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JP2012094942

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DESCRIPTION JP2012094942
An object of the present invention is to reduce the influence of individual differences in virtual
sound field reproduction and to allow natural sounds to be heard from outside. A left headphone
body (120L) and a right headphone body (120R) have a speaker array (130) comprising a
plurality of speaker units (131) arranged so as to surround the pinna. The speaker arrays 130
and 130 of the headphone bodies 120L and 120R reproduce the sound field in the closed curved
surfaces 140L and 140R near the pinna by the wavefront synthesis method. The sound field in
the closed surface in the vicinity of the pinna is reproduced by the wave field synthesis method
by the speaker array 130, and the reflection and diffraction effects occur in the individual's ear,
so the influence by the individual difference hardly occurs. Become. In addition, the speaker
array 130 is composed of a plurality of speaker units 131 arranged so as to surround the pinna,
so that it is possible to naturally listen to the external sound instead of the shape blocking the
listener's ear. . [Selected figure] Figure 1
Headphone device
[0001]
The present invention relates to a headphone device, and more particularly to a headphone
device provided with a speaker array composed of a plurality of speaker units.
[0002]
Conventionally, various studies have been conducted as sound field reproduction methods.
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As for speaker reproduction, surround reproduction such as 5.1ch and 7.1ch is generally
proposed and commercialized. The advantage of this method is that not only the front, but also
the speakers called rear surround can be used to realistically reproduce the back and the
environmental sound.
[0003]
However, in this surround reproduction, there is a problem regarding the listening position that
the service area at the center of installation is the best sound field reproduction point and the
reproduction ideal position is limited. In addition, in this surround reproduction, there is a
problem with the speaker installation that it is difficult to arrange the speaker behind in an actual
home.
[0004]
There is a front surround using a transaural method as a measure to the problem about a
speaker installation. In this front surround, it is possible to enjoy virtual surround using head-tohead transfer functions using only the front speakers. The advantage of this approach is that the
speakers are easy to install and the system is simple. On the other hand, since the head related
transfer function is used, there is a problem that the effect varies depending on individuals. In
addition, even with this method, there is a problem regarding the listening position that the
reproduction ideal position is limited.
[0005]
There is also a sound field reproduction method using wavefront synthesis as a measure for the
problem related to the listening position (Non-Patent Document 1). This method is a method in
which the sound field in the closed surface can be completely controlled if the speaker array is
configured and the sound pressure in the form of a closed surface without a sound source and
the particle velocity in the normal direction can be completely controlled. By using the sound
field reproduction method using the wavefront synthesis, the sound field in the closed surface is
completely reproduced, and the freedom of the listening position is also increased.
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[0006]
For example, Patent Document 1 describes a three-dimensional sound field reproduction
apparatus in which a plurality of speakers of a speaker array is configured to cover the entire
head of a listener and can reproduce high reality. However, in this three-dimensional sound field
reproducing apparatus, since it is necessary to configure an array using a large number of
speakers, there is a problem that the scale becomes large. Further, in the case of using a speaker
array, there is a problem that the frequency band to be reproduced is limited by the speaker
interval due to the problem of space aliasing.
[0007]
On the other hand, on the other hand, in the field of headphone reproduction, there is virtual
surround using head related transfer functions. With this virtual surround, it is possible to enjoy
an ideal sound field with a handy headphone device, and there is no problem with the listening
position.
[0008]
JP, 2008-118559, A
[0009]
Waseda University Research Center for Science and Technology, Acoustics Information
Processing Laboratory, Yoshio Yamazaki, "Study on 3D Virtual Reality Based on Kirchhoff
Integral Equation", [online], April 1997, [October 1, 2010] ], Internet <URL: http:
www.coust.rise.waseda.ac.jp/publications/happyou/1997-h9.html>
[0010]
However, as described above, in virtual surround using head related transfer functions in the
field of headphone reproduction, the sound pressure in the vicinity of the entrance of the ear
canal is reproduced in "points", thus taking into account the influence of the individual's pinna
There is a problem that you can not do this and some individuals can not get the ideal effect.
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Further, in general, since the headphones are shaped to block the ears, there is also a problem
that although external sense can be obtained in virtual surround, external sounds can not be
heard.
[0011]
An object of the present invention is to provide a headphone device which is less likely to be
affected by individual differences in virtual sound field reproduction and which can naturally
hear external sounds.
[0012]
The concept of the present invention comprises: a speaker array consisting of a plurality of
speaker units arranged to surround the pinna, and the speaker array reproduces the sound field
in the closed surface near the pinna by the wavefront synthesis method. Yes in the headphone
device.
[0013]
In the present invention, a speaker array is provided.
The speaker array comprises a plurality of speaker units arranged to surround the pinna.
Then, the sound field in the closed curved surface in the vicinity of the pinna is reproduced by
the wavefront synthesis method by this speaker array.
In this case, sound pressure signals for respectively emitting sound for reproducing the sound
field in the closed curved surface near the pinna are supplied as driving signals to the plurality of
speaker units of the speaker array.
[0014]
As described above, in the present invention, the sound field in the closed surface in the vicinity
of the pinna is reproduced by the wavefront synthesis method by the speaker array, and the
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reflection and diffraction effects occur in the individual's ear, The influence of individual
differences is less likely to occur. Further, in the present invention, the speaker array is
composed of a plurality of speaker units disposed so as to surround the pinnae, and it is possible
to naturally listen to the external sound, not the shape blocking the listener's ear. It becomes
possible.
[0015]
In the present invention, for example, the plurality of speaker units of the speaker array may be
disposed so as to be inclined inward toward the closed surface. Thereby, the propagation velocity
of particles in each direction such as upper and lower and right and left can be well reproduced
in the closed surface. For example, it further has a toroidal-shaped ear pad having an opening
into which the pinna can be inserted, and the plurality of speaker units of the speaker array are
disposed along the circular end opposite to the listener contact side of the ear pad Be done.
[0016]
In the present invention, for example, when the maximum reproduction frequency is fmax [Hz]
and the sound speed is c [m / s], the interval Δd [m] between the plurality of speaker units of the
speaker array is Δd <c / ( The equation 2 · fmax is satisfied. This enables the reproduction of the
frequency band up to the maximum reproduction frequency fmax [Hz] without being affected by
the spatial aliasing.
[0017]
According to this invention, it is difficult for the influence of the individual difference to occur in
the virtual sound field reproduction, and it is possible to naturally listen to the external sound.
That is, in the speaker array, the sound field in the closed surface in the vicinity of the pinna is
reproduced by the wavefront synthesis method, and the reflection and diffraction effects occur in
the individual's ear. It becomes difficult. In addition, the speaker array is composed of a plurality
of speaker units arranged to surround the pinna, and it is possible to naturally listen to the
external sound instead of the shape blocking the listener's ear.
[0018]
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It is a figure showing an example of composition of a headphone device as an embodiment of this
invention. It is a figure which shows an example of the closed surface where the sound field is
reproduced by the speaker array which a headphone main body has. It is a figure for
demonstrating that the several speaker unit of the speaker array which a headphone main body
has inclines inward toward the closed curve which reproduces an acoustic field, and is arrange ¦
positioned. It is a figure for demonstrating that the several speaker unit of a speaker array is
arrange ¦ positioned along the circular edge part on the opposite side to the listener contact side
of an ear pad. It is a figure for demonstrating the arrangement ¦ positioning space ¦ interval of
several speaker units of the speaker array which a headphone main body has. It is a block
diagram which shows the example of a circuit structure which supplies a sound pressure signal
to each speaker unit of the speaker array which a headphone main body has.
[0019]
Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments
will be described. The description will be made in the following order. 1. Embodiment 2.
Modified example
)
[0020]
<1. Embodiment> [Configuration Example of Headphone Device] FIGS. 1A to 1C show a
configuration example of a headphone device 100 according to an embodiment. 1 (a) is a top
view, FIG. 1 (b) is a front view, and FIG. 1 (c) is a side view. The headphone device 100 has a
configuration in which a left headphone main body 120L and a right headphone main body
120R are connected to the left and right end portions of the headband 110.
[0021]
The left headphone main body 120L has a speaker array 130. The speaker array 130 is
composed of a plurality of speaker units 131 arranged to surround the listener's pinna (left side).
The speaker array 130 included in the left headphone main body 120L reproduces the sound
field in the closed curved surface 140L near the pinna (left side) shown in FIG. A plurality of
speaker units 131 of the speaker array 130 of the left headphone main body 120L have sound
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pressure signals for emitting sound at respective positions as drive signals so that the sound field
in the closed curved surface 140L can be reproduced. Supplied.
[0022]
The right headphone main body 120R also has a speaker array 130. The speaker array 130 is
composed of a plurality of speaker units 131 disposed so as to surround the auricle (right side)
of the listener. The speaker array 130 included in the right headphone main body 120R
reproduces the sound field in the closed curved surface 140R near the pinna (right side) shown
in FIG. 1B by the wavefront synthesis method. A plurality of speaker units 131 of the speaker
array 130 of the right headphone main body 120R have sound pressure signals for emitting
sound at respective positions as drive signals so that the sound field in the closed surface 140R
can be reproduced. Supplied.
[0023]
As for the wave-field synthesis method, detailed explanation is omitted, but, for example, as
shown in "Yamasaki Yoshio," Study on 3D virtual reality based on Kirchhoff integral equation ",
the Kirchhoff integral formula is used. There is a method etc. In this method, the sound field in
the closed surface S is obtained by discretizing the closed surface S at N points and reproducing
the sound pressure P (rj) and the particle velocity un (rj) at N points on the closed surface S.
Reproduce In this embodiment, the sound pressure signal supplied to each speaker unit 131 of
the speaker array 130 of the headphone bodies 120L and 120R is generated based on such a
wavefront synthesis method.
[0024]
FIG. 2A shows an example of a closed curved surface 140L in which a sound field is reproduced
by the speaker array 130 of the left headphone main body 120L. The closed curved surface
140L is a narrow region having a diameter of 8 to 10 cm centering on the ear canal as viewed
from the side of a human (listener). FIG. 2B shows the positional relationship between the left
headphone main body 120L and the closed curved surface 140L when the headphone 100 is
worn. Although a detailed description is omitted, the closed surface 140R in which the sound
field is reproduced by the speaker array 130 of the right headphone main body 120R is similarly
a narrow area having a diameter of 8 to 10 cm centering on the ear canal.
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[0025]
The plurality of speaker units 131 of the speaker array 130 included in the headphone bodies
120L and 120R are, as shown in FIG. 3, inclined inward toward the closed curved surfaces 140L
and 140R where the sound field is to be reproduced. That is, the central axis S of each speaker
unit 131 is inclined with respect to the central axis Z of the speaker array 130. As described
above, by arranging the plurality of speaker units 131 of the speaker array 130 in an inclined
manner, the propagation velocity of particles in each direction such as upper, lower, right, and
left in the closed curved surfaces 140L and 140R can be well reproduced. Is possible.
[0026]
Although not shown in FIG. 1 described above, the headphone bodies 120L and 120R have a
toroidal-shaped ear pad 150 having an opening into which the pinna can be inserted. As shown
in FIG. 4, the plurality of speaker units 131 of the speaker array 130 described above are
disposed along the circular end 150 a of the ear pad 150 on the side opposite to the listener
contact side.
[0027]
The plurality of speaker units 131 of the speaker array 130 included in the headphone main
bodies 120L and 120R are disposed with an interval of Δd [m] as shown in FIG. This interval Δd
[m] is set so as to satisfy the following equation (1) when the reproduction maximum frequency
is fmax [Hz]. However, c is the speed of sound (about 340 m / s). This enables the reproduction
of the frequency band up to the maximum reproduction frequency fmax [Hz] without being
affected by the spatial aliasing. Δd <c / (2 · fmax) (1)
[0028]
In general, spatial aliasing is a problem in wavefront synthesis systems. From the concept of
spatial sampling, aliasing occurs at a frequency that is the speed of sound divided by twice the
interval, and the reproducible boundary frequency is determined. For example, if arranged at 5
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cm intervals, about 3.4 kHz would be the frequency of spatial aliasing. This is a very low
frequency compared to the human audible band of 20 kHz. The spatial aliasing frequency f alias
[Hz] is expressed by the following equation (2). falias = c / (2 · Δd) (2)
[0029]
When the interval is narrowed, the upper limit of the frequency rises, which means that the
sound pressure emitted from the speaker unit 131 also decreases, and there is a trade-off
relationship between space aliasing and sound pressure, which is difficult in sound reproduction
of a large room etc. . However, in the headphone device 100, since the speaker array 130 is in
the vicinity of the pinna, even a small speaker unit 131 can present sufficient sound pressure to
the listener. For example, when an 8 mm ultra-small speaker unit is used, Δd = 0.008 m.
Therefore, according to equation (2), the spatial aliasing frequency f alias becomes 20 kHz or
more, and sufficient sound field reproduction is possible.
[0030]
FIG. 6 shows an example of the circuit configuration of the headphone main body 120 (120L,
120R). The sound pressure signal corresponding to each speaker unit 131 of the speaker array
130 is supplied to the headphone main body 120 from the sound pressure signal output unit
160. The sound pressure signal is generated on the basis of the wavefront synthesis method as
described above. For example, this sound pressure signal can be obtained by collecting sound
with a microphone disposed at each speaker unit position. Also, for example, this sound pressure
signal can be obtained by performing conversion processing on multi-channel signals such as 5.1
ch and 7.1 ch.
[0031]
The headphone main body 120 includes a digital filter unit 121, a D / A converter 122, and an
amplifier circuit 123 together with the speaker array 130. The sound pressure signal
corresponding to each speaker unit 131 from the sound pressure signal output unit 160 is
subjected to filter processing by the digital filter unit 121, and then is transmitted to the speaker
array 130 via the D / A converter 122 and the amplifier circuit 123. Supplied.
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[0032]
For example, the filter processing in the digital filter unit 121 is filter processing for area control.
In this case, the sound radiated from each of the speaker units 131 of the speaker array 130 is
made to be a sound at a position slightly inside of the position of the speaker unit 131, and the
influence of space aliasing is reduced. Also, for example, the filter processing in the digital filter
unit 121 is filter processing for correcting the characteristics of each speaker unit 131.
[0033]
As described above, in the headphone device 100 shown in FIG. 1, the sound field in the closed
curved surfaces 140L and 140R in the vicinity of the pinna is reproduced by the wavefront
synthesis method with the speaker array 130 of the headphone bodies 120L and 120R.
Therefore, the reflection and diffraction effects occur in the individual's ear, making it difficult
for the influence of individual differences to occur in virtual sound field reproduction. That is,
compared to speaker reproduction, individual differences can be eliminated with a simple system
configuration of headphone type.
[0034]
Further, in the headphone device 100 shown in FIG. 1, the speaker array 130 included in the
headphone bodies 120L and 120R is composed of a plurality of speaker units 131 arranged so
as to surround the pinna. Therefore, it is possible to naturally hear the external sound, not the
shape that blocks the listener's ear. As a result, an effect combining the virtual sound field and
the sound field in the real world, which can not be achieved by the conventional headphone
device, is also possible, and natural conversation between two parties is also possible while
wearing the headphone device.
[0035]
<2. Modified Example> In the above-described embodiment, the speaker array 130 included
in the headphone main bodies 120L and 120R has a plurality of speaker units 131 arranged in a
circle. However, the arrangement shape may not necessarily be circular, and may be oval, square,
or any other arrangement shape. The point is that it should be arranged so as to surround the
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pinna. Further, in the above-described embodiment, the speaker arrays 130 included in the
headphone bodies 120L and 120R are illustrated as having a plurality of speaker units 131
arranged in a single circle, but may be arranged in two or three. Conceivable.
[0036]
100 ... headphone device 110 ... head band 120 ... headphone body 120 L ... left headphone body
120 R ... right headphone body 121 ... digital filter section 122 ... D / A converter 123 · · ·
Amplifier circuit 130 ··· Speaker array 131 ··· Speaker unit 140L, 140R · · · Closed curved surface
150 · · · Ear pad 150a · · · · circular end portion 160 · · · sound pressure signal output section
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