JPH0728471B2 - Drive - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a drive device for driving a vibrator arranged in a cabinet having a resonance opening.

[Prior Art] Conventionally, a phase inversion (bass reflex) speaker system is known as an acoustic device in which a vibrator is disposed in a cabinet having a resonance opening (resonance boat). 21st
(A) and (b) are a perspective view and a sectional view showing an example of composition of such a bass reflex type speaker system. In the speaker system shown in the figure, a hole is formed in the front surface of a cabinet 1, a diaphragm (speaker unit) 4 including a diaphragm 2 and an electrodynamic electroacoustic transducer 3 is attached, and an opening 6 and a sound path are provided below the vibrator. A resonance port 8 having 7 is provided. The cabinet 1 and the resonance port 8 form a Helmholtz resonator.

As a drive device for driving the speaker unit 4 of such a speaker system, a power amplifier having an output impedance of substantially 0 has been generally used.

FIG. 22 shows an electric equivalent circuit when the bass reflex speaker system of FIGS. 21 (a) and 21 (b) is driven by a so-called constant voltage by a power amplifier having an output impedance of 0. In the figure, E _V is the output voltage of the constant voltage source that is a power amplifier, R _V is the voice coil resistance of the speaker unit 4, and L _O and C _O are the dynamic impedances generated by the movement of the voice coil of the speaker unit 4. Equivalent capacitance (or equivalent mass) and equivalent inductance (or inverse of equivalent stiffness), L _C is equivalent inductance of cabinet 1 (or inverse of equivalent stiffness), and C _P is equivalent capacitance (or equivalent mass) of port 8 ing.

FIG. 23 shows the electric impedance frequency characteristic of the circuit of FIG. In the figure, f ₁ is a first resonance system (hereinafter, referred to as “the first resonance system” substantially formed by the dynamic impedances L _O and C _O of the speaker unit 4 and the equivalent stiffness 1 / L _{C of the} cabinet 1).
The resonance frequency (first resonance frequency) of the unit-side resonance system, f ₂ is the second resonance system (hereinafter, referred to as “the resonance frequency of the unit side resonance system”) formed by the equivalent mass C _P of the port 8 and the special stiffness 1 / L _{C of the} cabinet 1. The resonance frequency (second resonance frequency) of the resonance side (second resonance frequency) and f ₃ do not become the sound pressure, but substantially the dynamic impedances L _O and C _O of the speaker unit 4 and the equivalent mass C _{P of the} port 8 It is the resonance frequency of the third resonance system formed by.

Among these resonance frequencies, the resonance frequencies f ₁ and f ₂ are
Direct effect on the sound pressure, the Q value Q ₂ of the resonant-side resonance system at the Q value Q ₁ and the resonance frequency f ₂ of the unit side resonance system at the resonant frequency f ₁ is a large influence on the frequency characteristics and the sound quality of the output sound pressure.

By the way, such a bass reflex type speaker system
When driving at constant voltage, for example, when the resonance frequency f ₂ on the resonance side is lowered, the Q value Q ₁ on the unit side increases and the Q value Q ₂ on the resonance side increases.
Since the resonance frequency and Q value depend on each other such that the Q value decreases, the Q value Q ₁ on the unit side, for example, is set to flatten the frequency characteristic of the output sound pressure. Resonant side resonance frequency f ₂ It is necessary to highly match the unit side and the resonance side, such as setting to, and there is a disadvantage that there are many design restrictions.

Further, when the cabinet is downsized, the equivalent stiffness 1 / L _{C of the} cabinet becomes large and the equivalent inductance L _C becomes small. As a result, Q ₁ is large and Q ₂ is small. For this reason, the conventional constant voltage drive system is difficult to operate normally as a bass reflex speaker system, and the cabinet of the bass reflex speaker system is downsized without sacrificing the frequency characteristics and sound quality of the output sound pressure. It was difficult.

FIG. 24 shows a negative impedance generating circuit shown in Japanese Patent Application No. 62-334262 (Japanese Patent Laid-Open No. 1-302997) previously filed by the present applicant. The circuit shown in the figure is an amplifier circuit with a gain of A.
The output of 31 is applied to a load 32 such as a speaker, the current flowing through this load 32 is detected by a detection resistor (value R _S ), and the detected voltage is amplified through a feedback circuit 33 of transfer gain β.
It is configured to feed back positively to 31. The output impedance value of this circuit is R _S (1-Aβ), where A
If β> 1, an open stable negative impedance (negative resistance) is obtained. If such a negative impedance generating circuit is used as a driving device in the equivalent circuit of FIG. 22 and the negative resistance −R _O is included in the output impedance, the voice coil resistance R _V is reduced or invalidated, and the output The Q ₁ can be made smaller and the Q ₂ can be made larger than that in the case where a power amplifier having an impedance of 0 drives at a constant voltage, which is effective for downsizing a bass reflex type speaker system.

However, even in this case, if the negative resistance −R _O is constant,
Since Q ₁ and Q ₂ cannot be set independently, Q ₁ and Q ₂
There is an inconvenience that some restrictions remain on the speaker unit and the cabinet to set the respective values to desired values.

[Problems to be Solved by the Invention] In view of the problems in the above-mentioned conventional type, the present invention provides a drive device for driving a vibrator of an acoustic device in which the vibrator is disposed in a cabinet having a resonance opening, The respective Q values at the first resonance frequency due to the vibrator and the stiffness of the cabinet and at the second resonance frequency due to the stiffness of the cabinet and the resonance aperture can be independently set, thereby reducing the size of the acoustic device and improving the braking force. It is an object of the present invention to improve the performance of a system including the acoustic device and the driving device of the present invention.

[Means for Solving the Problems] In order to solve the above-mentioned problems, according to the present invention, in a drive device for driving the vibrator of an acoustic device in which the vibrator is arranged in a cabinet having a resonance opening, the vibrator is provided. The first resonance frequency by the stiffness of the cabinet and the cabinet and the second by the stiffness of the cabinet and the resonance aperture.
At least one of the output impedances at the resonance frequency is a negative impedance, and the output impedance values are different from each other.

[Operation] The output impedance of the driving device is negative impedance-
Z _O and completely nullifies the impedance Z _V (for example, R _{V in} FIG. 22) unique to the vibrator, that is, Z _V −Z _O = 0 (R _V − in FIG. 22) When R _O = 0), the equivalent circuit of FIG. 22 will be described. A parallel resonance circuit on the unit side (unit side resonance system) including an equivalent inductance L _O and an equivalent capacitance C _{O of} the speaker unit is a driving device. Since it is short-circuited via the constant voltage source E _V , Q ₁ becomes 0, and resonance does not substantially occur. In other words the unit-side resonance circuit will be driven in a state of being fully braked from the drive E _V. The resonance side series resonance circuit (resonance side resonance system) consisting of the equivalent stiffness 1 / L _{C of} the cabinet and the equivalent mass C _{P of the} resonance aperture is also short-circuited via the drive unit E _V. Being a circuit, the calculated Q ₂ is ∞, ignoring the acoustic equivalent resistance of the cabinet and the resonant aperture. Also in this case,
Since the unit side resonance circuit and the resonance side resonance circuit would be driven independently each from the drive E _V, interdependence between the the unit side resonance circuit and the resonance resonant circuit is eliminated, the resonant frequency The f ₁ and f ₂ and the Q values Q ₁ and Q ₂ can be set independently. In addition, R _V -R _O > 0
, Or if the acoustic equivalent resistance of the cabinet and the resonant aperture cannot be ignored, Q ₁ and Q ₂ are 0 and ∞, and the output impedance of the driving device is 0. It becomes a value between the Q value in the case of. Further, when the output impedance of the driving device has a positive value, Q ₁ increases and Q ₂ decreases as the output impedance increases.

Considering a bass reflex speaker system in which the resonance frequency between the cabinet and the boat (resonance opening) is set low while using a small cabinet, this is a large Q ₁ compared to a standard design bass reflex speaker system. With a small Q ₂ . Then, the negative resistance −R _O (R _V
When driven with -R _O ≧ 0), Q ₁ becomes smaller and Q ₂ becomes larger as the absolute value of the negative resistance −R _O becomes larger as described above. First
The figure shows the relationship between such negative resistance −R _O and Q ₁ and Q ₂ .

In the figure, when R _O = 0, it is a conventional general constant voltage drive state. Here, -R _O is made smaller than 0, and -R _V
Q ₁ decreases almost linearly toward 0 and Q ₂ increases on the contrary, but it does not become ∞ and approaches the value determined by the acoustic resistance of the cabinet and port. .

Therefore, at some -R _O , Q ₁ and Q ₂ may have desired values, but as shown in FIG.
₁ value of -R _O to (= A) is obtained (-R _O = -R _A) and the desired Q ₂ '
(= B) the value of -R _O which is obtained (-R _O = -R _B) and many may be different.

According to the invention, in such a case, the driving impedance -Z _O at the frequency f ₁ of the (= Z ₁₎ to -R _A, Frequency
By setting the drive impedance −Z _O (= Z ₂ ) at f ₂ to −R _B , desired Q ₁ and Q ₂ can be obtained.

Further, depending on the design of the cabinet, both Q ₁ and Q ₂ may become large, and it may be desirable to reduce the Q value of both. In such a case, according to the present invention, the second
As shown in the figure, drive impedance at frequency f ₁
The Z ₁ negative (-R _A), may be set a driving impedance Z ₂ at the frequency f ₂ to the positive (R _B). Further, on the contrary, when it is desired to make both Q ₁ and Q ₂ large values, according to the present invention, the driving impedance Z ₁ at the frequency f ₁ is made positive (R _A ) and the driving impedance Z ₂ at the frequency f ₂ is set. the may be set to a negative (-R _B).

It should be noted that there is no particular limitation on the other resonance point f ₃ because it is not related to the output sound pressure, but in order to suppress unnecessary operation, the impedance Z ₃ at this frequency f ₃ is set to Z ₃ <
It is desirable to set it to 0.

[Effect] As described above, according to the present invention, it is substantially determined by the vibrator and the cabinet when driving the vibrator of the acoustic device in which the vibrator is arranged in the cabinet having the resonance opening. The driving impedances (output impedances of the driving device) Z ₁ and Z ₂ at the first resonance frequency f ₁ and the second resonance frequency f ₂ determined by the cabinet and the resonance opening are both negative values, and By setting Z ₁ ≠ Z ₂ or by setting one of Z ₁ and Z ₂ to be positive or 0 and the other to be negative, Q ₁ and Q ₂ can be set independently. This makes it possible to design an acoustic device having a resonant aperture, for example a loudspeaker system, without being bound by the usual bass reflex type constraints. For example, it is possible to downsize the cabinet and downsize the system without sacrificing sound pressure and sound quality. Further, since an appropriate Q value is obtained at each resonance frequency f ₁ and f ₂ , the degree of freedom in design is further improved than that when the output impedance is negative (−Z _O ) and constant, and depending on the conditions, − performance improvement than those of Z _O constant can be expected. Further, the driving impedance Z ₁ at the first resonance frequency f ₁ is set to a negative value and Q ₁ is lowered to drive the unit side in a braking state.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows a basic circuit configuration of a driving device according to an embodiment of the present invention. In the drive device shown in FIG.
The output of the amplifier circuit 31 is applied to the load Z _L by the speaker 32. Then, the current I _L flowing through the load Z _L is detected and positively fed back to the amplifier circuit 31 via the feedback circuit 33 having the transfer gain β.
In this way, the drive output impedance Z
_O is calculated as Z _O = Z _S (1-Aβ), where Z _S is the impedance of the sensor that detects the current I _L. From this equation, if Aβ> 1, Z _O becomes an open stable negative impedance. Here, if A, β, or Z _S has a frequency characteristic, the output impedance Z _O can have a frequency characteristic.

Figure 4, both the output impedance Z ₁ and Z ₂ in each of the frequencies f ₁ and f ₂ is negative impedance,
A circuit diagram in the case where values close to each other is sufficient is shown. The circuit of the figure uses a current detection resistor R _S as a sensor for detecting the current I _L , and has a frequency characteristic including a capacitor C ₁ and resistors R ₁ and R ₂ as a negative feedback circuit 33 (within a required band). CR circuit 33a having a non-flat frequency characteristic and an amplifier having no frequency characteristic (flat frequency characteristic in the required band)
33b is used to impart a frequency characteristic to the transfer gain β of the negative feedback circuit 33. This circuit is based on the CR circuit 33.
If a is included in the current detection sensor Z _S , it can be considered that the sensor Z _S has frequency characteristics. Figure 5 shows
4 shows frequency characteristics of the circuit of FIG. In FIG. Z ₂ = R _S (1-A _{β O} ). Further, when the output impedance curve is approximated to the broken line according to the Nyquist method, the frequency f _P of the break point P at which the output impedance falls from Z ₁ to Z ₂ is approximately 1 / 2πC.
₁ R ₂ .

FIG. 6 shows a circuit example when Z ₁ <Z ₂ <0, and FIG. 7 shows frequency characteristics of the circuit of FIG.

In Fig. 6, Z ₁ = R _S (1-A _βO ) And the corner frequency f _P is approximately 1 / 2πC ₁ R ₁ .

FIG. 8 shows an example of a circuit when Z ₁ <Z ₂ and Z ₂ is greatly changed with respect to Z ₁ . In the circuit of the figure, the frequency is set by the twin T circuit 35 in which the dip frequency is set to f _2.
A signal having a dip in f ₂ is fed back to the amplifier circuit 31.
Therefore, as shown in FIG. 9, the output impedance can be increased only in the output impedance near the frequency f ₂ . In the circuit of FIG. 8, the output impedances Z ₁ and Z _{3 at} frequencies f ₁ and f ₃ are Z ₁ = Z ₃ = R _S (1-A _βO ), and _βO can be set to an arbitrary value. be able to. Further, the variable resistor VR _{1 in} the circuit of FIG. 8 allows the shape of the curve of FIG. 9 to be varied as shown in FIG. 10, and the variable resistor VR ₂ causes the shape of the curve of FIG. It can be changed.

In the circuit of FIG. 8, if the dip frequency of the twin T circuit 35 is set to f ₁ , as shown in FIG. 12, Z ₁ >
It can be Z ₂ , Z ₃ .

The resonance at the frequency f _{3 is} a resonance not related to sound pressure,
Figure 4 thereof, in the circuit of FIG. 6 and FIG. 8, lower the Q value Q ₃ in this frequency f ₃ output impedance Z ₃ at this frequency f ₃ as a negative impedance, the speaker 32 is unnecessary movement You have braked enough to prevent

FIG. 13 shows an LC resonance circuit 36 in place of the twin T circuit 35 in the circuit of FIG. By using the LC resonance circuit 36 in this way, the same operation as the circuit of FIG. 8 can be performed.

FIG. 14 shows the LC resonance circuit 37 connected in series to the feedback system. In the circuit of the figure, the resonance frequency of this LC resonance circuit 37 Since the feedback amount (transmission gain β) becomes maximum at, the output impedance can be minimized at the frequency f, as shown in FIG.

Therefore, by setting this frequency f to f ₁ or f ₂ ,
Output impedance, as shown in Figure 16 or Figure 17.
Z ₁ and Z ₂ can be significantly different.

FIG. 18 shows a circuit in which a second LC resonance circuit 38 resonating at a frequency f ₃ is added to the circuit of FIG. 15, and as shown in FIG. 19, the output impedance at the frequency f ₃ is lowered. Has lowered the Q value Q ₃ . This is effective in preventing unnecessary movement of the speaker 32. First
In Figure 19, Is.

In the above embodiments, the output impedance Z _O is Z _O
= R _S (1-Aβ), and when β ≧ 0, the maximum value of Z _O is R _S
However, by using the feedback circuit 33 for both positive feedback and negative feedback, it is possible to set one of Z ₁ and Z ₂ to a negative value and the other to a positive value of R _S or more. .

FIG. 20 shows an example of a circuit in which the transfer gain β is β = β _O {F (X) -F (Y)} and has both positive and negative components.

As shown in the figure, the feedback circuit 33 has a transfer characteristic F
With (X) and -F (Y), β> 0 in the band where the gain of F (X) exceeds F (Y), and Z _O = R _S (1
-Aβ), the output impedance becomes R _S or less, and a negative impedance can be realized when Aβ> 1, and conversely β <0 in the band where the gain of F (Y) exceeds F (X). Therefore, the output impedance is a positive impedance above R _S.

As described above, in the speaker system having the bass reflex type structure, at least one of the resonance points f ₁ and f ₂ related to the sound pressure is driven with a negative impedance, and the resonance points f ₁ and f ₂ are also driven.
By setting the output impedance values Z ₁ and Z ₂ at Z ₁ ≠ Z ₂ , the Q values Q ₁ and Q ₂ at the resonance points f ₁ and f ₂ can be set independently, and the braking force and performance can be improved. And the sound quality can be improved.

[Modification of Embodiment] In the above-described embodiments, an example in which the resistor R _S is used as a sensor for current detection is shown. However, as this sensor, a current probe such as a current transformer (CT) or a Hall element is used. May be used. Further, a reactance element such as a capacitor or an inductance may be used as this sensor, and in this case, the sensor itself can have frequency characteristics. Furthermore, by differentiating or integrating the outputs of these sensors, it is possible to impart frequency characteristics or flatten them. For example, by detecting the current I _L by the terminal voltage of the resistor R _S and differentiating or integrating this in the feedback circuit 33, it is possible to give the transfer gain β a frequency characteristic,
The current I _L is detected by the terminal voltage of the capacitor, and the feedback circuit
If this is differentiated in 33, the frequency characteristic of the transfer gain β becomes flat.

Further, in order to give the feedback circuit 33 frequency characteristics, the feedback amplifier (for example, 33b in FIG. 4) itself may be internally fed back with current or voltage to give the frequency characteristics.

[Brief description of drawings]

1 and 2 are characteristic diagrams showing the relationship between the output impedance and the Q value for explaining the basic concept of the present invention, and FIG. 3 shows the basic configuration of the audio device according to the embodiment of the present invention. Explanatory diagram, FIG. 4 is a circuit diagram showing a first embodiment of the present invention, FIG. 5 is a frequency characteristic diagram of output impedance of the circuit of FIG. 4, and FIG. 6 is a second diagram of the present invention. FIG. 7 is a frequency characteristic diagram of output impedance of the circuit of FIG. 6, FIG. 8 is a circuit diagram of a third embodiment of the present invention, and FIGS. FIG. 13 is a frequency characteristic diagram of output impedance according to setting of each constant in the circuit of FIG. 8, FIG. 13 is a circuit diagram showing a fourth embodiment of the present invention which operates similarly to the circuit of FIG. FIG. 14 is a circuit diagram showing a fifth embodiment of the present invention, and FIGS. 15 to 17 are circuit diagrams of FIG. FIG. 18 is a frequency characteristic diagram of the output impedance according to the setting of each constant in FIG. 18, FIG. 18 is a circuit diagram showing a sixth embodiment of the present invention, and FIG. 19 is a frequency characteristic diagram of the output impedance of the circuit of FIG. FIG. 20 is a circuit diagram showing a seventh embodiment of the present invention, FIGS. 21 (a) and 21 (b) are sectional views showing the structure of a conventional bass reflex type speaker system, and FIG. FIG. 23 is an electrical equivalent circuit diagram when the bass reflex type speaker system is driven at a constant voltage, FIG. 23 is an electrical impedance frequency characteristic diagram of the equivalent circuit of FIG. 22, and FIG. 24 is a negative impedance generation according to the prior application. It is a basic block diagram of a circuit. 1 …… Cabinet 4 …… Vibrator (speaker unit) 8 …… Resonance port (resonance opening) 31 …… Amplifier circuit 32 …… Speaker 33 …… Feedback circuit f ₁ …… First resonance frequency f ₂ …… First 2 Resonance frequency Z ₁ ... Output impedance at frequency f ₁ Z ₁ ... Output impedance at frequency f ₂

Claims (1)

[Claims] 1. A vibrator disposed in a cabinet having a resonance opening for directly radiating sound and driving a Helmholtz type resonator constituted by the resonance opening and the cabinet for radiating resonance sound through the resonance opening. A driving device for driving a first resonance frequency which is substantially determined by a dynamic impedance of the vibrator and an equivalent stiffness of the cabinet, and a second resonance which is a resonance frequency of the Helmholtz resonator. At least one of the output impedances at each frequency is a negative impedance, and is configured to have different output impedance values from each other.