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DESCRIPTION JPH11289596

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DESCRIPTION JPH11289596
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker device capable of reproducing an acoustic signal in a frequency band of 20 kHz or more.
[0002]
2. Description of the Related Art A typical speaker device of the prior art is configured as shown
in FIG. This is called a dynamic type speaker, and the magnetic circuit of this speaker device
comprises a donut shaped magnet 1, first and second magnetic yokes 2 and 3 made of a
magnetic material such as iron, and an air gap. (Gap) 4 is comprised. The first magnetic yoke 2 is
composed of a columnar pole piece 2a and a disk-shaped flange portion 2b orthogonal to the
center pole portion 2a. The second magnetic yoke 3 is called a plate, and has a donut shape
whose inner diameter is larger than the outer diameter of the pole piece 2 a by the space 4.
[0003]
Then, with the pole piece 2 a inserted in the inner peripheral hollow portion of the magnet 1 and
the inner peripheral hollow portion of the plate 3, the magnet 1 is formed by the front surface of
the flange portion 2 b of the first magnetic yoke 2 and the plate 3. Is attached in place. The
contact portion between the front surface of the flange portion 2b and the surface of the plate 3
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and the magnet 1 is bonded.
[0004]
Then, the voice coil 6 wound around the non-conductive voice coil bobbin 5 is disposed so as to
be located in the air gap 4 between the plate 3 and the pole piece 2 a. Further, an acoustic
diaphragm 7, for example, a cone paper is attached to and attached to the voice coil bobbin 5.
The acoustic diaphragm 7 is attached and fixed to the speaker frame 8 at its edge portion. A
signal input line (lead line) 9 is derived from the voice coil 6.
[0005]
In the speaker apparatus shown in FIG. 5, when current I by an acoustic signal flows through
voice coil 6, a driving force F for vibrating acoustic diaphragm 7 is generated by the interaction
with magnetic flux B of magnetic gap 4. The driving force F can be expressed as F = B × I × D
(Equation 3). Here, D is the length of the voice coil 6 in the magnetic field.
[0006]
By the way, along with recent advances in recording technology and recording media, sound of
20 kHz or more, which is above the audio frequency band of the human ear that has not been a
major problem until now It has been found that the component affects the aurally reproduced
sound output, and a microphone having a wide band of 100 kHz has also appeared.
[0007]
Therefore, in response to this, there is a demand for a speaker apparatus that can satisfactorily
reproduce also a sound component of 20 kHz or more, which is equal to or higher than an
audible frequency band.
[0008]
By the way, in the case of the conventional typical speaker device of FIG. 5 described above, since
the voice coil 6 has the inductance component L1 together with the direct current resistance R1,
the input impedance Zin of the speaker device is greater than the resonance frequency f0. R1 + j ·
2 · π · f · L1 (4).
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[0009]
From (Equation 4), it can be seen that the input impedance Zin increases as the frequency f
increases.
From this, when the frequency becomes high, the current I flowing through the voice coil 6
decreases, and the driving force F decreases in the speaker device of the configuration of FIG.
For this reason, the speaker device having the configuration of FIG. 5 is not suitable for
reproduction of an acoustic component of 20 kHz or more which is the audio frequency band or
more.
[0010]
In view of the above points, the present invention aims to provide a speaker device capable of
satisfactorily reproducing an acoustic component having a frequency of 20 kHz or more.
[0011]
SUMMARY OF THE INVENTION In order to solve the above problems, a speaker device according
to the present invention is provided in the vicinity of an air gap in a magnetic circuit, and a
primary coil supplied with a current according to an input audio signal. The secondary coil
disposed in the air gap, in which a current is induced according to the current flowing in the
primary coil, and the interaction between the current induced in the secondary coil and the
magnetic flux in the air gap A diaphragm which vibrates when the next coil vibrates, wherein the
DC resistance value of the primary coil is R1, the inductance is L1, the number of turns is N, and
the DC resistance value of the secondary coil is R2; When the coupling coefficient k of the
primary coil and the secondary coil is used, the relationship between the constants thereof is set
so as to satisfy the equation (1).
[0012]
According to the invention of claim 1, an electromagnetic induction system is used as a method
of driving the acoustic diaphragm, and the relationship between the respective constants is
determined so as to satisfy the above (equation 1). The inductance component is reduced, and a
predetermined current can be supplied to a high frequency range, and a predetermined driving
force can be obtained even in a high frequency range of 20 kHz or more.
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[0013]
The invention according to claim 2 is the speaker apparatus according to claim 1, wherein each
of the constants R1, L1, N, R2, and k satisfies the above (formula 2) at the frequency f on the
high band side of the desired band for reproduction. It is characterized by
[0014]
In the invention of claim 2, by setting each constant so as to satisfy the above (formula 2), the
magnitude of the induced current at the desired reproduction frequency f can be within -10 dB of
the maximum current. In the high frequency band of 20 kHz or more, predetermined necessary
driving force can be obtained.
[0015]
DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the speaker
apparatus according to the present invention will be described below with reference to the
drawings.
In the present invention, an electromagnetic induction system is used as a drive system of the
acoustic diaphragm.
[0016]
FIG. 1 shows the structure of an electromagnetic induction type speaker device according to this
embodiment.
Also in the speaker device of this example, the magnetic circuit is configured in the same manner
as the speaker device of the example of FIG. 5, and includes the first yoke 12 including the
columnar pole piece 12a and the disk-like flange portion 12b; 2 and a doughnut-shaped plate 13
constituting a yoke, a doughnut-shaped magnet 11 disposed between the flange portion 12b of
the first yoke 12 and the plate 13, a gap between the plate 13 and the pole piece 12a A magnetic
circuit is constituted by 14.
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[0017]
Then, a drive coil as an excitation primary coil is disposed on either or both of the outer
peripheral surface portion of the pole piece 12 a and the inner peripheral surface portion of the
plate 13 facing each other across the air gap 14.
In this embodiment, an excitation primary coil 15 is disposed on the outer peripheral surface of
the pole piece 12a.
In order to dispose the primary coil 15, a small diameter portion having a length corresponding
to the winding width of the primary coil 15 may be provided in the vicinity of the top of the pole
piece 12a.
[0018]
The signal input wire (lead wire) 16 derived from the primary coil 15 is extended to the back side
of the flange portion 12 b through the through hole 17 provided in the flange portion 12 b of the
first magnetic yoke 12.
[0019]
And in this embodiment, the secondary coil 18 which consists of a short coil electromagnetically
coupled to the primary coil 15 is inserted into the air gap 14.
In this example, the secondary coil 18 is configured as a one-turn short coil by a cylindrical ring
of nonmagnetic and conductive material such as aluminum.
Then, the conductive one turn ring made of aluminum that constitutes the secondary coil 18 is
adhesively fixed to the bobbin 19.
The bobbin 19 is made of a nonmagnetic and nonconductive material such as cardboard.
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[0020]
The width of the secondary coil 18 (corresponding to the height of one turn ring) is the minimum
necessary length that is longer than the length in the vibration direction of the air gap 14 by the
amplitude of the vibration of the secondary coil 18 The length of
[0021]
Then, the acoustic diaphragm 20, for example, cone paper is attached to the bobbin 19.
The acoustic diaphragm 20 is attached to the speaker frame 21 via a flexible edge (not shown).
[0022]
In the electromagnetic induction type speaker device having the above-described configuration,
when a signal current is supplied to the primary excitation coil 15, an induced current is
generated in one turn of the secondary coil 18 disposed opposite to the primary coil. Flow. The
driving force F for driving the secondary coil 18 in the height direction of the ring is generated
from the induced current I flowing through the secondary coil 18 and the magnetic flux density B
in the air gap 14, whereby the acoustic diaphragm 20 is It vibrates according to the signal
current.
[0023]
In this case, assuming that the length of one turn ring (length of the ring circumference) as the
secondary coil 18 is L, the driving force F is F = B × I × L (Equation 5)
[0024]
In this embodiment, the DC resistance value of the primary coil 15 is R1, the inductance is L1,
the number of turns is N, the DC resistance value of the secondary coil 18 is R2, and the primary
coil Assuming that the coupling coefficient of 15 and the secondary coil 18 is k, the respective
constants R1, L1, R2, and k are selected so as to satisfy the following equation (6).
[0025]
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N × (R1 × R2) 1/2 / (2π × L1 × (1−k2) 1/2) ≧ 20000 (Equation 6) Further, each constant
R1 is set so as to satisfy the following (Equation 7) , L1, R2, k are selected.
[0026]
2π × f × L12 × (N2 × R2 + R1) / (N2 × X1 / 2) ≧ 0.3 X = (2π × f) 2 × (L1 × R2 + L1 ×
R1 / N2) 2 + {− R1 × R2 + (2π × f) ) 2 × L 12 × (1 − k 2) / N 2} 2 (Equation 7) By selecting
each of the constants R1, L1, R2 and k in this manner, a constant current is obtained even in a
high frequency band of 20 kHz or more It becomes possible to flow the fluid and to obtain the
necessary driving force.
In particular, by setting the respective constants R1, L1, R2, and k to satisfy the equation 7, the
reduction value of the induced current at the desired high frequency is suppressed within 10 dB
with respect to the value of the maximum induced current. Can.
This will be further described below.
[0027]
The electrical equivalent circuit of the electromagnetic induction unit of the above-described
electromagnetic induction speaker device can be expressed as shown in FIG.
In FIG. 2, as described above, R1 and L1 are the DC resistance value and inductance of the
primary coil 15 for excitation, respectively, and R2 and L2 are the DC resistance value and
inductance of the secondary coil 18 respectively. is there. And M is a mutual induction
inductance and Zin is an input impedance of the speaker device.
[0028]
From the equivalent circuit of FIG. 2, when the input impedance Zin of the speaker device is
determined, Zin = (R1 + A2 × R2) + jω (L1−A2 × L2) (Expression 8) A2 = ω2 × M2 / (ω2 ×
L22 + R22 ) M2 = k2 x L1 x L2. Here, ω is an angular frequency.
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[0029]
Considering the case where the frequency f is high, A2 = M2 / L22 = k2 × L1 / L2, and therefore
the above (equation 8) becomes Zin = (R1 + k2 × R2 × L1 / L2) + jωL1 (1-k2) ((2) Formula 9)
[0030]
Further, the input impedance Zin in the case of only the exciting primary coil 15 is expressed as
follows: Zin = R1 + jωL1 (Equation 10)
[0031]
From the comparison of (Eq. 9) and (Eq. 10), it can be seen that the inductance component is
reduced by the coupling coefficient k by attaching the secondary coil 18 in the high frequency
range.
In particular, it can be seen that when the coupling coefficient k is k = 1, the inductance
component becomes very small in the high frequency range, and the input impedance becomes
constant with respect to the frequency.
[0032]
As described above, even if the inductance component of the excitation primary coil 15 is not
reduced, the inductance component of the input impedance Zin is reduced, so that a constant
current can flow in a high frequency range of 20 kHz or more. It is possible to obtain a constant
driving force.
[0033]
Now, when the speaker device of the electromagnetic induction system is driven at constant
voltage, the frequency characteristics of the induced current flowing in one turn ring as the
secondary coil 18 acting as a driving force are as follows.
[0034]
That is, assuming that the drive voltage is V1 and the induction current of secondary coil 18 is
I2, the frequency characteristic of induction current I2 with respect to drive voltage V1 is I2 / V1
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= ω · k (L1 × L2) 1/2 / Y1 / 2Y = .Omega.2 * (L1.times.R2 + L2.times.R1) 2 + {-R1.times.R2 +
.omega.2.times.L1.times.L2.times. (1-k2)} 2 (Equation 11).
[0035]
From the equation (11), the frequency f0 at which the induced current I2 is maximum is f0 = N
× (R1 × R2) 1/2 / {2π × L1 × (1−k2) 1/2} (12) It becomes.
Satisfying the equation (6) means that f 0 ≧ 20000 and the induced current can be maximized in
the high frequency range of 20 kHz or more.
[0036]
Then, by satisfying the above (formula 7), the reduction value of the induction current at the
desired frequency f in the high frequency region of 20 kHz or more can be made within 10 dB
with respect to the value of the maximum current.
[0037]
Embodiment A specific embodiment of the excitation primary coil 15 and the secondary coil 18
of the speaker apparatus having the above-described configuration will be described.
[0038]
In this embodiment, the dimensions and characteristics of one turn ring as the exciting primary
coil 15 and the secondary coil 18 were as follows.
[0039]
The excitation primary coil 15 has a diameter of 13 mm, a winding width of 2.6 mm, the number
of winding layers: 2, a total number of turns (N): 33, a direct current resistance (R1): 3.22 Ω, and
an inductance (L1): 34 .5 μH
[0040]
The secondary coil 18 (one turn ring) has a diameter (inner diameter): 13.36 mm, a width: 3.0
mm, a thickness: 0.2 mm, a material: aluminum, a direct current resistance (R2): 0.00207 Ω,
Inductance (L2): 0.032 μH
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[0041]
In this case, the inductance L2 has a value substantially equal to L1 / N2.
[0042]
An example of the measurement result of the frequency characteristic of the input impedance of
the speaker device of this embodiment is shown in FIG.
In FIG. 3, points indicated by “•” indicate measurement examples of frequency characteristics
of input impedance when the secondary coil 18 is not present.
Moreover, the point of the "+" mark has shown the example of measurement of the frequency
characteristic of the input impedance at the time of attaching the secondary coil 18. As shown in
FIG.
[0043]
As can be seen from this measurement value, the inductance component of the input impedance
of the electromagnetic induction type speaker device is significantly reduced.
Substituting the values of the above constants R1, L1, N, R2 into the left side of the above
(Equation 6) (same as (Equation 1)), the value becomes 22907, which satisfies (Equation 6).
The value of the coupling coefficient k is k = 0.84 from the measurement result.
[0044]
Then, when the values of these constants R1, L1, N, R2, and k are substituted into the left side of
the (formula 2), the value becomes 0.67, and the same as (formula 7) (formula 2) The
relationship of) is also satisfactory.
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[0045]
Next, FIG. 4 shows an example in which the frequency characteristics of the relative value of the
induced current are calculated from the values of the constants R1, L1, N and R2 and the above
(formula 12).
As mentioned above, in this embodiment with a coupling coefficient k = 0.84, the reduction of the
induced current at 100 kHz is a reduction of 3.5 dB relative to the value at 20 kHz.
[0046]
As another example, when the coupling coefficient k = 1.0, a constant drive current (induction
current) can be supplied to the secondary coil from 20 kHz to 100 kHz.
Also, for a coupling coefficient k = 0.74, the reduction in induced current at 100 kHz is a 6 dB
reduction relative to the value at 20 kHz.
[0047]
As described above, the values of the constants R1, L1, N, R2, and k should be satisfied by (Eq. 6)
(same as (Eq. 1)) and (Eq. 7) (Same as (Eq. 2)) By setting each of them, it is possible to reduce the
induced current to 10 dB or less to a desired high frequency of 20 kHz or more.
[0048]
As described above, according to the present invention, the reduction of the drive current (the
induced current) is very small even in the high frequency range of 20 kHz or more, and hence
the speaker device with the very small reduction of the drive power Can be realized.
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