JPS6016157Y2 - MFB circuit - Google Patents

Description

[Detailed description of the invention] This invention detects the movement of the diaphragm of a speaker, converts it into an electrical signal, and feeds this electrical signal back to the input circuit of the power amplifier that drives the speaker.
Regarding the tional feed back) circuit, a detector for detecting the movement of a diaphragm is realized with an extremely simple configuration, and moreover, it is possible to perform accurate detection.

2. Description of the Related Art Conventionally, an MFB circuit has been known that uses a feedback circuit as shown in FIG. 1 to control the drive of a speaker.

That is, in FIG. 1, an electrical signal applied to an input terminal 1 is supplied to a power amplifier 3 via a comparator 2, where it is amplified and then applied to a speaker 4.

The vibration of the diaphragm of the speaker 4 is detected by the detector 5, converted into an electrical signal, and then fed back to the comparator 2 via the feedback circuit 6.

The comparator 2 compares the input signal and the feedback signal, and the difference is supplied to the power amplifier 3.

Conventionally, the detection section of this type of MFB circuit has been constructed as shown in FIG.

In FIG. 2, 7 is a voice coil bobbin, 8 is a movable electrode attached to the voice coil bobbin 7, 9 is a center pole, 10 is an insulator fixed on the center pole 9, and 11 is the movable electrode on the insulator 10. A fixed electrode is attached at a position opposite to 8, and 12 is a diaphragm.

With this configuration, the voice coil bobbin 7 is driven in the left-right direction in the figure according to the input signal, and the diaphragm 12 is vibrated accordingly.

Since the facing area of the movable electrode 8 and the fixed electrode 11 changes according to the driving of the voice coil bobbin 7, the capacitance formed between these electrodes 9 and 12 changes.

Since this change in capacitance corresponds to the change in the diaphragm 12, it can be detected and fed back to the input circuit of the power amplifier.

However, in this case, the movable electrode 8 must be attached to the voice coil bobbin 7, the insulator 10 must be attached to the center pole 9, and the fixed electrode 11 must be attached on top of it, which complicates the machining of the speaker. The problem is that it is difficult to apply it to popular types of speakers because of the high cost.

Further, when applied to a squawker or a tweeter, there is a problem that the detector becomes an obstacle to sound.

Furthermore, no matter if it is applied to a woofer, squawker, or tweeter, it is inevitable that the efficiency will deteriorate.

This invention was designed to solve these conventional problems.■
This provides an integrated circuit.

That is, in the present invention, the voice coil bobbin itself is substantially made of metal foil, and the capacitance change due to the change in the opposing area between the voice coil bobbin itself and the center pole itself is detected, and this is converted into an electrical signal. This electrical signal is fed back to the power amplifier.

An embodiment of the present invention will be described below with reference to FIGS. 3 to 5.

FIG. 3 is a block diagram showing the MFB circuit according to the present invention, and parts having the same symbols as those in FIG. 1 have the same functions.

The detection unit 5 includes a detector 13 including a center pole 28 of the speaker 4 and a voice coil bobbin 30, which will be described later, an inductance 14, an oscillation circuit 15, a detection circuit 16, and a low-pass filter 17.

On the other hand, the feedback circuit 6 includes differentiators 18 and 19, buffer amplifiers 20 to 22, volumes 23 to 25, and an adder 26.

FIG. 4 shows a specific configuration of the detector 13 shown in FIG. 3.

In FIG. 4, 27 is a yoke, 28 is a center pole, 29 is a magnet, 30 is a voice coil bobbin, 31 is a voice coil wound around the voice coil bobbin 30, 32 is a diaphragm, and 33 and 34 are voice coil bobbin 30, respectively.
, are terminals connected to the center pole 28.

Note that the voice coil bobbin 30 is made of metal foil such as aluminum, or is made of a non-metallic bobbin with metal foil adhered or metal vapor-deposited.

Therefore, depending on the input signal, the voice coil bobbin 30
When is driven in the left-right direction in the figure, the diaphragm 32 is vibrated and at the same time the opposing area of the voice coil bobbin 30 and the center pole 28 changes, and the capacitance formed between them changes.

This change in capacitance corresponds to the displacement of the diaphragm 32.

At this time, the magnet 29 acts as an insulator and the yoke 27 is separated from the center pole 28, so that the induction from the voice coil 31 to the yoke 27 is caused by the center pole 2.
It is not transmitted to the voice coil 31.
It is possible to avoid the effects of the electric field generated by the voltage applied to the

FIG. 5 shows an example of the detection circuit 16 shown in FIG. 3, where 35 is the output of the oscillator 15, 36 is a coil with an inductance value of Ld, 37 is a capacitor with a capacitance value of Cd, and 38 is a buffer amplifier. , 39 is a detection diode, 4
0 is an output terminal connected to the low-pass filter 17.

In addition to the methods shown in Figures 3 and 5, there is also a method for converting changes in capacitance into electrical signals, in which a bias is applied to the capacitor and the signal is received by a high input impedance amplifier. This is undesirable because the coil induction is large.

In the above configuration, the input signal applied to the input terminal 1 in FIG. 3 is supplied to the power amplifier 3 via the comparator 2, where it is amplified and then applied to the speaker 4.

In the speaker 4, the voice coil bobbin 30 is driven in accordance with this input signal as described above, and the capacitance formed between the voice coil bobbin 3° and the center pole 28 changes accordingly.

At this time, the change in capacitance and the voice coil bobbin 30
The amplitude of is directly proportional.

That is, if the capacitance when the voice coil bobbin 30 is stationary is Co, the change in capacitance when the voice coil bobbin 30 is displaced by ΔX is ΔC, and the specific constant of ΔX and ΔC is k, then Δc = ΔX ...(1).

If the capacitance at this time is C, then C=C0+ΔC=Co++ΔX (2).

If the value of the inductance 14 combined with the capacitance C is L, then the resonant frequency f is f = 1 / (2?
r-'LC)...(31.

That is, the resonant frequency f is proportional to the 111th division of the capacitance C.

Therefore, if this resonant frequency f is detected as it is, a voltage directly proportional to the change in capacitance C cannot be obtained.

Therefore, a detection circuit as illustrated in FIG. 5 is used.

That is, if the output of the oscillator 15 (voltage 35 in FIG. 5) is e+, and the voltage across the capacitor 37 is ep, then ep=1+Om)"LdCde' 1 . 7 l...(
4)°0ω)2LdCd (where 1((jω)2LdCd).

This is passed through the buffer amplifier 38 to the detection diode 3.
9 and then taken out through a low-pass filter 17, the output voltage Ed is Ed = I e p 1 = l ell (j,)2LdCd = Eo/ (ω''LdCd) (Eo = l e + l ) becomes.

Therefore, from equations (2), (3), and (6), LCo
kLE.

Ed=LdCd" 10LdCdΔX ...(5) A = A ten.

6ΔX...(6) (A-back 4) LdCd, and a voltage proportional to the displacement ΔX of the voice coil bobbin 30 is obtained.

The electrical signal thus obtained (i.e. voltage Ed)
is first supplied to the buffer amplifier 20 as an amplitude signal, and then added to the adder 26 via the volume 23.

It is also differentiated by the differentiator 18, supplied to the buffer amplifier 21 as a speed signal, and sent to the adder 2 via the volume 24.
Added to 6.

Further, the output of the differentiator 18 is differentiated by a differentiator 19, supplied as an acceleration signal to a buffer amplifier 22, and added to an adder 26 via a volume 25.

These signals are then added from adder 26 to comparator 2 and multiplied by MFB.

In addition, when configured as shown in FIG. 4, the voice coil 31
Electrostatic induction occurs toward the center pole 28 and a signal with a frequency within the audible band is generated. However, if the oscillation frequency of the oscillation circuit 15 determined by the capacitance value of the detector 13 and the inductance value of the inductance 14 in FIG. By setting it to a sufficiently high value, accurate detection can be performed without being affected by the electrostatic induction.

According to the above embodiment, the structure of the speaker itself can be greatly simplified, and as a result, manufacturing becomes easier and productivity can be increased, so it can be easily applied to popular type speakers. can.

As described above, the present invention essentially consists of the voice coil bobbin itself of a speaker made of metal foil, and detects the change in capacitance formed between this and the center pole.
Since the FB is applied, the following excellent effects can be obtained.

(a) Processing for the speaker is extremely easy, as it is only necessary to pull out two lead wires from the voice coil bobbin and center pole, which are made of metal foil.

In particular, in recent years, speakers in which the voice coil bobbin is made of aluminum foil have been used in order to enhance the heat dissipation effect of the voice coil bobbin, but when applying the present invention to such speakers, it is extremely easy and inexpensive to apply the present invention. It can be realized.

(b) Since it is efficient and can be made compact, the detector will not become an obstacle even when applied to squawkers or tweeters.

(c) The circuit is simple and requires no special parts, so it can be constructed at a relatively low cost.

(b) Since the voice coil and the detector are directly connected, there is little phase rotation from the speaker input to the detector output, so deep MFB can be applied over a wide band.

(E) Distortion 9 frequency characteristics of the detection section, dynamic range S
/N etc. are also very good, so the degree of performance improvement after MFB is also large.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for explaining the principle of the MFB circuit, FIG. 2 is a sectional view showing the main parts of a conventional MFB circuit, and FIG. 3 is a block diagram showing an embodiment of the MFB circuit according to the present invention.
FIG. 4 is a sectional view showing the detection section, and FIG. 5 is a circuit diagram showing the detection circuit used in the above embodiment. 1...Input terminal, 2...Comparator, 3.
...Power amplifier, 4...Speaker, 5.
...Detector, 6...Return circuit, 13...
...Detection section, 14...Inductance, 1
5... Oscillator, 16... Detection circuit, 1
7...Low pass filter, 18.19...Differentiator, 20~22...Buffer amplifier, 23~
25... Volume, 26... Adder, 27... Yoke, 28... Center pole, 29... Magnet, 30... ...Voice coil bobbin, 31...Voice coil, 32
...Vibration plate, 33.34...Output terminal.

Claims (3)

[Scope of utility model registration request] (1) The voice coil bobbin of the speaker itself is substantially made of metal foil, and a change in capacitance due to a change in the opposing area between the voice coil bobbin itself and the center pole itself is detected and converted into an electric signal, An MFBI circuit characterized in that this electrical signal is fed back to an input circuit of a power amplifier that drives the speaker. (2) The MFB circuit according to claim 1, which is a utility model registration, characterized in that a voice coil bobbin in which metal foil is bonded to a non-metallic bobbin is used. (3) The sum circuit according to claim 1 of the utility model registration claim, characterized in that a voice coil bobbin in which a metal is deposited on a non-metallic bobbin is used.