JP2005333497

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DESCRIPTION JP2005333497
PROBLEM TO BE SOLVED: A voice of a plurality of speakers can be naturally spread over a
substantially entire range of a sound field with a sense of presence, and each speaker can fully
understand the content of the other speakers' speech Provision of electroacoustic devices.
SOLUTION: An electroacoustic apparatus D1 includes a plurality of microphones M1, M2, ..., Mn,
a mixing unit 11, a first speaker 15, an automatic gain adjustment unit 12, and the plurality of
microphones M1 and M2. ,..., And Mn are provided with electroacoustic transducers S1, S2,. The
mixing means 11 combines output signals of the plurality of microphones M1, M2,..., Mn to
generate a combined signal. The first speaker 15 converts the synthesized signal into voice. The
automatic gain adjustment means 12 applies a gain to the combined signal and automatically
adjusts the gain in accordance with the level of the combined signal. The electroacoustic
transducers S1, S2,..., Sn convert the output signal of the automatic gain adjustment means 12
into speech. [Selected figure] Figure 3
Electro-acoustic device
[0001]
The present invention provides electricity separately for providing the user of the microphone as
a voice separately as well as providing the person other than the user of the microphone as a
voice as a synthesized signal obtained by combining the output signals of a plurality of
microphones. It relates to an acoustic device.
[0002]
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In addition to combining the output signals of a plurality of microphones, converting the
combined signal into voice and individually providing it to the user of the microphone, it is also
required to provide the combined signal as voice to persons other than the user of the
microphone. There is a sound field.
A typical example is a conference hall.
[0003]
For example, if a congressional meeting is held in a congress hall, members of this congress will
be participants in the meeting. In a conference hall, there may be a listener, for example, in a
hearing seat besides a member who is a participant in the conference.
[0004]
The statements of each member participating in the conference must be told to other members
and the listener. In addition, each member of the meeting must attend the statement of the other
members clearly.
[0005]
Therefore, each seat may be provided with a device called a speaker unit.
[0006]
The speaker unit is provided with a microphone and a small speaker.
The speech of each member is received by the microphone of the speaker unit, and is loudened
from the speaker of the speaker unit of the seat of the other member.
[0007]
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In addition, the speech of each member of the Diet is received by the microphone of the speaker
unit, and is also loudened from the speaker for providing voice over substantially the entire area
of the conference hall. As a result, not only other legislators but also the listeners can hear the
remarks.
[0008]
In a meeting, there are cases where a small number of members speak at the same time
(including the case where only one member speaks), and there are also cases where many
members speak at the same time. When a small number of members speak at the same time, the
level is small even if the voices of all the speakers are synthesized. When a large number of
members speak at the same time, the level becomes large when the voices of all the speakers are
synthesized.
[0009]
The listeners would like to hear the contents of the conference in a natural voice as well as
listening to the statements of each deputy. Therefore, it is desirable that the voices of all the
members who speak are synthesized from the speaker that provides the voice over substantially
the entire area of the conference hall, and the synthesized voice is naturally amplified without
processing.
[0010]
However, if the voices of all the members of the legislator are synthesized and the synthesized
voice is amplified from the speaker of the speaker unit without processing it, the speech may be
difficult to hear. One of the causes is that the speaker of the speaker unit is small. In other words,
although the speaker unit generally has a volume for adjusting the volume of the speaker, if it is
assumed that a small number of members will speak, the number of members will be adjusted.
The speaker's loud sound may be distorted when speaking. In addition, if this volume is adjusted
on the assumption that a large number of members will speak, a situation may occur where the
loud sound from the speaker is too small when a small number of members speak. Moreover,
although this problem may be avoided by adjusting the volume each time according to the
number of speakers, such volume adjustment is very troublesome.
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[0011]
In addition, the apparatus for conferences which used the echo control technique is also
proposed (for example, patent document 1). The use of this device in a conference room where
large echoes occur can, to a certain extent, prevent a drop in speech intelligibility due to the
echoes. However, it is not possible to clearly tell each deputy's remarks. Unexamined-JapanesePatent No. 5-7170
[0012]
The object of the present invention is to allow the voices of a plurality of speakers to be naturally
spread over a substantially entire range of the sound field with a sense of presence, while each
speaker is sufficient for the content of the other speakers' voices Providing an electroacoustic
device as can be understood by
[0013]
In order to solve the above problems, an electroacoustic apparatus according to the present
invention corresponds to a plurality of microphones, a mixing unit, a first speaker, an automatic
gain adjustment unit, and at least one of the plurality of microphones. And an electro-acoustic
transducer provided, the mixing means combining the output signals of the plurality of
microphones to generate a combined signal, the first speaker converting the combined signal
into speech, The automatic gain adjustment means applies a gain to the combined signal and
automatically adjusts the gain according to the level of the combined signal, and the electroacoustic transducer converts the output signal of the automatic gain adjustment means into
speech. Convert.
[0014]
The first speaker can voice the synthesized signal with linearity to provide the sound to the
sound field.
On the other hand, the electro-acoustic transducer provides sound whose level has been adjusted
by the automatic gain adjustment means.
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Therefore, it is possible to more clearly provide the content of the utterance issued to the
microphone.
[0015]
According to the electro-acoustic device of the present application, it is possible to hear a natural
sound with a sense of presence in substantially the entire range of the sound field. Also, the user
of the microphone can listen clearly to the content of the user of other microphone users.
[0016]
In the electro-acoustic device of the present invention, the electro-acoustic transducer may be a
second speaker, a headphone, or an earphone.
[0017]
In the above-mentioned electroacoustic apparatus, the output signals of the plurality of
microphones may be sent to the mixing means by the first wireless communication apparatus.
[0018]
Still further, in the electro-acoustic device, the first wireless communication device may be a first
infrared wireless communication device.
[0019]
Still further, in the above-mentioned electroacoustic apparatus, the output signal of the automatic
gain adjustment means may be sent to the electroacoustic transducer by the second wireless
communication apparatus.
In a wireless communication device, the bandwidth of the carrier frequency of the wireless signal
that can be used is limited.
Wireless transmission of voice signals with a large dynamic range requires a wide occupied
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frequency band.
Therefore, multi-channel wireless transmission becomes difficult. However, if the level of the
audio signal is adjusted by the automatic gain adjustment means, the dynamic range of the audio
signal can be reduced. Therefore, although there is a limitation on the bandwidth of the carrier
frequency of the usable radio signal, multi-channel radio transmission becomes easy. Further, by
narrowing the dynamic range and narrowing the occupied frequency band, problems such as
intermodulation, second harmonics, IF interference, IM interference are less likely to occur. The
wireless communication device may be a second infrared wireless communication device. In an
infrared wireless device, the adjustment of the level of the audio signal by the automatic gain
adjustment means is more effective because the limitation of the carrier frequency bandwidth
which can be used is particularly large.
[0020]
Furthermore, the above-mentioned electroacoustic device is provided in the conference hall, and
the plurality of microphones are microphones provided corresponding to each of a plurality of
seats for participants in the conference, and the first speaker is It may be a speaker provided to
provide voice over substantially the entire area of the conference hall. That is, the electroacoustic
device may be used as a conference room electroacoustic device.
[0021]
An electroacoustic apparatus according to an embodiment of the present invention will be
described below with reference to the drawings.
[0022]
FIG. 1 is a diagram of the inside of the conference hall where the electroacoustic apparatus D1 is
installed.
There are an area provided with a plurality of seats B1, B2, B3... And an area provided with a
plurality of hearing seats C in this conference room. Both areas are separated by a divider P.
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[0023]
In the conference hall, for example, a parliamentary meeting is held. Each member of parliament
sits in each seat B1, B2, B3 ... and becomes a participant in the meeting. The listener sits at the
hearing seat C. Observers can not attend meetings.
[0024]
A speaker 15 is attached to the side wall of the conference hall.
[0025]
The number of seats in this conference hall is n, and one speaker unit is placed in each seat.
That is, speaker units U1, U2, U3,..., Un are installed in each of the seats B1, B2, B3,. The
configurations of the plurality of speaker units U1, U2, U3, ..., Un are all the same.
[0026]
FIG. 2 is an external view of the speaker unit U1. The speaker unit U1 includes a microphone M1
and a small speaker S1. Further, this speaker unit U1 includes a volume V1 (not shown) and a
push button switch W1. FIG. 2 shows a cylindrical knob T which is an operation part of the
volume V1. The speaker unit U1 incorporates a microphone head amplifier H1 (not shown) and
an amplifier A1 (not shown) for driving a small speaker.
[0027]
Referring again to FIG. 1, for example, when a member of the seat B1 speaks, the member
presses the push button switch W1 of the speaker unit U1 installed in the seat B1. Then, the
microphone M1 of the speaker unit U1 is turned on. This microphone M1 receives the voice of a
member of the Diet speaking. An output signal of the microphone M1 is amplified by an amplifier
and is amplified from a first speaker 15 as a speaker. The rated output level of the speaker 15 is
relatively large. Therefore, the loud sound of the speaker 15 can be heard over substantially the
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entire range of the conference room.
[0028]
On the other hand, the output signal of the microphone M1 which has received the voice of a
member to speak is also amplified from a small speaker as an electroacoustic transducer
provided in each speaker unit U1, U2, U3, ..., Un . The rated output level of this small speaker is
small. The small speaker of the speaker unit is for providing loud sound to individual members of
the Diet. Incidentally, the adjustment of the volume of the small speaker can be adjusted by
operating the volume knob.
[0029]
FIG. 3 is a schematic block diagram of the electroacoustic apparatus D1. The electroacoustic
apparatus D1 mainly includes n microphones M1, M2, ..., Mn, n microphone head amplifiers H1,
H2, ..., Hn, and n push button switches W1. , W2, ..., Wn, n small speakers S1, S2, ..., Sn, n
amplifiers A1, A2, ..., An, n volumes V1, V2, ... , Vn, a mixing device 11, an automatic gain
adjustment device 12, a volume 13, an amplifier 14, and a speaker 15.
[0030]
The microphones M1, M2, ..., Mn, the microphone head amplifiers H1, H2, ..., Hn, the push button
switches W1, W2, ..., Wn, and the small speakers S1, S2, ... , Sn, amplifiers A1, A2,..., An, and
volumes V1, V2,..., Vn are members provided in the speaker units U1, U2,.
[0031]
The microphone unit M1 of FIG. 3, the head amplifier H1 for the microphone, the push button
switch W1, the small speaker S1, the amplifier A1, and the volume V1 are provided in the caller
unit U1 of FIGS. There is.
Further, the microphone unit M2, the head amplifier H2 for microphone, the push button switch
W2, the small speaker S2, the amplifier A2, and the volume V2 are provided in the caller unit U2
of FIG. The speaker unit Un is provided with a microphone Mn, a microphone head amplifier Hn,
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a push-button switch Wn, a small speaker Sn, an amplifier An, and a volume Vn.
[0032]
Thus, the small speaker S1 is provided corresponding to the microphone M1, the small speaker
S2 is provided corresponding to the microphone M2, and the small speaker Sn is provided
corresponding to the microphone Mn.
[0033]
The microphone head amplifiers H1, H2,..., Hn are connected to the subsequent stages of the
microphones M1, M2,..., Mn, and the push button switches W1, W2,. · · · Wn is connected.
The output signals of all the push button switches W1, W2, ..., Wn are synthesized by the mixing
device 11. The synthesized signal is branched and sent to the volume 13 and the automatic gain
adjustment device 12. An amplifier 14 is connected to the subsequent stage of the volume 13
and a speaker 15 is connected to the subsequent stage.
[0034]
The output signal of the automatic gain adjustment device 12 is branched into n volumes V1, V2,.
Amplifiers A1, A2,..., An are connected to the subsequent stages of the respective volumes V1,
V2,..., Vn, and small speakers S1, S2,. ing.
[0035]
Each of the microphones M1, M2,..., Mn is turned on by pressing the corresponding push button
switch W1, W2,. As described above, it is howling that the microphones M1, M2, ..., Mn are
turned on by pressing the corresponding push button switches W1, W2, ..., Wn. This is to avoid
the occurrence. The connection switches are also provided on the small speakers S1, S2, ..., Sn
side, and the connection switches are interlocked with the push button switches W1, W2, ..., Wn,
and the microphones M1, M2, ... The small-sized speakers S1, S2,..., Sn may be configured to be in
the off state when the Mn is in the on state. With this configuration, it is more effectively avoided
that howling occurs between the small speakers S1, S2, ..., Sn and the corresponding
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microphones M1, M2, ..., Mn. Can.
[0036]
As described above, each of the microphones M1, M2,..., Mn is turned on by pressing the
corresponding push button switch W1, W2,. Output signals of all of the microphones M1, M2,...,
Mn which are turned on are synthesized by the mixing device 11. The synthesized signal is
amplified by the speaker 15. The volume of the speaker 15 can be adjusted by the volume 13.
The speaker 15 is a relatively large speaker, and the loud sound is large. Therefore, the loud
sound can be provided over substantially the entire range of the conference hall. The listener can
understand the contents of the conference mainly by listening to the loud sound from this
speaker.
[0037]
Generally speaking, the level of the combined signal output from the mixing device 11 increases
as the number of microphones in the on state increases among the n microphones M1, M2, ...,
Mn. That is, even if only a few members speak at the same time, the level of the combined signal
output from the mixing device 11 is small, but if multiple members speak simultaneously, the
level of the combined signal output from the mixing device 11 increases .
[0038]
The magnitude of the loud sound from the speaker 15 is roughly proportional to the magnitude
of the synthesized signal output from the mixing device 11. That is, if the level of the synthesized
signal output from the mixing device 11 is twice the reference level, the level of the loud sound
from the speaker 15 is also doubled, and the level of the synthesized signal output from the
mixing device 11 is When the level becomes half of the reference level, the level of the loud
sound from the speaker 15 also becomes half. As described above, the synthesized signal output
from the mixing device 11 is amplified from the speaker 15 with linearity.
[0039]
As a result, the listener can not only hear the contents of the remarks of each member of the Diet,
but also hear natural speech of the contents of the meeting, and can fully feel the realism of the
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meeting.
[0040]
Since the speaker 15 is a speaker for providing a loud sound over substantially the entire range
of the conference hall, the rated output is large.
Even if the output level of the speaker 15 is much lower than its rated output level, it is possible
to provide audio at a normal sound pressure level in the conference hall. That is, the speaker 15
has a considerable margin in the output level in the normal use state.
[0041]
If the number of on-state microphones among the n microphones M1, M2,..., Mn is large, or the
voice of a member who speaks becomes much larger than usual, the mixing apparatus The level
of the synthesized signal output from 11 is also significantly increased, but the speaker 15
provides a loud sound without distortion.
[0042]
Hearing people, of course, would like to hear the contents of each member's remarks, but also
wish to hear the natural sound of the meeting contents.
Therefore, as described above, it is desirable that the output signal (combined signal) of the
mixing device 11 from the speaker 15 be loudened with linearity.
[0043]
On the other hand, the combined signal which is the output signal of the mixing device 11 is also
sent to the automatic gain adjustment device 12. The automatic gain adjustment device 12 is a
device abbreviated as "AGC", which gives a gain to an input signal so that the level of the output
signal becomes constant regardless of the magnitude of the level of the input signal. . That is, the
gain is varied according to the level of the input signal.
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[0044]
The output signal of the automatic gain adjustment device 11 is amplified by each of the small
speakers S1, S2,. It should be noted that the members of each seat B1, B2, ..., Bn can adjust the
small speakers S1, S2, ..., Vn by adjusting the volumes V1, V2, ..., Vn of the speaker units U1, U2,
..., Un. The volume of S2, ..., Sn can be adjusted.
[0045]
The members of each seat B1, B2, ..., Bn can hear the other members' statements from the small
speakers S1, S, ..., Sn of the speaker units U1, U2, ..., Un. .
[0046]
Earlier, he explained that the listener wanted to hear the contents of each member's remarks and
to hear the natural sound of the meeting contents.
Further, it has been described that the speaker 15 has a considerable margin in the output level
in the normal use state.
[0047]
On the other hand, each member of parliament, who is a participant in the meeting, emphasizes
clearly listening to the contents of other members of the parliament rather than listening to the
natural sound of the contents of the meeting. The small-sized speakers S1, S2, ..., Sn of the
speaker units U1, U2, ..., Un have small rated output levels. That is, the small speakers S1, S2, ...,
Sn do not have much margin in the output level.
[0048]
As in the case of the speaker 15, when attempting to use the small speakers S1, S2,..., Sn to
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louden the output signal (synthetic signal) of the mixing device 11 with linearity, the small
speakers S1, S2,. ..., amplified sound from the Sn is must be set to be significantly smaller. If not
set as such, when the level of the synthetic signal output from the mixing device 11 becomes
considerably larger than that at normal time, the loud sound from the small speakers S1, S2, ...,
Sn is distorted. Because it When the loud sound from the small speakers S1, S2,..., Sn is distorted,
each deputy can not clearly hear the contents of remarks of other deputies.
[0049]
However, in the electroacoustic device D1, the output signal (combined signal) of the mixing
device 11 is subjected to gain adjustment by the automatic gain adjustment device 12, and then
provided to each of the small speakers S1, S2,.
[0050]
If the number of on-state microphones among the n microphones M1, M2,..., Mn is large, or the
voice of a member who speaks becomes much larger than usual, the mixing apparatus The level
of the combined signal output from 11 also becomes considerably large.
As described above, even when the level of the combined signal output from the mixing device
11 becomes considerably larger than that in the normal state, the combined signal is subjected to
gain adjustment by the automatic gain adjustment device 12, so that the small speakers S1, S2,. ..,
The loud sound from Sn is not distorted. Therefore, each deputy can clearly hear the contents of
other deputies.
[0051]
In addition, when the number of microphones in the on state is small among n microphones M1,
M2, ..., Mn, or the voice of a member to speak is considerably smaller than usual, The level of the
combined signal output from the mixing device 11 is also considerably reduced. As described
above, even when the level of the combined signal output from the mixing device 11 becomes
considerably smaller than that in the normal state, the combined signal is also gain-adjusted by
the automatic gain adjustment device 12, so the small speakers S 1, S 2, ..., The loud noise from
Sn does not become too small. Therefore, each deputy can clearly hear the contents of other
deputies.
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[0052]
As described above, appropriate gain adjustment is performed according to the level of the level
of the combined signal output from the mixing device 11. Therefore, the small speakers S1, S2,.
Each deputy can always hear the contents of other deputies clearly.
[0053]
In the electroacoustic apparatus D1 of the first embodiment described above, the audio signal
adjusted by the automatic gain adjustment device 12 is provided to all the small speakers S1, S2,
..., Sn.
[0054]
However, it is not necessary to provide the audio signal adjusted by the automatic gain
adjustment device 12 to all the small speakers S1, S2, ..., Sn.
The audio signal adjusted by the automatic gain adjustment device 12 may be provided to a part
of the small speakers S1, S2, ..., Sn, or the small speakers S1, S2, ..., Sn It may be provided to only
one of them.
[0055]
FIG. 4 is a schematic block diagram of an electroacoustic apparatus D2 according to a second
embodiment.
The electroacoustic device D1 of FIG. 3 and the electroacoustic device D2 of FIG. 4 are different
only in the following points, and the other points are the same.
[0056]
That is, in the electroacoustic apparatus D1 of FIG. 3, the audio signal adjusted by the automatic
gain adjustment device 12 is provided to all the small speakers S1, S2,. On the other hand, in the
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electroacoustic device D2 of FIG. 4, the audio signal adjusted by the automatic gain adjustment
device 12 is provided only to the small speaker S1. The small speaker S1 is provided in the
speaker unit U1, and the speaker unit U1 is provided with the microphone M1. That is, the small
speaker S1 is provided corresponding to the microphone M1.
[0057]
The output signal of the mixing device 11 is provided to the other small speakers S2, ..., Sn
without passing through the automatic gain adjustment device 12.
[0058]
Also in the electro-acoustic apparatus D2 of FIG. 4, it is possible to provide a speaker who uses
the small speaker S1 with an amplified sound whose gain is adjusted in accordance with the level
of the synthetic signal output from the mixing apparatus 11.
Therefore, even if the level of the synthetic signal output from the mixing apparatus 11 becomes
considerably larger than usual, or when it becomes considerably smaller, the member can clearly
hear the contents of the statements of other members.
[0059]
Although not explicitly shown in the electroacoustic apparatus D1 of the first embodiment
described above, the output signals of the microphones U1, U2,..., Un may be sent to the mixing
apparatus 11 by the wireless communication apparatus. Further, the output signal of the
automatic gain adjustment device 12 may be sent to the small speakers S1, S2, ..., Sn by the
wireless communication device.
[0060]
FIG. 5 is a schematic block diagram of the electroacoustic apparatus D3 according to the third
embodiment, but in this figure, a wireless communication apparatus 30 for sending out the
output signals of the microphones M1, M2, ..., Mn to the mixing apparatus 11. And the wireless
communication device 40 for transmitting the output signal of the automatic gain adjustment
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device 12 to the small-sized speakers S1, S2, ..., Sn. The other configuration of the electroacoustic
apparatus D3 of FIG. 5 is the same as the electroacoustic apparatus D1 of FIG.
[0061]
The wireless communication device 30 is an infrared wireless communication device. The
wireless communication device 30 is configured of a transmission unit 32 and a reception unit
34. The transmission unit 32 includes a light transmitter 33, and the reception unit 34 includes a
light receiver 35. When the light receiver 35 receives infrared light emitted from the light
transmitter 33, multi-channel (n-channel) communication is performed between the transmission
unit 32 and the reception unit 34.
[0062]
The wireless communication device 40 is also an infrared wireless communication device. The
wireless communication device 40 is configured of a transmission unit 42 and a reception unit
44. The transmission unit 42 includes a light transmitter 43, and the reception unit 44 includes a
light receiver 45. When the light receiver 45 receives the infrared rays emitted from the light
transmitter 43, multi-channel (n-channel) communication is performed between the transmission
unit 42 and the reception unit 44.
[0063]
As previously mentioned. In the electroacoustic device D3, the output signal of the automatic
gain adjustment device 12 is sent by the wireless communication device 40 to the small speakers
S1, S2,. As described above, when the voice signal is transmitted by the wireless communication
device 40, if the voice signal is subjected to gain adjustment by the automatic gain adjustment
device 12, the use frequency band width of the carrier wave used in wireless communication can
be narrowed. Is good.
[0064]
The reason is as follows. That is, in a wireless communication apparatus in general, the
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bandwidth of the carrier frequency of usable wireless signals (infrared and radio waves) is
limited. Wireless transmission of voice signals with a large dynamic range requires a wide
occupied frequency band. Therefore, multi-channel wireless transmission becomes difficult.
[0065]
However, as in the electroacoustic device D3, adjusting the level of the audio signal by the
automatic gain adjustment device 12 can reduce the dynamic range of the audio signal.
Therefore, wireless transmission of multiple channels is facilitated despite the limited bandwidth
of the carrier frequency of the wireless signal (infrared) that can be used. In addition, by
narrowing the dynamic range and narrowing the occupied frequency band, problems such as
intermodulation, second harmonics, IF interference, IM interference, etc. are less likely to occur
in the wireless communication device 40 in the electroacoustic device D3. Although it is an
infrared wireless communication device, in infrared wireless communication, the gain adjustment
of the audio signal by the automatic gain adjustment device 12 is more effective because the
limitation of the bandwidth of the usable carrier frequency is particularly large.
[0066]
In the above, various embodiments of the electroacoustic apparatus according to the present
invention have been described with reference to FIGS.
[0067]
In the first to third embodiments, the electroacoustic transducers provided corresponding to the
microphones M1, M2,..., Mn are speakers (small speakers S1, S2,..., Sn), The electroacoustic
transducer does not have to be a speaker.
For example, headphones or earphones may be used as the electroacoustic transducer.
[0068]
In the third embodiment, the wireless communication devices 30 and 40 are infrared wireless
communication devices, but the wireless communication devices do not have to be infrared
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wireless communication devices. For example, a wireless communication device using radio
waves can also be used.
[0069]
By using the electroacoustic device according to the present invention, it becomes possible to
hear natural sounds with a sense of realism in substantially the entire range of the sound field,
and the user of the microphone is the speech content of the user of the other microphone Can be
heard clearly. Therefore, the electroacoustic apparatus of the present invention is useful in the
technical field of electroacoustics, particularly in the technical field of electroacoustic apparatus
for conference halls.
[0070]
It is a figure of the inside of the meeting place where the electroacoustic apparatus was installed.
It is an external view of a speaker unit. It is a schematic block diagram of an electroacoustic
device. It is a schematic block diagram of an electroacoustic device. It is a schematic block
diagram of an electroacoustic device.
Explanation of sign
[0071]
D1, D2, D3 Electro-Acoustic Devices M1, M2, ..., Mn Microphones H1, H2, ..., Hn Microphone
Head Amplifiers W1, W2, ..., Wn Push Button Switches S1, S2, ...・, Sn small speaker A1, A2, ...,
An amplifier V1, V2, ..., Vn volume 11 mixing device 12 automatic gain adjustment device 13
volume 14 amplifier 15 speaker 30, 40 wireless communication device 32, 42 transmission unit
33, 43 light transmitter 34, 44 receiver unit 35, 45 light receiver
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