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JPS5489618

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DESCRIPTION JPS5489618
Description 1, title of the invention
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3. Detailed Description of the Invention The present invention relates to an electrodynamic
speaker system, in which a force factor in a drive unit, that is, a so-called "Bl product"
represented by a product of a magnetic flux density B and a length l of a voice coil is constant.
Control to improve the linearity as an electromechanical transducer to realize a speaker system
with less distortion. Generally, distortion in a speaker system is known to occur due to nonlinearity of a mechanical system such as an edge or a damper in the low frequency range, but is
known to occur due to magnetostriction or current distortion in the high frequency range. In
order to reduce the latter distortion, that is, distortion caused by magnetostriction or current
distortion, various proposals have been made in the prior art and it is JP-A-54-89618 (2). The
main ones are as follows. (1) As the material in the vicinity of the gap formed by the center pole
and the plate, for example, one with a small hysteresis such as a laminated core is used. This
improves the non-linearity of the voice coil impedance and reduces current distortion. (11) The
magnetic flux generated by the voice coil is canceled by spreading the copper cap on the center
pole. Qii) Place an aluminum ring or the like in the magnetic circuit to cancel the magnetic flux
created by the voice coil. However, since the strain reduction methods in these conventional
examples are so-called passive measures that are limited by the conductivity of the material, the
magnitude of hysteresis, etc., it is impossible to reduce the strain as desired. I have the drawback
I said. The present invention ameliorates the drawbacks of the above-described example, and is
intended to reduce distortion of an electrodynamic speaker drive unit by active electric control.
The present invention will be described with reference to the drawings. . Page 5 Figure 1 shows
an embodiment of the present invention, wherein 1 is a center pole, 2 is a magnet, 3 is a plate,
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and 4 is a voice coil bobbin inserted into the gap between the center pole 1 and the plate 3. , 5 is
a voice coil wound on a bobbin 4, 6 is an upper magnetic flux detection coil, 7 is a lower
magnetic flux detection coil, 8 is an amplifier having an integration characteristic, and S is a
feedback coil. First, the operation of the embodiment of FIG. 1 will be described qualitatively.
Now, when the current 1 flows in the voice coil 5, the voice coil 5 is driven axially between the
center pole 1 and the plate 30, that is, vertically in FIG. 1, and the diaphragm coupled to the
voice coil bobbin 4 accordingly. (Not shown) is driven. At this time, the upper and lower magnetic
flux detection coils ?, 7 respectively detect the magnetic flux crossing the upper end and the
lower end of the voice coil 5, and the output voltage or output current is supplied to the positive
and negative input terminals of the amplifier 8, respectively.
The amplifier 8 amplifies the difference between the input voltage or the input current, and the
output is applied to the feedback coil 9. Here, when the gain of the amplifier 8 is sufficiently
high, the upper side 6 ,,. And a current such that the difference between the output voltage or the
output current of the lower magnetic flux detection coil 6.7 becomes zero flows from the
amplifier 8 to the feedback coil 9, and as a result, the total magnetic flux across the voice coil 5
becomes constant. Control works. The force f acting on the voice coil 5 is f according to the
equation representing the N-flow magnetic interaction, where f is the average density of
magnetic flux crossing the voice coil 6, E is the length of the voice coil 5, and ? is the voice coil
6. It becomes a flowing current. Since the average density i of the magnetic flux is constant due
to the control, the force f is exactly proportional to the current source. The above is an outline of
the qualitative operation, and then FIG. We will explain strictly outside work according to Fig.3.
FIG. 2 is a three-dimensional representation of the voice coil 6 and the upper and lower magnetic
flux detection coils 6.7 in the embodiment of FIG. In FIG. 2, da is an area segment of the surface S
on which the voice coil 5 is wound, I is a current EndPage flowing through the voice coil 5: page
27 and the arrow direction in FIG. "Co11il is a voice coil in the first turn, vector J is a current
density, and is uniformly distributed in the cross section of the voice coil 5. dli is a element vector
of JCo11iJ, dsl is an upper end face 9 ? 0 area segment vector, da2 is an area segment vector of
the lower end surface s2, 8 is a unit normal vector of the surface S on which the voice coil 5 is
wound, n Is an axial unit vector of the voice coil 5 and k is a tangent unit vector of the voice coil
winding, and the flow direction of the armature is taken in the positive direction. Furthermore,
reference numerals 6 and 7 denote upper and lower magnetic flux detection coils wound around
the upper and lower ends of the voice coil 6, and are wound the same number of times in the
direction of the arrow q. By doing this, the membrane property is not lost. Further, voltages e and
el of upper and lower magnetic flux detection coils 6.7 are voltages of 6a and 7a measured with
reference to 6b and 7b. Furthermore, B is the magnetic flux density. Further, FIG. 3 shows a cross
section of the voice coil 6. h is the height of the winding of the voice coil 6, and d is the width. In
addition, generalization of the discussion by making the cross section rectangular, the force
acting on the voice coil 5, vector F is a general integration of the product of the current density J
and the magnetic flux density B where the current flows It can be expressed in the form of F ?
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? f J X B dv...
Since the current flows uniformly in the cross section of the coil, the volume integral is only the
space occupied by the voice coil winding. For this reason, the volume element dv is dv =
?h?ds... , F 2 h / (JXB) da иииииииииииииииииииииииии Here, since the direction of the current density I is the
same as that of the vector, equation (3) is F = hJ, / 1cXBds... It becomes I = l work l. By the way,
to represent the control as described in FIG. 1, that is, the control such that the difference
between the electromotive forces e and el of the upper and lower magnetic flux detecting coils 6
and 7 becomes zero, Just do it. First, the electromotive forces e and el are t according to
Faraday's law, and the negative sign is attached to the second equation because the directions of
S1 and B2 are different. ???? Since the control described in FIG. 1 is such that the difference
between e and 01 becomes zero, the following equation (6) is obtained. ? [FB dB ? + fnds *) 20
(6) t There is no penetration in the magnetic flux density B. Therefore, if B is divided by an area
on a closed surface, it will be identically zero, but this property can be used For example, the area
fraction of the magnetic flux density B in one closed surface formed by sB1 + Bt and (8 и S) is
expressed as follows. fB (dLI work + dsS ten d8) twenty ..... where ds: 5ds10. Then, substituting
equation (7) into equation (6), ? / Bds = O... (8) If t is obtained and integration is performed, /
'Bds = ?. ?????????????????????????????????????
Equation (9) is the result of mathematical expression of the control described in FIG. 1, which
indicates that the total number of magnetic fluxes crossing the surface S on which the voice coil
5 is wound is constant. Now, at this time, it will be as follows if it investigates what the force
which acts on the voice coil 5 becomes. First, the unit vector 8 is n, from the direction p, a = k X n
иииииииииииииииииииииииииииииииии (1C) Become. If this equation is used to transform equation (9), first, fBds = fBsds
= fB (kXn), but the last term can be further transformed and eventually ?. =-F (kXB) ncig-(11) is
obtained. On the other hand, as shown in the equation (i), the force F acting on the voice coil 5 is
EndPage: Page 311: F = hIf (kXB) ds, substituting the equation 4) into the equation (11) F, n = HJ?.
........... (12) is obtained. Here ? ?. Is the total magnetic flux across the surface S on which the
voice coil 5 is wound, which is defined by the equation (9), but the average magnetic flux density
B of the surface on which the voice coil 5 is wound. If you introduce, ?. : BoS ииииииииииииииииииииииии (13)
where S is the area of the surface of the voice coil 5 is wound, 5 = 4Ci? ? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? (14) Here, l is the total length of the voice coil. Furthermore, there is a
relation of I = JX (nXd) (16) between the current density J and the current I. By substituting the
equations (13), (14) and (15) into the equation (12), F-n knee Bo-1-I ------ (16) is obtained. The
equation (16) shows that the force F-n acting in the axial direction n of the voice coil 6 is exactly
proportional to the current 1 flowing through the voice coil 5, as a result of applying the control
described in FIG. It is an expression which proves that the present invention is effective in
distortion reduction. Needless to say, B in equation (16). It is clear from the definition that p is a
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constant. As is apparent from the above description of FIGS. 2 and 3, the force generated in the
whiss coil 6 is a voice by performing control such that the differential voltage between the upper
and lower magnetic flux detection coils 6.7 becomes zero. It can be made to be exactly
proportional to the coil current. A method of realizing control to make the voltage or current
difference of the magnetic flux detection coil 6.7 described in FIG. 1 zero is as follows. The
amplifier 8, the feedback coil 9, and the upper and lower sides in FIG. The loop gain consisting of
the magnetic flux detection coil 6.7 is not special, and in general, since it is a minimum phase
shift circuit, feedback control can be sufficiently performed by using a negative feedback
technique. In addition, the control such that the voltage difference between the upper and lower
magnetic flux detection coils 6.7 becomes zero is essentially the same as the 13-based control
such that the current difference between the detection coils 6.7 becomes zero. The control to
make the current difference zero when the input impedance of the amplifier 8 is extremely low,
and the control to make the voltage difference zero when the input impedance of the amplifier 8
is high, regardless of which control There is no change in the effect of the present invention.
Further, from the above description, if the drive unit having the electrical control according to
the present invention is driven by an amplifier without current distortion regardless of load, socalled constant current amplifier, the force generated by the drive unit is completely undistorted
Thus, a distortion-free speaker system can be configured.
Next, the specific arrangement of the upper and lower magnetic flux detection coils 6.7 will be
described with reference to FIGS. FIG. 4 shows the upper magnetic flux detection coil 6 and the
lower magnetic flux detection coil 7 wound closely to the upper end and the lower end of the
voice coil 6, whereby the voice coil 5 vibrates with a large amplitude. Even in this case, the
magnetic flux detection coil 6.7 can move together with the voice coil 5 to 14l- so that the
magnetic flux crossing the upper and lower end faces of the voice coil 5 can be accurately
detected. On the other hand, when the amplitude of the voice coil 5 is small, for example, in a
tweeter, it is not necessary to wind the magnetic flux detection coil 6 ░ 7 in close contact with
the voice coil 6 in particular, as shown in FIG. The magnetic flux detection coil 6.7 may be wound
at a position corresponding to the upper end and the lower end of the coil, and for the same
reason, as shown in FIG. You may wrap 6.7. Even in this case, substantially the same effects can
be obtained. FIG. 7 is another embodiment showing a method for extracting a differential voltage
by connecting the upper magnetic flux detection coil 6 and the lower magnetic flux detection coil
7 in reverse polarity. If the number of turns of the upper and lower magnetic flux detection /
output coils 6.7 is made the same, the differential voltage is proportional to the difference of the
magnetic flux crossing the both coils 6.7. 8 (a), l (b) and I (Q) show the specific arrangement of
the feedback coil 9, and the feedback coil 9 EndPage: page 415, the upper, lower and upper and
lower sides of the plate 3, respectively. The case of winding on both sides is shown. The magnetic
field produced by the feedback coil 9 crosses the wound surface of the voice coil 5, and in either
case, operates as a feedback coil. FIG. 9 shows an embodiment in which the feedback coil 9 is
wound under the center pole 1. Also in this case, the magnetic field generated by the feedback
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coil 9 crosses the wound surface of the voice coil 5 and can operate as a feedback coil. . As
described above, according to the present invention, the upper and lower magnetic flux detection
coils for detecting the magnetic flux crossing the upper and lower ends of the voice coil are
provided, and the difference between the output voltage or output current of each magnetic flux
detection coil This is applied to the feedback coil separately provided in the magnetic circuit, and
the force coefficient of the drive unit is made constant, so that distortion due to magnetostriction
and current distortion can be greatly improved. . Also, if the voice coil itself is driven by a socalled constant current amplifier without current distortion regardless of load, the force
generated by the drive section is completely free of distortion, and a speaker system with no
distortion is constructed. Can.
? FIG. 1 is a cross sectional view showing an embodiment of the present invention, and FIGS. 2
and 3 are perspective and cross sectional views for explaining the operation of FIG. 1, FIG. 4, FIG.
6 and FIG. The figure is a cross-sectional view showing the specific attachment of the magnetic
flux detection coil. Fig. 7 is a connection diagram showing a connection state for taking out the
differential voltage of the magnetic flux detection coil, and Fig. 8 (a) l (b), (C) and Fig. 9 show
specific attachment of the feedback coil. Is a cross-sectional view showing a state. 1? и и и и и и и и
Center pole, 2 и и и и и и и и и и и и и и и и и и и и и и и и и и plate и 4 и и old voice coil bobbin, 5 ░ и и и и и voice coil,
6 и и и и Upper magnetic flux detection coil, и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и
и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и feedback coil. Name of agent Attorney Nakao Toshio
Nakano has 1 person Figure 1 Figure 2 Figure 4 End Page: 5 Figure 4 Figure 5 Figure 7 f Figure
8 Figure 9/9 End Page: ?
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