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
  • H04R3/002—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.
• FIG. 1 relating to the prior art, schematically represents the components of an electrodynamic loudspeaker.
• a loudspeaker (100) of substantially conical shape comprises:
• a coil (130) consisting of a wire wound in turns surrounding the permanent magnet (120) without contact;
• a membrane (140) of substantially conical shape attached to the frame (1 10) on the periphery of its larger diameter and to the coil on the periphery of its smaller diameter.
• 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 invention aims to solve the disadvantages of the prior art and concerns for this purpose a method for controlling the temperature of an electrodynamic loudspeaker comprising a membrane excited by an electric motor powered by an excitation signal, which method comprises the steps of: a. obtain the spectral distribution of the electrical impedance of the motor at time tj;
• step b identify an impedance peak in a predefined frequency range of the spectral distribution obtained in step a);
• step e determine the temperature of the speaker according to the result of step c) and the correlation of step d).
• 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.
• Bt (ti-t 0 ) when the loudspeaker is in operation.
• step e) comprises the steps of:
• T an instantaneous temperature
• step eii determining the temperature of the loudspeaker at a time (h + z) such that ⁇ > 5t.
• the method which is the subject of the invention comprises, after step e), a step consisting of:
• the method which is the subject of the invention comprises, according to one of its embodiments, the steps of:
• step 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.
• 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 method of the invention comprises after step c) and before step d) the steps of:
• 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 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:
• step f determining, before step f), the characteristics of a filter capable of selectively reducing the spectral power of the signal during said step f);
• step j determining, before step j), the characteristics of a filter capable of selectively reducing the spectral power of the excitation signal during said step j).
• 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 speaker.
• 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. .
• 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 majority spectral content of the human voice, the attenuation of the signal power in this frequency band thus effectively limits the heating of the speaker without degrading the sound volume felt by the listener especially in the case of an application on mobile phone in conference mode.
• 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:
• iii means for measuring the spectral distribution of the impedance of the loudspeaker, characterized in that said means comprises a measuring resistance, impedance of less than 1/50 of the impedance of the loudspeaker, connected 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.
• the device of the invention can be easily adapted to a device without significant modification.
• the apparatus forming the subject of the invention comprises means able to implement 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 mode of boosting is selected.
• the apparatus of the invention can be used at a high volume without risk of overheating.
• FIGS. 1 to 6 The invention is explained below according to its preferred embodiments, in no way limiting, and with reference to FIGS. 1 to 6 in which:
• FIG. 1 relating to the prior art shows in a sectional view a schematic diagram of an electrodynamic loudspeaker
• FIG. 3 shows a functional diagram of the means for measuring the spectral distribution of the impedance of the loudspeaker according to an exemplary embodiment of the device that is the subject of the invention
• FIG. 4 shows, in FIG. 4A, a functional diagram of the computer implementing spectral analysis and filtering according to an exemplary embodiment of the device which is the subject of the invention and represents, FIG. 4B, an example of comparison of spectra of FIG. impedances measured at different temperatures of the loudspeaker;
• FIG. 5 shows, FIG. 5A, an example of a Bode diagram of a low-pass filter and FIG. 5B, an example of a Bode diagram of a band rejection filter;
• FIG. 6 represents a flowchart of a method for measuring and monitoring the temperature of a loudspeaker according to an exemplary embodiment of the method that is the subject of the 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 (21 1) originating from an audio source, and outputs a digital signal (212) that has been processed in one of the modes. 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 (21 1) introduced into the device that is the subject of the invention.
• 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), that is to say 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).
• the computer (240) of the device comprises a processor, memory means for storing data and instruction programs of the processor to perform calculations and only 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 Fa and the half-height width, f, an impedance peak, in a frequency range included, according to an exemplary embodiment, between 300 Hz and 1000 Hz.
• a comparison program (444) compares the position of the central frequency Fa of the last impedance peak recorded at time t with the position of the center frequency Fc 0 of the impedance peak in the previous record, at the time t 0 , in the same frequency range. Said program (444) delivers information, for example the quantity (Fci-Fc 0 ), relative to the displacement of the impedance peak.
• a correlation program (445) determines the temperature, T, of the loudspeaker at time t; of the recording, by reading a correlation table connecting the impedance peak displacement and the speaker temperature. 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 (accord to the English acronym of "Erasable Programmable Read Only Memory”) and having a record of the correlation table for the speaker model considered.
• the center frequency of the impedance peak changes from 800 Hz to 400 Hz when the speaker temperature goes from 70 ° C to 120 ° C.
• the device comprises a program (447) for calculating the spectral power of the digital signal (21 1) originating 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, ⁇ , of said loudspeaker. speaker after a lapse of time 5t, after the time t according to the spectral power of the signal (21 1) audio.
• the program (447) of calculation performs the operations of:
• Qd is the amount of heat dissipated without heating the loudspeaker
• M the mass of the loudspeaker
• C the mass heat of said loudspeaker.
• the signal processing means (250) is a program implemented by the computer (240) and which performs a digital filtering of the audio signal (21 1).
• the filtering comprises a low-pass filter, a band-cut filter or a single-band or multi-band band rejection filter.
• 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.
• a stability control step (635) the difference
• F stab a stability criterion
• the subsequent stages of signal processing are implemented only if the loudspeaker heating is proven.
• the difference (Fci-Fc 0 ) is correlated with the temperature T of the loudspeaker, thus determining the temperature of said loudspeaker at time t ⁇ .
• a signal analysis step (650) the spectral distribution of the power of the excitation signal is obtained.
• a prediction step (660) said spectral distribution of the power of the excitation signal is used to predict heating, ⁇ , of the loudspeaker at time (ti + z) with ⁇ > ht.
• a thermal risk analysis step (665) the quantity (T + AT) is compared with a critical temperature Te. If (T + AT) ⁇ Te then a filter to reduce 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 Fa according to a bandwidth /; 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 Fa and according to a bandwidth, called band mechanical, corresponding to /; 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).

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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)

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• 2012
  • 2012-04-20 FR FR1253670A patent/FR2989858A3/fr active Pending
• 2013
  • 2013-01-15 FR FR1350321A patent/FR2989859B1/fr not_active Expired - Fee Related
  • 2013-04-15 WO PCT/EP2013/057801 patent/WO2013156439A1/fr active Application Filing
  • 2013-04-15 EP EP13716782.1A patent/EP2839676B1/de not_active Not-in-force
  • 2013-04-15 CN CN201380020967.XA patent/CN104429099A/zh active Pending

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