EP2839676B1 - Method and device for controlling the operating temperature of a loudspeaker - Google Patents

Method and device for controlling the operating temperature of a loudspeaker Download PDF

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Publication number
EP2839676B1
EP2839676B1 EP13716782.1A EP13716782A EP2839676B1 EP 2839676 B1 EP2839676 B1 EP 2839676B1 EP 13716782 A EP13716782 A EP 13716782A EP 2839676 B1 EP2839676 B1 EP 2839676B1
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EP
European Patent Office
Prior art keywords
loudspeaker
signal
power
impedance
excitation signal
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EP13716782.1A
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German (de)
French (fr)
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EP2839676A1 (en
Inventor
Ivan Bourmeyster
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Arkamys SA
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Arkamys SA
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    • 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
    • H04R3/002—Damping circuit arrangements for transducers, e.g. motional feedback circuits
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R29/00—Monitoring arrangements; Testing arrangements
    • H04R29/001—Monitoring arrangements; Testing arrangements for loudspeakers
    • H04R29/003—Monitoring arrangements; Testing arrangements for loudspeakers of the moving-coil type
    • 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
    • H04R3/007—Protection circuits for transducers
    • 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

Definitions

  • the invention relates to a method and a device for controlling the operating temperature of a loudspeaker.
  • the invention is more particularly, but not exclusively, adapted to the field of electrodynamic loudspeakers for mobile phones.
  • the coil (130) and magnet (120) assembly constitutes a motor.
  • a periodic electric signal called the excitation signal
  • this motor transforms the electrical energy into mechanical energy, in the form of vibrations, which vibrations are transmitted to the membrane (140), which vibrates, produces fluctuations in air pressure, that is to say a sound.
  • the efficiency of this engine is not perfect, a portion of the electrical energy of the excitation signal is converted into heat, especially Joule effect.
  • This heat increases the temperature of the loudspeaker and leads, when said temperature reaches critical levels, to a distortion of the sound emitted, by the modification of the electromagnetic characteristics of the engine, the thermal expansion of the materials and the loss of linearity in the electromechanical transformation. excitation signal. This heating may even result in the irreversible degradation of the loudspeaker, for example, by the breaking of the constituent wire the turns of the coil.
  • the document EP 2369852 discloses a power management system for an audio system, comprising: a parameter computer configured to develop an estimated operational characteristic of a loudspeaker based on a measured actual parameter of an audio signal driving the loudspeaker; speaker, a threshold comparator in communication with the parameter computer, the threshold comparator being configured to develop and monitor a threshold based on the actual parameter measured and the estimated operational characteristic, and a limiter in communication with the comparator of threshold, the limiter being positioned between an audio source providing the audio signal and the loudspeaker upon receiving the audio signal, the limiter being configured to selectively adjust the audio signal according to the threshold.
  • the invention aims to solve the disadvantages of the prior art and for this purpose concerns a method according to claim 1 for controlling the temperature of an electrodynamic loudspeaker.
  • the method that is the subject of the invention makes it possible to determine the temperature of the loudspeaker without using a specific probe, and without increasing the size of said loudspeaker.
  • the invention can be implemented according to the advantageous embodiments described below, which can be considered individually or in any technically operative combination.
  • the temperature of said speaker can be controlled during its operation.
  • the method according to the invention allows, according to this embodiment, to provide for the heating of the loudspeaker when it is in operation.
  • the method according to the invention makes it possible to protect the loudspeaker against overheating by acting directly on the excitation signal, without integrating additional cooling device.
  • the method that is the subject of the invention makes it possible, by analyzing the signal in the same frequency band as for measuring the temperature, to mechanically protect the membrane of the loudspeaker.
  • the attenuation of the excitation signal is realized only when necessary in order to avoid “pumping” phenomena, that is to say close fluctuations in the sound level or the audio spectrum of the sound emitted from above. loudspeaker.
  • the selective action of the method that is the subject of the invention limits the audible effect of the thermal and mechanical protections on the sound emitted by the loudspeaker. Updating the characteristics of the filters makes it possible to adapt the protection and its effect to the real risk.
  • the excitation signal is a digital signal converted into an analog signal to excite the loudspeaker motor and the filters of steps o) and p) are digital filters applied to the excitation signal before it is converted into an analog signal.
  • the characteristics of the filtering can be adapted very precisely to obtain the mechanical and thermal protection of the speaker by limiting the audible effect of these filters on the sound emitted by the loudspeaker.
  • the predefined frequency range of step c) is between 300 Hz and 1000 Hz.
  • the Applicant has determined that the impedance peaks in this frequency range are particularly correlated with the speaker temperature. .
  • ⁇ t is equal to 5.10 -3 seconds. This delay is at the same time sufficient to carry out the calculations necessary for the analysis of the signals and sufficiently short to realize the thermal and mechanical protections of the loudspeaker without it being necessary to significantly reduce the power of the excitation signal. that is, without degrading too much the excitation signal and hence the sound.
  • the frequency range framing the thermal band is centered on a frequency of 3.10 3 Hz.
  • This frequency of 3 kHz is greater than the the majority of the human voice, the attenuation of the signal power in this frequency band thus makes it possible to effectively limit the heating of the loudspeaker without degrading the sound volume felt by the listener, particularly in the case of a loudspeaker. application on mobile phone in conference mode.
  • the spectral distribution of the impedance is obtained in step a) of the method that is the subject of the invention, by measuring a transfer function between a signal proportional to the current of the analog excitation signal of the loudspeaker. and the delayed digital excitation signal of said loudspeaker.
  • the method can be implemented easily on any device comprising a digital audio source, by adapting the delay time, without significant branch on the speaker side.
  • the device of the invention can be easily adapted to a device without significant modification.
  • the invention also relates to a sound diffusion apparatus, in particular a mobile telephone, comprising a loudspeaker, which apparatus comprises a device according to one of the embodiments of the invention.
  • the apparatus forming the subject of the invention comprises means capable of implementing a mode of over-amplification of the sound diffusion and means able to implement a method of attenuation of the excitation signal according to one of the embodiments of the method which is the subject of the invention, when said over-amplification mode is selected.
  • the apparatus of the invention can be used at a high volume without risk of overheating.
  • FIG. 2 according to an exemplary embodiment of the device (200) object of the invention, it is inserted into the audio processing chain of an apparatus such as a telephone.
  • the device according to the invention receives as input a digital signal (211) coming from an audio source, and outputs a digital signal (212) that has been processed according to one of the embodiment of the method which is the subject of the invention.
  • This digital signal (212) at the output of the device (200) which is the subject of the invention is amplified and converted into a signal (221) for excitation of the loudspeaker (100) by a module (220) for converting and amplification according to a method known from the prior art.
  • the device according to the invention comprises means (230) for measuring the spectral distribution of the impedance of the loudspeaker (100), a computer (240), and a means (250) for processing the signal.
  • the computer (240) is able to modify the characteristics of the processing performed by the signal processing means (250) on the signal (211) introduced into the device that is the subject of the invention.
  • the means (230) for measuring the spectral distribution of the impedance comprises a measurement resistor (331) connected in series with the loudspeaker (100) at the output of the module (220) conversion and amplification. Said measurement resistor (331) is thus traversed by the excitation signal (221). The resistance value of this resistance (331) measurement is low, of the order of 50 to 100 times lower than the speaker impedance (100). Thus for a loudspeaker (100) whose electrical impedance is of the order of 8 ohms, the impedance of the resistor (331) measurement is chosen to be of the order of 0.1 Ohm.
  • Said spectral distribution measuring means (230) comprises a module (332) voltmeter, connected in shunt across the resistor (331) measurement, and delivering a signal (340) proportional to the voltage across said resistor ( 331), ie proportional to the intensity of the loudspeaker excitation signal (221), which intensity is a function of the electrical impedance of said loudspeaker (100).
  • the signal (340) from the module (332) voltmeter is amplified by a low noise amplifier (333) and converted by an analog / digital converter (334) into a digital signal (341).
  • FIG. 4A according to an exemplary embodiment of the computer (240) of the device according to the invention, the latter comprises a processor, memory means for storing data and instruction programs of the processor for performing calculations as well as input and output ports and a clock.
  • the digital signal (341) from the analog / digital converter (334) is introduced into said computer (240), which computer comprises a spectral analysis program (441).
  • the digital excitation signal (212) of the loudspeaker is delayed by a delay module (440) and the delayed signal (412) is also inputted to the spectral analysis program (441). .
  • the delay applied by the delay module (440) to the digital excitation signal (212) of the loudspeaker makes it possible to compensate the processing time of the excitation signal (221) until the delivery of the digital signal (341) from the measurement module of the spectral distribution.
  • the spectral analysis program (441) determines the transfer function of the loudspeaker from the ratio of the two signals (341, 412) at the input of said program and delivers information corresponding to the spectral distribution of the electrical impedance of the loudspeaker. speaker.
  • the time delay applied by the delay module (440) is adjusted to the application.
  • the device of the invention makes it possible, by a simple method, a limited number of components and without significant intervention on the audio circuit, to obtain, in real time, the spectral distribution of the electrical impedance of the loudspeaker.
  • a program (442) included in the computer memory determines, from the spectral distribution provided by the spectral analysis program (441), the position of the center frequency Fc 1 and the half-height width, l 1 , an impedance peak, in a frequency range comprised, according to an exemplary embodiment, between 300 Hz and 1000 Hz.
  • a comparison program (444) compares the position of the center frequency Fc 1 of the last impedance peak recorded at time t 1 with the position of the center frequency Fc 0 of the impedance peak in the previous record. at time t 0 in the same frequency range. Said program (444) delivers information, for example the quantity (Fc 1 -Fc 0 ), relative to the impedance peak displacement.
  • a correlation program (445) determines the temperature, T, of the loudspeaker, at time t 1 of the recording, by reading a correlation table connecting the impedance peak displacement and the temperature of the speaker. Said correlation table is read by said program (445) in a memory (446), called a characteristics memory, accessible in read-only mode, preferably of type ROM (according to the acronym for " Read Only Memory” ) or EPROM ( according to the English acronym of " Erasable Programmable Read Only Memory ”) and having a record of the correlation table for the speaker model considered.
  • Figure 4B according to an exemplary behavior of the loudspeaker, when the temperature of said loudspeaker increases, the spectral distribution of the impedance at time t 1 is plotted (471) in a diagram having on the abscissa the frequency (480) and the ordinate impedance (490), a peak centered on a frequency Fc 1 , which frequency Fc 1 is greater than the center frequency Fc 0 of the peak detected in the plot (470) of the impedance at time t 0 prior to t 1 .
  • the center frequency of the peak impedance goes from 800 Hz to 400 Hz when the temperature of the speaker passes 70 ° C to 120 ° C .
  • the signal processing means (250) is a program implemented by the computer (240) and which performs a digital filtering of the audio signal (211).
  • the filtering comprises a low-pass filter, a band-cut filter or a single-band or multi-band band rejection filter.
  • the filter applied to the audio signal is a low-pass filter whose Bode diagram (570) in a logarithmic reference with the abscissa frequency (580) and the ordinate (590) the gain, comprises a band pass (571) and a rejected band (572) beyond a cut-off frequency (575) corresponding to an attenuation of -3 dB relative to the gain of the pass-through portion.
  • said cut-off frequency (575) is chosen in the upper part of the spectrum of the speech signal, which is greater than or equal to 3.10 3 Hz for a high used to essentially broadcast conversations.
  • the attenuation of the filter is -6 dB / octave.
  • the parameter adjusted as a function of the temperature of the loudspeaker is, on the one hand, the application of the filter to the signal, cutting frequencies above 3.10 3 Hz essentially affecting the tone of the voice without affecting the volume felt by the listener, while reducing the signal excitation power, then the gain in the bandwidth (571) of the filter, this gain then being adjusted to a value less than 0 dB.
  • the filter applied is a band rejection filter.
  • the plot (577) of the Bode diagram of such a filter has attenuation centered on a frequency (576) characterized by a bandwidth l f about this center frequency (576) at -3 dB relative to the gain in the bandwidth.
  • the adjustable parameters of such a filter are the gain in the pass-through portion, the center frequency (576) of the rejected band, and the bandwidth 1 f around this center frequency.
  • the digital filtering of the signal makes it possible to combine the different types of filters according to the desired result in order to minimize the audible degradation of the sound emitted by the loudspeaker.
  • the appropriate filter combination is determined experimentally or by simulation.
  • Figure 6 according to an exemplary embodiment of the method which is the subject of the invention, implemented by a device as described above, said method comprises a first measurement step (610) of obtaining the spectral distribution of the electrical impedance of the speaker, preferably in a frequency range between 300 Hz and 1000 Hz.
  • an identification step (620) an impedance peak, centered on a frequency Fc 1 , is identified in the spectral distribution obtained during of step (610) of measurement.
  • a comparison step (630) the position of the center frequency Fc 1 of said peak is compared with the position of the center frequency Fc 0 of the impedance peak in the spectral distribution obtained at an earlier date t 0 .
  • a stability control step (635) the difference ⁇ Fc 1 - Fc 0 ⁇ is compared with a criterion of stability F stab .
  • the subsequent stages of signal processing are implemented only if the heating of the loudspeaker is proven.
  • the difference (Fc 1 -Fc 0 ) is correlated with the temperature T of the loudspeaker, thus determining the temperature of said loudspeaker at time t 1 .
  • a signal analysis step (650) the spectral distribution of the power of the excitation signal is obtained.
  • said spectral power distribution of the excitation signal is used to provide heating, ⁇ T, the speaker at time (t 1 + ⁇ ) with ⁇ ⁇ ⁇ t.
  • a thermal risk analysis step (665) the quantity ( T + ⁇ T ) is compared with a critical temperature Tc. If (T + ⁇ T ) ⁇ Tc then a filter aimed at reducing the power of the excitation signal according to a selected frequency spectrum is calculated during a parameterization step (670).
  • a step (680) of mechanical analysis the power of the excitation signal in a frequency band centered on Fc 1 according to a bandwidth 11 is analyzed.
  • the power determined during the mechanical analysis step is compared to a critical value defining a risk of displacement of the speaker diaphragm out of its allowable mechanical travel . If the power determined during the step (680) of mechanical analysis is greater than the allowable power, then the characteristics of a band rejection filter, centered on the frequency Fc 1 and in a bandwidth, called mechanical band, corresponding to l 1 are calculated during a step (690) of mechanical parameterization.
  • the filters calculated during the mechanical and thermal parameterization steps (670, 690) are applied to the signal during a filtering step (695).
  • the invention achieves the desired objectives, in particular, it makes it possible, particularly in the context of a mobile phone application, to protect the loudspeaker of said telephone when it is used in over-amplification, especially in meeting mode.
  • the selective action on the sound spectrum and the real-time control and anticipation of the heating of the loudspeaker allow to keep said speaker at an acceptable operating temperature while preserving the sound volume felt.
  • the fully digital signal processing allows great flexibility in the signal processing and in the selection of the parameterization of the filters applied to said signal.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Circuit For Audible Band Transducer (AREA)

Description

L'invention concerne un procédé et un dispositif pour le contrôle de la température de fonctionnement d'un haut-parleur. L'invention est plus particulièrement, mais non exclusivement, adaptée au domaine des haut-parleurs électrodynamiques pour téléphones mobiles.The invention relates to a method and a device for controlling the operating temperature of a loudspeaker. The invention is more particularly, but not exclusively, adapted to the field of electrodynamic loudspeakers for mobile phones.

La figure 1, relative à l'art antérieur, représente schématiquement les composants d'un haut-parleur électrodynamique. Un tel haut-parleur (100) de forme sensiblement conique, comprend :

  • un châssis (110) supportant l'ensemble des composants dudit haut-parleur ;
  • un aimant permanent (120) fixé audit châssis ;
  • une bobine (130) constitué d'un fil enroulé en spires entourant sans contact l'aimant permanent (120) ;
  • une membrane (140) de forme sensiblement conique fixée au châssis (110) sur la périphérie de son plus grand diamètre et à la bobine sur la périphérie de son plus petit diamètre.
The figure 1 , relating to the prior art, schematically shows the components of an electrodynamic loudspeaker. Such a loudspeaker (100) of substantially conical shape, comprises:
  • a chassis (110) supporting all the components of said speaker;
  • a permanent magnet (120) attached to said frame;
  • a coil (130) consisting of a wire wound in turns surrounding the permanent magnet (120) without contact;
  • a substantially conical diaphragm (140) attached to the frame (110) on the periphery of its larger diameter and to the coil on the periphery of its smaller diameter.

L'ensemble bobine (130) et aimant (120) constitue un moteur. Lorsqu'un signal électrique périodique, dit signal d'excitation, est appliqué aux bornes (135, 136) d'alimentation de la bobine (130), ce moteur transforme l'énergie électrique en énergie mécanique, sous la forme de vibrations, lesquelles vibrations sont transmises à la membrane (140), qui en vibrant, produit des fluctuations de pression de l'air, c'est-à-dire un son. Le rendement de ce moteur n'étant pas parfait, une partie de l'énergie électrique du signal d'excitation est transformée en chaleur, notamment par effet joule. Cette chaleur accroît la température du haut-parleur et conduit, lorsque ladite température atteint des niveaux critiques, à une distorsion du son émis, par la modification des caractéristiques électromagnétiques du moteur, la dilatation thermique des matériaux et la perte de linéarité dans la transformation électromécanique du signal d'excitation. Cet échauffement peut même entraîner la dégradation irréversible du haut-parleur, par exemple, par la rupture du fil constituant les spires de la bobine.The coil (130) and magnet (120) assembly constitutes a motor. When a periodic electric signal, called the excitation signal, is applied to the terminals (135, 136) supplying the coil (130), this motor transforms the electrical energy into mechanical energy, in the form of vibrations, which vibrations are transmitted to the membrane (140), which vibrates, produces fluctuations in air pressure, that is to say a sound. The efficiency of this engine is not perfect, a portion of the electrical energy of the excitation signal is converted into heat, especially Joule effect. This heat increases the temperature of the loudspeaker and leads, when said temperature reaches critical levels, to a distortion of the sound emitted, by the modification of the electromagnetic characteristics of the engine, the thermal expansion of the materials and the loss of linearity in the electromechanical transformation. excitation signal. This heating may even result in the irreversible degradation of the loudspeaker, for example, by the breaking of the constituent wire the turns of the coil.

Selon l'art antérieur, différentes techniques permettent de limiter l'échauffement du haut-parleur et de le protéger de la surchauffe. Ces techniques, sont par exemple, de nature passive, consistant à réaliser le haut-parleur en combinant des composants dont les caractéristiques permettent de limiter l'échauffement, notamment en augmentant le nombre de spires de la bobine, en réduisant la masse de la membrane, en assurant une bonne ventilation et en augmentant l'entrefer entre la bobine et l'aimant. Ces solutions techniques sont difficiles de mise en oeuvre dans le cas où le haut-parleur est de taille réduite et est logé dans un espace restreint. Des solutions techniques de nature active visant à réguler la température dudit haut-parleur sont également utilisées. Ainsi, le document US-A-2005/0039465 décrit un dispositif utilisant une sonde de température et un module de refroidissement par effet Peltier liés au haut-parleur. Un circuit électronique déclenche le fonctionnement du module à effet Peltier de manière à refroidir le haut-parleur, lequel module est alimenté par le signal d'excitation, lorsque la température mesurée par la sonde atteint une valeur critique.According to the prior art, various techniques can limit the heating of the speaker and protect it from overheating. These techniques are, for example, passive in nature, consisting in producing the loudspeaker by combining components whose characteristics make it possible to limit the heating, in particular by increasing the number of turns of the coil, by reducing the mass of the membrane. , ensuring good ventilation and increasing the gap between the coil and the magnet. These technical solutions are difficult to implement in the case where the speaker is reduced in size and is housed in a small space. Technical solutions of an active nature for regulating the temperature of said loudspeaker are also used. Thus, the document US-2005/0039465 describes a device using a temperature probe and a Peltier effect cooling module connected to the loudspeaker. An electronic circuit triggers the operation of the Peltier effect module so as to cool the loudspeaker, which module is powered by the excitation signal, when the temperature measured by the probe reaches a critical value.

Cet exemple de régulation thermique de l'art antérieur est également difficilement applicable lorsque le haut-parleur est intégré dans un système de taille réduite comme un téléphone mobile, et de plus, produit une atténuation importante du volume sonore lorsqu'il est mis en fonction. Or, l'utilisateur d'un téléphone mobile souhaite pouvoir utiliser ledit téléphone en mode réunion et à cette fin, ledit téléphone mobile comprend un mode de suramplification permettant à partir du haut-parleur de ce téléphone de produire un son audible à plusieurs mètres, pendant un temps pouvant atteindre plusieurs dizaines de minutes. Le document EP 2369852 décrit une système de gestion de l'alimentation pour un système audio, comprenant: un ordinateur de paramètre configuré pour développer une caractéristique opérationnelle estimée d'un haut-parleur en fonction d'un paramètre réel mesuré d'un signal audio pilotant le haut-parleur, un comparateur de seuil en communication avec l'ordinateur de paramètre, le comparateur de seuil étant configuré pour développer et pour suivre un seuil en fonction du paramètre réel mesuré et de la caractéristique opérationnelle estimée, et un limiteur en communication avec le comparateur de seuil, le limiteur étant positionné entre une source audio fournissant le signal audio et le haut-parleur à la réception du signal audio, le limiteur étant configuré pour ajuster de manière sélectif le signal audio en fonction du seuil. L'invention vise à résoudre les inconvénients de l'art antérieur et concerne à cette fin un procédé selon la revendication 1 pour le contrôle de la température d'un haut-parleur électrodynamique.This example of thermal regulation of the prior art is also difficult to apply when the loudspeaker is integrated in a reduced size system such as a mobile phone, and moreover, produces a significant attenuation of the sound volume when it is turned on. . However, the user of a mobile phone wishes to use said phone in meeting mode and for this purpose, said mobile phone includes a mode of amplification allowing from the speaker of this phone to produce an audible sound several meters, for a period of up to several tens of minutes. The document EP 2369852 discloses a power management system for an audio system, comprising: a parameter computer configured to develop an estimated operational characteristic of a loudspeaker based on a measured actual parameter of an audio signal driving the loudspeaker; speaker, a threshold comparator in communication with the parameter computer, the threshold comparator being configured to develop and monitor a threshold based on the actual parameter measured and the estimated operational characteristic, and a limiter in communication with the comparator of threshold, the limiter being positioned between an audio source providing the audio signal and the loudspeaker upon receiving the audio signal, the limiter being configured to selectively adjust the audio signal according to the threshold. The invention aims to solve the disadvantages of the prior art and for this purpose concerns a method according to claim 1 for controlling the temperature of an electrodynamic loudspeaker.

Ainsi, le procédé objet de l'invention permet de déterminer la température du haut-parleur sans faire appel à une sonde spécifique, et sans augmenter l'encombrement dudit haut-parleur.Thus, the method that is the subject of the invention makes it possible to determine the temperature of the loudspeaker without using a specific probe, and without increasing the size of said loudspeaker.

L'invention peut être mise en oeuvre selon les modes de réalisation avantageux exposés ci-après, lesquels peuvent être considérés individuellement ou selon toute combinaison techniquement opérante.The invention can be implemented according to the advantageous embodiments described below, which can be considered individually or in any technically operative combination.

Avantageusement, les étapes a) à e) sont répétées pour chaque intervalle de temps δt = (t1-t0) lorsque le haut-parleur est en fonctionnement. Ainsi, la température dudit haut-parleur peut être contrôlée au cours de son fonctionnement.Advantageously, steps a) to e) are repeated for each time interval δ t = (t 1 -t 0 ) when the loudspeaker is in operation. Thus, the temperature of said speaker can be controlled during its operation.

Avantageusement, l'étape e) comprend les étapes consistant à :

  • ei. déterminer une température instantanée, T, au temps t1 par l'écart de fréquence entre les pics d'impédance ;
  • eii. déterminer la puissance du signal d'excitation et la part d'énergie de ce signal convertie en chaleur ;
  • eiii. déterminer en fonction du résultat de l'étape eii), la température du haut-parleur à un temps (t1 + ε) tel que ε ≥ δt.
Advantageously, step e) comprises the steps of:
  • ei. determining an instantaneous temperature, T , at time t 1 by the frequency difference between the impedance peaks;
  • eii. determining the power of the excitation signal and the energy portion of this signal converted into heat;
  • EIII. depending on the result of step eii), determining the temperature of the loudspeaker at a time (t 1 + ε ) such that ε ≥ δ t .

Ainsi le procédé objet de l'invention permet, selon ce mode de réalisation, de prévoir l'échauffement du haut-parleur lorsque celui-ci est en fonctionnement.Thus the method according to the invention allows, according to this embodiment, to provide for the heating of the loudspeaker when it is in operation.

Avantageusement le procédé objet de l'invention comprend après l'étape e) une étape consistant à :

  • f. réduire la puissance du signal d'excitation dans une bande de fréquence, dite bande thermique, si la température déterminée à étape e) dépasse un seuil critique.
Advantageously, the method which is the subject of the invention comprises, after step e), a step consisting of:
  • f. reduce the power of the excitation signal in a band of frequency, called thermal band, if the temperature determined in step e) exceeds a critical threshold.

Ainsi, le procédé objet de l'invention permet, selon ce mode de réalisation, de protéger le haut-parleur contre la surchauffe en agissant directement sur le signal d'excitation, sans intégrer de dispositif de refroidissement supplémentaire.Thus, according to this embodiment, the method according to the invention makes it possible to protect the loudspeaker against overheating by acting directly on the excitation signal, without integrating additional cooling device.

Avantageusement, le procédé objet de l'invention comprend selon un de ses modes de réalisation, les étapes consistant à :

  • g. obtenir la répartition spectrale de la puissance du signal d'excitation ;
  • h. à partir de la répartition obtenue à l'étape g) déterminer la puissance du signal dans une bande de fréquence, dite bande mécanique, centrée sur la fréquence centrale, Fc1 , du pic d'impédance obtenu à l'étape b) ;
  • i. obtenir une puissance d'excitation admissible pour la tenue de la membrane du haut-parleur ;
  • j. si la puissance obtenue à l'étape h) est supérieure ou égale à la puissance admissible obtenue à l'étape i), réduire la puissance du signal d'excitation dans la bande mécanique.
Advantageously, the method which is the subject of the invention comprises, according to one of its embodiments, the steps of:
  • boy Wut. obtain the spectral distribution of the power of the excitation signal;
  • h. from the distribution obtained in step g) determining the power of the signal in a frequency band, called the mechanical band, centered on the central frequency, Fc 1 , of the impedance peak obtained in step b);
  • i. obtain a permissible excitation power for holding the membrane of the loudspeaker;
  • j. if the power obtained in step h) is greater than or equal to the allowable power obtained in step i), reduce the power of the excitation signal in the mechanical band.

Ainsi, le procédé objet de l'invention permet, par l'analyse du signal dans une même bande de fréquence que pour la mesure de la température, de protéger mécaniquement la membrane du haut-parleur.Thus, the method that is the subject of the invention makes it possible, by analyzing the signal in the same frequency band as for measuring the temperature, to mechanically protect the membrane of the loudspeaker.

Selon un perfectionnement du mode de réalisation permettant la protection thermique du haut-parleur, le procédé objet de l'invention comprend après l'étape c) et avant l'étape d) les étapes consistant à :

  • k. obtenir une valeur de fréquence, Fstab , dite critère de stabilité ;
  • l. comparer l'écart de fréquence obtenu à l'étape c) avec le critère de stabilité ;
  • m. exécuter les étapes d), e) et f) si la condition (∥Fc0-Fc1 ∥ ≤ Fstab ) est vraie et retourner à l'étape a) si cette condition n'est pas vérifiée.
According to an improvement of the embodiment allowing the thermal protection of the loudspeaker, the method of the invention comprises after step c) and before step d) the steps of:
  • k. obtain a frequency value, F stab , called stability criterion;
  • l. comparing the frequency difference obtained in step c) with the stability criterion;
  • m. perform steps d), e) and f) if the condition (∥ Fc 0 -Fc 1 ∥ ≤ F stab ) is true and return to step a) if this condition is not satisfied.

Ainsi, l'atténuation du signal d'excitation n'est réalisée que lorsque nécessaire afin d'éviter les phénomènes de « pompage » c'est-à-dire des fluctuations rapprochées du niveau sonore ou du spectre audio du son émis par le haut-parleur.Thus, the attenuation of the excitation signal is realized only when necessary in order to avoid "pumping" phenomena, that is to say close fluctuations in the sound level or the audio spectrum of the sound emitted from above. loudspeaker.

Avantageusement, les réductions de puissance du signal d'excitation des étapes f) et j) sont réalisées par des filtrages dudit signal dans des bandes de fréquences sélectives et le procédé objet de l'invention comprend selon ce mode de réalisation les étapes consistant à :

  • o. déterminer avant l'étape f) les caractéristiques d'un filtre apte à réduire sélectivement la puissance spectrale du signal au cours de ladite étape f);
  • p. déterminer avant l'étape j) les caractéristiques d'un filtre apte à réduire sélectivement la puissance spectrale du signal d'excitation au cours de ladite étape j).
Advantageously, the power reductions of the excitation signal of the steps f) and j) are performed by filtering said signal in selective frequency bands and the method according to the invention comprises according to this embodiment the steps of:
  • o. determining, before step f), the characteristics of a filter capable of selectively reducing the spectral power of the signal during said step f);
  • p. determining, before step j), the characteristics of a filter capable of selectively reducing the spectral power of the excitation signal during said step j).

Ainsi, l'action sélective du procédé objet de l'invention limite l'effet audible des protections thermiques et mécaniques sur le son émis par le haut-parleur. L'actualisation des caractéristiques des filtres permet d'adapter la protection et son effet au risque réel.Thus, the selective action of the method that is the subject of the invention limits the audible effect of the thermal and mechanical protections on the sound emitted by the loudspeaker. Updating the characteristics of the filters makes it possible to adapt the protection and its effect to the real risk.

Avantageusement, le signal d'excitation est un signal numérique converti en signal analogique pour exciter le moteur du haut-parleur et les filtres des étapes o) et p) sont des filtres numériques appliqués au signal d'excitation avant sa conversion en signal analogique. Ainsi, les caractéristiques du filtrage peuvent être adaptées de manière très précise pour obtenir les protections mécaniques et thermiques du haut-parleur en limitant l'effet audible de ces filtres sur le son émis par le haut-parleur.Advantageously, the excitation signal is a digital signal converted into an analog signal to excite the loudspeaker motor and the filters of steps o) and p) are digital filters applied to the excitation signal before it is converted into an analog signal. Thus, the characteristics of the filtering can be adapted very precisely to obtain the mechanical and thermal protection of the speaker by limiting the audible effect of these filters on the sound emitted by the loudspeaker.

Avantageusement, la plage de fréquence prédéfinie de l'étape c) est comprise entre 300 Hz et 1 000 Hz. La demanderesse a déterminé que le déplacement des pics d'impédance dans cette plage de fréquence est particulièrement corrélé avec la température du haut-parleur.Advantageously, the predefined frequency range of step c) is between 300 Hz and 1000 Hz. The Applicant has determined that the impedance peaks in this frequency range are particularly correlated with the speaker temperature. .

Avantageusement, δt est égal à 5.10-3 secondes. Ce délai est à la fois suffisant pour effectuer les calculs nécessaires à l'analyse des signaux et suffisamment court pour réaliser les protections thermiques et mécaniques du haut-parleur sans qu'il soit nécessaire de réduire de manière importante la puissance du signal d'excitation, c'est-à-dire, sans dégrader de manière trop importante le signal d'excitation et par suite, le son.Advantageously, δ t is equal to 5.10 -3 seconds. This delay is at the same time sufficient to carry out the calculations necessary for the analysis of the signals and sufficiently short to realize the thermal and mechanical protections of the loudspeaker without it being necessary to significantly reduce the power of the excitation signal. that is, without degrading too much the excitation signal and hence the sound.

Avantageusement, la plage de fréquences encadrant la bande thermique est centrée sur une fréquence de 3.103 Hz. Cette fréquence de 3 kHz est supérieure au contenu spectral majoritaire de la voix humaine, l'atténuation de la puissance du signal dans cette bande de fréquence permet ainsi de limiter efficacement l'échauffement du haut-parleur sans dégrader le volume sonore ressenti par l'auditeur notamment dans le cas d'une application sur téléphone mobile en mode conférence.Advantageously, the frequency range framing the thermal band is centered on a frequency of 3.10 3 Hz. This frequency of 3 kHz is greater than the the majority of the human voice, the attenuation of the signal power in this frequency band thus makes it possible to effectively limit the heating of the loudspeaker without degrading the sound volume felt by the listener, particularly in the case of a loudspeaker. application on mobile phone in conference mode.

Avantageusement, la répartition spectrale de l'impédance est obtenue à l'étape a) du procédé objet de l'invention, par la mesure d'une fonction de transfert entre un signal proportionnel au courant du signal d'excitation analogique du haut-parleur et le signal d'excitation numérique retardé dudit haut-parleur. Ainsi, le procédé peut être mis en oeuvre facilement sur n'importe quel appareil comprenant une source audio numérique, en adaptant le délai de retard, sans branchement important côté haut-parleur.Advantageously, the spectral distribution of the impedance is obtained in step a) of the method that is the subject of the invention, by measuring a transfer function between a signal proportional to the current of the analog excitation signal of the loudspeaker. and the delayed digital excitation signal of said loudspeaker. Thus, the method can be implemented easily on any device comprising a digital audio source, by adapting the delay time, without significant branch on the speaker side.

L'invention concerne également un dispositif apte à mettre en oeuvre le procédé objet de l'invention sur un haut-parleur dont le moteur est alimenté par un signal d'excitation, lequel dispositif comprend :

  1. i. un moyen de traitement du signal ;
  2. ii. un calculateur, apte à modifier les caractéristiques du traitement opéré par le moyen de traitement du signal ;
  3. iii. un moyen de mesure de la répartition spectrale de l'impédance du haut-parleur, caractérisé en ce que ledit moyen comporte une résistance de mesure, d'impédance inférieure à 1/50ème de l'impédance du haut-parleur, montée en série sur l'alimentation du moteur du haut-parleur et traversée par le signal d'excitation, et des moyens aptes à délivrer un signal proportionnel à la tension aux bornes de ladite résistance.
The invention also relates to a device adapted to implement the method of the invention on a loudspeaker whose motor is powered by an excitation signal, which device comprises:
  1. i. signal processing means;
  2. ii. a computer, able to modify the characteristics of the processing performed by the signal processing means;
  3. iii. a means for measuring the spectral distribution of the impedance of the loudspeaker, characterized in that said means comprises a measurement resistor, of impedance less than 1/50 th of the impedance of the loudspeaker, mounted in series on the power supply of the loudspeaker motor and traversed by the excitation signal, and means adapted to deliver a signal proportional to the voltage across said resistor.

Ainsi le dispositif objet de l'invention peut être facilement adapté à un appareil sans modification importante.Thus the device of the invention can be easily adapted to a device without significant modification.

L'invention concerne également un appareil de diffusion sonore, notamment un téléphone mobile, comportant un haut-parleur, lequel appareil comporte un dispositif selon un des modes de réalisation de l'invention.The invention also relates to a sound diffusion apparatus, in particular a mobile telephone, comprising a loudspeaker, which apparatus comprises a device according to one of the embodiments of the invention.

Avantageusement, l'appareil objet de l'invention comporte des moyens aptes à mettre en oeuvre un mode de sur-amplification de la diffusion sonore et des moyens aptes à mettre en oeuvre un procédé d'atténuation du signal d'excitation selon un des modes de réalisation du procédé objet de l'invention, lorsque ledit mode de sur-amplification est sélectionné. Ainsi, l'appareil objet de l'invention peut être utilisé à un volume sonore élevé sans risque de surchauffe.Advantageously, the apparatus forming the subject of the invention comprises means capable of implementing a mode of over-amplification of the sound diffusion and means able to implement a method of attenuation of the excitation signal according to one of the embodiments of the method which is the subject of the invention, when said over-amplification mode is selected. Thus, the apparatus of the invention can be used at a high volume without risk of overheating.

L'invention est exposée ci-après selon ses modes de réalisation préférés, nullement limitatifs, et en référence aux figures 1 à 6 dans lesquelles :

  • la figure 1 relative à l'art antérieur représente selon une vue en coupe un schéma de principe d'un haut-parleur électrodynamique ;
  • la figure 2 est un diagramme fonctionnel d'ensemble d'un exemple de réalisation du dispositif objet de l'invention ;
  • la figure 3 montre un diagramme fonctionnel du moyen de mesure de la répartition spectrale de l'impédance du haut-parleur selon un exemple de réalisation du dispositif objet de l'invention ;
  • la figure 4, montre, figure 4A, un diagramme fonctionnel du calculateur mettant en oeuvre l'analyse spectrale et le filtrage selon un exemple de réalisation du dispositif objet de l'invention et représente, figure 4B, un exemple de comparaison de spectres d'impédances mesurés à des températures différentes du haut-parleur ;
  • la figure 5 montre, figure 5A un exemple d'un diagramme de Bode d'un filtre passe-bas et figure 5B, un exemple d'un diagramme de Bode d'un filtre de réjection de bande ;
  • et la figure 6 représente un organigramme d'un procédé de mesure et de contrôle de la température d'un haut-parleur selon un exemple de réalisation du procédé objet de l'invention.
The invention is explained below according to its preferred embodiments, which are in no way limiting, and with reference to Figures 1 to 6 in which :
  • the figure 1 relating to the prior art shows in a sectional view a schematic diagram of an electrodynamic loudspeaker;
  • the figure 2 is a block diagram of an exemplary embodiment of the device object of the invention;
  • the figure 3 shows a functional diagram of the means for measuring the spectral distribution of the impedance of the loudspeaker according to an embodiment of the device which is the subject of the invention;
  • the figure 4 , shows, Figure 4A a functional diagram of the computer implementing the spectral analysis and the filtering according to an embodiment of the device which is the subject of the invention and represents, Figure 4B an example of comparison of impedance spectra measured at different temperatures of the loudspeaker;
  • the figure 5 shows Figure 5A an example of a Bode diagram of a low-pass filter and Figure 5B , an example of a Bode diagram of a band rejection filter;
  • and the figure 6 represents a flowchart of a method for measuring and monitoring the temperature of a loudspeaker according to an embodiment of the method that is the subject of the invention.

Figure 2, selon un exemple de réalisation du dispositif (200) objet de l'invention, celui-ci est inséré dans la chaîne de traitement audio d'un appareil tel qu'un téléphone. Le dispositif objet de l'invention, reçoit en entrée un signal (211) numérique provenant d'une source audio, et délivre en sortie un signal (212) numérique ayant fait l'objet d'un traitement selon l'un des modes de réalisation du procédé objet de l'invention. Ce signal numérique (212) en sortie du dispositif (200) objet de l'invention, est amplifié et converti en un signal (221) d'excitation du haut-parleur (100) par un module (220) de conversion et d'amplification selon un procédé connu de l'art antérieur. Le dispositif objet de l'invention comprend un moyen (230) de mesure de la répartition spectrale de l'impédance du haut-parleur (100), un calculateur (240), et un moyen (250) de traitement du signal. Le calculateur (240) est apte à modifier les caractéristiques du traitement opéré par le moyen (250) de traitement du signal sur le signal (211) introduit dans le dispositif objet de l'invention. Figure 2 , according to an exemplary embodiment of the device (200) object of the invention, it is inserted into the audio processing chain of an apparatus such as a telephone. The device according to the invention, receives as input a digital signal (211) coming from an audio source, and outputs a digital signal (212) that has been processed according to one of the embodiment of the method which is the subject of the invention. This digital signal (212) at the output of the device (200) which is the subject of the invention is amplified and converted into a signal (221) for excitation of the loudspeaker (100) by a module (220) for converting and amplification according to a method known from the prior art. The device according to the invention comprises means (230) for measuring the spectral distribution of the impedance of the loudspeaker (100), a computer (240), and a means (250) for processing the signal. The computer (240) is able to modify the characteristics of the processing performed by the signal processing means (250) on the signal (211) introduced into the device that is the subject of the invention.

Figure 3, selon un exemple de réalisation, le moyen (230) de mesure de la répartition spectrale de l'impédance, comprend une résistance (331) de mesure montée en série avec le haut-parleur (100) à la sortie du module (220) de conversion et d'amplification. Ladite résistance (331) de mesure est ainsi traversée par le signal (221) d'excitation. La valeur ohmique de cette résistance (331) de mesure est faible, de l'ordre de 50 à 100 fois plus faible que l'impédance de haut-parleur (100). Ainsi pour un haut-parleur (100) dont l'impédance électrique est de l'ordre de 8 Ohms, l'impédance de la résistance (331) de mesure est choisie de l'ordre de 0,1 Ohm. Ledit moyen (230) de mesure de la répartition spectrale comprend un module (332) voltmètre, branché en dérivation aux bornes de la résistance (331) de mesure, et délivrant un signal (340) proportionnel à la tension aux bornes de ladite résistance (331) de mesure, c'est-à-dire proportionnel à l'intensité du signal (221) d'excitation du haut-parleur, laquelle intensité est fonction de l'impédance électrique dudit haut-parleur (100). Le signal (340) issu du module (332) voltmètre est amplifié par un amplificateur (333) à faible bruit puis converti par un convertisseur (334) analogique/numérique en un signal (341) numérique. Figure 3 according to an exemplary embodiment, the means (230) for measuring the spectral distribution of the impedance comprises a measurement resistor (331) connected in series with the loudspeaker (100) at the output of the module (220) conversion and amplification. Said measurement resistor (331) is thus traversed by the excitation signal (221). The resistance value of this resistance (331) measurement is low, of the order of 50 to 100 times lower than the speaker impedance (100). Thus for a loudspeaker (100) whose electrical impedance is of the order of 8 ohms, the impedance of the resistor (331) measurement is chosen to be of the order of 0.1 Ohm. Said spectral distribution measuring means (230) comprises a module (332) voltmeter, connected in shunt across the resistor (331) measurement, and delivering a signal (340) proportional to the voltage across said resistor ( 331), ie proportional to the intensity of the loudspeaker excitation signal (221), which intensity is a function of the electrical impedance of said loudspeaker (100). The signal (340) from the module (332) voltmeter is amplified by a low noise amplifier (333) and converted by an analog / digital converter (334) into a digital signal (341).

Figure 4A, selon un exemple de réalisation du calculateur (240) du dispositif objet de l'invention, celui-ci comprend un processeur, des moyens de mémoire pour y enregistrer des données et des programmes d'instructions du processeur pour réaliser des calculs ainsi que des ports d'entrée et de sortie et une horloge. Le signal (341) numérique issu du convertisseur (334) analogique/numérique est introduit dans ledit calculateur (240), lequel calculateur comprend un programme (441) d'analyse spectrale. Selon un exemple de réalisation, le signal (212) numérique d'excitation du haut-parleur est retardé par un module (440) de retard et ledit signal retardé (412) est également introduit en entrée du programme (441) d'analyse spectrale. Le retard appliqué par le module de retard (440) au signal (212) numérique d'excitation du haut-parleur permet de compenser le temps de traitement du signal d'excitation (221) jusqu'à la délivrance du signal (341) numérique issu du module de mesure de la répartition spectrale. Le programme (441) d'analyse spectrale détermine la fonction transfert du haut-parleur à partir du rapport des deux signaux (341, 412) en entrée dudit programme et délivre une information correspondant à la distribution spectrale de l'impédance électrique du haut-parleur. Le retard temporel appliqué par le module (440) de retard est ajusté à l'application. Ainsi, le dispositif objet de l'invention permet, par une méthode simple, un nombre limité de composants et sans intervention importante sur le circuit audio, d'obtenir, en temps réel, la répartition spectrale de l'impédance électrique du haut-parleur. Un programme (442) compris dans la mémoire du calculateur détermine, à partir de la répartition spectrale fournie par le programme (441) d'analyse spectrale, la position de la fréquence centrale Fc1 et la largeur à mi-hauteur, l1 , d'un pic d'impédance, dans une plage de fréquence comprise, selon un exemple de réalisation, entre 300 Hz et 1 000 Hz. Si un tel pic d'impédance est détecté, les informations relatives à sa fréquence centrale, Fc1 , sa largeur à mi-hauteur, l1 , et la date de mesure sont enregistrées dans une mémoire (443) vive accessible en lecture et en écriture, dite RAM d'historique, selon l'acronyme anglo-saxon de « Random Access Memory ». Un programme (444) de comparaison, compare la position de la fréquence centrale Fc1 du dernier pic d'impédance enregistré à l'instant t1, avec la position de la fréquence centrale Fc0 du pic d'impédance dans l'enregistrement précédent, au temps t0, dans la même plage de fréquences. Ledit programme (444) délivre une information, par exemple la quantité (Fc1-Fc0), relative au déplacement du pic d'impédance. Un programme (445) de corrélation, détermine la température, T, du haut-parleur, à l'instant t1 de l'enregistrement, par la lecture d'une table de corrélation reliant le déplacement du pic d'impédance et la température du haut-parleur. Ladite table de corrélation est lue par ledit programme (445) dans une mémoire (446), dite de caractéristiques, accessible en lecture seule, préférentiellement de type ROM (selon l'acronyme anglo-saxon de « Read Only Memory ») ou EPROM (selon l'acronyme anglo-saxon de « Erasable Programmable Read Only Memory ») et comportant un enregistrement de la table de corrélation pour le modèle de haut-parleur considéré. Figure 4A , according to an exemplary embodiment of the computer (240) of the device according to the invention, the latter comprises a processor, memory means for storing data and instruction programs of the processor for performing calculations as well as input and output ports and a clock. The digital signal (341) from the analog / digital converter (334) is introduced into said computer (240), which computer comprises a spectral analysis program (441). According to an exemplary embodiment, the digital excitation signal (212) of the loudspeaker is delayed by a delay module (440) and the delayed signal (412) is also inputted to the spectral analysis program (441). . The delay applied by the delay module (440) to the digital excitation signal (212) of the loudspeaker makes it possible to compensate the processing time of the excitation signal (221) until the delivery of the digital signal (341) from the measurement module of the spectral distribution. The spectral analysis program (441) determines the transfer function of the loudspeaker from the ratio of the two signals (341, 412) at the input of said program and delivers information corresponding to the spectral distribution of the electrical impedance of the loudspeaker. speaker. The time delay applied by the delay module (440) is adjusted to the application. Thus, the device of the invention makes it possible, by a simple method, a limited number of components and without significant intervention on the audio circuit, to obtain, in real time, the spectral distribution of the electrical impedance of the loudspeaker. . A program (442) included in the computer memory determines, from the spectral distribution provided by the spectral analysis program (441), the position of the center frequency Fc 1 and the half-height width, l 1 , an impedance peak, in a frequency range comprised, according to an exemplary embodiment, between 300 Hz and 1000 Hz. If such an impedance peak is detected, the information relating to its central frequency, Fc 1 , its width at half height, l 1 , and the measurement date are recorded in a memory (443) live access to read and write, called historical RAM, according to the English acronym of " Random Access Memory " . A comparison program (444) compares the position of the center frequency Fc 1 of the last impedance peak recorded at time t 1 with the position of the center frequency Fc 0 of the impedance peak in the previous record. at time t 0 in the same frequency range. Said program (444) delivers information, for example the quantity (Fc 1 -Fc 0 ), relative to the impedance peak displacement. A correlation program (445) determines the temperature, T, of the loudspeaker, at time t 1 of the recording, by reading a correlation table connecting the impedance peak displacement and the temperature of the speaker. Said correlation table is read by said program (445) in a memory (446), called a characteristics memory, accessible in read-only mode, preferably of type ROM (according to the acronym for " Read Only Memory" ) or EPROM ( according to the English acronym of " Erasable Programmable Read Only Memory ") and having a record of the correlation table for the speaker model considered.

Figure 4B, selon un exemple de comportement du haut-parleur, lorsque la température dudit haut-parleur croît, la répartition spectrale de l'impédance au temps t1 présente selon un tracé (471) dans un diagramme ayant en abscisse la fréquence (480) et en ordonnée l'impédance (490), un pic centré sur une fréquence Fc1 , laquelle fréquence Fc1 est supérieure à la fréquence centrale Fc0 du pic détecté dans le tracé (470) de l'impédance au temps t0 antérieur à t1. À titre d'exemple, pour un haut-parleur d'une puissance électrique de 1 Watt, la fréquence centrale du pic d'impédance passe de 800 Hz à 400 Hz lorsque la température du haut-parleur passe 70 °C à 120 °C. Figure 4B according to an exemplary behavior of the loudspeaker, when the temperature of said loudspeaker increases, the spectral distribution of the impedance at time t 1 is plotted (471) in a diagram having on the abscissa the frequency (480) and the ordinate impedance (490), a peak centered on a frequency Fc 1 , which frequency Fc 1 is greater than the center frequency Fc 0 of the peak detected in the plot (470) of the impedance at time t 0 prior to t 1 . For example, for a speaker with an electric power of 1 Watt, the center frequency of the peak impedance goes from 800 Hz to 400 Hz when the temperature of the speaker passes 70 ° C to 120 ° C .

En revenant à la figure 4A, selon un exemple de réalisation du dispositif objet de l'invention, celui-ci comprend un programme (447) de calcul de la puissance spectrale du signal numérique (211) provenant de la source audio. Ledit programme (447) de calcul de la puissance, utilise des informations contenues dans la mémoire (446) de caractéristiques, relatives au haut-parleur et à son implantation dans l'appareil le recevant, lesquelles caractéristiques permettent de calculer l'échauffement, ΔT, dudit haut-parleur au bout d'un laps de temps δt, postérieur au temps t1 , en fonction de la puissance spectrale du signal (211) audio. À titre d'exemple, non limitatif, le programme (447) de calcul effectue les opérations consistant à :

  • calculer l'énergie d'excitation Ee du haut-parleur en fonction de la puissance, Pe, du signal d'excitation du haut-parleur, estimée à partir de la puissance spectrale du signal (211) numérique audio et des caractéristiques d'amplification de ce signal : Ee = Pe . ε avec ε ≥ δt ;
  • calculer la part Qe de l'énergie d'excitation Ee, transformée en chaleur ;
  • calculer ΔT : ΔT = (Qe - Qd) / (Mx C),
où Qd est la quantité de chaleur dissipée sans échauffer le haut-parleur, M la masse du haut-parleur et C la chaleur massique dudit haut-parleur. Ces quantités sont déterminées par simulation ou par expérimentation et les lois empiriques correspondantes sont stockées dans la mémoire (446) de caractéristiques, par exemple sous la forme de tables de coefficients. Un programme (448) de sommation et de comparaison effectue la somme T + ΔT et compare le résultat à un seuil critique Tc enregistré dans la mémoire (446) de caractéristiques. En fonction des résultats du programme (448) de sommation et de comparaison, un programme (449) de paramétrage calcule les paramètres d'un filtre numérique devant être appliqué au signal (211) audio, lesquels paramètres sont transmis au moyen (250) de traitement du signal.Returning to Figure 4A , according to an exemplary embodiment of the device according to the invention, it comprises a program (447) for calculating the spectral power of the digital signal (211) from the audio source. Said power calculation program (447) uses information contained in the memory (446) of characteristics relating to the loudspeaker and its location in the receiving apparatus, which characteristics make it possible to calculate the heating, Δ T , said speaker after a lapse of time δ t , subsequent to time t 1 , depending on the spectral power of the audio signal (211). By way of example, without limitation, the program (447) of calculation performs the operations of:
  • calculating the excitation energy Ee of the loudspeaker as a function of the power, Pe , of the excitation signal of the loudspeaker, estimated from the spectral power of the digital audio signal (211) and the amplification characteristics of this signal: Ee = Pe. ε with ε ≥ δ t ;
  • calculate the part Qe of the excitation energy Ee , transformed into heat;
  • calculate ΔT: ΔT = ( Qe - Qd ) / ( Mx C ),
where Qd is the amount of heat dissipated without heating the loudspeaker, M the mass of the loudspeaker and C the mass heat of said loudspeaker. These quantities are determined by simulation or by experimentation and the corresponding empirical laws are stored in the memory (446) of characteristics, for example in the form of coefficient tables. A summation and comparison program (448) performs the sum T + Δ T and compares the result to a critical threshold Tc stored in the memory (446) of features. Based on the results of the summation and comparison program (448), a parameter program (449) calculates the parameters of a digital filter to be applied to the audio signal (211), which parameters are transmitted by means (250) of signal processing.

Selon un exemple de réalisation du dispositif objet de l'invention, le moyen (250) de traitement du signal est un programme mis en oeuvre par le calculateur (240) et qui réalise un filtrage numérique du signal (211) audio. Ainsi, plusieurs filtres peuvent être appliqués en cascade audit signal (211) audio. À titre d'exemple non limitatif, le filtrage comprend un filtre passe bas, un filtre coupe bande ou un filtre à réjection de bande à bande unique ou multiple.According to an exemplary embodiment of the device according to the invention, the signal processing means (250) is a program implemented by the computer (240) and which performs a digital filtering of the audio signal (211). Thus, several filters may be cascaded to said audio signal (211). By way of nonlimiting example, the filtering comprises a low-pass filter, a band-cut filter or a single-band or multi-band band rejection filter.

Figure 5A, selon un exemple de réalisation le filtre appliqué au signal audio est un filtre passe-bas dont le diagramme de Bode (570) dans un repère logarithmique avec en abscisse la fréquence (580) et en ordonnée (590) le gain, comprend une bande passante (571) et une bande rejetée (572) au-delà d'une fréquence de coupure (575) correspondant à une atténuation de -3 dB par rapport au gain de la partie passante. Selon un exemple de réalisation du filtrage réalisé par le dispositif objet de l'invention, ladite fréquence (575) de coupure est choisie dans la partie haute du spectre du signal de parole, soit supérieure ou égale à 3,103 Hz pour un haut-parleur utilisé pour diffuser essentiellement des conversations. Au-delà de la fréquence (575) de coupure, l'atténuation du filtre est de -6 dB/octave. Selon un exemple de réalisation du procédé objet de l'invention, lorsqu'un tel filtre passe-bas est appliqué au signal audio, le paramètre ajusté en fonction de la température du haut-parleur est, d'une part, l'application du filtre au signal, la coupure des fréquences au-delà de 3,103 Hz affectant essentiellement le timbre de la voix sans affecter le volume ressenti par l'auditeur, tout en réduisant la puissance d'excitation du signal, puis le gain dans la bande passante (571) du filtre, ce gain étant alors ajusté à une valeur inférieure à 0 dB. Figure 5A according to an exemplary embodiment, the filter applied to the audio signal is a low-pass filter whose Bode diagram (570) in a logarithmic reference with the abscissa frequency (580) and the ordinate (590) the gain, comprises a band pass (571) and a rejected band (572) beyond a cut-off frequency (575) corresponding to an attenuation of -3 dB relative to the gain of the pass-through portion. According to an exemplary embodiment of the filtering performed by the device according to the invention, said cut-off frequency (575) is chosen in the upper part of the spectrum of the speech signal, which is greater than or equal to 3.10 3 Hz for a high used to essentially broadcast conversations. Beyond the cut-off frequency (575), the attenuation of the filter is -6 dB / octave. According to an exemplary embodiment of the method which is the subject of the invention, when such a low-pass filter is applied to the audio signal, the parameter adjusted as a function of the temperature of the loudspeaker is, on the one hand, the application of the filter to the signal, cutting frequencies above 3.10 3 Hz essentially affecting the tone of the voice without affecting the volume felt by the listener, while reducing the signal excitation power, then the gain in the bandwidth (571) of the filter, this gain then being adjusted to a value less than 0 dB.

Figure 5B, selon un autre exemple de réalisation du procédé objet de l'invention, le filtre appliqué est un filtre à réjection de bande. Le tracé (577) du diagramme de Bode d'un tel filtre présente une atténuation centrée sur une fréquence (576) caractérisée par une largeur de bande lf autour de cette fréquence (576) centrale à -3 dB par rapport au gain dans la bande passante. Ainsi, les paramètres ajustables d'un tel filtre sont le gain dans la partie passante, la fréquence (576) centrale de la bande rejetée et la largeur de bande lf autour de cette fréquence centrale. Le filtrage numérique du signal permet de combiner les différents types de filtres en fonction du résultat recherché afin de minimiser la dégradation audible du son émis par le haut-parleur. La combinaison de filtres appropriée est déterminée expérimentalement ou par simulation. Figure 5B , according to another exemplary embodiment of the method which is the subject of the invention, the filter applied is a band rejection filter. The plot (577) of the Bode diagram of such a filter has attenuation centered on a frequency (576) characterized by a bandwidth l f about this center frequency (576) at -3 dB relative to the gain in the bandwidth. Thus, the adjustable parameters of such a filter are the gain in the pass-through portion, the center frequency (576) of the rejected band, and the bandwidth 1 f around this center frequency. The digital filtering of the signal makes it possible to combine the different types of filters according to the desired result in order to minimize the audible degradation of the sound emitted by the loudspeaker. The appropriate filter combination is determined experimentally or by simulation.

Figure 6, selon un exemple de réalisation du procédé objet de l'invention, mis en oeuvre par un dispositif tel que décrit ci-avant, ledit procédé comprend une première étape (610) de mesure, consistant à obtenir la répartition spectrale d'impédance électrique du haut-parleur, préférentiellement dans une plage de fréquences comprise entre 300 Hz et 1 000 Hz. Selon une étape (620) d'identification, un pic d'impédance, centré sur une fréquence Fc1 , est identifié dans la répartition spectrale obtenue lors de l'étape (610) de mesure. Au cours d'une étape (630) de comparaison, la position de la fréquence centrale Fc1 dudit pic est comparée à la position de la fréquence centrale Fc0 du pic d'impédance dans la répartition spectrale obtenue à une date t0 antérieure. Selon une étape (635) de contrôle de la stabilité, l'écart ∥ Fc1 - Fc0 ∥ est comparé à un critère de stabilité Fstab. Le processus d'échauffement du haut-parleur étant progressif, un écart trop important entre les fréquences centrales des pics, lorsque les dates de mesure t0 et t1 sont rapprochées, relève d'un artefact de mesure. Ainsi, les étapes ultérieures de traitement du signal ne sont mises en oeuvre que si l'échauffement du haut-parleur est avéré. Selon une étape (640) de corrélation, la différence (Fc1-Fc0) est corrélée à la température T du haut-parleur, déterminant ainsi la température dudit haut-parleur au temps t1 . Selon une étape (650) d'analyse du signal, la répartition spectrale de la puissance du signal d'excitation est obtenue. Selon une étape (660) de prévision, ladite répartition spectrale de la puissance du signal d'excitation est utilisée pour prévoir d'échauffement, ΔT, du haut-parleur au temps (t1 + ε) avec ε ≥ δt. Selon une étape (665) d'analyse du risque thermique, la quantité (T + ΔT) est comparée à une température critique Tc. Si (T + ΔT) ≥ Tc alors un filtre visant à réduire la puissance du signal d'excitation selon un spectre de fréquences sélectionné est calculé au cours d'une étape (670) de paramétrage. Parallèlement, selon une étape (680) d'analyse mécanique, la puissance du signal d'excitation dans une bande de fréquence centrée sur Fc1 selon une largeur de bande l1 est analysée. Au cours d'une étape (685) de comparaison mécanique, la puissance déterminée au cours de l'étape d'analyse mécanique est comparée à une valeur critique définissant un risque de déplacement de la membrane du haut-parleur hors de son débattement mécanique admissible. Si la puissance déterminée au cours de l'étape (680) d'analyse mécanique est supérieure à la puissance admissible, alors les caractéristiques d'un filtre de réjection de bande, centrée sur la fréquence Fc1 et selon une largeur de bande, dite bande mécanique, correspondant à l1 sont calculées au cours d'une étape (690) de paramétrage mécanique. Les filtres calculés au cours des étapes (670, 690) de paramétrage mécanique et thermique sont appliqués au signal au cours d'une étape de filtrage (695). Figure 6 according to an exemplary embodiment of the method which is the subject of the invention, implemented by a device as described above, said method comprises a first measurement step (610) of obtaining the spectral distribution of the electrical impedance of the speaker, preferably in a frequency range between 300 Hz and 1000 Hz. According to an identification step (620), an impedance peak, centered on a frequency Fc 1 , is identified in the spectral distribution obtained during of step (610) of measurement. During a comparison step (630), the position of the center frequency Fc 1 of said peak is compared with the position of the center frequency Fc 0 of the impedance peak in the spectral distribution obtained at an earlier date t 0 . According to a stability control step (635), the difference ∥ Fc 1 - Fc 0 ∥ is compared with a criterion of stability F stab . As the heating process of the loudspeaker is progressive, a too large difference between the central frequencies of the peaks, when the measurement dates t 0 and t 1 are close together, pertains to a measuring artifact. Thus, the subsequent stages of signal processing are implemented only if the heating of the loudspeaker is proven. According to a correlation step (640), the difference (Fc 1 -Fc 0 ) is correlated with the temperature T of the loudspeaker, thus determining the temperature of said loudspeaker at time t 1 . According to a signal analysis step (650), the spectral distribution of the power of the excitation signal is obtained. In a step (660) of prediction, said spectral power distribution of the excitation signal is used to provide heating, Δ T, the speaker at time (t 1 + ε) with ε ≥ δ t. According to a thermal risk analysis step (665), the quantity ( T + ΔT ) is compared with a critical temperature Tc. If (T + ΔT ) ≥ Tc then a filter aimed at reducing the power of the excitation signal according to a selected frequency spectrum is calculated during a parameterization step (670). In parallel, according to a step (680) of mechanical analysis, the power of the excitation signal in a frequency band centered on Fc 1 according to a bandwidth 11 is analyzed. During a step (685) of mechanical comparison, the power determined during the mechanical analysis step is compared to a critical value defining a risk of displacement of the speaker diaphragm out of its allowable mechanical travel . If the power determined during the step (680) of mechanical analysis is greater than the allowable power, then the characteristics of a band rejection filter, centered on the frequency Fc 1 and in a bandwidth, called mechanical band, corresponding to l 1 are calculated during a step (690) of mechanical parameterization. The filters calculated during the mechanical and thermal parameterization steps (670, 690) are applied to the signal during a filtering step (695).

La description ci-avant et les exemples de réalisation montrent que l'invention atteint les objectifs visés, en particulier, elle permet dans le cadre notamment d'une application sur téléphone mobile, de protéger le haut-parleur dudit téléphone lorsque celui-ci est utilisé en sur-amplification, notamment en mode réunion. L'action sélective sur le spectre sonore et le contrôle en temps réel et en anticipation de l'échauffement du haut-parleur, permettent de conserver ledit haut-parleur à une température de fonctionnement acceptable en préservant le volume sonore ressenti. Le traitement entièrement numérique des signaux autorise une grande souplesse dans le traitement du signal et dans la sélection du paramétrage des filtres appliqués audit signal.The above description and the exemplary embodiments show that the invention achieves the desired objectives, in particular, it makes it possible, particularly in the context of a mobile phone application, to protect the loudspeaker of said telephone when it is used in over-amplification, especially in meeting mode. The selective action on the sound spectrum and the real-time control and anticipation of the heating of the loudspeaker, allow to keep said speaker at an acceptable operating temperature while preserving the sound volume felt. The fully digital signal processing allows great flexibility in the signal processing and in the selection of the parameterization of the filters applied to said signal.

Claims (12)

  1. Method for controlling the temperature of an electrodynamic loudspeaker (100) comprising a diaphragm (140) excited by an electric motor supplied with an excitation signal (221), characterized in that it comprises the steps consisting of:
    a. obtaining (610) the spectral distribution of the electrical impedance of the motor at time t1;
    b. identifying (620) an impedance peak in a predefined frequency range of the spectral distribution obtained in step a);
    c. determining (630) the frequency difference between the centre frequency, Fc1 , of the impedance peak identified in step b) and the centre frequency, Fc0, of an impedance peak, identified in the same predefined frequency range in an electrical impedance spectral distribution of the motor obtained at a time t0 prior to t1;
    d. obtaining a correlational relationship between the frequency difference (Fc0-Fc1 ) and the temperature of said loudspeaker;
    e. determining (640, 670) the temperature of the loudspeaker as a function of the result of step c) and the correlation of step d);
    in that steps a) to e) are repeated for each time period δt = (t1 -t0 ) when the loudspeaker is in operation;
    in that it comprises, after step e), a step consisting of:
    f. decreasing (670, 695) the power of the excitation signal in a frequency band, referred to as the thermal band, if the temperature determined in step e) exceeds a critical threshold;
    and in that the spectral distribution of the impedance is obtained in step a) by measuring a transfer function between a signal (340) that is proportional to the current of the analogue excitation signal (221) of the loudspeaker and the delayed digital (412) excitation signal (212) of said loudspeaker.
  2. Method according to Claim 1, characterized in that step e) comprises the steps consisting of:
    ei. determining (640) an instantaneous temperature, T, at time t1 by means of the frequency difference between the impedance peaks;
    eii. determining (650) the power of the excitation signal and determining the portion of energy of this signal that is converted to heat;
    eiii. determining (660), as a function of the result of step eii), the temperature of the loudspeaker at a time (t1 + ε) such that ε ≥ δt.
  3. Method according to Claim 1, characterized in that it comprises the steps consisting of:
    g. obtaining (650) the spectral distribution of the power of the excitation signal;
    h. on the basis of the distribution obtained in step g), determining (680) the power of the signal in a frequency band, referred to as the mechanical band, centred on the centre frequency, Fc1 , of the impedance peak obtained in step b);
    i. obtaining a permissible excitation power that the diaphragm of the loudspeaker is capable of withstanding;
    j. if (685) the power obtained in step h) is higher than or equal to the permissible power obtained in step i), the power of the excitation signal in the mechanical band is decreased (690, 695).
  4. Method according to Claim 1, characterized in that it comprises, after step c) and before step d), the steps consisting of:
    k. obtaining a frequency value, Fstab, referred to as the stability criterion;
    l. comparing (635) the frequency difference obtained in step c) with the stability criterion;
    m. executing steps d), e) and f) if the condition (∥Fc0-Fc1 ∥ ≤ Fstab ) is true and returning to step a) if this condition is not verified.
  5. Method according to Claim 3, characterized in that the decreases in power of the excitation signal in steps f) and j) are achieved by filtering said signal in selective frequency bands and that said method comprises the steps consisting of:
    o. determining (670), before step f), the characteristics of a filter that is capable of selectively decreasing the spectral power of the signal during said step f);
    p. determining (690), before step j), the characteristics of a filter that is capable of selectively decreasing the spectral power of the excitation signal during said step j).
  6. Method according to Claim 5, characterized in that the excitation signal (221) is a digital signal (212) that is converted to an analogue signal in order to excite the motor of the loudspeaker and that the filters of steps o) and p) are digital filters that are applied to the excitation signal (211) before its conversion to an analogue signal.
  7. Method according to Claim 1, characterized in that the predefined frequency range of step c) is between 300 Hz and 1000 Hz.
  8. Method according to Claim 1, characterized in that δt is equal to 5.10-3 seconds.
  9. Method according to Claim 1, characterized in that the frequency range encompassing the thermal band is centred on a frequency of 3.103 Hz.
  10. Device (200) capable of implementing the method according to Claim 1, on a loudspeaker (100) the motor of which is supplied with an excitation signal (221), said device comprising:
    i. a means (250) for processing the signal;
    ii. a computer (240) capable of modifying the characteristics of the processing operation performed by the means (250) for processing the signal;
    iii. a means (230) for measuring the spectral distribution of the impedance of the loudspeaker, characterized in that said means (230) comprises a measurement resistor (331), the impedance of which is less than 1/50 of the impedance of the loudspeaker, connected in series with the power supply of the motor of the loudspeaker and through which the excitation signal (221) passes, and means (332, 333) that are capable of delivering a signal that is proportional to the voltage across the terminals of said resistor.
  11. Sound broadcasting apparatus, in particular a mobile telephone, comprising a loudspeaker, characterized in that it comprises a device according to Claim 10.
  12. Apparatus according to Claim 11, characterized in that it comprises means that are capable of implementing a mode of over-amplifying the sound broadcast, characterized in that it comprises means that are capable of implementing a method according to Claim 1, when said over-amplification mode is selected.
EP13716782.1A 2012-04-20 2013-04-15 Method and device for controlling the operating temperature of a loudspeaker Not-in-force EP2839676B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR1253670A FR2989858A3 (en) 2012-04-20 2012-04-20 METHOD FOR THERMAL PROTECTION OF A SPEAKER AND THERMAL PROTECTION DEVICE OF AN ASSOCIATED LOUDSPEAKER
FR1350321A FR2989859B1 (en) 2012-04-20 2013-01-15 METHOD FOR THERMAL PROTECTION OF A SPEAKER AND THERMAL PROTECTION DEVICE OF AN ASSOCIATED LOUDSPEAKER
PCT/EP2013/057801 WO2013156439A1 (en) 2012-04-20 2013-04-15 Method and device for controlling the operating temperature of a loudspeaker

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EP2839676B1 true EP2839676B1 (en) 2017-06-14

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CN107172561A (en) * 2017-07-10 2017-09-15 顾康 A kind of audio amplifier digital indicator
CN109297614B (en) * 2018-08-13 2020-05-19 厦门傅里叶电子有限公司 Loudspeaker temperature protection method based on phase change measurement

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DE69416129T2 (en) * 1994-10-10 1999-07-01 Endress + Hauser GmbH + Co., 79689 Maulburg A method for operating an ultrasonic transducer and circuit arrangement for performing the method
FR2852779B1 (en) * 2003-03-20 2008-08-01 PROCESS FOR PROCESSING AN ELECTRICAL SIGNAL OF SOUND
US7082772B2 (en) 2003-08-20 2006-08-01 Directed Electronics, Inc. Peltier temperature control system for electronic components
JP4769238B2 (en) * 2007-08-24 2011-09-07 日本電信電話株式会社 Signal separation device, signal separation method, program, and recording medium
US9066171B2 (en) * 2009-12-24 2015-06-23 Nokia Corporation Loudspeaker protection apparatus and method thereof
WO2011079875A1 (en) * 2009-12-31 2011-07-07 Nokia Corporation Monitoring and correcting apparatus for mounted transducers and method thereof
EP2357726B1 (en) * 2010-02-10 2016-07-06 Nxp B.V. System and method for adapting a loudspeaker signal
US8194869B2 (en) * 2010-03-17 2012-06-05 Harman International Industries, Incorporated Audio power management system

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EP2839676A1 (en) 2015-02-25
CN104429099A (en) 2015-03-18
FR2989859B1 (en) 2016-07-01

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