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JP2007027821

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DESCRIPTION JP2007027821
The present invention provides an "audio apparatus" capable of listening to an audio signal
without giving a sense of discomfort to the user even when performing protection processing
against temperature rise. An audio apparatus adjusts an audio signal having a predetermined
frequency and outputs an audio signal whose level is adjusted, and outputs the amplified audio
signal to a speaker. The audio output amplification unit 12, the temperature detection unit 13 for
detecting the temperature in the vicinity of the audio output amplification unit 12, and the
temperature detected by the temperature detection unit 13 for the audio output processing unit
14 have a predetermined temperature And a control unit (15) for adjusting a signal level of a low
frequency according to the predetermined temperature of the audio signal when exceeding. The
control unit 15 may cause the audio output processing unit 14 to remove a signal equal to or
lower than the low cutoff frequency according to the predetermined temperature, or may reduce
the level of the signal. [Selected figure] Figure 2
Audio device
[0001]
The present invention relates to an audio device adapted to eliminate the disadvantages caused
by the protection against temperature rise of the device.
[0002]
The audio device basically includes a player such as a CD or MD, a power amplifier for amplifying
a signal output from the player, and a speaker for converting an electrical signal output from the
08-05-2019
1
power amplifier into sound and outputting the sound. doing.
In such an audio device, in order to realize high fidelity reproduction, the frequency
characteristic of the power amplifier is often flat in an audio frequency band (a band of
approximately 20 Hz to 20 kHz). However, when an actual music signal is recorded on the
medium, the amplitude level of the high-tone component of the signal components of each
frequency is lowered to increase the amplitude level of the bass component.
[0003]
This is shown in the iso-sensitivity curve (Robinson-Dadson curve) of FIG. It is because it is
necessary to enlarge. The equal sensitivity curve is a curve connecting sound pressure levels
when pure tones having different frequencies are heard in the same magnitude.
[0004]
In addition, it is also performed to correct acoustic characteristics in a predetermined space (for
example, a vehicle interior) as a whole audio frequency band using an equalizer to make the
acoustic characteristics according to the user's preference. For example, the volume may be
adjusted for each frequency band so that only the volume (amplitude) of the low range is
increased to emphasize the low range.
[0005]
On the other hand, when the above-described power amplifier is kept operating at a large output,
power loss may increase in circuit elements constituting the power amplifier, such as FETs and
capacitors, and heat may be generated. This heat adversely affects the device inside the audio
device, for example, an IC for signal processing, and the operation of the device may become
unstable, and in some cases, the device may be destroyed with ignition and smoke.
[0006]
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2
As a method of preventing the instability of the device caused by such heat and the destruction
of the device, an element for detecting a temperature rise is provided in the vicinity of the device
of the audio device, and the temperature is adjusted so as not to exceed the predetermined
temperature. A temperature protection process to control is performed. For example, the power
supply of the apparatus is shut down or the output level of the audio signal is lowered according
to the detected temperature. Thus, the generation of heat is suppressed by preventing the
generation of power consumption or reducing the power consumption. There is also a method of
limiting the voltage or current of the output signal by a limiter circuit. Also in this case, since the
voltage value or the current value is reduced, the power consumption can be reduced and the
generation of heat can be suppressed. By performing such a protection operation alone or in
combination, the temperature rise of the device is suppressed, and the destruction or the like of
the device is prevented.
[0007]
Further, as a technique related to the above-mentioned temperature protection, as described in,
for example, Patent Document 1, the temperature rise of the amplifier is detected, the audio input
signal is attenuated, and the amount of attenuation is changed periodically to prevent voice
interruption. There is also one that did. Unexamined-Japanese-Patent No. 11-355059 gazette
[0008]
As described above, in the conventional temperature protection process, since the shutdown of
the power supply of the apparatus is performed by the detected temperature, the temperature
rise can be suppressed, and the destruction of the device can be prevented.
[0009]
However, there is a problem that the user who is listening to the audio sound may give a sense of
hearing discomfort as described below.
[0010]
That is, among the above-described protection operations, the method of shutting down the
power supply causes the output to suddenly stop or suddenly operate depending on the set
temperature, and the operation of the apparatus becomes unstable near the set temperature, so
that listening may occur. It may cause discomfort to the user who is
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3
Moreover, although the method of reducing the output level can reduce the generated power, the
volume level of the entire audio frequency band is reduced, so it is known that the volume has
become smaller, and the user enters the temperature protection operation. Make them aware of
As a result, there is a possibility of giving a sense of discomfort in hearing. Although the method
of limiting the voltage or current of the output signal can also suppress the generated power to a
low level, this method distorts the waveform of the output signal, so the audio signal can not be
reproduced faithfully. It may cause discomfort.
[0011]
Although Patent Document 1 discloses a method for preventing the audio signal from being
completely blocked in the temperature protection circuit, it is possible to reduce the volume level
of the entire audio frequency band or to repeat blocking for a short time. Since the output is
performed, the user may be aware that the user is in the temperature protection operation as in
the above method, which may cause a sense of discomfort in hearing.
[0012]
Further, as described above, in the audio apparatus, the sound pressure level (amplitude) of the
low band part is relatively higher than that of the high band part.
Therefore, the power consumed in the power amplifier is relatively greater in the low tone
component than in the high tone component. Therefore, even if the volume (amplitude) of the
entire audio frequency band is uniformly reduced, the power of the bass portion is relatively
larger than the power of the treble portion. Furthermore, depending on the aperture of the
speaker, the bass part may hardly be detected by humans even if the volume is increased, and
outputting such a bass part consumes more power than necessary.
[0013]
The present invention has been made in view of the problems of the prior art, and an audio
apparatus capable of listening to an audio signal without giving a sense of discomfort to the user
even when protection processing against temperature rise is performed. Intended to be provided.
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[0014]
According to one aspect of the present invention, an audio output processing unit that adjusts
and outputs a signal level of a predetermined frequency with respect to an input audio signal,
and the level is adjusted according to an embodiment of the present invention. An audio output
amplification unit for amplifying an audio signal and outputting it to a speaker, a temperature
detection unit for detecting a temperature near the audio output amplification unit, and a
temperature detected by the temperature detection unit with respect to the audio output
processing unit There is provided an audio device comprising: a control section for adjusting a
signal level of a low frequency according to the predetermined temperature of the audio signal
when the temperature exceeds a predetermined temperature.
[0015]
In the audio apparatus according to the above aspect, the control unit may control the audio
output processing unit to reduce a signal level lower than a low frequency according to the
predetermined temperature, or the predetermined temperature It may be controlled to remove
signals lower than the low frequency according to
[0016]
In the audio apparatus according to this aspect, the temperature in the vicinity of the audio
output amplification unit is detected, and a signal below a predetermined frequency of the output
signal is removed or the signal level is reduced according to the detected temperature. .
As a result, since the bass component of the output signal is removed or the volume of the bass is
reduced, it is possible to reduce the power consumed by the audio output amplification unit and
prevent the temperature rise.
In addition, since only the volume of the bass which has little influence on the sense of hearing is
reduced as compared with the case of adjusting the signal of other frequencies, it is possible to
make the user not aware that the temperature protection operation is in progress.
The predetermined frequency depends on the aperture of the speaker to which the audio signal
is output. For example, when the aperture of the speaker is 10 cm, the cutoff frequency is 180
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Hz.
[0017]
Hereinafter, embodiments of the present invention will be described with reference to the
attached drawings.
[0018]
First Embodiment (Configuration of Audio Device) FIG. 1 is a block diagram showing a schematic
configuration of an audio device according to a first embodiment of the present invention.
[0019]
The audio device 10 according to the present embodiment has a speaker 11, an audio output
amplification unit 12, a temperature detection unit 13, a low frequency adjustment unit (audio
output processing unit) 14, a control unit 15, and a storage as a basic configuration. And a unit
16.
Although not particularly shown for the sake of simplicity of the description, a plurality of
speakers 11 are actually provided.
[0020]
The audio output amplification unit 12 basically has a function of amplifying the signal of the
audio source 17 input via the low band adjustment unit 14 and supplying the amplified signal to
the speaker 11.
[0021]
The temperature detection unit 13 is configured of a temperature sensor such as a thermistor.
The temperature detection unit 13 is disposed in the vicinity of a component (for example, an
FET) having a large amount of heat generation among components constituting the audio output
amplification unit 12.
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For example, when the FET is molded in the form of a package and disposed on the heat sink, the
temperature sensor and the FET heat each other by fixing the temperature sensor with a metal
bracket in the vicinity of the FET on the heat sink Combined. As a device for detecting the
temperature, in addition to the above-mentioned thermistor, a temperature detection IC or a
temperature detection circuit using the temperature dependency of the base-emitter voltage of
the transistor may be used.
[0022]
The signal detected by the temperature detection unit 13 is amplified to the extent that the
control unit 15 can perform predetermined processing through the amplifier 20, and then
supplied to the control unit 15 through the interface 21. When the signal detected by the
temperature detection unit 13 is at a sufficient level for the control unit 15, it is not necessary to
provide the amplifier 20.
[0023]
The low band adjustment unit 14 is formed of, for example, a high pass filter (HPF), and basically
removes a signal of a predetermined frequency or less. The low band adjustment unit 14 is
formed of, for example, a DSP (Digital Signal Processor), receives a signal indicating a low band
cutoff frequency or the like from the control unit 15, and forms an appropriate high pass filter.
[0024]
Note that the low band adjustment unit 14 may correspond to a plurality of frequencies by
switching several filters.
[0025]
Further, in the present embodiment, although the low frequency band adjustment unit 14 targets
low frequency adjustment, the user performs various adjustments (for each frequency band) to
the audio signal to be supplied to the audio output amplification unit 12 in the subsequent stage.
Level adjustment, removal of a specific frequency band, and the like may be performed.
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[0026]
The control unit 15 is formed of, for example, a microcomputer, reads a signal detected by the
temperature detection unit 13, calculates a temperature, and determines the cutoff frequency of
the high pass filter of the low band adjustment unit 14 according to the temperature. Control of
the slope of the signal below the cut-off frequency.
[0027]
The storage unit 16 is formed of, for example, a semiconductor memory such as a flash memory,
and stores a correspondence table between the diameter of the speaker 11 and the low cutoff
frequency.
A hard disk (HDD) may be used instead of the semiconductor memory.
[0028]
In the audio apparatus configured as described above, the control unit 15 operates based on a
preset program, and controls the operation of the low band adjustment unit 14 based on the
temperature detected by the temperature detection unit 13. Do the processing.
[0029]
Specifically, when the detected temperature detected by the temperature detection unit 13
exceeds a predetermined temperature (for example, 100 ° C.), the low frequency cut-off
frequency is determined for the low frequency adjustment unit 14, or Control is performed to
adjust the slope of the signal at a frequency lower than the low cutoff frequency.
The low frequency cutoff frequency determined here depends on the diameter of the speaker 11.
[0030]
FIG. 3A shows the frequency characteristics of the speaker for each aperture.
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As can be seen from FIG. 3 (a), the cutoff frequency of the low frequency band differs depending
on the aperture of the speaker.
Thus, even within the range of general audio frequency (20 Hz to 20 kHz), the aperture of the
speaker may make the human ear inaudible. Therefore, the control unit 15 determines the value
of the frequency to be removed or to reduce the level according to the aperture of the speaker.
As a result, although the power consumption is large, the bass portion which can not be heard by
the human ear can be removed or its level can be reduced, the power consumption can be
reduced, and the temperature rise can be suppressed. Even when the temperature protection
operation is performed as described above, since the sound that can not be heard by the human
ear is removed or reduced, there is almost no discomfort from the viewpoint of hearing.
[0031]
(Low Frequency Adjustment Processing) The low frequency adjustment processing in the audio
device of the present embodiment will be described below with reference to FIG. 4 showing an
example of the processing flow.
[0032]
As an initial state, an audio signal from the audio source 17 is supplied to the audio output
amplification unit 12 through the interface (I / F) 18, the low band adjustment unit 14 and the
interface 19, and from the audio output amplification unit 12 through the speaker 11 It is
assumed that voice is output.
[0033]
First, in step S11, data indicating a temperature detected by the temperature detection unit 13 is
taken in via the amplifier 20 and the interface 21.
[0034]
In the next step S12, it is determined whether the detected temperature is higher than or equal to
a predetermined set temperature (for example, 100 ° C.) (YES) or not (NO) based on the taken-in
temperature data.
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In the case where the judgment result is "yes", control proceeds to step S13, and in the case
where the judgment result is "no", this processing flow ends.
[0035]
In the next step S13, the control unit 15 determines the low cutoff frequency and the low signal
level.
[0036]
That is, as shown in FIG. 3B, the lower cutoff frequency is determined according to the aperture
of the speaker, or the slope of the signal level lower than the lower cutoff frequency is
determined.
In order to determine the low-pass cutoff frequency, the aperture of the speaker and the
corresponding low-pass cutoff frequency are prepared in advance as a table and stored in the
storage unit 16, and the aperture of the loudspeaker is referred to with reference to this table.
The lower cutoff frequency may be determined in accordance with.
[0037]
In the next step S14, the low band adjusting section 14 is controlled to adjust the low band
portion of the audio signal by the control signal from the control section 15.
That is, the filter coefficients of the FIR (Finite Impulse Response) filter constituting the low band
adjustment unit 14 are adjusted by the LMS (Least Mean Square) adaptive algorithm, and the low
band cutoff frequency and the slope of the signal level are set.
When the high pass filter is composed of a resistor, a capacitor or an inductor, the values of
these elements are appropriately set or selected to set the low cutoff frequency and the like.
[0038]
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If the detected temperature rises near the heat resistance temperature of the device, prioritize
the device protection to determine the low cutoff frequency or adjust the slope of the signal level
even if there is an auditory effect. It is also good.
[0039]
FIG. 5 shows an example of adjusting the low frequency cutoff frequency.
As shown in FIG. 5, when the detected temperature is higher than a predetermined temperature,
the set value may be changed so as to increase the value of the low cutoff frequency. For
example, assuming that the low cutoff frequency at a detection temperature of 100 ° C. is f1, if
the detection temperature exceeds 100 ° C. by a predetermined value, the cutoff frequency is f2
and the detection temperature rises further. In this case, the cutoff frequency may be set to f3.
Furthermore, when the detected temperature rises to near the upper temperature limit of the
device, the low frequency signal is removed, and the signal level in the entire audio frequency
band is lowered to reduce power consumption and protect the device. You may
[0040]
Moreover, as a result of performing the above processing, when the detected temperature
becomes lower than a predetermined temperature (100 ° C.), the low band portion may be
adjusted as described above, or the low band portion may be A signal may be output.
[0041]
As described above, in the audio apparatus according to this embodiment, the temperature in the
vicinity of the audio output amplifier 12 is detected, and when the predetermined temperature is
reached, the signal of the low frequency is removed or the signal level is reduced. It is like that.
By performing such processing, power consumption in the audio output amplifier 12 can be
reduced, and heat generation can be suppressed. Also, at this time, since the low frequency
signals are removed and the signal level is reduced, there is less influence on hearing compared
to the case of adjusting the signals of other frequencies, and the temperature protection
operation is performed to the listener And the listener can listen to music and the like without
discomfort.
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[0042]
In the embodiment described above, the method of adjusting the low frequency signal is
described, but not limited to the low frequency, it is possible to adjust a signal higher than the
high frequency audible frequency band. Although a signal higher than the high audio frequency
band is not recognized as a single sound, a difference between different frequencies may be
recognized as a beat (beat sound). At the same time as removing such unnecessary sound, it can
contribute to the reduction of the power consumption in the audio output amplifier. For example,
as shown in FIG. 3 (a), the frequency at which high sound is difficult to produce is 25 kHz, so a
low pass filter with a high frequency cutoff frequency of 25 kHz constitutes a low pass filter. It
may be made to pass through a low pass filter.
[0043]
Second Embodiment (Configuration of Audio Device) FIG. 6 is a block diagram showing a
schematic configuration of an audio device according to a second embodiment of the present
invention.
[0044]
The audio device 30 according to the present embodiment has, as a basic configuration, a
speaker 31, an audio output amplification unit 32, a temperature detection unit 33, a band
adjustment unit (audio output processing unit) 34, a characteristic measurement unit 35, and
control A section 36, a storage section 37, and a microphone (microphone) 38 are provided.
Although not particularly shown for the sake of simplicity of the description, a plurality of
speakers 31 are actually provided. The audio output amplification unit 32 and the temperature
detection unit 33 have the same functions as those described in the first embodiment, and thus
the description thereof is omitted here.
[0045]
The band adjustment unit 34 is formed of, for example, a DSP (Digital Signal Processor), is not
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limited to a high pass filter (HPF), and can also realize a band pass filter (BPF), a low pass filter
(LPF), and the like. It is assumed that these filter configurations can be changed according to the
acoustic characteristics at the listening point of the speaker 31 and the target space where the
audio signal is to be heard.
[0046]
The characteristic measurement unit 35 measures acoustic characteristics in the space where the
audio signal is listened to. The characteristic measurement unit 35 is configured of, for example,
software for generating a sound source for measuring an acoustic characteristic, and an FFT (Fast
Fourier Transform) analyzer for analyzing an observed sound signal.
[0047]
The control unit 36 is formed of, for example, a microcomputer, reads the signal detected by the
temperature detection unit 33, calculates the temperature, and outputs the sound to the band
adjustment unit 34 according to the temperature and the acoustic characteristics of the space to
listen to the audio signal. Control to adjust the signal.
[0048]
The storage unit 37 is, for example, a hard disk, and stores frequencies outside the audible range
measured by the characteristic measurement unit 35.
[0049]
The microphone 38 is installed at the listening point, detects the sound output from the speaker
31, and converts it into an electric signal.
The microphone 38 uses, for example, a unidirectional microphone that can observe sounds in
almost all directions except the rear.
[0050]
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In the audio apparatus configured as described above, acoustic characteristics in a target space
are measured in advance before actually listening to an audio signal.
The acoustic characteristic is, for example, the level of each frequency component of the audio
signal, or a value (Q value) representing the frequency value and the strength of level change
characteristics on both sides of the frequency. Such acoustic characteristics (frequency
characteristics of the target space) are generated from the speaker 31 using a predetermined
sound source (for example, a sound output using test signal generation software capable of
outputting sounds of various frequencies). The sound is detected by the microphone 38 installed
at the listening point and converted into an electric signal. The sound converted into the
electrical signal is transmitted to the control unit 36 through the interface 44, and the
characteristic measuring unit 35 and the control unit 36 determine whether the sound can be
heard by the human ear. The characteristic measuring unit 35 determines a frequency at which
the audio signal may be cut based on the measurement result. For example, in measurement of
acoustic characteristics, frequency components that can not be heard as sound in human ears are
recorded and stored in the storage unit 37.
[0051]
After performing such acoustic characteristic measurement in advance, the control unit 36
operates based on a preset program, and the band adjustment unit 34 operates based on the
temperature in the audio output unit 32 detected by the temperature detection unit 33. Perform
processing to control the operation of Specifically, similarly to the first embodiment, when the
detected temperature exceeds a predetermined temperature (for example, 100 ° C.), control is
performed to adjust the low band portion. Furthermore, control is performed so as to adjust the
signal level of the frequency outside the audibility range that is less affected by the audibility,
which is calculated based on the acoustic characteristics measured in advance.
[0052]
(Band Adjustment Processing) Hereinafter, the band adjustment processing in the audio
apparatus of the present embodiment will be described with reference to FIG. 7 showing an
example of the processing flow.
[0053]
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As an initial state, an audio signal from the audio source 39 is supplied to the audio output
amplification unit 32 through the interface 40, the band adjustment unit 34, and the interface
41, and audio is output from the audio output amplification unit 32 through the speaker 31. It
shall be.
Also, it is assumed that the acoustic characteristics of the target space have been measured in
advance.
[0054]
First, in step S21, data indicating the temperature detected by the temperature detection unit 33
is taken in via the amplifier 42 and the interface 43.
[0055]
In the next step S22, it is determined whether the detected temperature is higher than a
predetermined set temperature (for example, 100 ° C.) (YES) or not (NO) based on the taken-in
temperature data.
If the determination result is YES, the process proceeds to step S23. If the determination result is
NO, the present process flow ends.
[0056]
In the next step S23, the band adjustment unit 34 is controlled by the control signal from the
control unit 36 to adjust the low band portion of the audio signal. That is, the low cutoff
frequency is determined according to the aperture of the speaker, or the slope of the signal level
lower than the low cutoff frequency is determined, and the filter coefficients of the FIR filter
constituting the band adjustment unit 34 are adjusted. Set the low frequency cutoff frequency
and the slope of the signal level.
[0057]
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In the next step S24, the control signal from the control unit 36 causes the band adjustment unit
34 to adjust the signal level of a specific frequency (a frequency outside the audible range) based
on the acoustic characteristics of the target space measured in advance. Control to do. For
example, if measurement results are obtained that the audio signal in the frequency band (f11 to
f12) can not be heard by the human ear in the target space, the filter of the band adjustment unit
34 is configured to remove the signal in this frequency band. To do. Specifically, the filter
coefficients are appropriately set by the FIR filter and the LMS adaptive algorithm to construct a
band elimination filter.
[0058]
As described above, in the audio apparatus according to the present embodiment, the
temperature in the vicinity of the audio output amplifier 32 is detected, and when the
predetermined temperature is reached, the signal of the low frequency is removed or the signal
level is reduced. It is like that. Furthermore, signal levels of frequencies outside the pre-measured
audible range are adjusted. By performing such processing, it is possible to reduce the power
consumed in the audio output amplifier 32 and to suppress the generation of heat. Also, at this
time, because low frequency signals and signals of frequencies outside the audible range are
removed or the signal level is reduced, there is less influence on hearing compared to the case of
adjusting signals of other frequencies. Because the listener is not aware that the temperature
protection operation is in progress, the listener can listen to music and the like without
discomfort.
[0059]
It is a figure which shows an isometric curve. FIG. 1 is a block diagram schematically showing a
configuration of an audio device according to a first embodiment of the present invention. FIG.
3A is a diagram showing an example of the frequency characteristic of the speaker. FIG. 3 (b) is a
diagram showing the relationship between the low-frequency reproducible frequency and the
aperture of the speaker. It is a flowchart which shows an example of the audio signal processing
which the control part in FIG. 2 performs. It is a figure explaining the process which the control
part in FIG. 2 performs. It is a block diagram which shows roughly the structure of the audio
apparatus based on the 2nd Embodiment of this invention. It is a flowchart which shows an
example of the audio signal processing which the control part in FIG. 6 performs.
Explanation of sign
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[0060]
10, 30: Audio device 11, 11, 31: Speaker, 12, 32: Audio output amplification unit, 13, 33:
Temperature detection unit, 14: Low frequency adjustment unit (audio output processing unit),
15, 36: Control unit, 16, 37: storage unit 17, 39: audio source 34: band adjustment unit (audio
output processing unit) 38: microphone.
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