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JPH104599

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DESCRIPTION JPH104599
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker device such as an electromagnetic coupling speaker.
[0002]
2. Description of the Related Art As a speaker for sound reproduction, a magnetic circuit having
an air gap between a center pole portion of a center pole yoke and a plate is formed by
sandwiching a magnet by the center pole yoke and the plate, and the magnetic circuit The
primary coil which is the drive coil is fixed to the center pole portion or plate in the air gap of the
circuit, and is fixed to the diaphragm so as to face it, and the secondary coil constituting the short
coil is formed in the air gap of the magnetic circuit. An electromagnetically coupled speaker
arranged is known and put to practical use.
[0003]
In this electromagnetically coupled speaker, the secondary current is induced in the secondary
coil that constitutes the short coil by the signal current flowing through the primary coil that is
the drive coil, and the interaction with the magnetic flux generated in the air gap of the magnetic
circuit According to the left-hand rule, a driving force corresponding to the secondary current is
generated in the secondary coil, and the diaphragm to which the secondary coil is fixed is
displaced.
[0004]
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In this electromagnetically coupled speaker, the primary coil through which the signal current
flows is fixed to the center pole portion or plate made of a magnetic material such as iron, so that
it has an advantage of being excellent in heat dissipation and being able to withstand a large
input.
Further, if the secondary coil constituting the short coil is formed of a non-magnetic conductive
material such as aluminum and made of a pipe or a cylinder for one turn, distortion can be
reduced.
[0005]
In addition, as a speaker, a voice coil bobbin is disposed in the gap of the magnetic circuit by
fixing to a diaphragm, and a dynamic speaker etc. in which a voice coil as a drive coil is wound
around this voice coil bobbin is put to practical use. ing.
[0006]
In the electromagnetic coupling speaker as described above, for example, coils corresponding to
the number of bits of the digital audio signal are provided as primary coils, and each coil
corresponds to each bit of the digital audio signal. It is conceivable to play back the sound by
driving with the signal of each bit.
[0007]
FIG. 5 shows the possible digital drive type speaker device, in the serial-to-parallel converter 220,
for example, digital audio signal Ds of serial data digitized into 16 bits at a sampling frequency of
44.1 kHz or 48 kHz, It is converted into parallel data digital audio signal Dp.
However, this example is the case where the 16-bit digital audio signals Ds and Dp are natural
binary codes and linearly quantized.
[0008]
The speaker unit 10 is an electromagnetically coupled speaker, and a primary coil which is a
drive coil thereof is configured by 16 coils 1A to 1N, 1P, and 1Q, and the coil 1A is an LSB (least
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significant bit) of the digital audio signal Dp. In the following, coils 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1I,
1J, 1K, 1L, 1M, 1N, 1P, 1Q, 15SB, 14SB, 13SB, 12SB, 11SB, 10SB, 9SB, 8SB, 7SB, 6SB, 5SB, 4SB,
3SB, 2SB, MSB (most significant bit).
[0009]
Then, constant current sources 61A to 61N, 61P and 61Q are respectively connected to coils 1A
to 1N, 1P and 1Q via switch circuits 62A to 62N, 62P and 62Q, respectively, and switch circuits
62A to 62N and 62P. , 62Q are switched by the signal of the corresponding bit of the digital
audio signal Dp from the serial to parallel converter 220.
[0010]
In this case, as an example, the coil 1A has 2 turns, the coil 1B has 4 turns, the coil 1C has 8
turns, etc., corresponding to the weight of each bit of the digital audio signal Dp, each coil 1A to
1N, 1P , And 1Q are twice the number of turns of the coil corresponding to one lower bit, and the
currents Ia to In, Ip, and Iq of the respective constant current sources 61A to 61N, 61P, and 61Q
are mutually Make it equal.
すなわち、Iq=Ip=In=……=Iaとする。
[0011]
Alternatively, the coils 1A to 1N, 1P, and 1Q all have the same number of turns, and the current
Ib of the constant current source 61B corresponding to 15SB of the digital audio signal Dp is the
current Ia of the constant current source 61A corresponding to LSB. Of the constant current
sources 61C, 61D, 61E... Corresponding to 14SB, 13SB, 12SB..., The currents Ib, Ic, Id The route
of ... is doubled.
[0012]
The driving force F of the vibration system of the electromagnetic coupling speaker is the
secondary current i induced in the secondary coil, the density B of the magnetic flux generated in
the air gap of the magnetic circuit, and the length of the secondary coil in the air gap of the
magnetic circuit Since the magnetic flux density B and the length L are constant expressed as F =
BLi as a product with L, the driving force F of the vibration system is proportional to the
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secondary current i induced in the secondary coil Become.
The secondary current i induced in the secondary coil is proportional to the product of the
square of the signal current flowing through the primary coil and the number of turns
(impedance) of the primary coil.
[0013]
Therefore, in the speaker device of FIG. 5, in the speaker unit 10, as described above, the
diaphragm to which the secondary coil is fixed is proportional to the weight of each bit of the
digital audio signal Dp from the serial to parallel converter 220 in one direction. The audio is
reproduced faithfully to the digital audio signal Dp from the serial to parallel converter 220.
[0014]
In general, electromagnetically coupled speakers are excellent in heat dissipation, can withstand
large inputs, and can reduce distortion, but electromagnetic coupling force in which the
secondary current is induced in the secondary coil by the signal current flowing through the
primary coil is It becomes smaller at a low frequency range of several kHz to 1 kHz or less, and it
is difficult to reproduce up to 20 Hz, which is necessary for reproducing audio.
Therefore, electromagnetically coupled speakers are conventionally used mainly as speakers for
high-pitched sound reproduction.
[0015]
However, the digital audio signal Dp from the serial to parallel converter 220 in FIG. 5 is digitized
at a sampling frequency of 44.1 kHz or 48 kHz, for example, and the primary coils 1A to 1Q are
driven by digital signals of the same sampling frequency. Therefore, low frequency components
such as several kHz to 1 kHz or less of the audio signal before being digitized also have high
frequencies exceeding 20 kHz as the signal current flowing through the primary coils 1A to 1Q.
[0016]
Therefore, the speaker unit 10, which is an electromagnetic coupling speaker, enables
reproduction up to the low frequency range, and a full range speaker that reproduces from bass
to treble can be realized.
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[0017]
However, in this case, when the switch circuits 62A to 62Q are switched by the signal of each bit
of the digital audio signal Dp from the serial to parallel converter 220, back electromotive force
is generated in the coils 1A to 1Q, and the coils 1A to 1Q Spike noise occurs at the connection
point of the switch circuits 62A to 62Q.
[0018]
Referring to the coil 1A and the switch circuit 62A corresponding to the LSB of the digital audio
signal Dp, the current flowing through the coil 1A is turned on and off as shown in the upper
part of FIG. 4 according to the value of the LSB of the digital audio signal Dp. Ru.
The voltage at the connection point between the coil 1A and the switch circuit 62A is changed at
time t1 when the current flowing through the coil 1A changes from 0 to Ia, as shown in the lower
part of FIG. At time t2 when the current flowing through the coil 1A changes from Ia to 0, spike
noise is generated at the connection point between the coil 1A and the switch circuit 62A.
However, Vcc is the power supply voltage, R is the resistance of coil 1A, L is the inductance of
coil 1A, di / dt is the time derivative of the current flowing through coil 1A, di / dt is positive at
time t1, and di / dt at time t2. dt is negative.
[0019]
Then, for example, when the switch circuits 62A to 62Q are configured by MOS.FETs, there is a
possibility that the MOS.FETs may be destroyed when the spiked electromotive voltage exceeds
the allowable maximum voltage between the drain and source of the MOS.FETs. .
Further, in the case of using a MOS • FET having a large withstand voltage in order to prevent
the destruction, the cost of the speaker drive circuit 40 is increased.
In addition, this spike voltage causes the reproduction sound quality to deteriorate.
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[0020]
Therefore, the present invention prevents the destruction of the switching element for switching
the current flowing in the drive coil without increasing the cost of the device when driving the
drive coil of a speaker such as an electromagnetic coupling speaker with a digital audio signal. It
is possible to improve the reproduction sound quality while being able to
[0021]
SUMMARY OF THE INVENTION In the present invention, a speaker device includes a speaker
unit and a speaker driving circuit, and the speaker driving circuit excludes the most significant
bit of the input digital audio signal supplied thereto. The constant current source corresponding
to each bit including the bit or the most significant bit and the signal of each bit excluding the
most significant bit of the input digital audio signal or each bit including the most significant bit
A switch circuit for switching the supply of current to the drive coil of the speaker unit and a
switch circuit that reduces an electromotive voltage generated in the drive coil when switching
the supply of current from the constant current source to the drive coil And the circuit to be
[0022]
In the speaker device of the present invention thus configured, the current from the constant
current source to the drive coil is set by the signal of each bit except the most significant bit of
the input digital audio signal or each bit including the most significant bit. When the supply is
switched, the induced voltage in the drive coil is reduced.
Therefore, the destruction of the switching elements constituting the switch circuit is prevented.
In addition, since the circuit for reducing the electromotive voltage generated in the drive coil
can be formed of, for example, a capacitor and a resistor, cost reduction of the device can be
realized as compared with the case of using a high withstand voltage switching element.
Furthermore, the playback sound quality is improved.
[0023]
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a
speaker device according to the present invention, in which a serial-to-parallel converter 220
digitalizes serial data digitized to 16 bits at a sampling frequency of 44.1 kHz or 48 kHz, for
example. The audio signal Ds is converted to a digital audio signal Dp of parallel data.
[0024]
However, in this example, when the 16-bit digital audio signals Ds and Dp are natural binary
codes, or the digital audio signal Ds of serial data supplied to the serial-to-parallel converter 220
has 2 'complement Code, which is converted to parallel data in the serial / parallel converter 220
and is converted to a natural binary code, and the digital audio signal Dp of the parallel data from
the serial / parallel converter 220 is a natural binary code It is the case.
Also, in this example, the digital audio signals Ds and Dp are linearly quantized ones.
[0025]
The speaker unit 10 is an electromagnetic coupling speaker.
FIG. 2 shows an example of the speaker unit 10, in which a recess 13 is formed around the tip of
the center pole portion 12 of the center pole yoke 11, and the primary coil 1 as a drive coil is
fitted into the recess 13. Is attached to the center pole portion 12.
[0026]
The primary coil 1 is wound as an air core coil, and is attached to the center pole portion 12 by
being press-bonded to the recess 13, or, although not shown, wound around a magnetic bobbin,
The magnetic bobbin is attached to the center pole portion 12 by press-adhering in the recess 13
or attached to the center pole portion 12 by being wound directly on the recess 13.
[0027]
An opening 15 is formed in the flange portion 14 of the center pole yoke 11 at a position close to
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the center pole portion 12, and a terminal plate 16 is attached to the rear surface of the flange
portion 14.
Then, a coil lead wire 17 made of, for example, a tinsel wire of the primary coil 1 is adhered to
the circumferential surface of the center pole portion 12 and inserted into the opening 15 and
connected to the input terminal 18 on the terminal plate 16 by soldering.
[0028]
The coil lead-outs 17 are respectively provided at the winding start and end of the primary coil 1
and are respectively connected to separate input terminals. Also, as described later, when the
primary coil 1 is configured by a plurality of coils, the coil leader 17 of each coil is bonded to the
circumferential surface of the center pole portion 12 and inserted into the opening 15 to form a
terminal plate 16 is connected to the input terminal 18.
[0029]
The magnet 21 is adhered to the front surface of the flange portion 14 of the center pole yoke
11, and the plate 22 is adhered to the front surface of the magnet 21. The outer peripheral
surface of the tip of the center pole portion 12 and the inner periphery of the plate 22 A
magnetic circuit 20 is formed having an air gap 23 between it and the surface.
[0030]
In the air gap 23 of the magnetic circuit 20, the secondary coil 2 constituting a short coil is
inserted.
The secondary coil 2 is a one-turn cylindrical body made of a nonmagnetic conductive material,
for example, aluminum, whereby the bobbin around which the secondary coil 2 is wound can be
omitted.
[0031]
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The inner periphery of a cone 32 with an edge 31 on the outer periphery, the center cap 33, and
the inner periphery of a damper 34 are attached to the secondary coil 2. Further, the speaker
frame 35 is attached to the plate 22, the edge 31 of the outer periphery of the cone 32 and the
gasket 36 are attached to the speaker frame 35, and the outer periphery of the damper 34 is
attached to the speaker frame 35.
[0032]
However, although not shown, a part of the primary coil may be attached to the circumferential
surface of the tip of the center pole portion 12 and the remaining coils may be attached to the
inner circumferential surface of the plate 22. In this case, the coil leader of the coil attached to
the plate 22 is inserted, for example, between the plate 22 and the magnet 21 and connected to
the input terminal on the terminal plate attached to the outer peripheral surface of the plate 22 .
Alternatively, all primary coils may be attached to the inner circumferential surface of the plate
22.
[0033]
In the example of FIG. 1, the primary coil 1 of the above speaker unit 10 is composed of 16 coils
1A to 1N, 1P, and 1Q, and constant current sources 61A to 6A are applied to the coils 1A to 1N,
1P, and 1Q, respectively. 61N, 61P, 61Q are connected via switch circuits 63A to 63N, 63P, 63Q,
respectively, and the switch circuits 63A to 63N, 63P, 63Q are controlled by signals of respective
bits of the digital audio signal Dp from the serial to parallel converter 220. Switching element 64
is switched.
[0034]
Furthermore, in this example, the snubber circuit 65 is connected in each of the switch circuits
63A to 63Q.
That is, switch circuits 63A to 63Q are configured by a MOS • FET as switching element 64 and a
snubber circuit 65 connected in parallel between the drain and source thereof as shown in FIG. 3
as representative of switch circuit 63A. Be done. The snubber circuit 65 is one in which a
capacitor 66 and a resistor 67 are connected in series.
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[0035]
Therefore, by selecting the capacitance of the capacitor 66 and the resistance value of the
resistor 67, the MOS • FET 64 of the switch circuits 63A to 63Q is switched by the signal of each
bit of the digital audio signal Dp from the serial to parallel converter 220 When the spikes occur
in the coils 1A to 1Q, i.e., at the connection point Xa of the coils 1A to 1Q and the MOS.FET 64,
the spike voltage decreases to a value smaller than the maximum allowable voltage between the
drain and source of the MOS.FET 64.
[0036]
Therefore, even if one having a large withstand voltage is not used as the MOS · FET 64, the
destruction of the MOS · FET 64 can be prevented.
Further, since the snubber circuit 65 can be configured by the capacitor 66 and the resistor 67,
cost reduction of the device can be realized as compared with the case of using a MOS · FET 64
having a large withstand voltage. Furthermore, the playback sound quality is improved.
[0037]
As the switching element 64 of the switch circuits 63A to 63Q, one other than the MOS • FET can
be used, and even in that case, the same effect can be obtained by the same operation.
[0038]
As described above, the driving force F of the vibration system of the speaker unit 10 that is an
electromagnetic coupling speaker is proportional to the secondary current i induced in the
secondary coil 2, and the secondary current i flows in the primary coil 1. It is proportional to the
product of the square of the signal current and the number of turns (impedance) of the primary
coil 1.
[0039]
Then, in the speaker apparatus of the example of FIG. 1, corresponding to the weight of each bit
of the digital audio signal Dp, for example, 2 turns of the coil 1A, 4 turns of the coil 1B, 8 turns of
the coil 1C, etc. The number of turns of each coil 1A to 1N, 1P, 1Q is twice the number of turns
of the coil corresponding to one lower bit, and the current Ia of each constant current source
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61A to 61N, 61P, 61Q .About.In, Ip, Iq are equal to one another.
すなわち、Iq=Ip=In=…=Iaとされる。
[0040]
Alternatively, all the coils 1A to 1N, 1P, and 1Q have the same number of turns, and the current
Ib of the constant current source 61B corresponding to 15SB of the digital audio signal Dp
corresponds to the current of the constant current source 61A corresponding to LSB. .. Of
constant current sources 61C, 61D, 61E... Corresponding to 14SB, 13SB, 12SB... Are Ib, current
Ib, and so on. The route of Ic, Id ... is doubled.
[0041]
Therefore, in the speaker device of the example of FIG. 1, in the speaker unit 10, the cone 32 is
displaced in one direction by an amount proportional to the weight of each bit of the digital
audio signal Dp from the serial to parallel converter 220, Audio is reproduced faithfully to the
digital audio signal Dp from the serial to parallel converter 220.
[0042]
As in the case of a general speaker, the vibration system of the speaker unit 10 hardly responds
to high frequencies, and in particular, hardly reproduces high frequency components exceeding
20 kHz.
Therefore, even if the primary coil 1 is driven by a digital signal at a sampling frequency of 44.1
kHz or 48 kHz, the sampling frequency component is hardly reproduced.
Even if the sound is reproduced with a very small sound pressure, sounds over 20 kHz can
hardly be heard by the human ear, so no problems occur even when listening to music.
In addition, it is also easy to intentionally form a mechanical filter having a stop band of 20 kHz
or more and incorporate it into the speaker unit 10.
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[0043]
In addition, it is possible to realize a speaker apparatus with small distortion and a large
maximum output, which reproduces the audio directly by the digital audio signal without using
the D / A converter and the power amplifier.
[0044]
Then, in the speaker device of the example of FIG. 1, the snubber circuit 65 is connected to the
switching elements 64 of the switch circuits 63A to 63Q. While destruction of the switching
element 64 can be prevented, cost reduction of the device can be realized as compared with the
case of using a switching element 64 having a large withstand voltage.
[0045]
The snubber circuits may be connected in parallel to the primary coils 1A to 1Q, respectively.
Further, in the above-described speaker device, the speaker drive circuit 40 and the speaker unit
10 can be integrated or separated.
[0046]
In the above-described example, the digital audio signals Ds and Dp are linearly quantized, and
the number of turns of the coils 1A to 1Q or the current values of the constant current sources
61A to 61Q can be changed geometrically. However, when the digital audio signals Ds and Dp
are non-linearly quantized, the number of turns of the coils 1A to 1Q or the current value of the
constant current sources 61A to 61Q, depending on the mode of the quantization. Change the
[0047]
In the example described above, the primary coil 1 is composed of 16 coils 1A to 1Q, but one
primary coil 1 is common to each bit of the digital audio signal Dp from the serial to parallel
converter 220. It may be composed of a coil of
Of course, in that case, it is necessary to change the currents Ia to Iq of the constant current
sources 61A to 61Q as described above.
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[0048]
Furthermore, the primary coil 1 can also be configured by a plurality of coils common to a
plurality of bits of a part of the digital audio signal Dp from the serial-to-parallel converter 220,
respectively.
[0049]
When the digital audio signals Ds and Dp are 2's complement codes, or the digital audio signal Ds
of serial data supplied to the serial-to-parallel converter 220 is a natural binary code, this is a
serial-to-parallel conversion. When the digital audio signal Dp of parallel data from the serial /
parallel converter 220 is converted to parallel data and converted to 2's complement code, and
the digital audio signal Dp of the parallel data is converted to 2's complement code , The constant
current source 61Q and the switch circuit 63Q corresponding to the MSB of the digital audio
signal Dp are eliminated, and the constant current sources 61A to 61P corresponding to the least
significant bits (LSB to 2SB) are respectively the MSB of the digital audio signal Dp. Depending on
the value, when the MSB is 0, the pair It is sufficient to supply a current in the positive direction
to the primary coil when the lower bit is active, and to supply a current in the negative direction
to the primary coil when the corresponding lower bit is active when the MSB is 1. .
[0050]
Thereby, in the speaker unit 10, the cone 32 is displaced in the direction according to the value
of the MSB of the digital audio signal Dp from the serial / parallel converter 220 by an amount
proportional to the weight of each bit excluding the MSB, Audio is reproduced faithfully to the
digital audio signal Dp from the serial to parallel converter 220.
[0051]
In the example described above, the primary coil which is the drive coil of the electromagnetic
coupling speaker is driven by the digital audio signal, but the present invention drives the drive
coil of another speaker such as a dynamic speaker by the digital audio signal. The case can also
be applied.
[0052]
As described above, according to the present invention, when driving a drive coil of a speaker
such as an electromagnetic coupling speaker by a digital audio signal, the current flowing
through the drive coil without increasing the cost of the device. As a result, it is possible to
prevent the destruction of the switching element for switching and to improve the reproduction
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sound quality.
[0053]
Brief description of the drawings
[0054]
1 is a connection diagram showing an example of a speaker device of the present invention.
[0055]
2 is a cross-sectional view showing an example of a speaker unit of the speaker apparatus of FIG.
[0056]
3 is a connection diagram showing an example of a switch circuit of the speaker device of FIG.
[0057]
4 is a diagram for explaining the operation of the possible speaker device.
[0058]
5 is a connection diagram showing an example of a possible speaker device.
[0059]
Explanation of sign
[0060]
DESCRIPTION OF SYMBOLS 10 ... Speaker unit, 1, 1A-1N, 1P, 1Q ... Primary coil, 2 ... Secondary
coil, 11 ... Center pole yoke, 12 ... Center pole part, 14 ... Flange part, 16 ... Terminal board, 17 ...
Coil Lead wire, 18: input terminal, 20: magnetic circuit, 21: magnet, 22: plate, 23: air gap, 32:
cone, 40: speaker drive circuit, 61A to 61N, 61P, 61Q, constant current source, 63A to 63N ,
63P, 63Q: switch circuit, 64: switching element, 65: snubber circuit, 66: capacitor, 67: resistor,
220: serial parallel converter
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