JPS603298A - Motional feedback speaker - Google Patents

Abstract

PURPOSE:To eliminate shock sound when a servo loop is locked by detecting the displacement of a vibrating system of a speaker and controlling the gain of the servo loop. CONSTITUTION:The displacement of the vibrating system of the speaker is detected by a photodetector 5, an output from a subtraction circuit 9 is given to a comparator circuit 11 so as to drive a driving coil 16 via a phase correcting filter 14 and a driving circuit 15. The displacement of a diaphragm 1 is subject to a servo so as to follow an audio signal applied to an input terminal 12 with fidelity. While the power is applied and the servo loop is locked, since the error signal of the comparator circuit 21 exceeds a reference value of comparator circuits 28, 29, a transistor 33 is turned off, an FET25 is turned on, a resistor 24 is inserted in parallel with a resistor 23 so as to decrease the gain of the servo loop.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a motion feedback system (hereinafter referred to as MFB) suitable for use in, for example, digital audio systems.
(abbreviated as ) type speaker.

Background technology and its problems In general, LP, which is the conventional recording medium for audio signals
For records, cassette tapes, etc., the low range, especially 100
Although it was not possible to sufficiently reproduce low frequencies below Hz, with the advent of so-called compact discs, for example, 10
It has become possible to obtain a reproduced signal that has flat frequency characteristics from the low frequency range including the low frequency range below 0 Hz to the area 1, and has a good S/C ratio.

For this reason, there is a growing demand for higher quality speakers, especially woofers, which are bass speakers, for converting electrical signals reproduced from such recording media through amplifiers, etc. into M-line signals. be. However, for bass sounds like this [.

The woofers used in the There is a problem in accuracy in the electrical-mechanical-acoustic conversion that causes an error in the sound pressure, and as a result, the sound pressure frequency characteristic is not flat, and there are problems such as distortion and nonlinear distortion.

Therefore, in order to flatten the sound pressure frequency characteristics and reduce nonlinear distortion, the MFB method has been proposed.

This MFB method detects the momentum of the speaker's vibration system,
The detection output is fed back to the speaker drive system to control the movement of the speaker's vibration system. Various methods have been proposed for feedback of the detection output in this MFB method.For example, the first method is to apply a voltage proportional to the speed of the diaphragm to the input side. The second method is to feed back a voltage proportional to the acceleration of the diaphragm of the speaker, and the third method is to feed back a voltage proportional to the displacement of the diaphragm.

Among these methods, the first method is particularly commonly used, and specifically, this method detects the back electromotive force of the current flowing through the drive coil of the speaker and feeds it back to the input side. With this method, it is easy to detect the momentum of the speaker's vibration system, but the detection output does not correspond to the movement of the speaker's diaphragm, which generates sound waves at the interface with the air. However, since the movement of the drive coil is detected essentially as a fast-reaction change, there is a problem that the signal detected by the coil does not necessarily correspond to the movement of the diaphragm.

Therefore, in order to obtain good sound, it is necessary that the movement of the speaker's diaphragm correspond faithfully to the electrical signal.
From this point of view, of the three methods described above, the third method seems to be the most preferable.

Therefore, a motional feedback speaker is developed that can detect the displacement of the diaphragm of a speaker that actually moves air, and feed this displacement information back to the speaker's drive system to improve the fidelity between the electrical signal and the diaphragm. considered, first
The figure is an example.

That is, in FIG. 1, (1) is a diaphragm of a speaker that moves in parallel, and a mirror (2) can be attached to this. (3) is a light source that makes a light beam incident on this mirror (2), and uses, for example, an I, -F semiconductor laser beam. The light beam (laser beam) from this semiconductor laser beam (3) is made incident on the mirror (2) via the lens (4). (5) is a photodetector which receives the reflected light beam from the mirror (2) at a position on the light receiving portion corresponding to the amount of displacement of the diaphragm (1). This photodetector (5) is arranged so that the longitudinal direction (line direction) of its light-receiving surface is located within a plane containing the incident and reflected light rays and the normal line N (FIG. 2).

The optical system of the displacement detecting means for detecting the displacement of the vibration system of the syspee force is constituted by (1) to (5), and its operation will be further explained with reference to FIG. Note) In the same figure, N is the mirror (2) of the beam from the laser beam (3).
indicates the normal at the point of incidence to .

Further, θ is the angle of incidence and reflection of the incident light beam and the reflected light beam, respectively, on the mirror (2), and these angles are equal to each other.

Now, if the diaphragm (1) is translated in parallel as shown by the broken line, that is, displaced by t in the normal mN direction, the photodetector (5)
The position of the reflected light beam from the mirror (2) that is incident on the light receiving surface of the mirror (2) is displaced by X in its longitudinal direction (line direction). This X is expressed as in the following equation.

x = 2 L slnθ , 1 In this equation, if θ is chosen to be 30°, SiH6 becomes normal, so it becomes x-t.

Therefore, the reflected light from the mirror (2) is detected by the photodetector (5).
What is captured is the diaphragm (1) that responds to the displacement of the light receiving surface.
location information can be obtained.

As an example of the above-mentioned photodetector (5), a semiconductor device detector using a PIN photodiode, the equivalent circuit of which is shown in FIG. 3, is used. In this semiconductor device detector, a photocurrent generated by an incident light beam flows through a uniform resistive layer to two output terminals tl and t2, and the difference between the resulting differential first and second position detection currents is determined. In particular, the position of the incident light beam is detected. In FIG. 3, t3 is an input terminal to which a bias voltage is supplied.

Further, R8 is a surface resistance with a constant resistivity, and depending on the position of the light incident on this resistor Rs, the resistance value between that position and each of the rays t1rj2 is proportional to its length. The output terminal tl+t is determined according to the ratio of the reciprocal of the resistance.
2, the current obtained changes. This output terminal tl,
11. obtained at t2. The point where the currents are equal corresponds to the neutral point of the speaker's vibration system. In addition, P is military, source, D is science M
C1 is the junction capacitance, and RsN is the parallel resistance.

Returning to FIG. 1 again, each current that is the first or second position detection output obtained at the output terminal jl+t2 of the photodetector (5) as described above is transmitted to the current-voltage conversion circuit (6) and (
7) and is converted into a voltage signal, and then added to an adder circuit (8).
) and the subtraction circuit (9).

Here, when the amount of light incident on the photodetector (5) changes,
The detected position information contains a large error.

Therefore, the output of the adder circuit (8) is sent to the light amount control circuit (10).
The output of this control circuit αO causes a laser light source (
3) to keep the amount of light incident on the photodetector (5) constant, and the output of the adder circuit (8) to be always constant, the amount of displacement of the diaphragm (1), that is, absolute To enable accurate detection of location information.

Also, the subtraction output from the subtraction circuit (9) is the comparison circuit 01)
is supplied to the inverting input terminal of

On the other hand, the audio signal supplied to the input terminal α is converted into a signal having a characteristic of 12 dBloc by the range limiting filter α→, and then supplied as a reference voltage to the non-inverting input terminal of the comparator circuit α. The comparison circuit α force is the difference between this reference voltage and the diaphragm (
1) is compared with the output from the subtraction circuit (9) corresponding to the displacement information, and the comparison error signal is sent to the drive coil (voice coil) αG through the speaker's phase compensation filter α→ and the drive circuit α. Supplied.

As a result, the servo is applied so that the displacement of the diaphragm (1) corresponds to the audio signal supplied to the input terminal 0. The servo is applied so that the output of the comparison circuit α force becomes 0.

Looking at the relationship between the reference voltage supplied to the non-inverting input terminal of the comparison circuit α→ and the displacement of the diaphragm (1), as shown in Figure 4, when the servo is not in use, the relationship is as shown by the broken line. Although they are in a relationship, when the servo reaches nine pieces, it is said to be a linear female relationship, as shown by the solid line. That is, the displacement of the diaphragm (1) comes to correspond to the audio signal, and nonlinear distortion is reduced.

Also, looking at the sound pressure and ΔR characteristics at this time, as shown in Figure 5, when the servo is not heated, the frequency characteristics are reduced, as shown by the broken line, especially at frequencies below 100 Hz, the sound pressure and R are reduced. However, as described above, when surf 1ζ is applied, the sound pressure rail extends to a low frequency range, and therefore the sound pressure frequency characteristic becomes flat.

Furthermore, looking at the transient characteristics at the start of operation at this time, as shown in Figure 6, in the normal FLA power method, a force signal of about 10 Hz, for example, of a rectangular wave as shown in Figure 6A, is supplied. In this case, the displacement of the diaphragm (1) changes approximately in the shape of a triangular wave as shown in FIG. 6B. This is because the diaphragm (1) moves with the start-up time determined by the resonance frequency fO of the speaker's vibration system and the damping factor of the air.

On the other hand, as shown in Fig. 1, the method of feeding back the displacement information of the speaker vibration system to the speaker drive system dramatically shortens the start-up time, as shown in Fig. 6C. The diaphragm (1) moves in the same waveform state as the rectangular wave of the input signal, and its transient characteristics are significantly improved.

By the way, this significant improvement in transient characteristics is very desirable depending on the sound, but on the other hand, practical problems arise. In other words, since the transient characteristics are good as mentioned above,
On the other hand, when the servo loop locks, a loud impact noise is generated.

This is because in Fig. 7, which shows the relationship between the displacement of the diaphragm (1) and the detected voltage related to the displacement of the diaphragm (1), that is, the output voltage of the subtraction circuit (9), when the power is turned on, If the diaphragm (1) is at its stroke center C1 when the servo loop is closed and the output ηi pressure is O, no impact noise will be generated when the servo is closed. If the neutral point is shifted in the range shown by the frame (vertical to the diaphragm) 9, or due to the placement of the speaker, for example, when the diaphragm (1) is placed horizontally, the neutral point is located at the location shown by arrow C3. In many cases, the neutral point is shifted or the detected voltage is not zero before closing the servo loop due to a shift in the neutral point or an offset in the electric circuit. If the loop is locked momentarily, a large valence 93 note will be generated when the servo loop is locked due to its good transient characteristics (rise characteristics).

This solicitation sound not only gives audible discomfort, but also has the risk of damaging the speaker in some cases.

Purpose of the Invention In view of W, the present invention detects the displacement of the vibration system of the speaker and controls the gain of the servo roots that feeds back the displacement information to the drive system of the speaker. The present invention provides a motion feedback type speaker that can eliminate impact noise.

Summary of the Invention The present invention detects a locked state of the servo roots in a motional feedback speaker equipped with servo roots that detect displacement of the vibration system of the speaker and feed back the displacement information to the drive system of the speaker. The present invention is characterized in that it comprises a detection means and a gain control means for controlling the separately listed servo roots according to the output of the detection means, and the gain is made small until the servo roots are properly locked. This is a motion feedback type speaker, which eliminates the impact noise caused by servo lock, thereby preventing discomfort and damage to the speaker.

Hereinafter, one embodiment of the present invention will be described in detail based on FIG. 8.

FIG. 8 shows the circuit configuration of this embodiment. In the figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In this embodiment, a buffer circuit Q1) is provided between the comparison circuit α and the filter α→, and the input side of this buffer circuit Q is connected to the output side of the comparison circuit 0 through the resistor (c). At the same time, connect the output side 1 of the buffer circuit (c) to the input (rag) of the filter (141).Also, connect a variable resistor and a series-connected resistor between the input side of the buffer circuit 01 and ground. (c) and a switching element (hereinafter abbreviated as FET) (c) are connected in parallel.As will be described later, when the servo roots are not properly locked, the FET (J!l) By turning on the
A resistor (C) and a variable resistor (C) are connected in parallel to reduce the gain of the servo roots, and on the other hand, when the servo roots lock, the FET (C) turns off and the resistor (C) is effectively turned off. Excluded variable resistor B? As a single unit 9, the gain of the servo loop settles to a predetermined value preset by the variable resistor stem.

Also, a rotor or filter Q0 is connected to the output side of the comparator circuit Qη.
and an amplifier (c) are provided, and the output side of this amplifier (a) is connected to the inverting input terminal of the first comparator circuit (c) and the second comparator circuit (c), respectively.
is connected to the non-inverting input terminal of the comparator circuit (c).

The non-inverting input terminal of the comparator circuit (c) and the inverting input terminal of the comparator circuit (c) are grounded via variable resistors (g) and (31), respectively. These variable resistors provide first and second reference values for determining whether or not the servo roots are locked. In other words, whether or not the servo roots are locked is determined by the difference between the detected voltage corresponding to the displacement information of the diaphragm and the reference voltage based on the audio signal, and the output (comparison error signal) of the comparison circuit Q1).
Since the output of this comparison circuit (c) is within the first and second reference values mentioned above, the servo roots are in a locked state, and if it is outside the reference values, the servo roots are locked. It is assumed that it has not been done. These first and second reference values are mainly determined by the gain of the servo loop and the time constant of the low A filter (c).

For example, if the gain of the servo loop is 46 dB and the diaphragm (1
) is 10 hazy, and the sensitivity of the position signal (the detection voltage of the comparison circuit α◇ of the amplitude of vibrating (1))
If it is IV/mm, the error is 10mm = 10 =
46 dB 200 0.05mm. Converting this to voltage is 0.05
It becomes V. If this 0.05 V error signal is multiplied by, for example, 20 times using an amplifier (B), a signal of 1.0 V is obtained.

Therefore, the reference value of the comparator circuits (a) and (c) is set to h+IV
, -IV, it is possible to determine whether the servo is locked or not, regardless of whether the error signal is within the range of ±1v. It is assumed that the comparison circuits Q→ and (c) generate a positive output signal when the input code exceeds the reference value.

The output sides of the comparison circuit Q and a9) are connected in common and then connected to the Δ-s of the transistor 09 via a resistor 0. The emitter of this transistor 03 is the positive power supply terminal +
VCC, its collector is connected to the negative power terminal -CO through a resistor 0, and an appropriate bias voltage is applied to its base as compared to the positive power terminal VOC. Then, the dart of the FET el'5) mentioned above is connected to the collector of the transistor 0 through the diode 0→.

Now, until the power is turned on and the servo loop is properly locked, if the neutral point of this force is shifted due to the reasons mentioned above, some kind of comparison error signal will appear on the output side of comparison circuit 01). The rail of the signal obtained by passing this comparison error signal through the low-pass filter (C) and lamp 0 exceeds the reference value of the comparison circuit (C) and (C). A positive output signal is obtained on the output side of c). Due to this positive output signal, transistor 0→ is turned off, diode 00 becomes conductive, and FET (c) is turned on.

As a result, a resistor (C) is inserted in parallel with the variable resistor (C), and the gain of the servo loop becomes smaller.

As shown in Figure 6, the transient characteristics when the gain of the servo loop is reduced by 7F are such that the rise time becomes slow, thereby preventing the generation of impact noise. Note that this start-up time becomes shorter as the gain of the servo loop is increased.

On the other hand, the servo loop is locked and the comparison circuit α → sends the comparison error signal to the low-pass filter (20 and amplifier 07).
When the amplitude of the signal obtained through 1 comes to be within the reference value of the comparator circuits @ and (c), a negative output coefficient is obtained at the output side of the comparator circuits (c) and (c). This negative output signal turns on transistor 04, causing diode 0
→ becomes non-conductive and FET (c) turns off. As a result, the resistor (C) inserted in parallel with the variable resistor (C) is effectively divided by υ1, and the gain of the servo loop increases to a predetermined value (maximum), returning to the normal operating state. Go in.

The transient characteristics when the gain of this servo loop is increased to a predetermined value without any control are approximately the same as those shown in FIG. Although sound is generated, the generation of impact noise can be prevented by making the transient characteristics slow as shown in Figure 6 by switching (reducing) the gain as described above.

Note that instead of using a switching element or the like as described above to switch the gain of the servo loop, other switching means,
For example, in a multi-silver, the gain may be made small until the servo loop is properly locked, and then increased once it is locked. , if the audio signal supplied to the input terminal (2) is a digital signal, the filter Q
In addition to using circuits capable of digital processing as j and comparison circuit 1llL1), an analog/digital conversion circuit is provided on the output side of the subtraction circuit (9), and a digital/analog conversion circuit is provided on the output side of the comparison circuit (c). Bye.

Effects of the Invention As described above, according to the present invention, the gain of the servo loop that feeds back displacement information of the speaker vibration system to the speaker drive system is made small until the servo loop is properly locked. There is no impact sound during lube locking9, and discomfort and damage to the speaker are prevented.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an example of a conventional circuit, FIG. 2 is a layout diagram showing an example of the displacement detection means for the diaphragm of FIG. 1, and FIG.
The figure is a circuit diagram showing an equivalent circuit of the photodetector of the displacement detection means in Figure 2, Figures 4 and 5 are characteristic diagrams for explaining the operation of Figure 1, and Figures 6 and 7 are FIG. 8, which is a diagram for explaining the present invention, is a circuit configuration diagram showing one embodiment of the present invention. (1) is a diaphragm, (2) is a mirror, (3) is a light source, (5
) is a photodetector, (8) is an addition circuit, (9) is a subtraction circuit,
αD, (c), Q9) is a comparison circuit, αQ is a drive coil,
(c)+e;'A, (:+i+ is variable resistor, φ
■ is a resistor, B is a field effect transistor (FET)
, (C) is a low-pass filter, (C) is an amplifier, 0→ is a transistor, and 0→ is a diode. Agent Sadado Ito Hide Matsukuma Wave number for Mori q/Figure 5 (1-1,) Figure 6 Figure 7

Claims (1)

[Claims] In a motion feedback type speaker biased to a servo loop that detects displacement of a vibration system of a speaker and returns all of the displacement information to the drive system of the speaker, a detection means detects a locked state of the servo loop; a gain control means for controlling the gain of the servo loop according to the output of the detection means, and the gain is made small until the servo loop is properly locked. .