Audio signal distribution for thermal optimization of loudspeakers

Abstract

Method for broadcasting an audio signal by an audio system (1) comprising a plurality of audio channels (4, 5a, 5b, 6a, 6b, 7), comprising the steps of: - broadcasting the audio signal using a primary distribution of the audio signal; - evaluating the temperature of a loudspeaker (9) - when the temperature of the loudspeaker becomes higher than a first temperature threshold, modifying the primary distribution to obtain an optimized distribution of the audio signal, in which the primary audio signal of the loudspeaker is applied at least partially to at least one other audio channel; - broadcasting the audio signal using the optimized distribution.

Description

[0001] The invention relates to the field of multi-channel audio systems, integrated into one or more audio reproduction devices. BACKGROUND OF THE INVENTION

[0002] A set-top box, or STB (for Set-Top Box ), is an electrical device whose primary function is to acquire an audio-video stream, to decode this stream, and to broadcast the video signal through a television and the audio signal through the television speakers and / or possibly through other audio reproduction equipment (sound bar, connected speakers, etc.).

[0003] Some recent set-top boxes include one or more speakers. The speaker(s) can be used in a voice assistant function, or even to implement a multi-channel audio system.

[0004] The multi-channel audio system then includes one or more audio channels comprising one or more speakers of the decoder box, as well as possibly audio channels comprising speakers of equipment connected to the decoder box (sound bar and / or connected speakers for example).

[0005] The design of such a set-top box and, more generally, of any compact equipment incorporating one or more loudspeakers, creates difficulties in terms of heat dissipation because all the components, including the loudspeakers, are located in a very small space with little or no ventilation. As a result, the loudspeakers can be very thermally stressed in their reduced air volume, which is detrimental to their lifespan.

[0006] A number of prior art solutions are known to attempt to solve this problem.

[0007] A known solution is to control the power sent to the speaker after the amplifier based on temperature. This solution therefore requires an analog-to-digital converter to measure and digitize the signal at the amplifier output, as well as a sensor measuring the temperature of the speaker to be protected. The signal is attenuated if the measured temperature exceeds a limit defined by the manufacturer.

[0008] Another known solution is to connect a resistive circuit to the magnet of the speaker to be protected. The resistance of this circuit varies with the temperature of the magnet. The resistance is then measured, and the temperature is deduced. The information is transmitted to a signal limiter. The audio signal is attenuated if the estimated temperature exceeds a limit set by the manufacturer.

[0009] These known solutions have the following drawbacks.

[0010] They require the addition of sensors and electronic components, which increases the complexity and cost of the equipment in which they are integrated.

[0011] Additionally, these solutions all offer to protect the speaker by attenuating the signal sent if the temperature limit is exceeded. This results in a reduction in the overall sound level of the product and therefore a significant deterioration in the user experience. SUBJECT OF THE INVENTION

[0012] The subject of the invention is a solution making it possible to limit the risks of premature degradation and therefore to increase the lifespan of the loudspeakers of a multi-channel audio system, said solution being simple and inexpensive to implement, and not degrading the user experience. SUMMARY OF THE INVENTION

[0013] In order to achieve this aim, a method is proposed for broadcasting a multi-channel audio signal by an audio system comprising a plurality of audio channels each comprising at least one loudspeaker, the broadcasting method being implemented by a processing unit and comprising the steps of: broadcasting the multi-channel audio signal using a primary distribution of the multi-channel audio signal, which defines a primary audio signal for each audio channel, and applying said primary audio signals to the audio channels; evaluating an operational temperature of at least one particular loudspeaker belonging to a particular audio channel; when the operational temperature of the particular loudspeaker becomes higher than a first predefined temperature threshold, modifying the primary distribution to obtain an optimized distribution of the multi-channel audio signal, in which a particular primary audio signal of the particular audio channel is applied at least partially to at least one other audio channel, the optimized distribution thus defining an optimized audio signal for each audio channel;broadcasting the multi-channel audio signal by applying the optimized audio signals to the audio channels until the operational temperature of the particular loudspeaker becomes lower than a second predefined temperature threshold. ;

[0014] Thus, when a speaker heats up or risks heating up too much, the processing unit distributes at least partially the audio signal of said speaker to the other audio channels, until the temperature of said speaker normalizes. This virtually reproduces the overheated audio channel and thus reduces the temperature of the speaker without degrading the user experience. This limits the risks of premature degradation and increases the lifespan of the speakers.

[0015] The temperature of the speakers can be assessed without adding a temperature sensor to the electrical equipment. The implementation of the diffusion process therefore requires no (or very few) electronic components. (hardware) additional and is therefore simple and inexpensive to implement.

[0016] Further provided is a broadcasting method as previously described, wherein modifying the primary distribution comprises the step of applying at least a portion of an overall level of the particular primary audio signal to at least one other audio channel.

[0017] Further provided is a broadcasting method as previously described, the plurality of audio channels comprising a center channel and two side channels, the particular audio channel being the center channel, at least a portion of the overall level of the particular primary audio signal being applied to the two side channels.

[0018] Further provided is a broadcasting method as previously described, the plurality of audio channels comprising a center channel, two front side channels and two rear side channels, the particular audio channel being a particular side channel, at least a portion of the overall level of the particular primary audio signal being applied to the center channel and to another side channel on the same side as said particular side channel.

[0019] A broadcasting method is further provided as previously described, the plurality of audio channels comprising two front side channels and two rear side channels, the particular audio channel being a front (or rear) side channel, at least a portion of the overall level of the particular primary audio signal being applied to another side channel on the same side as said particular side channel, and to the other front (or rear) side channel.

[0020] Further provided is a broadcasting method as previously described, wherein modifying the primary distribution comprises the step of applying at least a portion of frequency components of the particular primary audio signal to at least one other audio channel.

[0021] Further provided is a diffusion method as previously described, wherein modifying the primary distribution comprises the step of modifying a cutoff frequency of a crossover filter.

[0022] A broadcasting method is further provided as previously described, the plurality of audio channels comprising a low frequency channel and at least one other audio channel, the particular audio channel being one of the at least one other audio channels, frequency components of frequencies lower than a predefined frequency threshold of the particular primary audio signal being applied to the low frequency channel.

[0023] A broadcasting method is further provided as previously described, in which the step of applying at least a portion of the frequency components of the particular primary audio signal to at least one other audio channel is implemented if a number of particular loudspeakers, the operational temperature of which becomes greater than the first predefined temperature threshold, is greater than a predefined number.

[0024] Further provided is a broadcasting method as previously described, wherein the particular primary audio signal continues to be partially applied to the particular audio channel until the operational temperature of the particular loudspeaker becomes lower than the second predefined temperature threshold.

[0025] Further provided is a broadcasting method as previously described, wherein the particular primary audio signal is progressively attenuated on the particular audio channel.

[0026] Further provided is a diffusion method as previously described, wherein evaluating the operational temperature of the particular loudspeaker comprises the steps of: performing a frequency analysis of the particular primary audio signal to evaluate levels of different frequency components of the particular primary audio signal; evaluating a real-time temperature of the particular loudspeaker as a function of said levels.

[0027] Further, a diffusion method as previously described is provided, comprising the step of applying an ADSR envelope to the temperature in real time to obtain the operational temperature.

[0028] Further provided is a diffusion method as previously described, wherein the operational temperature is a future temperature.

[0029] Further, a broadcasting method as previously described is provided, wherein the evaluation of the operational temperature is based on an analysis of the particular primary audio signal carried out prior to its broadcasting.

[0030] We further propose a diffusion method as previously described, in which the evaluation of the operational temperature is carried out from a past temperature and a current temperature.

[0031] We further propose a broadcasting method as previously described, comprising the step of implementing a servo controller, which receives as input a setpoint and a measurement, and which produces as output a command, the setpoint being a maximum temperature, the measurement being the evaluation of the operational temperature, and the command being a part of the particular primary audio signal to be applied to the at least one other audio channel.

[0032] We further propose equipment comprising a processing unit in which the diffusion method as previously described is implemented.

[0033] We also propose equipment as previously described, the equipment being a decoder box.

[0034] We also propose equipment as previously described, in which the decoder box integrates at least one speaker of the plurality of audio channels.

[0035] Further provided is a computer program comprising instructions which cause the processing unit of the equipment as previously described to execute the steps of the diffusion method as previously described.

[0036] Further provided is a computer-readable recording medium on which the computer program as previously described is recorded.

[0037] The invention will be better understood in light of the following description of particular non-limiting embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Reference will be made to the attached drawings, including: [ Fig. 1 ] there figure 1 represents a multi-channel audio system; [ Fig. 2 ] there figure 2 represents a graph comprising a curve of measurements of the temperature of a loudspeaker as a function of time, an equivalent curve but without an applied signal, and an equivalent theoretical curve; [ Fig. 3 ] there figure 3 represents a graph comprising a curve of the temperature of a loudspeaker as a function of frequency, and a curve of the power of the applied audio signal as a function of its frequency; [ Fig. 4 ] there figure 4 represents a graph comprising a curve of the impedance of a loudspeaker as a function of frequency; [ Fig. 5 ] there figure 5 represents a graph comprising a curve of an ADSR envelope; [ Fig. 6 ] there figure 6 is a figure similar to the figure 1 , illustrating a first overheating scenario; [ Fig. 7 ] there figure 7 is a figure similar to the figure 1 , illustrating a second overheating scenario; [ Fig. 8 ] there figure 8 is a figure similar to the figure 1 , illustrating a third overheating scenario; [ Fig. 9 ] there figure 9 is a figure similar to the figure 1 , illustrating a fourth overheating scenario; [ Fig. 10 ] there figure 10 illustrates the processing by a mixing matrix of input audio signals to produce output audio signals; [ Fig. 11 ] there figure 11 represents a first mixing matrix; [ Fig. 12 ] there figure 12 represents a second mixing matrix, corresponding to a primary distribution of the multi-channel audio signal; [ Fig. 13 ] there figure 13 represents the second mixing matrix, this time corresponding to an optimized distribution; [ Fig. 14 ] there figure 14 represents a graph comprising a curve of the frequency response of a center channel loudspeaker and a woofer; [ Fig. 15 ] there figure 15 represents steps in the diffusion process; [ Fig. 16 ] there figure 16 represents a block diagram implemented in the processing unit to implement the diffusion method. DETAILED DESCRIPTION OF THE INVENTION

[0039] In reference to the figure 1 , a multi-channel audio system 1 is integrated into an audio-video reproduction system comprising a television 2 and a decoder box 3.

[0040] The multi-channel audio system here comprises a plurality of audio channels including a central channel 4, two front side channels 5a, 5b (right and left), two rear side channels 6a, 6b (right and left) and a low frequency channel 7.

[0041] Here, by "front" we mean the side channels closest to the TV 2 and by "rear" we mean the side channels closest to the ideal listening location, also called sweet spot, of the auditor 8.

[0042] In the 5.1 format, the front right channel 5a corresponds to the right channel, the front left channel 5b to the left channel, the center channel 4 to the center channel, the rear right channel 6a to the surround right side and rear, left rear route 6b to the canal surround side and rear left, and low frequency channel 7 to the LFE channel (for Low Frequency Effects ).

[0043] Here, the center channel 4 is integrated into the decoder box 3. The side channels 5a, 5b, 6a, 6b are each integrated into connected speakers (therefore four connected speakers). The low-frequency channel 7 is integrated into a subwoofer.

[0044] The decoder box 3 therefore integrates at least one loudspeaker 9. All the loudspeakers 9 of the different channels are loudspeakers of the type « midrange » (or medium, medial), except the speaker of the low frequency channel 7 which is a bass speaker, also called " boomer » Or " woofer ».

[0045] The design of midrange speakers is optimized for the reproduction of medium and high frequencies (frequencies between 500 Hz and 5 kHz, for example).

[0046] The design of the woofer speaker is optimized for the reproduction of low frequencies (frequencies between 50 Hz and 500 Hz, for example).

[0047] It is noted that the invention can be implemented in a multi-channel audio system different from that of the figure 1 The invention applies to any type of multi-channel audio system. It would be possible in particular to integrate several or even all of the audio channels (and therefore all of the loudspeakers 9) into the decoder box 3.

[0048] The decoder box 3 comprises a processing unit 10 (electronic and software). The processing unit 10 comprises at least one processing component 10a, which is for example a “generalist” processor, a processor specialized in signal processing (or DSP, for Digital Signal Processor), a specialized processor for artificial intelligence algorithms (NPU type, for Neural Processing Unit), a microcontroller, or a programmable logic circuit such as an FPGA (for Field Programmable Gate Arrays) or an ASIC (for Application Spécifie Integrated Circuit) .

[0049] The processing unit 10 also comprises one or more memories 10b, connected to or integrated in the processing component 10a. At least one of these memories 10b forms a computer-readable recording medium, on which is recorded at least one computer program comprising instructions which cause the processing component 10a to execute at least some of the steps of the broadcasting method which will be described.

[0050] The broadcasting method is a method of broadcasting a multi-channel audio signal.

[0051] The multi-channel audio signal comes for example (but not necessarily) from an audio-video stream, the video signal being broadcast by TV 2.

[0052] The processing unit 10 of the set-top box 3 normally broadcasts the multi-channel audio signal using a primary distribution of the multi-channel audio signal, which defines a primary (separate) audio signal for each audio channel. The processing unit 10 applies said primary audio signals to the audio channels. However, when the temperature of one or more loudspeakers 9 becomes too high, the processing unit 10 modifies this primary distribution to reduce the temperature of said one or more loudspeakers 9.

[0053] The processing unit 10 therefore evaluates an operational temperature of at least one particular loudspeaker 9 belonging to a particular audio channel. Here, the processing unit 10 evaluates the operational temperature of each loudspeaker 9 of the multi-channel audio system 1.

[0054] When the operational temperature of a particular loudspeaker 9 of a particular audio channel becomes higher than a first predefined temperature threshold, the processing unit 10 modifies the primary distribution to obtain an optimized distribution of the multi-channel audio signal, in which the particular primary audio signal of the particular audio channel is applied at least partially to at least one other audio channel. The first predefined temperature threshold may be different depending on the audio channels and the loudspeakers 9.

[0055] The audio signal on speaker 9, whose temperature is too high, is therefore reduced and distributed over one or more other audio channels.

[0056] The optimized distribution thus defines an optimized (distinct) audio signal for each audio channel. The processing unit 10 distributes the multi-channel audio signal by applying the optimized audio signals to the audio channels until the operational temperature of the particular loudspeaker 9 becomes lower than a second predefined temperature threshold. The second predefined temperature threshold may be equal to the first predefined temperature threshold, but not necessarily. The second predefined temperature threshold may be different depending on the audio channels and the loudspeakers 9.

[0057] For each loudspeaker 9, the evaluation of the temperature of said loudspeaker 9 is carried out here without a temperature sensor.

[0058] The operational temperature is evaluated according to a temperature evaluation method described below. Here, in one embodiment, the operational temperature is the current temperature, i.e., the temperature at the present time. It is noted that the temperature evaluation method can also make it possible to evaluate the temperature at a future time (in which case it is referred to as a “future temperature”).

[0059] Theoretical analyses and laboratory measurements have made it possible to determine the evolution of the temperature of a loudspeaker as a function of time, at a fixed frequency.

[0060] Curve C1, on the figure 2 , represents the temporal evolution of the temperature of a loudspeaker while an audio signal is applied (zone 12), then without an audio signal applied (zone 13). This curve C1 was obtained from measurements carried out with a fixed frequency of 1 kHz, with an audio signal of power 1 W at the loudspeaker input. Curve C2 is a curve equivalent to curve C1, while no audio signal is applied.

[0061] On the basis of these tests, the mathematical laws of temperature growth and decrease were deduced. Temp ( time ) of a loudspeaker as a function of time according to the following formulas (curve C3): For the increasing part of curve C3: Temp time = Temp init + Temp asymptote − Temp init . 1 − e Q . time − time init For the decreasing part of curve C3: Temp time = Temp init + Temp asymptote − Temp init . e Q . time − time init

[0062] The Q coefficient is representative of the specific heat capacity of the system. This parameter is fixed and can be evaluated in the laboratory. It is of the order of 0.001.

[0063] The same goes for Temp asymptote which depends on the loudspeaker, its environment (fixed parameters), and the level of the audio signal applied to the loudspeaker terminals, which is known. For an electrical signal of 2 W, Temp asymptote is around 70°C. On the figure 2 , it is around 55°C.

[0064] The initial temperature of the speaker Temp init (equal to 25 °C for example) is also known because its value is based on the ambient temperature of the equipment and on the thermal evolution of the system according to the two laws previously formulated, including the application time of the signal also known.

[0065] We therefore understand that at a time t, the temperature of a loudspeaker depends on the following parameters: The ambient temperature; The signal level sent to the speaker terminals; The initial temperature of the speaker ( Temp init ) ; The signal application time time init .

[0066] The ambient temperature is supplied to the processing unit 10 by a sensor integrated in the decoder box 3. All modern digital electrical equipment (or almost all) includes a thermal sensor. The temperature sensor is therefore already present and is not dedicated to the implementation of the diffusion method described here.

[0067] The temperature of the speaker 9 also depends on the frequency of the audio signal.

[0068] At equal electrical voltage across a loudspeaker (e.g. 2 Vrms), using a single-frequency audio signal, the rise in the speaker's temperature depends on the frequency of the audio signal applied to its terminals. This is explained by the fact that the impedance of a loudspeaker (whether mounted in an enclosure or not) depends on the frequency of the audio signal.

[0069] We see on the figure 3 the temperature rise as a function of frequency (curve C4), and the electrical power of the audio signal as a function of frequency (curve C5).

[0070] We see on the figure 4 the impedance of the loudspeaker as a function of the frequency of the audio signal applied to its terminals (curve C6).

[0071] The power at the speaker terminals can be estimated by the following formula: Puissance = tension 2 / impédance

[0072] Comparing the temperature rise per frequency with the power across the loudspeaker, we see a similarity, which is consistent with the basic rules of thermals: Température = Constante × Puissance

[0073] The “real” audio signal, applied to the terminals of each loudspeaker 9 of the multi-channel audio system 1, comprises a plurality of frequency components each associated with a power level.

[0074] We can therefore, by knowing the frequency distribution of the audio signal, define the temperature rise of a loudspeaker which reproduces this audio signal, and therefore the temperature of said loudspeaker.

[0075] The processing unit 10 here performs an FFT calculation (for Fast Fourier Transform) to know the frequency distribution of the audio signal. The processing unit 10 therefore determines frequency components each associated with a power level.

[0076] The processing unit 10 then determines the temperature rise of the loudspeaker 9 resulting from the contributions of each of these frequency components, using the mathematical laws described earlier.

[0077] For each loudspeaker 9, the processing unit 10 therefore carries out a frequency analysis of the primary audio signal applied to the audio channel comprising said loudspeaker 9 to evaluate levels of different frequency components of the primary audio signal, then evaluates a real-time temperature of the loudspeaker 9 as a function of said levels (and the ambient temperature, the initial temperature and the signal application time).

[0078] The processing unit 10 therefore constantly knows the real-time temperature of each loudspeaker 9 at time t.

[0079] To ensure system stability at the system level and user perception, edge effects must be considered. If we consider a highly dynamic approach with an instantaneous system response, applying the correction will result in compensation for thermal risks and thus return the system to an equilibrium state, thereby reducing the action of the process. The system risks oscillating between equilibrium and risk states, potentially disrupting the user experience by constantly switching back and forth. This is what we refer to as a "pumping" effect from a dynamic point of view.

[0080] Some dynamic algorithms, such as audio compressors for example, incorporate solutions to prevent these oscillation effects.

[0081] These solutions are usually presented in the form of four parameters grouped in a set called an ADSR envelope, for Attack Decay Sustain Release. Attack: This is the time required to reach the maximum level of action of the algorithm after exceeding the threshold. This time is typically a few minutes; Decay: This is the time required to reduce the action of the algorithm after the attack peak. This time is typically a few minutes; Sustain: This is the level of action of the algorithm maintained while the signal remains above the trigger threshold. Release: This is the time required for the effect of the algorithm to dissipate completely after falling back below the trigger threshold. This time is typically a few minutes.

[0082] We see an ADSR envelope on the figure 5 (curve C7).

[0083] Here, in a clever and original way, we apply the ADSR envelope not to the audio signal but to the real-time temperature which is evaluated as just explained.

[0084] Here, for example, the following values ​​are used for the envelope parameters: Attack: 5 mins; Decay: 5 mins; Release: 5 mins.

[0085] These parameters can be adjusted to react to different constraints. Here, it is appropriate to approach values ​​that allow the effect of the algorithm to be smoothed over fairly long periods of time.

[0086] It should be noted that, for a loudspeaker 9 integrated into a decoder box 3, the maximum operating temperature of the loudspeaker 9 is usually around 80°C (this value being indicated precisely on the technical data sheet of the loudspeaker 9, and of course depends on the model of the loudspeaker 9).

[0087] Considering inertia, a safe temperature threshold can be 15°C below this threshold to ensure that the critical temperature is not reached.

[0088] On the figure 2 , on which we see the temporal evolution of the temperature of a loudspeaker 9 with audio signal at input then without audio signal, we note that the temperature stabilizes after a certain time, to reach the value Temp asymptote .

[0089] This value corresponds to the thermal stabilization of the system for a simple, constant-level signal.

[0090] However, a real audio signal encountered, such as music, voice, etc., fluctuates. Stabilization is determined dynamically by integrating the instantaneous level of the signal and its frequency distribution, smoothed by an envelope coefficient.

[0091] The real-time temperature consists of digital samples that are applied as input to a digital filter forming the ADSR envelope. The digital samples at the output of the filter are the current temperature values.

[0092] For each loudspeaker 9, the processing unit 10 therefore applies an ADSR envelope to the temperature in real time to obtain the current temperature.

[0093] For each loudspeaker 9 of the different audio channels, the processing unit 10 knows the current temperature of said loudspeaker 9 and therefore the margin with respect to the limit temperature of use of said loudspeaker 9, using the thermal feedback based on the predictive calculation described previously.

[0094] When a particular loudspeaker 9 (or more) exceeds the first predefined temperature threshold, which risks causing dangerous overheating for the loudspeaker (temperature > 80°C for example), the processing unit 10 distributes its particular primary audio signal to one or more other audio channels, dynamically and in a balanced manner, which makes it possible to reduce the temperature of the particular loudspeaker without a drop in overall sound level or degradation of the user experience.

[0095] The first predefined threshold is, for example, equal to 65°C (i.e. 15°C below the “dangerous” temperature of 80°C).

[0096] The processing unit 10 therefore modifies the primary distribution to obtain an optimized distribution of the multi-channel audio signal. The optimized audio signals are applied to the audio channels until the current temperature of the particular “overheated” loudspeaker 9 becomes lower than a second predefined temperature threshold. The second predefined temperature threshold is for example (but not necessarily) also equal to 65°C.

[0097] We now turn to the choice of audio channels on which the particular primary audio signal (or particular primary audio signals) is at least partially carried. We present some scenarios that may occur in audio system 1.

[0098] The first scenario is applicable for an audio system comprising a center channel and two (at least) side channels. The particular audio channel, comprising the particular overheated loudspeaker 9, is here the center channel 4. In this case, at least a part of the overall level of the particular primary audio signal is applied to the two side channels.

[0099] By "overall level" we mean here a level corresponding to the sum of the acoustic energy provided by all the frequency components of the signal.

[0100] Here, in reference to the figure 6 , the particular loudspeaker 9p whose operational temperature becomes higher than the first predefined temperature threshold is therefore the loudspeaker of the center channel 4.

[0101] The primary audio signal of said central channel 4 is for example applied to the two front side channels (front right channel 5a and front left channel 5b).

[0102] The primary audio signal of the center channel 4 continues to be applied partially to the center channel 4 by being progressively attenuated (for one minute for example), until the operational temperature of the loudspeaker 9p of the center channel 4 becomes lower than the second predefined temperature threshold and thus until a recovery of the temperature which will secure the loudspeaker 9p after stabilization. Here, “partially” is understood as a part of the overall level of the primary audio signal.

[0103] In the same proportions, the primary audio signal removed from the center channel 4 will be transferred identically to the loudspeakers 9 of the front right 5a and front left 5b channels, to create a virtual center channel, thus relieving the loudspeaker 9 of the center channel 4 without any degradation of either the spatialization or the overall sound level.

[0104] Note that in this first scenario, the primary audio signal of the center channel 4 could also be applied to the rear side channels 6a, 6b. The first scenario can therefore be implemented even when the audio system only has two side channels (i.e. front right and front left or rear right and rear left).

[0105] The second scenario is applicable for an audio system comprising a center channel, two front side channels and two rear side channels (at least). The particular audio channel, including the particular overheating speaker, is a particular side channel.

[0106] In this case, at least a portion of the overall level of the particular primary audio signal is applied to the center channel 4 and to another side channel on the same side as said particular side channel.

[0107] Here, in reference to the figure 7 , the particular loudspeaker 9p whose operational temperature becomes higher than the first predefined temperature threshold is the loudspeaker of a particular side channel, which is for example here the right front channel 5a.

[0108] The primary audio signal from the front right channel 5a is applied to the center channel 4 and to the rear right channel 6a.

[0109] The primary audio signal of the front right channel 5a continues to be applied partially to the front right channel 5a by being progressively attenuated (for one minute for example), until the operational temperature of the loudspeaker 9p of the front right channel 5a becomes lower than the second predefined temperature threshold and thus until a recovery of the temperature which will secure the loudspeaker after stabilization. Here, "partially" is understood as a part of the overall level of the primary audio signal.

[0110] In the same proportions, the primary audio signal removed from the front right channel 5a will be transferred identically to the loudspeaker 9 of the rear right channel 6a and to the loudspeaker 9 of the central channel 4, to create a virtual side channel, thus relieving the loudspeaker 9p of the front right channel 5a without any degradation of either the spatialization or the overall sound level.

[0111] Note that if the system does not have a rear channel, then the entire primary audio signal from the front right channel 5a will be transferred to speaker 9 of the center channel 4 to relieve the speaker concerned. In this case, there could be a slight subjective reduction in the spatialization effect, but without any change in the overall sound level.

[0112] This scenario can apply to another side lane: right rear, left front, left rear.

[0113] The third scenario is applicable for an audio system comprising two front side channels and two rear side channels. The particular audio channel, comprising the particular overheating 9p speaker, is a front (or rear) side channel.

[0114] In this case, at least a portion of the overall level of the particular primary audio signal is applied to another side channel on the same side as said particular side channel, and to the other front (or rear) side channel.

[0115] Here, in reference to the figure 8 , the particular loudspeaker 9p whose operational temperature becomes higher than the first predefined temperature threshold is the right rear channel loudspeaker 6a.

[0116] The primary audio signal from the right rear channel 6a is therefore applied to the left rear channel 6b and to the right front channel 5a.

[0117] The primary audio signal of the right rear channel 6a will be gradually attenuated (for one minute for example), until the temperature is restored which will secure the speaker 9p after stabilization.

[0118] The primary audio signal of the right rear channel 6a therefore continues to be applied partially to the right rear channel 6a by being progressively attenuated (for one minute for example), until the operational temperature of the loudspeaker 9p of the right rear channel 6a becomes lower than the second predefined temperature threshold and therefore until a recovery of the temperature which will secure the loudspeaker after stabilization. Here, “partially” is understood as a part of the overall level of the primary audio signal.

[0119] This scenario can apply to another side lane: front right, front left, rear left.

[0120] The fourth scenario is applicable for an audio system comprising a low-frequency channel and at least one other audio channel. The particular audio channel, comprising the particular overheating speaker, is one of the at least one other audio channel.

[0121] In this case, frequency components of frequencies lower than a predefined frequency threshold of the particular primary audio signal are applied to the low frequency channel 7. The predefined frequency threshold is for example equal to 100 Hz.

[0122] It can be expected that a number of particular loudspeakers 9, whose operational temperature becomes higher than the first predefined threshold, must be greater than a predefined number, for this scenario to apply (i.e. a situation in which there are too many loudspeakers overheating). The predefined number is for example equal to 3.

[0123] Here, in reference to the figure 9 , the particular 9p loudspeakers whose operational temperature becomes higher than the first predefined temperature threshold are the right front 5a, right rear 6a, left front 5b and left rear 6b ​​channel loudspeakers.

[0124] The low frequency components are then applied to the low frequency channel 7.

[0125] The low frequencies of the primary audio signals of the front right 5a, rear right 6a, front left 5b and rear left 6b channels will be gradually attenuated (for one minute for example), until the temperature is restored which will secure the 9p speakers after stabilization.

[0126] The low frequencies of the primary audio signals of the front right 5a, rear right 6a, front left 5b and rear left 6b channels therefore continue to be applied partially (for one minute for example), until the operational temperature of the loudspeakers 9p becomes lower than the second predefined temperature threshold and thus until a temperature recovery that will secure the loudspeakers after stabilization. Here, "partially" is understood as a part of the frequency components.

[0127] These scenarios can be combined or implemented successively depending, for example, on the temperatures of the speakers that are not overheating: for example, we could favor a scenario that does not transmit a signal to a speaker whose temperature is high without exceeding the first predefined temperature threshold.

[0128] We are now interested in how the particular primary audio signal from a particular audio channel including a particular loudspeaker whose temperature is too high, is distributed over the other audio channels.

[0129] Changing the primary distribution may involve applying at least a portion of a particular primary audio signal's overall level to at least one other audio channel. This adjusts the attenuation or gain level in each channel independently.

[0130] To avoid disrupting the user experience and maintain the tonal balance of the sound, it is necessary to ensure a robust acoustic level per frequency. The primary signal subtracted from the loudspeaker to be secured is distributed to the loudspeakers of other audio channels according to the following logic. By following the fundamental acoustic properties, we can evaluate the signal level to be injected into each loudspeaker to ensure a stable level and tonal balance.

[0131] We are considering the case of the distribution of the signal from a high-risk speaker to two side support speakers.

[0132] Before correction, we consider that: The overall level of the primary audio signal from speaker 9 of center channel 4 is equal to L1 [dB]; The overall level of the primary audio signals of the front right 5a and front left 5b side channels is respectively L2a [dB] and L2b [dB].

[0133] The processing unit 10 subtracts N dB from the primary signal of the center channel loudspeaker 4 and reinjects N2a and N2b on the front right 5a and front left 5b side channels.

[0134] We consider the notation: A ⊕ B = 20 ∗ log 10 A 20 + 10 B 20

[0135] So we have: L 1 ⊕ L2a ⊕ L2b = L1 − N ⊕ L2a + N2a ⊕ L2b + N2b

[0136] According to the principles of doubling coherent acoustic sources, we then have: N 2 a = N 2 b = N − 6 dB

[0137] We now consider the case of distributing part of the signal from one or more speakers at risk to a particular audio channel, for example the low frequency channel 7.

[0138] Before correction, we consider that: The overall levels of the primary signals of the loudspeaker channels at risk are equal to L1 [dB], L2 [dB], L3 [dB]..., Li [dB]; The overall level of the primary signal of the low-frequency channel is Lc [dB].

[0139] The processing unit 10 subtracts respectively N1, N2, ..., Ni dB from the sources at risk and reinjects Nc dB into the low frequency channel 7.

[0140] We have: L1 ⊕ L2 ⊕ .. ⊕ Li ⊕ Lc = L1 − N1 ⊕ L2 − N2 ⊕ .. ⊕ Li − Ni ⊕ Lc − Nc

[0141] According to the level relationships between coherent acoustic sources, we have: Nc = − 20 ∗ log 10 N 1 10 + 10 N 2 10 + .. + 10 Ni 10 i + 1

[0142] This model is an approach to possible distribution and can be adapted according to the physical capabilities of the enclosures considered.

[0143] It is noted that, in an existing audio system, in which the diffusion method described here is not implemented, the spatialization applied will be optimized for an ideal listening location, also called sweet spot.

[0144] The implementation of the diffusion process makes it possible to maintain the viability of the sweet spot whatever it is, since the adaptation of the distribution of the multi-channel audio signal ensures that the spatial and tonal balance of the sound transmitted in the listening area is maintained.

[0145] If the listener(s) move away from the sweet spot, Spatial balance may be degraded when applying the correction algorithm. A listener who is, for example, near a side speaker, to which an audio signal is being transferred, may feel the increase in channel level.

[0146] It is therefore advantageous to define limits for the level transmitted and / or diffused by each channel, in order to ensure relative spatial balance in the case where the listener(s) move away from the sweet spot. For example, it can be provided that the signal level transferred to another channel is lower than a maximum limit.

[0147] We can also consider the case of two listeners far from the sweet spot and each close to one of the speakers in the system. In the event of a loudspeaker overheating, an audio system according to the prior art would simply reduce the level of the speaker in danger, which would cause a flagrant imbalance for the two listeners, particularly the one placed close to the speaker in danger. The implementation of the diffusion method will make it possible not to lose the information delivered by the speaker placed in safety. For a listener far from the sweet spot, This information will be presented spatially shifted, slightly altering the perception of the original flow. This modification involves fairly fine perceptual analysis and is considered a less significant degradation than pure reduction and loss of information.

[0148] In the case where the audio channels are integrated into compact equipment, such as a set-top box, the notion of sweet spot is much wider because the speakers in the system are very close together. The change in distribution, if one speaker overheats, will be much less noticeable, because the listener is a similar distance away from each speaker.

[0149] The distribution of the multi-channel audio signal across the various audio channels is defined by mixing matrices dedicated to spatial sound processing. These mixing matrices are presented in the form of input / output connections with variable dimensions depending on requirements.

[0150] In reference to the figure 10 , the mixing matrix 15 is for example intended to process a mono audio signal 16 (of type 1.0) or stereo (of type 2.0), or a multi-channel audio signal 17 of type Dolby 5.1, Dolby 7.1, DTS 5.1, etc. The mixing matrix 15 generates a multi-channel audio signal 18 depending on the audio system which reproduces the signal.

[0151] There figure 11 represents a first mixing matrix 19 used by Dolby, processing audio formats up to 7.1 format as input, and generating audio signals in 5.1 format as output.

[0152] This first mixing matrix 19 corresponds to the primary multi-channel audio distribution used by the processing unit 10 to distribute the multi-channel audio signal.

[0153] When the temperature of one or more speakers 9 becomes too high, the processing unit 10 adapts the mixing matrix to adjust the level on one or more speakers 9 of the system at the same time, while respecting the broadcast content.

[0154] To do this, the processing unit 10 estimates the attenuation / gain level to be applied (see above) and translates it into the mixing matrix. To manipulate the digital audio data, the processing unit 10 integrates a conversion of the level in dB to the factor to be applied, by the relationship: c i = 10 Ni dB 20 Or c i is the factor to be applied to channel i, whose attenuation / gain level will have been estimated à Ni dB by processing unit 10.

[0155] In the case of a decoder box 3 integrating four loudspeakers 9 and forming a 3.1 type system, there is a second mixing matrix 20, visible on the figure 12 This matrix aims to acquire a 7.1 format as input, and to generate audio signals in 3.1 format as output.

[0156] We consider the case where it is the speaker 9 of the central channel 4 (in the decoder box 3) whose temperature becomes too high.

[0157] The processing unit 10 reduces the level of the primary signal on this loudspeaker 9 and distributes it to the side channels. In the case of a 6dB attenuation of the center channel 4, the audio signal sent to the center channel is therefore reduced by 0.5 (-6dB) and is sent to the left and right channels.

[0158] We obtain the mixing matrix 21 of the figure 13 .

[0159] The level of the left and right channels has increased, but the creation of the virtual center channel compensates for this level change.

[0160] We have seen that modifying the primary distribution can consist of applying at least part of the overall level of the particular primary audio signal to at least one other audio channel.

[0161] It is also possible to modify the primary distribution by applying at least part of the frequency components of the particular primary audio signal to at least one other audio channel (see the fourth scenario described earlier). It is also possible to implement these two methods in combination if the overheating is too significant.

[0162] A loudspeaker can indeed be relieved by attenuating the audio signal transmitted to it, but also by changing the frequency distribution of its signal. We have seen on the figure 3 the dependence that exists between the frequency of the audio signal and the temperature of the speaker.

[0163] Distributing part of the spectrum to one or more other 9 speakers allows the particular 9p speaker, whose temperature is too high, to be relieved, without applying a static gain to its entire signal.

[0164] Since low frequencies are very little or not at all directional, it is advantageous to choose instead a distribution of the low frequencies of the spectrum towards another loudspeaker, in order to minimize the impact on the spatialization of the sound. The most logical case would be to send the low / low-midrange parts towards the loudspeaker acting as the Woofer in the system.

[0165] We see on the figure 14 acoustic measurements of frequency response of two loudspeakers belonging to a multi-channel audio system: curve C8 is the curve of loudspeaker 9 of central channel 4 and curve C9 is that of loudspeaker 9 of low frequency channel 7.

[0166] The modification of the primary distribution, by a different distribution of the frequency components, would allow, for example, in the frequency band 22, to send part of the low frequency signal from the central channel 4 to the low frequency channel 7.

[0167] Changing the primary distribution involves changing (in this case increasing) the cut-off frequency of the crossover filter that distributes the frequencies between the different audio channels. This increases the spectrum reproduced by the low-frequency channel and reduces the spectrum reproduced by the other channels.

[0168] We now recall, with reference to the figure 15 , the different stages of the diffusion process.

[0169] For each loudspeaker 9, the processing unit 10 evaluates the real-time temperature Tr of said loudspeaker 9 from the levels of the frequency components of the primary audio signal applied to the audio channel comprising said loudspeaker 9: step E1.

[0170] The processing unit 10 then applies the ADSR envelope to obtain the operational temperature To of said loudspeaker 9: step E2.

[0171] The processing unit 10 compares the operational temperature To with the first predefined temperature threshold T1: step E3.

[0172] As long as the operational temperature of all the loudspeakers 9 remains lower (here lower than or equal to) the first predefined temperature threshold T1, the processing unit 10 does not modify the mixing matrix (step E4) nor the settings (cutoff frequency) of the crossover filter (step E5). The processing unit 10 broadcasts the multi-channel audio signal using the current coefficients of the mixing matrix (step E6) and the current settings of the crossover filter (step E7).

[0173] In step E3, if the operational temperature of at least one particular loudspeaker 9p is higher (here strictly) than the first predefined temperature threshold, the processing unit 10 modifies the primary distribution by applying at least part of an overall level of the particular primary audio signal to at least one other audio channel. The processing unit 10 modifies the coefficients of the mixing matrix: step E8.

[0174] The processing unit 10 then broadcasts the multi-channel audio signal using the current coefficients of the mixing matrix, which have just been modified (step E6).

[0175] Furthermore, in step E3, if the operational temperature of at least one particular loudspeaker 9p is higher than the first predefined temperature threshold, the processing unit 10 checks the number of loudspeakers whose operational temperature is higher than the first predefined temperature threshold: step E9.

[0176] If this number is greater than a predefined number, the processing unit 10 modifies the primary distribution by applying the low-frequency frequency components of the particular primary audio signals to at least one audio channel whose loudspeaker does not heat up (preferably to the low-frequency channel 7). The processing unit 10 modifies the cutoff frequency of the crossover filter for this purpose: step E10. The processing unit 10 broadcasts the multi-channel audio signal using the current settings of the crossover filter, which have just been modified (step E7).

[0177] In step E3, if the number is less than the predefined number (here less than or equal), the processing unit 10 does not modify the settings (cutoff frequency) of the crossover filter (step E5). The processing unit 10 broadcasts the multi-channel audio signal using the current settings of the crossover filter, unmodified (step E7).

[0178] The main tests to determine the model's action therefore assess whether the temperatures of the different loudspeakers exceed the first predefined temperature threshold. From then on, the level distribution in the different audio channels is calculated and translated into mixing matrix coefficients. In addition, the number of loudspeakers involved is taken into account to activate or not the frequency distribution. A calculation will then be made to increase the frequency of the crossover(s) in order to help the loudspeakers lower their temperature.

[0179] If these tests are presented as binary, the effect applied to the audio signal will actually be smoothed by the ADSR envelope applied to the real-time temperature of the speakers. With a well-tuned envelope, the effect of the various distributions will be brought back towards 0 before being completely disabled, with a similarly opposite logic when it is activated.

[0180] These different stages are combined in a logic described by the block diagram of the figure 16 .

[0181] The thermal simulation model 30 analyzes the primary audio signals Sap applied to the input of the loudspeakers 9. The processing unit 10 evaluates the temperature in real time and then the operational temperature. The distribution model 31 is implemented. The distribution by level results in an adaptation of the mixing matrix 32. The frequency distribution results in a modification of the crossover filter 33.

[0182] The multi-channel audio signal Sam is applied to the input of the mixing matrix 32 then to the crossover filter 33. The primary audio signals Sap (if no loudspeaker is overheating) or the optimized audio signals Sao (if at least one loudspeaker is overheating) are processed and shaped by a processing module 34 then amplified by the amplifiers 35 and applied to the input of the loudspeakers 9 which broadcast the sound signal Ss corresponding to the multi-channel audio signal Sam.

[0183] It is noted that the primary audio signals Sap, analyzed by the thermal simulation model 30, can be the input or output signals of the amplifiers 35.

[0184] An audio system could be designed that could do without a speaker, replaced by the other speakers as support. However, completely removing a speaker is complicated to achieve if we want to maintain the spatial balance of the sound. The compensation algorithm of the diffusion process places a little more stress on the other speakers compared to their initial use. Consequently, we increase the constraints on the electronics and we increase the thermal risk on the other speakers as well. The model is smoothed over a fairly long time, but it is not intended to be used continuously, but rather occasionally to overcome certain limitations, following long and intense uses for example.

[0185] The diffusion process therefore does not allow one to completely do without one or more sources, but rather to optimize their use and longevity by pushing back the limit conditions of the loudspeakers.

[0186] The diffusion process includes the step of increasing the gain applied to one or more loudspeakers. Therefore, the risk of saturation and damage to the equipment may increase with the action of the diffusion process. To compensate for this, it is possible to integrate into the audio system the protection devices usually used to limit the voltage level sent to the loudspeakers, and for example one or more dynamic limiters. Properly dimensioned (in particular by a set of ADSR parameters seen earlier), they allow a signal to be attenuated when it exceeds a certain threshold (70 °C for example). This attenuation will be very rapid if the threshold is close to the physical limit of the loudspeaker considered (80 °C for example).

[0187] From a reproduction and frequency point of view, the implementation of the diffusion process does not degrade the audio system. The cut-off frequency will correspond to that of the hardware components used.

[0188] As seen, the diffusion method consists of evaluating the operational temperature of at least one loudspeaker and, if this becomes too high, applying the particular primary audio signal at least partially to at least one other audio channel.

[0189] As we have seen, the operational temperature is not necessarily a current temperature, that is to say a temperature at the present time, but can be a temperature at a future time (we then speak of "future temperature").

[0190] Estimating the future temperature, and therefore applying the correction in advance, allows the process to react more quickly and thus be able to simply apply a smaller, and therefore less audible, correction. Rather than estimating the future temperature, the process can also use a feedback loop.

[0191] In one embodiment, the particular "future" primary audio signal is known, for example because the processing unit 10 is playing a local file and the entire file is available.

[0192] The processing unit 10 can therefore apply the method already described on this future signal to estimate the temperature. The evaluation of the operational temperature is therefore based on an analysis of the particular primary audio signal carried out prior to its broadcast.

[0193] In this case, if the processing unit determines that a correction is necessary, the signal actually played will be different from the future signal used to estimate the temperature, since the signal actually played will integrate the correction.

[0194] In another, simpler but less efficient embodiment, the future temperature is estimated based on the current (present) temperature and the evolution of the temperature in the near past (and therefore based on a “past temperature”).

[0195] For example, if T c (t) denotes the current temperature and T c (t-1) denotes the temperature 1 second in the past, we can estimate the temperature 1 second in the future with the formula: T f t = T c t + T c t − T c t − 1 .

[0196] In another embodiment, the processing unit 10 implements a servo controller (or corrector).

[0197] The servo controller is a module which receives an input setpoint and a measurement, and which produces an output command which, when applied to a system, tends to bring the measurement closer to the setpoint.

[0198] The setpoint here is the maximum desired temperature T max , set a little below the limit not to be exceeded since the usual controllers tend to oscillate around the setpoint, and therefore to exceed it a little.

[0199] The measurement is the current temperature estimated by the temperature estimation method described earlier.

[0200] The order represents the share G c (t) of the particular primary audio signal to be redistributed to other speakers when it is negative (in decibels).

[0201] An example implementation using a standard PID (Proportional-Integral-Derivative) controller is presented.

[0202] The following steps are repeated at regular intervals.

[0203] The processing unit 10 first estimates the current temperature T c (t).

[0204] The controller then calculates the deviation Δ(t) between the maximum temperature and the current temperature: Δ t = T max − T c t

[0205] Then the controller calculates the proportional terms P c (t), integral I c (t) and derived D c (t) : P c t = P × Δ t I c t = min I c t − 1 + I × Δ t , 0 D c t = D × Δ t − Δ t − 1 Or P, I And D are predetermined constants that allow the controller's responsiveness and stability to be adjusted.

[0206] Here we see a difference compared to a classic PID controller. Usually, we use either: I c t = I c t − 1 + I × Δ t , either : I c t = clamp I c t − 1 + I × Δ t , I min , I max , with I min < 0 and I max > 0 and predetermined.

[0207] The command is then given by: G c t = P c t + I c t + D c t .

[0208] It is noted that this embodiment is a generalization of the embodiment mentioned earlier and consisting of estimating the future temperature as a function of the current temperature and the past temperature.

[0209] The term P c (t) corresponds to the use of the current temperature, and the term D c (t) adds consideration of future temperature.

[0210] Especially if we ask P = D And I = 0, we obtain: which corresponds exactly to the use of the future temperature T f (t) as in the said embodiment mentioned earlier.

[0211] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0212] The broadcast process does not necessarily include monitoring the temperature of all speakers. It is possible to monitor only one or more "at risk" speakers.

[0213] As we have seen, the diffusion method can be implemented regardless of the multi-channel audio system. The speakers can be integrated into any number of devices, and even into a single device, which can be a set-top box, a sound bar, a speaker, etc.

[0214] The equipment in question can therefore in particular be a decoder box.

[0215] The decoder box can integrate at least one speaker from the plurality of audio channels used in the implementation of the broadcasting method.

[0216] The set-top box can thus integrate all the speakers used. In this case, the set-top box integrates the processing unit, audio amplifiers and at least two speakers, and for example four speakers forming four audio channels (left, right, center and bass).

[0217] The decoder box can also integrate one or more speakers, the other speakers used (for example those of the rear channels) being remote.

[0218] All speakers can also be positioned outside the set-top box.

[0219] The processing unit, in which the broadcasting method is implemented, can be integrated into one or more devices belonging or not to the multi-channel audio system (the broadcasting method could be implemented remotely, on a server of the cloud For example).

Claims

1. A method for broadcasting a multi-channel audio signal (Sam) by an audio system (1) comprising a plurality of audio channels (4, 5a, 5b, 6a, 6b, 7) each comprising at least one loudspeaker (9), the broadcasting method being implemented by a processing unit (10) and comprising the steps of: - broadcasting the multi-channel audio signal using a primary distribution of the multi-channel audio signal, which defines a primary audio signal (Sap) for each audio channel, and applying said primary audio signals to the audio channels; - evaluating an operational temperature (To) of at least one particular loudspeaker (9p) belonging to a particular audio channel;- when the operational temperature of the particular loudspeaker becomes higher than a first predefined temperature threshold (T1), modifying the primary distribution to obtain an optimized distribution of the multi-channel audio signal, in which a particular primary audio signal of the particular audio channel is applied at least partially to at least one other audio channel, the optimized distribution thus defining an optimized audio signal (Sao) for each audio channel; - broadcasting the multi-channel audio signal by applying the optimized audio signals to the audio channels until the operational temperature of the particular loudspeaker (9p) becomes lower than a second predefined temperature threshold.; 2. A broadcasting method according to claim 1, wherein modifying the primary distribution comprises the step of applying at least a portion of an overall level of the particular primary audio signal (Sap) to at least one other audio channel.

3. A broadcasting method according to claim 2, the plurality of audio channels comprising a central channel (4) and two side channels (5a, 5b, 6a, 6b), the particular audio channel being the central channel (4), at least a portion of the overall level of the particular primary audio signal being applied to the two side channels.

4. Broadcasting method according to one of claims 2 to 3, the plurality of audio channels comprising a central channel (4), two front side channels (5a, 5b) and two rear side channels (6a, 6b), the particular audio channel being a particular side channel (5a), at least a part of the overall level of the particular primary audio signal being applied to the central channel (4) and to another side channel (6a) on the same side as said particular side channel.

5. Broadcasting method according to one of claims 2 to 4, the plurality of audio channels comprising two front side channels (5a, 5b) and two rear side channels (6a, 6b), the particular audio channel being a front (or rear) side channel, at least part of the overall level of the particular primary audio signal being applied to another side channel on the same side as said particular side channel, and to the other front (or rear) side channel.

6. Broadcasting method according to one of the preceding claims, in which the modification of the primary distribution comprises the step of applying at least a part of frequency components of the particular primary audio signal (Sap) on at least one other audio channel.

7. A broadcasting method according to claim 6, wherein modifying the primary distribution comprises the step of modifying a cutoff frequency of a crossover filter (33).

8. Broadcasting method according to one of claims 6 to 7, the plurality of audio channels comprising a low frequency channel (7) and at least one other audio channel (4, 5a, 5b, 6a, 6b), the particular audio channel being one of the at least one other audio channels, frequency components of frequencies lower than a predefined frequency threshold of the particular primary audio signal being applied to the low frequency channel.

9. Broadcasting method according to one of claims 6 to 8, in which the step of applying at least part of the frequency components of the particular primary audio signal (Sap) to at least one other audio channel is implemented if a number of particular loudspeakers (9p), the operational temperature of which becomes higher than the first predefined temperature threshold (T1), is higher than a predefined number.

10. A broadcasting method according to one of the preceding claims, wherein the particular primary audio signal continues to be partially applied to the particular audio channel until the operational temperature of the particular loudspeaker (9p) becomes lower than the second predefined temperature threshold.

11. The broadcasting method of claim 10, wherein the particular primary audio signal is progressively attenuated on the particular audio channel.

12. A broadcasting method according to one of the preceding claims, wherein the evaluation of the operational temperature of the particular loudspeaker (9p) comprises the steps of: - performing a frequency analysis of the particular primary audio signal to evaluate levels of different frequency components of the particular primary audio signal; - evaluating a real-time temperature of the particular loudspeaker (9p) as a function of said levels.

13. The diffusion method of claim 12, comprising the step of applying an ADSR envelope to the real-time temperature to obtain the operational temperature.

14. Diffusion method according to one of the preceding claims, in which the operational temperature is a future temperature.

15. A broadcasting method according to claim 14, wherein the evaluation of the operational temperature is based on an analysis of the particular primary audio signal carried out prior to its broadcast.

16. Diffusion method according to claim 14, wherein the evaluation of the operational temperature is carried out from a past temperature and a current temperature.

17. Broadcasting method according to one of the preceding claims, comprising the step of implementing a servo controller, which receives as input a setpoint and a measurement, and which produces as output a command, the setpoint being a maximum temperature, the measurement being the evaluation of the operational temperature (To), and the command being a part of the particular primary audio signal to be applied to the at least one other audio channel.

18. Equipment (3) comprising a processing unit (10) in which the diffusion method according to one of the preceding claims is implemented.

19. Equipment according to claim 18, the equipment being a decoder box.

20. Equipment according to claim 19, in which the decoder box integrates at least one speaker of the plurality of audio channels.

21. Computer program comprising instructions which cause the processing unit (10) of the equipment according to one of claims 18 to 20 to execute the steps of the broadcasting method according to one of claims 1 to 17 when said program is executed by the processing unit.

22. Computer-readable recording medium, on which the computer program according to claim 21 is recorded.

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