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JP2012119842

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DESCRIPTION JP2012119842
The present invention provides a flat speaker which can reproduce the sound quality of a
conventional speaker and which can be reduced in thickness, size and weight. A carrier wave
generating unit generates a carrier wave of an ultrasonic frequency band modulated by an
acoustic signal in an audio frequency band, and a diaphragm 2 which vibrates by the carrier
wave and reproduces an acoustic signal. The ultrasonic wave generating elements are arranged
in an array, and the ultrasonic wave generating elements are driven and controlled according to
the acoustic signal, and the diaphragm 2 is emitted from the carrier wave generating unit and
propagates in the space between the ultrasonic wave generating elements 7 The carrier wave is
oscillated and the carrier wave is reflected. [Selected figure] Figure 2
Flat speaker
[0001]
The present invention relates to a flat loudspeaker driven by a digital signal.
[0002]
In recent years, demands for thinner, smaller, and lighter electronic devices equipped with
speakers have become stronger, and conventional cone-type speakers have become unable to
satisfy these requirements.
In addition, although digitization of signals is in progress, it has been necessary to convert a
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digital signal into an analog signal and drive it when driving a speaker. On the other hand, there
has been proposed a speaker for obtaining audio in the audio frequency band by arranging
transducers as ultrasonic generating elements on an array and directly driving them with a
digital signal of clock frequency in the ultrasonic band. For example, Patent Document 1
discloses a speaker that converts an ordinary digital signal into a primary digital signal, drives a
plurality of transducers according to the number of bits of the signal in a positive direction or a
negative direction, and obtains analog sound. There is. Further, for example, Patent Document 2
discloses a digital speaker configured to drive and control with a digital signal by arraying
transducers formed by MEMS technology.
[0003]
On the other hand, transducers of ultrasonic generating elements are arranged in an array, from
which ultrasonic waves modulated by acoustic signals in the audio frequency band are emitted
and reproduced into audio signals in the audio frequency band by the nonlinear effect of the
transmission medium (air). For example, Patent Document 3 discloses a technique of configuring
a so-called parametric speaker.
[0004]
The difference between the above digital speaker and the parametric speaker is that in the digital
speaker, the ultrasonic waves emitted from the respective transducers overlap, and as a result,
sound waves of audible frequency are generated to work as a speaker, while the parametric
speaker The sound is obtained on the different principle that the modulation signal is selfdemodulated by the non-linear effect of air and the sound in the audible range is reproduced
while ultrasonic waves are propagating.
[0005]
Patent No. 3492698 U.S. Patent No. 7089069 Patent No. 4285537
[0006]
In a conventional digital speaker, as described above, ultrasonic waves are emitted from a
plurality of minute transducers (ultrasound generating elements), and sound waves vibrating in
the ultrasonic area overlap to obtain audio frequency audio signals. It has become.
Therefore, since the ultrasonic wave is radiated into the air which is the transmission medium,
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the vibration in the air is different from the vibration of the original acoustic signal.
In addition, there has been a drawback that it is necessary to consider including an acoustic
reduction filter for removing ultrasonic waves in order to prevent adverse effects on animals and
the like, although they can not be heard by humans.
[0007]
In addition, the array requires a large number of transducers according to the number of bits,
requires an area, and does not operate with the operating ultrasound generating element among
a plurality of ultrasound generating elements in a certain moment The presence of the ultrasonic
wave generating element causes a problem that the overlapping of the emitted ultrasonic waves
changes with each reproduction time and is not localized at one point.
In addition, as the minimum volume was approached, the number of transducers driven in the
array was reduced, and the problem that the sound waves did not overlap well was likely to
occur. Alternatively, since each transducer is driven in the positive and negative directions by a
clock signal in the ultrasonic range, but is not always driven, a wide flat frequency characteristic
is required of the transducers, and the flat frequency characteristic is usually Since the
transducer is difficult to obtain, there is a problem that it impairs the sound fidelity.
[0008]
In the conventional parametric speaker, the reproduced sound is generated due to the non-linear
effect of the transmission medium, so that the sound pressure distribution is biased to the
negative sound pressure side, and there is a problem that the sound is such that the listener feels
uncomfortable. In addition, the sharp directivity determined by the propagation direction of
ultrasound is its feature, and it has a great advantage in the field where it can take advantage of
the feature of providing audio information to a specific person, but it is not specified like
ordinary analog speakers. It could not be used for the purpose of telling many people.
[0009]
An object of the present invention is to provide a flat speaker capable of solving the abovementioned problems and reproducing the sound quality of a conventional analog speaker, and
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being thin, compact and lightweight.
[0010]
In order to achieve the above object, the invention according to claim 1 of the present application
is a carrier generation unit for generating a carrier wave of an ultrasonic frequency band
modulated by an acoustic signal in an audio frequency band, and vibrating by the carrier wave to
reproduce the sound signal. The carrier wave generation unit includes a plurality of ultrasonic
wave generating elements arranged in an array, and the ultrasonic wave generating elements are
driven and controlled according to the acoustic signal, and the vibration board includes the
vibration plate. While being vibrated by the carrier wave emitted from the carrier wave generator
and propagated through the space between the ultrasonic wave generating element and the
diaphragm, the carrier wave is reflected.
[0011]
According to a second aspect of the present invention, in the flat loudspeaker according to the
first aspect, the ultrasonic wave generating element is formed on a first substrate, and overlaps
with the first substrate or the first substrate. A switch element for connecting the ultrasonic wave
generation element and a drive power source is formed on a second substrate, and drive control
of the ultrasonic vibration element is performed by controlling opening and closing of the switch
element. .
[0012]
According to the present invention, ultrasonic waves are not superimposed on reproduced sound,
and nonuniformity caused by overlapping of ultrasonic waves can be eliminated. Therefore, a
speaker capable of faithfully reproducing an acoustic signal (original sound) is provided. Can.
[0013]
Further, since the acoustic signal is reproduced by the vibration of the diaphragm and is not
generated by the overlapping of ultrasonic waves as in the conventional example, it is not
necessary to be based on the vibration frequency of the ultrasonic wave generating element.
There is an advantage that the reproduction sound of the band of can be obtained.
This reproduced sound does not cause the sound pressure distribution to be biased to the
negative sound pressure side due to the non-linear effect of the transmission medium, so the
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listener does not feel uncomfortable.
[0014]
Furthermore, the ultrasonic wave generating element is formed on the first substrate, and the
switch element formed between the ultrasonic wave generating element and the drive power
supply supplied to the ultrasonic wave generating element is also formed on the same first
substrate. Alternatively, since it can be formed over a second substrate overlapping with the first
substrate, it is suitable for reduction in thickness, size, and weight.
In this case, since drive control of the ultrasonic wave generation element may be control of the
switch element, there is also an advantage that it is easy to adjust.
[0015]
It is a figure explaining the flat speaker of this invention.
It is another figure explaining the flat speaker of this invention.
[0016]
The flat speaker of the present invention generates a carrier wave (ultrasound) in an ultrasonic
frequency band in accordance with an acoustic signal in an audible frequency band such as a
voice or an audio signal at a carrier wave generator.
The carrier wave generation unit arranges a plurality of ultrasonic wave generation elements in
an array. Then, the diaphragm is disposed at a predetermined interval so as to face the plurality
of ultrasonic wave generating elements. The diaphragm is made of a material that is significantly
different from the acoustic impedance of the transmission medium between the ultrasonic
generating elements, specifically, the air. Furthermore, the diaphragm is arranged such that the
carrier wave (ultrasound) is not reflected by the diaphragm and propagates in the direction of the
listener who can hear the reproduced sound.
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[0017]
According to this structure, when a carrier wave (ultrasonic wave) modulated by an acoustic
signal is emitted from the ultrasonic wave generation element, the ultrasonic wave propagates in
the space in the vicinity and reaches the diaphragm. In this diaphragm, acoustic radiation
pressure is generated by the non-linear effect of the carrier wave (ultrasound). The magnitude of
this acoustic radiation pressure is proportional to the energy intensity of the carrier wave
(ultrasound). As a result, the diaphragm vibrates in the traveling direction of the carrier wave,
and the acoustic signal is reproduced. At this time, the ultrasonic waves are mostly reflected due
to the difference in acoustic impedance, so they do not reach the listener's ear.
[0018]
As described above, since the reproduction of the acoustic signal is caused by the displacement
of the diaphragm, the change in overlapping of the ultrasonic waves due to the presence of the
active element and the inactive element among the plurality of ultrasonic wave generating
elements is It has no effect on the localization of the sound. Further, since the vibration
frequency of the acoustic signal can also be adjusted by the displacement of the diaphragm, the
vibration frequency of the ultrasonic wave generating element is not limited and there is an
advantage that a wide band signal can be obtained.
[0019]
As described above, according to the present invention, as in the conventional speaker, the sound
signal is reproduced by the displacement of the diaphragm, so that the sound quality of the
conventional speaker can be reproduced, and the thickness and size can be reduced. , Can be
reduced in weight. Hereinafter, specific embodiments will be described in detail.
[0020]
FIG. 1 is an explanatory view of a flat speaker of the present invention. FIG. 2 is an explanatory
view of a portion constituting the flat speaker of the present invention. As shown in the figure, 1
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is an ultrasonic wave generation element portion in which a plurality of ultrasonic wave
generation elements are arranged in an array, 2 is a diaphragm, 3 is a housing, 4 is a diaphragm
2 displaceable to the housing 3 A connection portion to be held, 5 is a switch element portion,
and 6 is a drive circuit portion. The ultrasonic wave generating element unit 1 is composed of a
plurality of ultrasonic wave generating elements 7, and can be formed of, for example, cMUT
(Capacitive Micromachined Ultrasonic Transducer) or the like. The switch element unit 5 is
composed of a plurality of switch elements 8 connected to the plurality of ultrasonic wave
generating elements 7 respectively. The drive circuit unit 6 includes an ultrasonic wave
generation element power supply 9 for driving the ultrasonic wave generation element 7 and a
switch element controller 10 for controlling the opening and closing of the switch element 8.
[0021]
As shown in FIG. 1, in the traveling direction of the carrier wave (ultrasonic wave) emitted from
the ultrasonic wave generating element unit 1, the diaphragm 2 is disposed so as to block the
traveling. The diaphragm 2 is held displaceably by being connected to the housing 3 by a
connecting portion 4 formed of, for example, a weak spring. The dimension between the
diaphragm 2 and the ultrasonic wave generation element unit 2 is adjusted so that the energy of
the propagation wave (ultrasound) reliably reaches the diaphragm 2 and can be reproduced
faithfully. Further, by making the size of the diaphragm 2 larger than that of the ultrasonic wave
generating element units 1 arranged in an array, the energy of the propagation wave
(ultrasound) can be reliably transmitted to the diaphragm 2. The diaphragm 2 is made of a
material that is largely different from the acoustic impedance of the space in which the carrier
wave travels, and it is necessary to reproduce a good sound quality, so it is preferable to select a
hard and light material like a conventional speaker.
[0022]
The ultrasonic wave generating elements 7 arranged in an array are driven and controlled by
controlling the opening and closing of the switch elements 8 constituting the switch element unit
5.
[0023]
As shown in FIG. 2, when the ultrasonic wave generating element 7 is formed of, for example,
cMUT, upper and lower electrodes and the like to be a vibrating film are formed on a silicon
semiconductor substrate using ordinary semiconductor device processing technology. be able to.
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The ultrasonic wave generating element 7 can be formed by processing a silicon substrate using
silicon micromachine technology as well as cMUT. Similarly, the switch element 8 is also formed
on the same silicon semiconductor substrate, or formed on another silicon substrate overlapping
the silicon semiconductor substrate, and both are electrically connected, which is suitable for
reduction in size, thickness and weight. .
[0024]
The drive control of the ultrasonic wave generation element unit 1 by the switch element unit 5
is performed in such a manner that one ultrasonic wave generation element 7 is connected to
one ultrasonic wave generation element 7 and one ultrasonic wave generation element 7 is
connected. The switch element 8 may be connected. In the latter case, the number of switches
can be a number according to the number of bits of the digital signal, for example, 255 for 8 bits,
65,535 for 16 bits, or an integral multiple thereof.
[0025]
As shown in FIG. 2, switching of the switch element 8 is controlled by the switch element
controller 10, and a propagation wave (ultrasound) is emitted to space from the ultrasonic wave
generation element 7 connected to the ultrasonic wave generation element power supply 9. . The
propagating wave (ultrasonic wave) emitted to the space reaches the diaphragm 2 and pushes
the diaphragm 2 with acoustic radiation pressure. At this time, the intensity of the propagation
wave (ultrasound) emitted is proportional to the number of ultrasonic wave generating elements
7 connected to the ultrasonic wave generating element power supply 9. Therefore, the
connection portion 4 may be adjusted so that the displacement amount of the diaphragm 2 is
proportional to the number of ultrasonic wave generation elements connected to the ultrasonic
wave generation element power supply. For example, when the connection part 4 is comprised
with a spring, it may adjust so that a spring constant may become a range which shows a linear
characteristic.
[0026]
Due to the temporal change of the displacement of the diaphragm 2, air in the vicinity of the
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diaphragm 2 vibrates, and an acoustic signal in the audio frequency band is reproduced. This is
the same as the conventional speaker reproduction method, and reproduction can be realized as
in the conventional case. At this time, the transmission wave (ultrasound) in which the diaphragm
2 is displaced does not pass through the diaphragm 2. Therefore, only the sound reproduced by
the diaphragm 2 is transmitted to the air, so that the original acoustic signal can be faithfully
reproduced.
[0027]
In order to vibrate the diaphragm 2 uniformly, it is preferable to control so that the operating
ultrasonic wave generating elements 7 are uniformly dispersed among the ultrasonic wave
generating elements 7 formed in an array. In addition, the number of operating ultrasound
generating elements can be adjusted according to the frequency band of the acoustic signal to be
reproduced, the volume, and the like.
[0028]
The ultrasonic wave generated from the ultrasonic wave generation element needs to be higher
than the frequency of the signal for operating the switch element controller 10. However, since
ultrasonic waves have higher attenuation in air as the frequency is higher, approximately 2 MHz
or so is preferable.
[0029]
1: Ultrasonic wave generation element part 2: 2: Diaphragm 3: 3: Housing 4: 4: Connection part
5: Switch element part 6: 6: Drive circuit part 7: 7: Ultrasonic wave generation element 8: Switch
element Power supply for acoustic wave oscillator, 10: switch element controller
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