therefore of filters to be implemented is particularly remarkable in the case of an acoustic device comprising a main actuator and secondary actuators distributed on a circle centered on the main actuator. Only three transfer functions can be used, in particular below the 1st resonance (low frequencies). Beyond the first resonance, a fourth transfer function will be advantageously used.
• the reduction in the number of transfer functions and therefore the reduction in the number of filters are particularly advantageous in the case where filters are used for finite impulse response or FIR (Finite Impulse Response in English terminology).
• FIR Finite Impulse Response in English terminology.
• the number of points or “taps” of the FIR filter is preferably at least 4096.
• an audio processor could be able to execute at least 65536 taps. Thanks to the reduction in the number of transfer functions, which can for example be reduced to 10, the number of taps to be executed is 40,960.
• FIR filters are particularly interesting at high frequencies.
• a series of filters 11 R is put in place, formed for example by a cascade of equidistant biquad filters (biquadratic filter) to introduce an almost phase shift -linear.
• biquadratic filter equidistant biquad filters
• IIR filters act locally on a reduced frequency band. For example, provision is made to identify the frequencies which interfere with the proper functioning of the acoustic device, such as the resonance frequencies, and to arrange the biquad filters exactly on these frequencies to cancel their contribution. A vibration localization similar or identical to that obtained by FIR filters can be obtained.
• FIG. 11 we can see the location of the vibrations obtained for a device according to the invention as shown in FIG. 7, implementing space-time filtering using IIR filters. The sum of the vibrations between 100 Hz and 1 kHz is shown. The device is controlled to generate a vibration at control point P4.
• the darkest areas correspond to the areas with the greatest amplitude deformation. There is a very good location at the P4 checkpoint.
• Figure 11 shows the sum of the vibrations between 100 Hz and 1 kHz for a device with 4 actuators but without space-time filtering.
• the darkest areas correspond to the areas with the greatest amplitude deformation.
• acoustic It is possible to provide, during the design of the acoustic device, for carrying out a step of decomposing the transfer functions in order to determine the close or identical transfer functions and a step of reducing the number of transfer functions to be used for the operation of the device. acoustic. It can also be provided when IIR filters formed by a cascade of biquad filters are used identify the frequencies that interfere with the proper functioning of the acoustic device such as the resonance frequencies and arrange the biquad filters exactly on these frequencies to cancel their contribution.
• the acoustic device thus designed comprises control means comprising fewer transfer functions than the product of a number of actuators by the number of control points.
• the number of actuators can range from one actuator up to typically four or five actuators. For larger surfaces a larger number can be used to effectively excite the surface as a speaker.
• an actuator is placed close to each attachment in order to be able to control / cancel the vibration at this location.
• the size of the actuator depends on the acoustic spectrum targeted by the surface loudspeaker.
• An exciter with a diameter of 25 mm and a thickness of 10 mm has a power of 1 W and further excites frequencies ranging from 500 Hz to 20 kHz.
• An exciter with a diameter of 50 mm and a thickness of 20 mm has a power of 10 W and excites frequencies from 100 Hz.
• the dimensions of the sensors are chosen according to the nature and the material of the surface.
• the TECTONIC ® brand electrodynamic exciters can be used in the acoustic devices according to the invention.
• the piezoelectric pads which typically have a diameter of the order of 20mm and a thickness of the order of 0.5mm, further excite the high frequencies, for example greater than 500Hz.
• Amplified piezoelectric actuators can drive lower frequencies.
• the actuators of the APA ® range manufactured by Cedrat Technologies or the PowerHap ® range manufactured by TDK are well suited. These actuators produce a displacement of up to a hundred pm for forces of up to a hundred Newton.
• the present invention is particularly suitable for the emission of sound by surfaces of complex shape and / or integrated into existing structures, for example partitions, since it makes it possible to take into account the constraints that can negatively modify the sound.
• the invention can then be used in the field of home automation in the form of a partition or decorative objects having the function of loudspeaker, in the field of transport, in the passenger compartment of a motor vehicle, in the aeronautics, in rail transport, maritime transport ...), in the telecommunications sector to produce speakers for smartphones, for touch tablets, in the production of Hi-Fi speakers.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Multimedia (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Otolaryngology (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)

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• 2018
  • 2018-12-14 FR FR1872903A patent/FR3090207B1/fr active Active
• 2019
  • 2019-12-12 WO PCT/FR2019/053031 patent/WO2020120909A1/fr unknown
  • 2019-12-12 EP EP19842389.9A patent/EP3878189A1/de active Pending

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