JPH0474919B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic electroacoustic transducer capable of detecting changes in magnetic flux in a magnetic field in which a voice coil is placed.

As shown in Fig. 1, the basic structure of a dynamic speaker is that a ring-shaped magnet 1 and a center pole 2 placed at the center are integrally connected at the bottom by a bottom yoke 3, and a ring-shaped magnet 1 is integrally connected to the center pole 2 at the bottom. The top yoke 4 is fixed, a gap 5 is formed between the top yoke 4 and the center pole 2, and a voice coil 6 is disposed within the gap 5.

Here, if the magnetic flux density of the magnetic flux penetrating the side surface of the voice coil 6 among the magnetic flux generated from the magnet 1 is B (Wb/m ² ), then the value of the driving force F acting on the voice coil 6 is F= It is expressed as B・L・I(N).

However, when a current flows through the voice coil 6, a new magnetic flux is generated from the voice coil itself as shown in FIG. 2, and this passes through the center pole 2, so that the magnetic flux inside the center pole 2 is changed. For this reason, there is a problem that the magnetic flux density B penetrating the peripheral surface of the voice coil, which is directly related to the driving force of the voice coil 6, changes, and the driving force F does not become linear with respect to the signal current I.

Furthermore, since the magnetic flux density within the magnetic gap 5 is not uniform along the gap 5, when the voice coil moves along the gap 5, the magnetic flux density B related to the voice coil also changes at each moving position.
This is also a factor that makes the driving force F nonlinear.

This invention was made in view of the above problems,
The objective is to provide an electroacoustic transducer that has linearity between the voice coil current I and the voice coil driving force F.

In order to achieve the above object, the present invention provides an electromagnetic electroacoustic transducer including a magnetic circuit and a voice coil, in which magnetic flux is attached to the voice coil and intersects with the side surface of the voice coil. a detection coil that detects a change in magnetic flux related to driving the voice coil; an integrator that integrates a signal corresponding to the change in magnetic flux; and an integrator that adds the output signal of the integrator and a DC voltage corresponding to a steady magnetic field. and a divider that divides the input signal to be reproduced by the output signal of the adder, and the voice coil is driven by the output of the divider.

A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

The force exerted by the current flowing in the magnetic field is the magnetic flux density B
The direction of , the direction of current I, and the direction of force F are all directions at right angles to each other, and in the case of a voice coil, the relationship is as shown in FIG. 3.

That is, the current I flows circularly along the voice coil, the magnetic flux density B flows radially from the inside of the coil to the outside (or from the outside to the inside), and the direction of the generated force F is vertical in Figure 3. .

Also, although the direction of magnetic flux density B is not necessarily perpendicular to the voice coil due to the characteristics of the yoke and poles, etc., the direction of vibration of the voice coil is limited to the vertical direction in the figure, so the voice coil is driven The magnetic flux related to the force can be considered as a projected magnetic flux onto a plane perpendicular to the direction of the driving force F in the figure.

Also, assuming that the voice coil is wound with uniform density over its entire length, even if the magnetic flux density B is not constant in all parts of the voice coil, it will still penetrate the circumferential surface of the voice coil. If the total magnetic fluxes Φ are equal, the driving forces can also be considered to be equal.

Therefore, it was concluded that if the magnetic flux perpendicular to the circumferential surface of the voice coil could be detected, this would be the entire magnetic flux related to the driving force of the voice coil.

Next, the form of the detection coil will be described. When the coil shown in Figure 3 is cut along the - line and stretched, the voice coil becomes rectangular as shown in Figure 4. In other words, by winding the detection coil along the outer periphery of this rectangle as shown by the dotted line, it is possible to detect changes in the total magnetic flux Φ that perpendicularly penetrates the circumferential side of the voice coil.

Specifically, _{the 1-1} line and _{the 2-1} line shown in Figure 4
When _{the two} wires are reconnected, the detection coil 7 can be wound as shown in FIG. 5, and it can be attached in close contact with the voice coil 6 as shown in FIG.

Next, a method for determining magnetic flux from the output of the detection coil will be described. When the means for detecting magnetic flux is a coil, the change in magnetic flux over time is detected as a voltage, so in order to obtain a signal corresponding to the magnetic flux density, the detection output must be integrated over time.

That is, if the output of the detection coil is e ₁ , e ₁ = -n∂Φ/∂t (n is the number of turns)...(1) Also, if the lateral area of the entire circumference of the coil is S, the total magnetic flux Φ is Φ=SB...(2), and from equations (1) and (2), e ₁ =-nS∂B/∂t...(3).

Therefore, if the amount of change in magnetic flux density B is ΔB, then ΔB=1/nS∫e ₁ dt (4), and it can be seen that the amount of change in magnetic flux can be found by integrating the detection output e ₁ .

FIG. 7 shows an integration circuit that specifically processes the above formula, and satisfies e ₂ =-1/RC∫e ₁ dt (5). Therefore, if equation (1), which is the output of the detection coil, is input to this circuit, ΔB=RCe ₂ /nS (6).

Note that a resistor R' indicated by a dotted line in the figure is a resistor inserted when avoiding DG integration.

Next, a method of correcting the nonlinearity of the driving force with respect to the input signal using the above detection coil will be described.

The driving force F is expressed as B, L, and I as mentioned above, but since the coil length L is constant, two methods can be considered to correct the fact that this becomes nonlinear due to fluctuations in the magnetic flux density B. . One is to apply feedback to the magnetic flux itself using the output of an integrator so that the magnetic flux density B becomes constant, and the other is to adjust the magnetic flux density so that B, L, and I become linear as a result. This is a method of correcting the variation in B by controlling the current I.

First, we will explain how to provide feedback to the magnetic flux. In this method, in order to change the magnetic flux density B in the magnetic circuit, an auxiliary coil 8 as shown in FIG.
It is necessary to provide That is, the audio signal obtained from the signal source 9 is amplified by the power amplifier 10 and then supplied to the voice coil 6, and the output of the detection coil 7 is sent to the center pole via the aforementioned integrator 11 and coil drive amplifier 12. It is supplied to the auxiliary coil 8 wound around 2.

The magnetic flux generated from the auxiliary coil 8 and the magnetic flux generated from the voice coil 6 are in opposite directions, so that the magnetic flux generated from the voice coil 6 is subjected to negative feedback control. Furthermore, although the integration band of the integrator 11 needs to be sufficiently wider than the frequency band of the music signal, it is not necessary to integrate even the DC component.

Next, to explain the effect, when there is an input signal as shown in Figure 9, the magnetic flux density B of a normal speaker fluctuates as shown in Figure 10, and as a result, the driving force F is distorted as shown in Figure 11. In contrast, in this invention, as shown in Fig. 12, the magnetic flux density B is always kept constant, so as shown in Fig. 13, such distortion is eliminated and positive and negative symmetry is maintained. That's why.

Next, a method for linearizing the driving force by controlling the input signal will be described. In this method, fluctuations in the magnetic flux density B are dealt with by controlling the input signal to the speaker. Since the driving force F is expressed as the product of B, L, and I, an electric circuit divider is used to divide the input signal by the output of the integrator to form a signal, and this signal is used to drive the speaker. Drive magnetic flux density B
This is to prevent fluctuations in the driving force from affecting the driving force.

That is, when the symmetrical signal v ₁ shown in FIG. 9 is applied to the input terminal V _IN in FIG. 14, the waveform shown in FIG. 15 is obtained at the output of the integrator 11.

Here, the integrator 11 is configured not to perform CD integration in consideration of problems such as drift. Therefore, the integrator 11 obtains an output corresponding only to the variation of the magnetic flux, and the output corresponding to the steady magnetic field (DC magnetic field ) cannot be obtained.

Next, the output of the integrator 11 is added with a DC voltage VB corresponding to a steady magnetic field in an adder 13, and then input to a divider 14. The value of this addition result is proportional to the magnetic flux density B, which is directly related to the driving force of the voice coil, and is hereinafter expressed as kB (k is a proportionality coefficient).

Next, the divider 14 performs the calculation V ₁ /kB, and outputs the calculation result as v ₂ .

Next, the output v ₂ of the divider 14 is amplified by a factor of A in the power amplifier 15 to become A·v ₂ , which becomes a drive signal for the voice coil 6 .

Here, the impedance of voice coil 6 is Z
Then, the current I flowing through the voice coil is I=A·v ₂ /Z _L (7). Further, the value of the output v ₂ of the divider 14 is v ₂ =v ₁ /kB (8) Therefore, I=A·v ₁ /Z _L ·kB (9).

Since the driving force of the voice coil is B・L・I, F=B・L・I …(10), and substituting equation (9) into equation (7), F=B・L・I・v ₁ / Z _L ·kB = L·A·v ₁ /Z _L ·k (11), which proves that the magnetic flux density B disappears and the influence of fluctuations in the magnetic flux density B disappears.

In the above embodiments, the present invention was applied to a dynamic speaker, that is, an electroacoustic transducer that converts an electrical input into an acoustic output. The present invention can be similarly applied to acoustic transducers.

As is clear from the above description of the embodiments, according to the present invention, it is possible to provide an electromagnetic electroacoustic transducer that has extremely accurate linearity between the voice coil current I and the voice coil driving force F. .

It also has an adder that adds the output signal of the integrator and the DC voltage corresponding to the steady magnetic field, and a divider that divides the input signal to be reproduced by the output signal of the adder. Since the distortion components are used to cancel the distortion, there is no need for a specially designed speaker system, and a general-purpose speaker or microphone can be used as is.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the conventional structure of a dynamic speaker, Figure 2 is a schematic diagram showing the magnetic flux generated in the voice coil by a signal current, and Figure 3 is a diagram showing the direction of magnetic flux density B in the voice coil and the current I. Fig. 4 is a diagram showing the voice coil in Fig. 3 cut along the - line and stretched, Fig. 5 is a diagram showing the form of the detection coil, Figure 6 is a perspective view showing the state in which the detection coil is attached to the voice coil, Figure 7 is an electric circuit diagram showing the configuration of an integrating circuit for determining magnetic flux from the output of the detection coil, and Figure 8 is a system using this invention. Figure 9 is a waveform diagram showing the input signal, Figure 10 is the influence of the input signal. Figure 11 is a waveform diagram showing the distorted driving force due to fluctuations in magnetic flux, and Figure 12 is a waveform diagram showing the state of magnetic flux corrected by the auxiliary coil. Figure 13 is a waveform diagram showing that the driving force is symmetrical when an auxiliary coil is attached and the magnetic flux is corrected, and Figure 14 is a waveform diagram showing that the driving force is linearized by controlling the input signal using this invention. FIG. 15 shows a circuit configuration of a dynamic speaker constructed as shown in FIG.
The figure shows the output waveform of the integrator, and Figure 16 shows the output waveform of the integrator.
5 is a waveform diagram showing a state in which a component corresponding to a DC magnetic field is superimposed on the waveform diagram of FIG. 5. FIG. 1...Ring magnet, 2...Center pole, 3...Bottom yoke, 4...Top yoke, 5...Gap, 6...Voice coil, 7...
...Detection coil.

Claims (1)

[Scope of Claims] 1. In an electromagnetic electroacoustic transducer equipped with a magnetic circuit and a voice coil, a magnetic flux attached to the voice coil intermingles with a magnetic flux passing through a side surface of the voice coil to drive the voice coil. a detection coil that detects a change in the magnetic flux; an integrator that integrates a signal corresponding to the change in the magnetic flux; an adder that adds the output signal of the integrator to a DC voltage corresponding to the steady magnetic field; an electromagnetic electroacoustic transducer comprising: a divider that divides an input signal to be output by an output signal of the adder; and an output of the divider drives the voice coil.