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JP2009118366

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DESCRIPTION JP2009118366
The present invention provides an acoustic reproduction apparatus capable of reproducing good
sound pressure frequency characteristics (flat sound pressure frequency characteristics) even at
a frequency at which a correction amount can not be set directly by an FIR filter. The sound
reproduction device corrects the sound pressure frequency characteristic of the output sound of
the speaker of the audio signal, and has a limited number of taps and a filter coefficient, and at
each frequency determined by the number of taps of the audio signal. An FIR de-filter 2 for
correcting the amount of correction determined by the filter coefficient with respect to the sound
pressure portion, and a cavity which is disposed on one of the front and rear surfaces of the
speaker 4 and which one surface faces It has a resonant opening 5b connected to a cavity, has a
resonant frequency which is different from each frequency determined by the number of taps,
causes the resonance of the resonant frequency by the output sound of the speaker 4 and causes
the speaker 4 to resonate. And Helmholtz resonance means 5 for enhancing and correcting the
sound pressure at the resonance frequency in the output sound of [Selected figure] Figure 1
Sound reproduction device
[0001]
The present invention relates to an audio reproduction apparatus that reproduces good acoustic
characteristics (sound pressure frequency characteristics) at a listening position.
[0002]
A conventional sound reproducing apparatus is a speaker system using a speaker unit that drives
a cone-type diaphragm, most of which is called a dynamic type, with a magnetic circuit. Such a
system includes the linearity and vibration of the speaker unit itself. Due to the cabinet (or
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enclosure) structure that confines the antiphase radiation emitted to the back side of the board,
and the installation structure of the speaker unit, etc., the sound pressure frequency
characteristics that are true (flat) to the original audio signal There were various factors that
inhibit reproduction.
[0003]
For example, when a cone type diaphragm is driven to reproduce sound, in order to reproduce
low frequency sound, it is necessary to drive the diaphragm with a long period and a large
amplitude, while high frequency sound is required. It is necessary to drive the diaphragm in a
short cycle and with a small amplitude to reproduce.
Therefore, when sound in a wide frequency band is sounded simultaneously, the high frequency
sound reaches the listening position more quickly, and the low frequency sound arrives late (that
is, the phases of those sounds at the listening position). Deviation of the sound quality such as
blurring of the sound image has occurred due to the occurrence of deviation).
[0004]
Also, for example, if the volume of the cabinet can not be secured sufficiently, the air pressure
inside the cabinet interferes with the drive of the diaphragm, the linearity with respect to the
audio signal is lost, or unnecessary resonance occurs due to standing waves generated inside the
cabinet Sound pressure frequency characteristics were disturbed.
[0005]
Further, for example, by providing a sound conduit and a perforated punching metal for
preventing collision damage on the front surface of the speaker unit, peaks and dips in the sound
pressure frequency characteristic due to a cabinet structure etc. or an acoustic low pass filter An
effect occurs and the output of the high range is attenuated, and the linearity with respect to the
audio signal is lost.
[0006]
As these improvement measures, conventionally, digital filters are used to correct the transfer
characteristics from the speaker to the listening position, and in particular, flatten and phase the
sound pressure frequency characteristics of the speaker system including the transfer space.
Attempts have been made to flatten the group delay characteristics, which means that the
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characteristics are linear, and reproduce the acoustic characteristics faithful to the original audio
signal.
[0007]
For example, using a non-recursive digital filter (FIR filter), the original audio signal is subjected
to correction based on the transfer characteristic corresponding to the inverse characteristic of
the sound pressure frequency characteristic from the speaker to the listening position. There is
one that corrects (Patent Document 2).
[0008]
In addition, for example, there is also one that corrects the sound pressure frequency
characteristic by inversely correcting the transfer function from the sound conduit on the front
of the speaker to the listening position, and eliminating the influence of the reproduction
characteristic of the speaker unit itself (Patent Literature 1).
[0009]
Also, for example, a tweeter unit that reproduces a high-pitched sound quickly reaching the
listening position exclusively to align the phase of the high-pitched area and the low-pitched area
at the listening position, behind a woofer unit specifically reproducing the low-pitched area Some
have a structure attached to (Non-patent Document 1).
[0010]
Also, for example, a bass reflex type speaker system using acoustic resonance is widely known as
a system for enhancing the bass range (Non-Patent Document 2).
[0011]
Moreover, in patent document 1, the sound reproduction apparatus which automates generation
| occurrence | production of the transmission characteristic corresponded to the reverse
characteristic of the sound pressure frequency characteristic from a speaker to a listening
position is shown.
[0012]
JP-A-8-228396 JP-A-58-50812 PoorAudio Life, SB-007 (Technics 007), "Search on July 24,
2007", Internet <URL: http://www.maugoten.com/ ~ kumayas / poor_audio / SB007 /
SB007.html> Takemoto Yamamoto, "Speaker System (bottom)" Radio Technology Co., Ltd., July
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15, 1977, p. 265-280
[0013]
In the conventional sound reproducing apparatus, as described above, the FIR filter is used to
perform correction on the audio signal based on the transfer characteristic corresponding to the
inverse characteristic of the sound pressure frequency characteristic from the speaker to the
listening position. Sound pressure frequency characteristics are corrected.
[0014]
However, the FIR filter generally has a multistage connection of basic elements (taps) in which a
delayer and a multiplier having filter coefficients are combined, and the resolution of the
correction of the sound pressure frequency characteristic is determined by the finite number of
taps. ing.
That is, the frequency at which the correction amount can be set directly by the FIR filter is
limited according to the number of taps.
Therefore, for frequencies where the correction amount can not be set directly by the FIR filter,
there is a problem that sound pressure frequency characteristics faithful to the original audio
signal can not be reproduced at the listening position.
[0015]
Further, since the frequency at which the correction amount can be set directly is limited by the
FIR filter, the sound reproduction frequency characteristics can not be reproduced well over a
wide band by expanding the bass reproduction range at the listening position. There was also a
point.
[0016]
The present invention has been made to solve the above-mentioned problems, and a first object
of the present invention is to provide a good sound pressure frequency characteristic (flat sound
even at a frequency at which the correction amount can not be set directly by the FIR filter). It is
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an object of the present invention to provide an acoustic reproduction device capable of
reproducing pressure frequency characteristics).
Another object of the present invention is to provide an acoustic reproducing apparatus capable
of reproducing a good sound pressure frequency characteristic over a wide band by expanding a
bass reproduction area.
[0017]
In order to solve the above problems, a first aspect of the present invention is an acoustic
reproduction device for correcting the sound pressure frequency characteristic of an output
sound from an audio signal speaker, which has a limited number of taps and a filter coefficient. A
non-recursive digital filter for performing correction of a correction amount determined by the
filter coefficient with respect to a sound pressure portion at each frequency determined by the
number of taps in the audio signal, and one of the front and rear surfaces of the speaker And a
resonant opening connected to the cavity, the resonant frequency being a frequency different
from the respective frequencies determined by the number of taps, the output sound of the
speaker The Helmholtz resonance hand, which causes the resonance of the resonance frequency
to increase and correct the sound pressure at the resonance frequency in the output sound of the
speaker by the resonance. It is those with a door.
[0018]
According to the first aspect of the present invention, an FIR filter and Helmholtz resonance
means are provided, and each frequency at which the resonance frequency of the Helmholtz
resonance means is determined by the number of taps of the FIR filter (that is, the correction
amount is set directly by the FIR filter) Because the frequency is set to a frequency different from
that of each possible), the sound pressure at each frequency at which the correction amount can
be set directly by the FIR filter can be corrected by the FIR filter, while the sound If the sound
pressure at the frequency where the amount can not be set is too low, enhancement correction
can be performed by Helmholtz resonance means, and thereby good sound pressure frequency
characteristics (flat sound pressure frequency characteristics over the entire reproduction area)
at the listening position It can be reproduced.
[0019]
Embodiment 1
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The sound reproducing apparatus according to this embodiment reproduces good sound
characteristics (sound pressure frequency characteristics) at the listening position, and as shown
in FIG. Filter coefficient holding means 9 such as a memory for holding filter coefficients for FIR
filter, and FIR filter 2 for correcting an audio signal input to the input terminal 1 based on the
filter coefficients held in the filter coefficient holding means 9; A power amplifier 3 for
amplifying an audio signal corrected by the FIR filter 2, a speaker 4 for outputting the audio
signal amplified by the power amplifier 3, and a porous punching plate 7 disposed on the front of
the speaker 4; A box-like cabinet (also referred to as an enclosure) 5a in which the speakers 4 are
disposed, and a bus formed in the cabinet 5a Fupoto (e.g. cylindrical opening) and a 5b.
[0020]
The speaker 4 is disposed on the front wall of the cabinet 5a such that the rear surface faces the
cavity 5c in the cabinet 5a.
The bass reflex port 5b is formed on the front wall of the cabinet 5a and functions as an opening
for resonance.
The Helmholtz resonance means 5 is constituted by the cabinet 5a and the bass reflex port 5b.
[0021]
That is, this sound reproducing apparatus corrects the sound pressure at the frequency that can
not be corrected by the FIR filter 2 in the sound pressure frequency characteristic by the
Helmholtz resonance means 5 to obtain a good sound pressure frequency characteristic (for
example, a bass reproduction region) at the listening position 8 Is reproduced to reproduce the
flattened sound pressure frequency characteristics) over a wide band.
[0022]
The punching plate 7 is, for example, a porous member provided on the front of the front panel
speaker in the case of a television, and is used for the purpose of protecting the speaker.
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The porous holes produce acoustical resistance and will have frequency characteristics.
Some of the speakers 4 do not have the punching plate 7 depending on the configuration of the
speakers 4.
[0023]
In FIG. 1, the symbol H 0 indicates a transfer function corresponding to the inverse characteristic
of the sound pressure frequency characteristic of the entire acoustic space from the speaker 4 to
the listening position 8, and the symbol H 1 indicates the inverse of the sound pressure
frequency characteristic of the speaker 4 A transfer function corresponding to the characteristic
is shown, a symbol H2 indicates a transfer function corresponding to the inverse characteristic of
the sound pressure frequency characteristic of the punching plate 7, and a symbol H3 indicates
the acoustic space from the front surface of the punching plate 7 to the listening position 8 The
transfer function corresponding to the inverse characteristic of the sound pressure frequency
characteristic is shown.
[0024]
As the above filter coefficient, coefficient data defining the transfer function H0 is used.
Thereby, the FIR filter 2 performs correction on the audio signal according to the transfer
function H0 (that is, the state of the entire acoustic space from the speaker 4 to the listening
position 8).
[0025]
The transfer function H0 may derive each transfer function H1, H2 and H3 separately and
connect them and derive them directly or may derive them directly.
Here, a method of deriving the transfer function H0 will be described by a method of deriving
directly based on FIG.
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[0026]
FIG. 2 is a schematic configuration diagram of a system for deriving the transfer function H0.
This system delays an audio signal input to the input terminal 20 to which an audio signal (for
example, an impulse signal, M-sequence noise, white noise, pink noise, etc.) is input, and the
input terminal 20 for a predetermined time Δt and outputs it. A delay 24, a power amplifier 11
for amplifying the audio signal inputted to the input terminal 20, a speaker 4 for outputting the
audio signal amplified by the power amplifier 11, and porosity provided in front of the speaker 4
A punching plate 7, a cabinet 5a in which the speakers 4 are disposed, a microphone 12 disposed
at the listening position 8 for collecting the output sound from the speakers 4, and a power
amplifier 13 for amplifying the output signal of the microphone 12 An adaptive filter 23 for
digitally filtering the output signal of the power amplifier 13; The difference between the output
signal and the output signal of the delay device 24 of the 23 calculated and an adder 27 for
outputting.
[0027]
More specifically, the adaptive filter 23 performs digital filtering on the output signal of the
power amplifier 13 so that the output signal of the adder 27 becomes minimum (value less than
a predetermined value) based on the output signal of the adder 27. It is carried out.
[0028]
The speaker 4, cabinet 5a, punching plate 7 and listening position 8 of this system are the same
(identical or reproduced) as the components 4, 5a, 7 and 8 of the sound reproducing apparatus
of FIG.
[0029]
That is, in this system, with respect to the audio signal input to the input terminal 20, the signal
passing through each of the components 11, 4, 7, 12, 13, 23 (that is, information of the original
audio signal and each component 4, 8) Between the signal including the information on the
acoustic space between them and the signal passing through the delay unit 24 (including only
the information of the original audio signal), and these two signals are generated by the adder
27. The difference of is calculated.
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At that time, the output signal of the power amplifier 11 is digitally filtered by the adaptive filter
23 so that the difference in the adder 27 is minimized.
Then, when the difference in the adder 27 is minimized, the signal obtained by the digital filter
processing of the adaptive filter 23 (a signal containing only information related to the acoustic
space between the components 48) is identified as the transfer function H0. .
In this manner, the transfer function H0 is directly obtained.
The coefficient data defining the transfer function H0 thus obtained is used as the abovementioned filter coefficient.
[0030]
In the digital filter processing of the adaptive filter 23, for example, the least mean square (LMS)
algorithm may be used.
[0031]
Here, although the target speaker system is incorporated into the system for deriving the transfer
function H0 and the adaptive filter 32 is operated in real time processing, this processing need
not be performed in real time, for example, the target speaker After data obtained by measuring
the impulse response characteristic of the system (not shown) is collected, it may be calculated
from the data by another system such as a PC (personal computer).
[0032]
The FIR filter 2 is configured by, for example, a DSP (digital signal processor) or the like.
For example, as shown in FIG. 3, the FIR filter 2 includes an input terminal 1, N delay elements
30 connected in series at a stage subsequent to the input terminal 1, an audio signal input to the
input terminal 1, and each delay element (N + 1) coefficient multipliers 31 for multiplying the
output signal branched from 30 and the output signal from the last delay unit 30 by constants
h0, h1,..., HN, and the outputs of these coefficient multipliers 31 And an adder 32 for adding the
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signals.
The filter coefficients held in the filter coefficient holding means 9 are used for the above
constants h0, h1,.
[0033]
With this configuration, the audio signal input to the input terminal 1 and the filter coefficient
held by the filter coefficient holding means 9 are convoluted to correct the sound pressure
frequency characteristics of the audio signal.
[0034]
The FIR filter 2 has a configuration in which basic elements (taps) C of the combination of the
delay unit 30 and the coefficient multiplier 31 are connected in multiple stages, and the
resolution of correction of the sound pressure frequency characteristic of the audio signal is
limited by the limited number of taps. It has been decided.
That is, the correction amount determined by the filter coefficient can be directly set only for the
frequency that is an integral multiple of the above resolution (that is, each frequency determined
by the number of taps). The correction amount can be directly corrected by the correction
amount set for each frequency.
[0035]
For example, in the case of correcting an audio signal of sampling frequency 48 kHz by FIR filter
2 with 256 taps, the resolution of the correction is 48 kHz / 256 = 187.5 Hz step, so the sound
pressure part at a frequency that is an integral multiple of the resolution Can be directly
corrected.
Although increasing the number of taps increases the resolution of correction, it increases the
computational load of the digital signal processor, so it is general to limit the design to a certain
number of taps.
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[0036]
For example, if the number of taps is set to 256 as described above, in the case of 48 kHz widely
used in DVD video audio signals, the resolution of correction becomes 187.5 Hz steps, which is
effective for bass reproduction called deep bass reproduction etc. For low frequencies lower than
100 Hz, where the frequency is lower than 100 Hz, the frequency is smaller than the resolution
of the correction, and the correction amount can not be set directly (that is, can not be corrected
directly).
In other words, a frequency located in the middle of the frequency at which the correction
amount can be set (for example, in the case of the used frequency of 48 kHz and the number of
taps 256), (2 · N-1) / 2 times 187.5 Hz (N = 1, 2, The correction amount can not be directly set
for 93.75 Hz, 281.25 Hz, 468.75 Hz, 656.25 Hz, and so on).
[0037]
In this sound reproducing apparatus, the sound pressure at the frequency at which the correction
amount can not be set directly by the FIR filter 2 is corrected by the Helmholtz resonance means
5 directly, so that a good sound pressure frequency at the listening position 8 It is designed to
reproduce the characteristics.
[0038]
The Helmholtz resonance means 5 has a resonance frequency determined by the mass of air in
the bass reflex port 5b corresponding to the weight of the spring vibration and the volume
(opening area x length) of the cabinet 5a corresponding to the spring of the spring vibration. ing.
The resonance frequency is set to a frequency different from each frequency (that is, each
frequency determined by the number of taps) for which the correction amount can be set directly
by the FIR filter 2.
The Helmholtz resonance means 5 causes the resonance of the above-mentioned resonance
frequency to occur by the output sound of the speaker 4, and the sound pressure at the abovementioned resonance frequency in the output sound of the speaker 4 is corrected by the
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resonance.
[0039]
In addition, since the method of designing said resonant frequency arbitrarily is described in the
nonpatent literature 2 in detail, the description is abbreviate | omitted here. Although the bass
reflex system using the bass reflex port 5b is taken as an example of the Helmholtz resonance
means 5 here, it is a passive radiator system that passively vibrates a diaphragm (also called a
drone cone) having no magnetic circuit. The same effect can be obtained.
[0040]
Next, a method of correcting the sound pressure frequency characteristic by the FIR filter 2 and
the Helmholtz resonance means 5 will be described with reference to FIG.
[0041]
The sound pressure frequency characteristic 40 of FIG. 4A is the target sound pressure
frequency characteristic to be obtained from this, and the bass reproduction range is expanded
and flattened over a wide band.
Further, the sound pressure frequency characteristic 41 omits the processing of the FIR filter 2
or gives the FIR filter 2 a filter coefficient such that the transfer characteristic of the transfer
function H0 becomes 1, and the enhancement correction effect by the Helmholtz resonance
means 5 Under the condition not to be added, the output sound of the speaker 4 is measured at
the listening position 8. As shown in the sound pressure frequency characteristic 41, generally,
the output sound of the speaker 4 has a peak with high sound pressure depending on frequency
or a dip with low sound pressure, and the linearity with respect to the input audio signal is
impaired .
[0042]
Note that fn in FIG. 4 indicates the lowest frequency among the frequencies for which the
correction amount can be set directly by the FIR filter 2. For example, in the case of correcting an
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audio signal with a sampling frequency of 48 kHz by the FIR filter 2 with 256 taps, the frequency
is 187.5 Hz.
[0043]
The sound pressure frequency characteristic 42 of FIG. 4 (b) shows the inverse characteristic of
the sound pressure frequency characteristic 41 of FIG. 4 (a), and is symmetrical with respect to
the sound pressure frequency characteristic 41 in which the peak and dip are inverted. These
characteristics are equivalent to the transfer characteristics of the transfer function H0 described
above.
[0044]
The sound pressure frequency characteristic 43 of FIG. 4C uses the coefficient data defining the
sound pressure frequency characteristic 42 of FIG. 4B (that is, the coefficient data defining the
transfer function H0) to generate an audio signal by the FIR filter 2 Is a sound pressure
frequency characteristic at the listening position 8 when correction is made.
[0045]
In the sound pressure frequency characteristic 43, for example, at the frequency fn, the
correction according to the correction amount set directly like the sound pressure level 44 is
performed on the audio signal, and the sound pressure frequency characteristic 40 of the target
is almost Similarly, correction is made to substantially match the sound pressure frequency
characteristic 40 of the target even at other frequencies where the correction amount can be set
directly, whereby the target sound is generated at frequencies above the frequency fn. The
pressure frequency characteristic 40 is flattened substantially in accordance.
However, since the frequency lower than the frequency fn is below the lower limit of the
frequency at which the correction amount can be set directly, the correction can not be
performed and remains considerably lower than the target sound pressure frequency
characteristic 40.
[0046]
The sound pressure frequency characteristic 45 in FIG. 4D is obtained by adding the
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enhancement correction effect by the Helmholtz resonance means 5 whose resonance frequency
is set to fr (<fn) to the sound pressure frequency characteristic 43 in FIG. 4C. It is a sound
pressure frequency characteristic at the listening position 8.
With this sound pressure frequency characteristic 45, the sound pressure at the frequency fr of
the output sound of the speaker 4 is enhanced like the sound pressure level 46 by the Helmholtz
resonance means 5 as compared to the sound pressure frequency characteristic 43 of FIG. By
being corrected, it is corrected that the frequency lower than the frequency fn substantially
matches the target sound pressure frequency characteristic 40. As a result, the sound pressure
frequency characteristic 45 is such that the bass reproduction range is expanded and flattened
over a wide band.
[0047]
According to the sound reproducing apparatus configured as described above, the FIR filter 2
and the Helmholtz resonance means 5 are provided, and each resonance frequency of the
Helmholtz resonance means 5 is determined by the number of taps of the FIR filter 2 (ie, the FIR
filter 2 Is set to a frequency different from that at which the correction amount can be set
directly, the sound pressure at each frequency at which the correction amount can be set directly
by the FIR filter 2 can be corrected by the FIR filter 2 On the other hand, if the sound pressure at
a frequency at which the correction amount can not be set directly by the FIR filter 2 is too low,
the Helmholtz resonance means 5 can perform an enhancement correction, whereby a good
sound pressure frequency characteristic (reproduction area Flat sound pressure frequency
characteristics) can be reproduced over the whole.
[0048]
Further, the resonance frequency of the Helmholtz resonance means 5 is lower than the lowest
frequency of the frequencies determined by the number of taps (that is, the frequencies at which
the correction amount can be set directly by the FIR filter 2). Can be expanded to reproduce good
sound pressure frequency characteristics over a wide band.
[0049]
In addition, the Helmholtz resonance means 5 includes a cabinet 5a on the front wall of which
the speaker 4 is disposed and a bass reflex port 5b formed on the front wall of the cabinet 5a. It
can be configured with a simple structure in which only the port 5b is provided.
[0050]
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In this embodiment, the value of the listening position 8 is not particularly described, but in the
case of a speaker for television, for example, although it is a position 3 to 5 meters away from the
speaker, the transfer function H0 is derived. In this case, the microphone 12 may be disposed at
a distance generally used in acoustic measurement such as a position near the speaker or a
position 1 meter away from the speaker instead of the listening position 8 to measure the sound
emitted from the speaker.
This is because as the distance from the speaker to the microphone 12 increases, the influence of
ambient noise and the influence of unnecessary radiation from the back of the cabinet increase.
[0051]
In this embodiment, as the Helmholtz resonance means 5, one composed of the cabinet 5a and
the bass reflex port 5b is used, but in general, it is disposed on one of the front and rear faces of
the speaker 4. Any Helmholtz resonance means may be used as long as it is a Helmholtz
resonance means having a cavity facing one surface and a resonance opening connected to the
cavity.
[0052]
Second Embodiment
In the sound reproducing apparatus according to this embodiment, as shown in FIG. 5, the
punching plate 7 is omitted in the first embodiment, and the Helmholtz resonance means 50 is
further added to the front of the speaker 4.
[0053]
This Helmholtz resonance means 50 is a sound conduit having a reverse horn shape (more
specifically, a shape in which the rear surface opening is disposed on the front surface of the
speaker 4 and the opening area is narrowed as it goes to the front surface opening 50a) Is
formed.
[0054]
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Like the Helmholtz resonance means 5, this Helmholtz resonance means 50 has a resonance
frequency determined by the mass of air near the opening 50a corresponding to the weight of
the spring vibration and the volume in the cavity corresponding to the spring of the spring
vibration. Have.
The Helmholtz resonance means 50 causes the resonance of the above-mentioned resonance
frequency to be generated by the output sound of the speaker 4 and the sound pressure at the
above-mentioned resonance frequency of the output sound of the speaker 4 is corrected by the
resonance.
The Helmholtz resonance means 50 can adjust the above-mentioned resonance frequency by
changing the volume of the cavity and the length and opening area of the opening 50a.
[0055]
Reference H2a in FIG. 5 denotes a transfer function corresponding to the inverse characteristic of
the sound pressure frequency characteristic of the Helmholtz resonance means 50, and reference
H3a denotes the sound in the acoustic space from the front of the Helmholtz resonance means
50 to the listening position 8. A transfer function corresponding to the inverse characteristic of
the pressure frequency characteristic is shown, and a code H0a indicates a transfer function
corresponding to the inverse characteristic of the sound pressure frequency characteristic of the
entire acoustic space from the speaker 4 to the listening position 8.
In this embodiment, the coefficient data defining the transfer function H0a is held in the filter
coefficient holding means 9 as a filter coefficient.
[0056]
Incidentally, a porous punching plate may be provided on the front surface of the Helmholtz
resonance unit 50 to prevent foreign matter mixing into the Helmholtz resonance unit 50 or for
design reasons, or a support for supporting the Helmholtz resonance unit 50 for reinforcement
purpose. It may be provided. The frequency characteristic generated in that case is added to the
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transfer function H0a.
[0057]
Next, a method of correcting the sound pressure frequency characteristic using the FIR filter 2
and the Helmholtz resonance means 5 and 50 will be described with reference to FIG.
[0058]
The sound pressure frequency characteristic 70 in FIG. 7A is the target sound pressure frequency
characteristic to be obtained from this, and the bass reproduction range is expanded and
flattened over a wide band.
Further, the sound pressure frequency characteristic 71 omits the processing of the FIR filter 2
or gives the FIR filter 2 a filter coefficient such that the transfer characteristic of the transfer
function H0a becomes 1, and the enhancement of the Helmholtz resonance means 5, 50 Under
the condition that the correction effect is not added, the output sound of the speaker 4 is
measured at the listening position 8.
[0059]
When sound in the middle to high range higher than the resonance frequency of the Helmholtz
resonance means 50 is emitted from the Helmholtz resonance means 50 and can be heard at the
listening position 8, as shown by the sound pressure frequency characteristic 71, The output
sound of 4 has a peak where the sound pressure is highly disturbed depending on the frequency
or a dip where the sound pressure is poorly disturbed, and the linearity with respect to the input
audio signal is lost. In particular, unnecessary peaks and dips such as standing waves appear as
high-order resonances by the Helmholtz resonance means 50. In FIG. 7, as an example, dips are
shown at frequency fr2 between the respective frequencies fn1 and fn2. The frequencies fn1 and
fn2 in the figure respectively indicate the lowest frequency and the second lowest frequency of
the respective frequencies for which the correction amount can be set directly by the FIR filter 2.
For example, in the case of correcting an audio signal with a sampling frequency of 48 kHz by
the FIR filter 2 with 256 taps, fn1 = 187.5 Hz and fn2 = 375 Hz.
[0060]
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The sound pressure frequency characteristic 72 of FIG. 7 (b) shows the inverse characteristic of
the sound pressure frequency characteristic 71 of FIG. 7 (a), and is symmetrical with respect to
the sound pressure frequency characteristic 71 in which the peak and dip are inverted. These
characteristics correspond to the transfer characteristics of the transfer function H0a described
above.
[0061]
The sound pressure frequency characteristic 73 of FIG. 7C uses the coefficient data defining the
sound pressure frequency characteristic 72 of FIG. 7B (that is, the coefficient data defining the
transfer function H0a) to generate an audio signal by the FIR filter 2 Is a sound pressure
frequency characteristic at the listening position 8 when correction is made.
[0062]
In the sound pressure frequency characteristic 73, for example, at each of the frequencies fn1
and fn2, correction corresponding to the correction amount set directly as the sound pressure
levels 74 and 75 is performed on the audio signal, thereby achieving the target sound. The
correction is made to substantially match the pressure frequency characteristic 70, and similarly,
it is corrected to substantially match the target sound pressure frequency characteristic 70 at
other frequencies for which the correction amount can be set directly, whereby At the frequency,
the sound pressure frequency characteristic 70 of the target is flattened to substantially match.
[0063]
However, at frequencies such as frequency fr2 where there is a large dip, and frequencies below
the lower limit of frequencies where the correction amount can be set directly, such as
frequencies lower than frequency fn1, the frequency is not sufficiently corrected and the target
Compared to the sound pressure frequency characteristic 70, it remains considerably lower.
[0064]
In such a case, for example, for the dip of the frequency fr2, the sound pressure level of the
frequency fr2 may be concomitantly increased by further increasing the sound pressure level 74,
75 of the frequency fn1 or fn2 in the vicinity thereof. Although possible, this will result in a peak
significantly exceeding the target sound pressure frequency characteristic 70 at the increased
frequency fn1 or fn2.
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Also, such excessive correction by the FIR filter 2 is not desirable because it causes excessive
energy to the speaker 4 and causes damage.
[0065]
The sound pressure frequency characteristic 76 of FIG. 7 (d) is the sound pressure frequency
characteristic 73 of FIG. 7 (c), with the enhancement correction effect by the Helmholtz
resonance means 5 whose resonance frequency is set to fr1 (<fn1) It is a sound pressure
frequency characteristic in listening position 8 at the time of adding the intensive amendment
effect by Helmholtz resonance means 50 set to fr2.
In this sound pressure frequency characteristic 76, compared with the sound pressure frequency
characteristic 73 of FIG. 7C, the Helmholtz resonance means 5 and 50 cause the frequency fr1 of
the output sound of the speaker 4 like the sound pressure levels 77 and 78. , Fr 2 is enhanced so
that the sound pressure frequency characteristic 70 of the target is almost matched even at
frequencies near the frequency fr 2 and frequencies lower than the frequency f n 1.
As a result, the sound pressure frequency characteristic 76 is such that the bass reproduction
range is expanded and flattened over a wide band.
[0066]
According to the sound reproducing apparatus configured as described above, in addition to the
same effects as in the first embodiment, since two Helmholtz resonance means 5 and 50 are
provided on both sides of the speaker, the FIR filter 2 is obtained. Even if the sound pressure is
too low at two of the frequencies (fr1 and fr2 in this case) among the frequencies for which the
correction amount can not be set directly, the Helmholtz resonance means 5 and 50 can perform
enhancement correction, respectively. Even in such a case, good sound pressure frequency
characteristics (flat sound pressure frequency characteristics over the entire reproduction area)
can be reproduced at the listening position 8.
The Helmholtz resonance means 50 is effective for correction when a standing wave is generated
and a large dip occurs in the sound pressure frequency characteristic.
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[0067]
Further, since the Helmholtz resonance means 50 is formed in a reverse horn shape, it can be
formed with a simple structure, and the presence of the speaker 4 is concealed by narrowing the
opening area so that a more stylish design is possible.
[0068]
In this embodiment, the Helmholtz resonance means 50 has been described as a sound pipe
having a reverse horn shape, but the present invention is not limited to such a shape.
For example, it may be a sound conduit having a horn shape (i.e., a shape in which the rear
surface opening is disposed on the front surface of the speaker 4 and whose opening area is
expanded to reach the front surface opening). Alternatively, it may be a sound conduit having a
box shape (for example, a box shape in which the front surface of the speaker 4 is disposed in the
opening formed on the rear surface and the cylindrical opening 50a is formed on the front
surface as shown in FIG. 6) . With such a shape, the Helmholtz resonance means 50 can be
formed with a simple structure.
[0069]
Further, in this embodiment, of the frequencies for which the correction amount can be set
directly by the FIR filter 2, the enhancement correction by the Helmholtz resonance means 50 is
performed on the intermediate frequency between the lowest frequency and the second lowest
frequency. However, it does not matter if it is performed for other intermediate frequencies.
[0070]
In this embodiment, the relationship between the resonance frequencies fr1 and fr2 of the
Helmholtz resonance means 5 and 50 is set as fr1 <fr2, but it may be set as fr1> fr2 or fr1 = fr2.
[0071]
In this embodiment, the Helmholtz resonance means 50 and 5 are provided on the front and rear
faces of the speaker 4, respectively. However, the Helmholtz resonance means 5 on the rear face
of the speaker 4 is eliminated (for example, the bass reflex port 5b The Helmholtz resonance
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means 5 may not be functional, so that only the Helmholtz resonance means 50 on the rear
surface of the speaker 4 may be removed.
In that case, the same effect as that of the first embodiment is obtained.
[0072]
Third Embodiment
The sound reproducing apparatus according to this embodiment is the one in which a resonator
80 is further added to the cabinet 5 in the first embodiment as shown in FIG.
[0073]
The resonator 80 is formed in a box shape having, for example, a cylindrical opening 80 a on one
surface (for example, the front surface) thereof.
[0074]
Like the Helmholtz resonance means 5, this resonator 80 has a resonance frequency (sound
absorption frequency) determined by the mass of air near the opening 80a corresponding to the
weight of the spring vibration and the volume in the box corresponding to the spring of the
spring vibration. )have.
The resonance frequency is set to a frequency different from each frequency (that is, each
frequency determined by the number of taps) for which the correction amount can be set directly
by the FIR filter 2. The resonator 80 resonates the above-mentioned resonance frequency with
the output sound of the speaker 4 and consumes the acoustic energy of the above-mentioned
output sound as heat energy, whereby the sound pressure at the above-mentioned resonance
frequency in the output sound of the speaker 4 To reduce the correction.
[0075]
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21
The symbol H 0 b in FIG. 8 indicates a transfer function corresponding to the inverse
characteristic of the sound pressure frequency characteristic of the entire acoustic space from
the speaker 4 to the listening position 8. In this embodiment, the coefficient data defining the
transfer function H0b is held in the filter coefficient holding means 9 as a filter coefficient.
[0076]
Next, a method of correcting the sound pressure frequency characteristic using the FIR filter 2,
the Helmholtz resonance means 5, and the resonator 80 will be described with reference to FIG.
[0077]
The sound pressure frequency characteristic 90 of FIG. 9A is the target sound pressure
frequency characteristic to be obtained from this, and the bass reproduction range is expanded
and flattened over a wide band.
The sound pressure frequency characteristic 91 omits the processing of the FIR filter 2 or gives
the FIR filter 2 a filter coefficient such that the transfer characteristic of the transfer function
H0b becomes 1, and the enhancement correction effect by the Helmholtz resonance means 5 and
The output sound of the speaker 4 is measured at the listening position 8 under the condition
that the reduction correction effect by the resonator 80 is not added.
[0078]
As shown in the sound pressure frequency characteristic 91, generally, the output sound of the
speaker 4 has a peak with high sound pressure depending on frequency and a dip with low
sound pressure, and the linearity with respect to the input audio signal is impaired. . In
particular, unnecessary peaks and dips such as standing waves appear as high-order resonances
by the Helmholtz resonance means 50. In FIG. 9, as an example, a peak is shown at the frequency
fr3 between the frequencies fn1 and fn2. Note that frequencies fn1 and fn2 in the figure
respectively indicate the lowest frequency and the second lowest frequency of the respective
frequencies for which the correction amount can be set directly by the FIR filter 2. For example,
in the case of correcting an audio signal with a sampling frequency of 48 kHz by the FIR filter 2
with 256 taps, fn1 = 187.5 Hz and fn2 = 375 Hz.
08-05-2019
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[0079]
The sound pressure frequency characteristic 92 of FIG. 9 (b) shows the inverse characteristic of
the sound pressure frequency characteristic 91 of FIG. 9 (a), and is symmetrical with respect to
the sound pressure frequency characteristic 91 in which the peak and dip are inverted. These
characteristics are equivalent to the transfer characteristics of the transfer function H0b
described above.
[0080]
The sound pressure frequency characteristic 93 shown in FIG. 9C uses the coefficient data
defining the sound pressure frequency characteristic 92 shown in FIG. 9B (that is, the coefficient
data defining the transfer function H0b) to generate an audio signal by the FIR filter 2 Is a sound
pressure frequency characteristic at the listening position 8 when correction is made.
[0081]
In the sound pressure frequency characteristic 93, for example, at each of the frequencies fn1
and fn2, correction corresponding to the correction amount set directly as the sound pressure
levels 94 and 95 is performed on the audio signal, thereby achieving the target sound. The
pressure frequency characteristic 90 is corrected so as to substantially match, and similarly, even
at other frequencies where the correction amount can be set directly, it is corrected so as to
substantially match the sound pressure frequency characteristic 90 of the target. At the
frequency, the sound pressure frequency characteristic 90 of the target is flattened to
substantially match.
[0082]
However, the frequency which is below the lower limit of the frequency where the correction
amount can be set directly, such as a frequency with a large top such as frequency fr 3 or a
frequency lower than frequency f n 1 is not sufficiently corrected. Compared to the sound
pressure frequency characteristic 70, it remains considerably high or quite low.
[0083]
In such a case, for example, for the top of the frequency fr3, the sound pressure level at the
frequency fr3 may be additionally reduced by further reducing the sound pressure levels 94 and
95 at the frequency fn1 or fn2 in the vicinity thereof. Although it is possible, this will result in a
dip significantly below the target sound pressure frequency characteristic 90 at the reduced
frequency fn1 or fn2.
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[0084]
The sound pressure frequency characteristic 96 of FIG. 9 (d) is based on the sound pressure
frequency characteristic 93 of FIG. 9 (c), and the resonance correction effect by the Helmholtz
resonance means 5 whose resonance frequency is set to fr1 (<fn1) It is a sound pressure
frequency characteristic in listening position 8 at the time of adding the reduction amendment
effect by resonator 80 which set sound absorption frequency to fr3.
With this sound pressure frequency characteristic 96, the sound pressure at the frequency fr1 of
the output sound of the speaker 4 is enhanced like the sound pressure level 97 by the Helmholtz
resonance means 5 as compared to the sound pressure frequency characteristic 93 of FIG. The
sound pressure at the frequency fr3 of the output sound of the speaker 4 is reduced and
corrected by the resonator 80 as well as the sound pressure level 98 by the resonator 80, so that
the target sound is generated near the frequency fr3 and lower than the frequency fn1. It is
corrected so as to substantially match the pressure frequency characteristic 90.
As a result, the sound pressure frequency characteristic 96 is such that the bass reproduction
range is expanded and flattened over a wide band.
[0085]
According to the sound reproducing apparatus configured as described above, in addition to
obtaining the same effect as the case of the first embodiment, the acoustic reproducing apparatus
further includes the resonator 80, and the resonance frequency of the resonator 80 is the
number of taps of the FIR filter 2. When the sound pressure at a frequency at which the
correction amount can not be set directly by the FIR filter 2 is too high because the frequency is
set to a frequency different from each determined frequency (that is, each frequency at which the
correction amount can be set directly by the FIR filter 2) However, reduction and correction can
be performed by the resonator 80, whereby good sound pressure frequency characteristics (flat
sound pressure frequency characteristics over the entire reproduction region) can be reproduced
at the listening position 8.
In particular, it is effective for correction when a standing wave is generated and a large dip is
generated in the sound pressure frequency characteristic as in the case where the Helmholtz
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resonance means 50 of reverse horn shape or the like is provided.
[0086]
In this embodiment, among the frequencies for which the correction amount can be set directly
by the FIR filter 2, the resonator 80 corrects the intermediate frequency between the lowest
frequency and the second lowest frequency. You may carry out to the middle frequency other
than them.
[0087]
In this embodiment, although the resonator 80 is disposed in the cabinet 5, it may be disposed
on the outer wall of the speaker 4, or may be separately installed in the listening room as an
independent structure. When the Helmholtz resonance means 50 is provided on the front surface
of the speaker 4 in the same manner, it may be disposed in the Helmholtz resonance means 50.
[0088]
FIG. 1 is a schematic view of the configuration of a sound reproduction device according to a first
embodiment.
FIG. 7 is a diagram for explaining a method of deriving a transfer function in the first
embodiment.
FIG. 2 is a schematic configuration diagram of a general FIR filter 2;
FIG. 6A is an example diagram of sound pressure frequency characteristics in the first
embodiment, and FIG. 7A is a diagram showing a target sound pressure frequency characteristic
40 at the listening position 8 and a sound pressure frequency characteristic 41 before correction;
b) shows the sound pressure frequency characteristic 42 which is the inverse characteristic of
the sound pressure frequency characteristic 41, and (c) shows the sound when only the FIR filter
2 is corrected with respect to the sound pressure frequency characteristic 41. FIG. 6D is a
diagram showing pressure frequency characteristics 43, and FIG. 7D is a diagram showing sound
pressure frequency characteristics 45 when the FIR filter 2 and the Helmholtz resonance means
5 are corrected with respect to the sound pressure frequency characteristics 41. .
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FIG. 7 is a schematic view of the configuration of a sound reproduction device according to a
second embodiment. FIG. 16 is a cross-sectional view of a modification of the Helmholtz
resonance means 50 of the second embodiment. FIG. 7A is an example diagram of sound
pressure frequency characteristics in the second embodiment, and FIG. 8A is a diagram showing
a target sound pressure frequency characteristic 70 at the listening position 8 and a sound
pressure frequency characteristic 71 before correction; b) shows the sound pressure frequency
characteristic 72 which is the reverse of the sound pressure frequency characteristic 71. FIG. 7
(c) shows the sound when only the FIR filter 2 is corrected with respect to the sound pressure
frequency characteristic 71. FIG. 8D is a diagram showing pressure frequency characteristics 73,
and FIG. 7D is a diagram showing sound pressure frequency characteristics 45 when the FIR
filter 2 and the Helmholtz resonance means 5 and 50 are corrected with respect to the sound
pressure frequency characteristics 71. It is. FIG. 10 is a schematic view of the configuration of a
sound reproduction device according to a third embodiment. FIG. 14A is an example diagram of
sound pressure frequency characteristics in the third embodiment, and FIG. 15A is a diagram
showing a target sound pressure frequency characteristic 90 at the listening position 8 and a
sound pressure frequency characteristic 91 before correction; b) shows the sound pressure
frequency characteristic 92 which is the inverse characteristic of the sound pressure frequency
characteristic 91, and (c) shows the sound when only the FIR filter 2 is corrected with respect to
the sound pressure frequency characteristic 91. (D) shows the sound pressure frequency
characteristic 96 when the FIR filter 2, the Helmholtz resonance means 5 and the lysogen 80 are
corrected with respect to the sound pressure frequency characteristic 91. FIG.
Explanation of sign
[0089]
DESCRIPTION OF SYMBOLS 1 audio signal input terminal, 2 FIR filter, 3 power amplifier, 4
speakers, 5 Helmholtz resonance means, 5a cabinet, 5b bass reflex port, 5c cavity, 7 punching
plate, 8 listening position, 9 filter coefficient holding means, 10 input terminals, DESCRIPTION
OF SYMBOLS 11 power amplifier, 12 microphones, 13 power amplifiers, 20 input terminals, 23
adaptive filters, 24 delay units, 30 delay units, 31 coefficient multipliers, 32 adders, 50
Helmholtz resonance means (reverse horn shaped sound conduit), 50a Opening, 80 resonator, C
tap, H0 to H3, H0a to H3a, H0b to H3b transfer function.
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