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JP2002010398

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JP2002010398
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sound field correction method for improving the feeling of stagnation of a sound field in a closed
space, and an audio apparatus for realizing the sound field correction, and in particular A sound
field that can significantly improve the feeling of stagnation in a closed space by suppressing the
occurrence of the rise of the sound pressure level of even-order harmonic components caused by
the lowest frequency standing wave that significantly affects The present invention relates to a
correction method and an audio device for realizing the sound field correction.
[0002]
In a sound field in a closed space such as a passenger compartment, the presence of a standing
wave causes a sense of stagnation. From now on, it is necessary to reduce the standing wave and
to improve the feeling of soundness of the sound field.
[0003]
2. Description of the Related Art As described in Japanese Patent Application Laid-Open No. 8331682, as shown in FIG. 5, a standing wave corresponding to the size of the passenger
compartment space (shown in FIG. 5). The thing is a standing wave of the lowest frequency,
which is a standing wave that greatly affects the sound quality.
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[0004]
From now on, at the position of the node of this standing wave, the phenomenon that the sound
pressure level of that frequency is depressed (dipping occurs) occurs.
[0005]
Then, as can be seen from FIG. 6, the sound pressure level of the even-order harmonic overtone
component of that frequency rises (a peak occurs) at the position of the node of this standing
wave, and the node of this standing wave At the position of, the phenomenon that the sound
pressure level of the odd-order harmonic overtone component of the frequency is depressed
occurs.
[0006]
As described in JP-A-7-131884, this low-frequency standing wave (about 80 Hz in the case of a
cabin space) will give a sense of stagnation.
[0007]
In the invention described in Japanese Patent Application Laid-Open No. 8-331682, in order to
prevent the occurrence of the depression of the sound pressure level due to the standing wave, a
speaker is disposed in the vicinity of the viewing position where the sound pressure level is
depressed. By outputting the sound of the depressed frequency component of the sound pressure
level to the speaker, a method is employed in which the sound at the viewing position becomes
close to the original sound.
[0008]
On the other hand, the invention described in Japanese Patent Application Laid-Open No. 7131884 also aims to improve the feeling of stagnation by arranging a speaker for bass
reproduction at the node position of the lowest frequency standing wave. .
[0009]
As described above, in the prior art, the standing wave generated in the closed space is reduced
by suppressing the generation of the depression of the sound pressure level generated by the
standing wave. This is a method to improve the feeling of sound of the sound field.
[0010]
On the other hand, as described above, when the sound pressure level is depressed due to the
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standing wave, a phenomenon occurs in which the sound pressure level of the even-order
harmonic overtone component of the frequency rises.
[0011]
However, in the prior art, no measures have been taken to reduce the standing wave by
suppressing the generation of the rise of the sound pressure level of the even-order harmonics
component.
[0012]
From now on, according to the prior art, there is a problem that the standing feeling of the sound
field in the closed space can not be sufficiently improved because the standing waves can not be
sufficiently reduced.
[0013]
The present invention has been made in view of the above circumstances, and is intended to be
closed by suppressing the generation of the rise of the sound pressure level of the even-order
overtone component caused by the lowest frequency standing wave which greatly affects the
feeling of stagnation. It is an object of the present invention to provide a new sound field
correction method capable of significantly improving the feeling of stagnation in a sound field in
a space, and to provide a new audio device for realizing the sound field correction.
[0014]
SUMMARY OF THE INVENTION In order to achieve the object, according to the sound field
correction method of the present invention, a speaker is supplied to a speaker in order to
improve the feeling of stagnation in a closed space. From the audio signal, the frequency
component below the specified frequency that can accept the noise component during
reproduction is extracted, the even-order harmonic component of the lowest frequency standing
wave included in the extracted frequency component is extracted, and they are added. The
distortion of the added signal is corrected, the audio signal is corrected by subtracting the signal
corresponding to the corrected signal, and the signal is processed to be supplied to the speaker.
[0015]
As described above, according to the present invention, since the processing is performed so as
to suppress the generation of the rise of the sound pressure level of the even-order overtone
component caused by the lowest frequency standing wave which greatly affects the feeling of
stagnation, the standing wave is By being able to reduce significantly, it will be possible to greatly
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improve the feeling of stagnation that the sound field in a closed space has.
[0016]
Then, the improvement of the feeling of stagnation can be realized only by adding a simple
circuit function without preparing a special speaker and without arranging the speaker in a
special position.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in
detail below according to an embodiment.
[0018]
An exemplary embodiment of the present invention is illustrated in FIG.
[0019]
As shown in this figure, in the vehicle compartment, the front left and right audio signals output
from the car stereo 5 are normally amplified using the amplifier 3 and the two left and right
front speakers disposed in the vehicle compartment While outputting to 1, it amplifies the audio
signal of the rear left and right output from the car stereo 5 using the amplifier 4 and outputs it
to the two left and right rear speakers 2 disposed in the vehicle compartment. There is.
[0020]
According to the present invention, when such a configuration is adopted, signal processing
circuit 6 is newly provided, and rear left and right audio signals output from car stereo 5 are
signaled by this signal processing circuit 6. After processing, amplification is performed using the
amplifier 4 and this is output to the rear speaker 2.
[0021]
One embodiment of the signal processing circuit 6 is shown in FIG.
[0022]
As shown in this figure, the signal processing circuit 6 selects frequency components lower than
7 to 12 KHz, which is a frequency that can tolerate noise components during reproduction, from
the rear left and right audio signals output from the car stereo 5. A low pass filter 60 for taking
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out, an adder 61 for extracting and adding even-order harmonic components of the lowest
frequency standing wave included in the output signal of the low pass filter 60, and a phase
inverting circuit for inverting the phase of the output signal of the adder 61 62, while shifting the
output signal of the phase inversion circuit 62 by about 5 to 16 ms (a correction value according
to the distance between the left and right speakers, which corresponds to a half wavelength of
the lowest frequency standing wave) − A delay circuit 63 for mixing about 4 to -8 db, a
distortion factor correction circuit 64 for compensating distortion of the signal mixed by the
delay circuit 63, distortion factor correction The signal corrected by the circuit 64 is attenuated
by -6 to -12 db and input to the amplifier 4, and the signal is added to the rear left and right
audio signals output from the car stereo 5 (because the phase is inverted, it becomes subtraction
And an attenuator 65).
[0023]
Here, the delay circuit 63 is prepared in order to improve the dip due to the lowest frequency
standing wave and to synthesize naturally for frequencies higher than that.
[0024]
The distortion factor correction circuit 64 is prepared to cope with the fact that the output signal
of the adder 61 has distortion because the cutoff frequency of the low pass filter 60 is as high as
7 to 12 KHz. It processes so that distortion which the signal mixed with the delay circuit 63 has
may be correct | amended according to the feedback structure of this.
[0025]
Further, the reason why the signal mixed by the delay circuit 63 is attenuated by -6 to -12 db
using the attenuator 65 is that the attenuation of -12 db or less is not effective, and -6 db or
more Attenuation of is likely to cause unnatural regeneration.
[0026]
One embodiment of the adder 61 is illustrated in FIG.
[0027]
As shown in this figure, if the adder 61 represents the frequency of the lowest frequency
standing wave as f 0, then n band pass filters 610-i (i = 1 to n: where n is the maximum value of
integers satisfying “2 n f 0 <7 to 12 KHz” and an adder circuit 611 that adds the output
signals of those band pass filters 610-i.
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[0028]
According to this configuration, adder 61 performs processing for extracting and adding evenorder harmonic overtone components of the lowest frequency standing wave contained in the
output signal of low pass filter 60.
[0029]
Here, since the frequency f0 can be calculated from the size of the cabin space (approximately 80
Hz), the controller (not shown) can set the parameters of the band pass filter 610-i according to
the vehicle type given. Will be processed as you set up.
[0030]
The feeling of stagnation (lack of feeling of spread) in the vehicle interior is considered to be
caused by the runaway of the mid-high frequency characteristics, and the runaway of the midhigh frequency characteristics is the low frequency standing wave, especially the lowest
frequency. It is thought that there is also the influence of standing waves of
[0031]
Therefore, in the present invention, the frequency component that rises due to the lowest
frequency standing wave, that is, the even-order overtone component of the lowest frequency
standing wave is extracted, mixed in the original sound while being attenuated in reverse phase.
In order to eliminate the bulging part, it is configured to be corrected.
[0032]
Incidentally, for the frequency components depressed by the lowest frequency standing wave,
that is, the odd-order harmonic components of the lowest frequency standing wave, since an
increase in noise is expected when amplified, special processing is not performed. .
[0033]
That is, in the present invention configured as described above, 7 to 12 KHz, which is a
frequency that allows noise components during reproduction, from the rear left and right audio
signals output from the car stereo 5 using the low pass filter 60. The lower frequency component
is extracted, and the even-order harmonic component of the lowest frequency standing wave
included in the output signal of the low pass filter 60 is extracted and added using the adder 61.
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[0034]
Then, the phase inversion circuit 62 is used to invert the phase of the output signal of the adder
61, and the delay circuit 63 is used to apply about 5 to 16 ms to the output signal of the phase
inversion circuit 62. Mix -4 to -8 db while shifting.
[0035]
Then, the distortion correction circuit 64 is used to correct the distortion of the signal mixed by
the delay circuit 63, and the attenuator 65 is used to correct the signal corrected by the
distortion correction circuit 64. The signal is attenuated by 12 db and input to the amplifier 4 to
correct the left and right rear audio signals output from the car stereo 5.
[0036]
According to this configuration, according to the present invention, it is possible to eliminate the
buildup of even-order harmonic overtone components caused by the lowest frequency standing
wave that greatly affects the feeling of stagnation, thereby achieving the standing wave in the
vehicle compartment. The effect of the noise can be reduced significantly, and this can greatly
improve the feeling of stagnation in the sound field in the passenger compartment.
[0037]
FIG. 4 illustrates the results of experiments conducted to verify the effectiveness of the present
invention.
[0038]
In this experiment, microphones are disposed in an actual vehicle interior provided with two
front speakers 1 on the left and two rear speakers 2 on the left and right, and pink noise signals
are output to these speakers, and collected at that time. Performed by Fourier-transforming the
acoustic signal of the microphone.
[0039]
The upper part shows experimental data when the correction process of the present invention is
not performed, and the lower part shows experimental data when the correction process of the
present invention is performed.
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The portion shown in the figure corresponds to the lowest frequency standing wave.
[0040]
From this experimental data, it can be understood that the use of the present invention makes it
possible to prevent the occurrence of the depression of the sound pressure level of the lowest
frequency standing wave itself, and to obtain a smooth curve as a whole. It turns out that
This verified the effectiveness of the present invention.
[0041]
Although the present invention has been described according to the illustrated embodiment, the
present invention is not limited thereto.
For example, although the signal processing circuit 6 for realizing the present invention is
provided between the car stereo 5 and the amplifier 4 in the embodiment example, the signal
processing circuit 6 may be incorporated in the car stereo 1 Is also possible.
[0042]
Although not particularly described in the embodiment, the signal processing circuit 6 for
realizing the present invention can be realized by full digital signal processing.
[0043]
In the embodiment, the audio signal output to the rear speaker 2 is subjected to the signal
processing by the signal processing circuit 6, but the audio signal output to the front speaker 1 is
processed for the audio signal. May be adopted.
[0044]
As described above, in the present invention, processing is performed so as to suppress the
generation of the rise of the sound pressure level of the even-order overtone component caused
by the lowest frequency standing wave which greatly affects the feeling of stagnation. Thus, by
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being able to significantly reduce standing waves, it is possible to significantly improve the
feeling of stagnation in a closed space.
[0045]
Then, the improvement of the feeling of stagnation can be realized only by adding a simple
circuit function without preparing a special speaker and without arranging the speaker in a
special position.
[0046]
Brief description of the drawings
[0047]
1 is an example embodiment of the present invention.
[0048]
2 is an example embodiment of the signal processing circuit.
[0049]
FIG. 3 is an example embodiment of an adder.
[0050]
4 is an explanatory view of the experimental results conducted to verify the effectiveness of the
present invention.
[0051]
5 is an explanatory view of a standing wave.
[0052]
6 is an explanatory view of a standing wave.
[0053]
Explanation of sign
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[0054]
DESCRIPTION OF SYMBOLS 1 front speaker 2 rear speaker 3 amplifier 4 amplifier 5 car stereo 6
signal processing circuit 60 low pass filter 61 adder 62 phase inverting circuit 63 delay circuit
64 distortion factor correction circuit 65 attenuator
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