JPH0584119B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a speaker drive device.

[Background of the invention]

In general, small speakers have the characteristic that the level of the low frequency component of the reproduced sound is lower than that of other frequency components, so to improve this, the frequency characteristics of the reproduced sound from the speaker are increased. In order to have a nearly flat characteristic not only in the high frequency range but also in the low frequency range, the amplitude of the low frequency components contained in the original signal is controlled by the drive device that drives the speaker (specifically, the amplifier for the original signal). Providing a boost circuit for amplification has been put into practical use.

FIG. 1 is a circuit diagram showing such a conventional Boosker circuit. In the figure, a circuit portion from an input terminal 1 to an output terminal 2 constitutes a low-frequency boost circuit A, and this circuit A is generally provided before and after a power amplifier 4 that drives a speaker 5.

In circuit A, 3 is an operational amplifier (operational amplifier), 6 is a variable resistor that determines the amount of boost, 7 is a capacitor, and 8 is a resistor. The turnover frequency _t when boosting the low range is determined by the following equation (1).

_t = 1/2πCR (1) Here, C is the capacitance of the capacitor 7, and R is the resistance value of the resistor 8.

When this low-frequency boost circuit A is used, the frequency characteristic of the speaker drive voltage shifts from 10 to 10' in Fig. 2a (where _t is the turnover frequency), and the sound pressure frequency characteristic of the speaker shifts from 9 to 9. ', and the frequency range of bass reproduction is expanded.

However, as shown in Figure 2b, in the frequency characteristic 10' at low voltage level and small output.
If you implement KdB low-range boost, if you move to high output with a high voltage level,
As seen in the frequency response of 10", the low range, which has been boosted by KdB, is the power amplifier 4.
The saturation voltage level 11 of
However, the disadvantage is that the dynamic range is reduced.

For example, if you want to boost the low range by 10dB,
Even if a 100W power amplifier is used, the power value at which saturation does not occur is 10W because there is a 10dB margin, which is extremely inefficient. For this reason, it becomes difficult to increase the amount of low-frequency boost, and therefore the effect of expanding the frequency range of low-frequency sound reproduction becomes insufficient.

[Purpose of the invention]

The present invention has been made to eliminate the drawbacks of the prior art as described above, and therefore, an object of the present invention is to improve bass reproduction without impairing the dynamic range of the power amplifier that drives the speaker. It is an object of the present invention to provide a speaker driving device that makes it possible to expand the frequency range.

[Summary of the invention]

In order to achieve the above object, the speaker driving device according to the present invention uses the low-frequency input signal level to adjust the gain of the VCA (voltage control amplifier) involved in amplifying the input signal of the power amplifier for driving the speaker, or the gain of the VCR ( By controlling the resistance value of the voltage controlled resistor (voltage controlled resistor), the amount of low-frequency boost can be automatically varied depending on the level of the input signal.

As a result, as shown in Figure 3a, the frequency characteristic of the speaker drive voltage shifts from 12 to 12' and then to 12'' as the voltage level increases, and as seen in this frequency characteristic, the frequency characteristic of the speaker drive voltage shifts from 12 to 12' and then to 12''. The maximum boost amount was when the frequency characteristic was 12.
It will be seen that the voltage decreases at 12' and decreases to zero at 12''. In this way, no loss of dynamic range occurs even at high voltage levels.

On the other hand, the frequency characteristic of the output sound pressure of the speaker at this time changes from 13 to 13' and then to 13" as shown in Figure 3b. In other words, when the sound pressure level is low and the output is small, the low frequency boost As the amount increases, the region where the sound pressure level is constant expands greatly to the low frequency region as seen in characteristic 13, but as the sound pressure level increases, the amount of low-frequency boost decreases. Therefore, the area where the sound pressure level is constant decreases as seen in characteristics 13' and 13''.

However, even if the bass characteristics are changed in accordance with the magnitude of the power output in this way, it does not sound so unnatural to the human ear because of the loudness characteristics of human hearing. This is because as the sound pressure level increases, the human's sense of bass pitch increases even more.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 4 is a block diagram showing one embodiment of the present invention. When the embodiment shown in the figure is compared with the conventional example shown in FIG. 1, the circuit configuration between the input terminal 1 and the output terminal 2 is different.

Please refer to FIG. First, the original signal input from the input terminal 1 is divided into two paths, one path is directly sent to the adder 14, and the other path is sent to the low pass filter (LPF) 15.
and adder 1 via VCA (voltage control amplifier) 16
4 to the other input terminal. That is, after the low frequency component extracted from the original signal via the LPF 15 is amplified by the VCA 16, it is added to the original signal in the adder 14 (corresponding to implementation of low frequency boost), and the added output is sent to the output terminal 2. The signal is input to the power amplifier 4 via the power amplifier 4. accordingly
Changing the gain of VCA 16 will change the amount of low-range boost.

When the gain in LPF15 is 0dB,
An example of a change in the amount of low-frequency boost with respect to a change in the gain of the VCA 16 is shown in FIG.

In Figure 5, as the VCA gain changes from a negative value to zero and then to a positive value,
You can see that the amount of low-frequency boost increases gradually from 0dB.

On the other hand, in VCA16, its control input terminal k
The relationship between the control voltage V _k input to the control voltage V k and the gain is shown in FIG. 6a. In other words, the control voltage V _k gradually increases from a negative value of −V _L until it reaches 0.
It will be seen that the gain increases linearly and monotonically as it reaches a positive value of +V _L.

Return to Figure 4. According to the principle of the present invention, the higher the level (amplitude) of the original signal input to input terminal 1 (and therefore the higher the output level of LOF 15), the lower the amount of low-frequency boost.
The gain of VCA16 must be reduced (that is, the control voltage V k input to the control input terminal _k
must be reduced).

The control voltage V _k that satisfies this relationship is determined by LPF1
The circuit generated from the output of step 5 is the control voltage generation circuit S shown surrounded by a broken line in FIG. This control voltage generating circuit S includes a rectifier circuit 17, a limiter circuit 18, an integrating circuit 19, an inverting circuit 20, and a level shift circuit 21.

FIG. 6b is a graph showing changes in the input signal amplitude of each part signal in the control voltage generating circuit S of FIG. 4. FIG.

See Figures 4 and 6b. LPF15
The output signal I is full-wave rectified by the rectifying circuit 17, enters the integrating circuit 19, and is converted into direct current. The DC output of the integrating circuit 19 is level-shifted in the direction of negative voltage by the level shift circuit 21, as shown in FIG.
The characteristic is as shown in the straight line 22 shown in FIG.

By inputting the output of the integrating circuit 19 to the inverting circuit 20, the output characteristic of the inverting circuit 20 is changed to the sixth
This results in a straight line 22' shown in Figure b. Next, in order to limit the maximum boost amount in consideration of the input resistance of the speaker, a limiter circuit 18 is provided on the output side of the inverting circuit 20, and the control voltage of the polygonal line 22'' shown in FIG. 6b is
Get V _k . The control voltage V k obtained when the level of the input signal component in the low frequency range reaches the power amplifier saturation level 11 (see Figure 2b) by adjusting the circuit constants of each part is the control voltage V _k obtained when the VCA 16 is off (the gain is -
∞, in other words, the output is zero), by setting the voltage (-V _L ) necessary for the power amplifier 4 to reach the voltage (-V
Saturation of low frequency signal components does not occur.

FIG. 7 is a circuit diagram showing a specific circuit example of the embodiment shown in the block diagram in FIG. 4, and the details will be explained below.

The resistor 23 and capacitor 24 constitute a low-pass filter 15, whose cutoff frequency is expressed by the same equation as equation (1) above. A ₁ , A ₂ , A ₃ ,
A ₄ are each operational amplifier (operational amplifier)
amplifier). The operational amplifier A ₁ constitutes a double-wave rectifier circuit 17 together with diodes 25 and 26 . The operational amplifier A ₂ constitutes an integration circuit 19 together with a resistor 30 and a capacitor 29, and its integration time constant τ is determined by the following equation (2).

τ=C _i ·R _i (2) where C _i is the capacitance of the capacitor 29 and R _i is the resistance value of the resistor 30. This time constant τ is the frequency
It is preferable to set a sufficiently large value so that a 20Hz signal is integrated.

The resistor 27 and the constant voltage source 28 constitute the level shift circuit 21, and by applying a positive voltage to the inverting input side of the operational amplifier _A2 , the level of the output of the operational amplifier _A2 is shifted to a negative voltage direction. Can be shifted.

The operational amplifier _A3 constitutes the inverting circuit 20, and its resistance value is set so that its gain is 0 dB. The diode 31 and the constant voltage source 32 constitute the limiter circuit 18, and the control voltage V _k
The upper limit voltage is limited by the constant voltage source 32. The operational amplifier _A4 constitutes the adder circuit 14, and its resistance value is set so that the two inputs are added to the output at the same weighting rate, for example.

Next, another embodiment of the present invention will be described.

FIG. 8 is a block diagram showing another embodiment of the present invention. The embodiment shown in the figure is different from the conventional circuit shown in FIG. 1 in the circuit configuration between the input terminal 1 and the output terminal 2.

A detailed explanation will be given below with reference to the drawings. First, the original signal input from input terminal 1 is divided into two paths,
One is applied to the low-frequency boost circuit A', and the other is applied to the low-pass filter 15'. Low frequency boost circuit
A' is a circuit in which the variable resistor 6 of the low frequency boost circuit A shown in FIG. 1 is replaced with a VCR (voltage control resistor) 33. The circuits after the low-pass filter 15' are circuits for creating a control signal for the VCR 33 in the same manner as in the embodiment of FIG. 4 using the VCA 16. In the case of FIG. 8, the inversion circuit is no longer necessary.

The operation is as follows. The original signal inputted from the input terminal 1 is given a low frequency boost through the low frequency boost circuit A', and is then inputted to the power amplifier 4 via the output terminal 2.

The amount of low frequency boost in circuit A' can be variably controlled by the VCR 33. Therefore, in the control voltage generation circuit S', the low frequency signal component extracted from the original signal via the LPF 15' is used, and if the level is high, the boost amount in the circuit A' is small, and if the level is low, the boost amount is increased.
A control voltage V _k for the VCR 33 is created and input to its control input terminal k.

FIG. 9 is a circuit diagram showing a specific circuit example of the embodiment shown in the block diagram in FIG. 8, and the details will be explained below.

The operational amplifier A ₆ constitutes a low-frequency _boost circuit like the operational amplifier 3 shown in FIG. , the following (3)
Determined by Eq.

K=1+R _x /R (3) However, R _x is the resistance value exhibited by the VCR 33, and R is the resistance value of the resistor 8.

Figure 10 shows the relative resistance value exhibited by VCR33.
5 is a graph showing the relationship between R _x '(=R _x /R) and the low-range boost amount A, and the relationship is expressed by a curve similar to that in FIG. 5. Generally, the relative resistance value R _x ' exhibited by the VCR 33 monotonically decreases as the DC control voltage V _k changes from negative to positive as shown in FIG. 11a.

Therefore, in order to control the resistance value exhibited by the VCR 33 by the level of the low-frequency input signal component, after converting the AC signal that is the signal component into a DC signal,
It is necessary to further shift the level and apply it to the control input terminal k.

Operational amplifiers A ₁ and A ₂ in FIG. 9 are parts that have the function of converting AC signals into DC signals, and
The operation is the same as A ₁ and A ₂ in the figure. Resistor 27 and constant voltage source 28 are operational amplifiers, similar to those in FIG.
Level shift the DC output of A ₂ towards the negative voltage direction,
This is the level shift circuit 21 for obtaining the control voltage _Vk shown by the straight line 38 in FIG. 11b.

The diode 31 and the constant voltage source 32 constitute a limiter circuit 18 for limiting the maximum boost amount, similar to that shown in FIG.
The lower limit voltage is limited by the straight line 3 in Figure 11b.
A control voltage V _k as shown at 8' is obtained.

When the circuit constants of each part are adjusted and the low-frequency input signal component reaches the saturation level 11 of the power amplifier, the control voltage V _k is set to the value necessary for the relative resistance value R _x ′ of the VCR 33 to become sufficiently close to 0. If the voltage is set to (+V _L '), the dynamic range of the power amplifier 4 will not be reduced as in the previous embodiment.

Operational amplifier A ₅ , together with capacitor 34, capacitor 35, resistor 36, and resistor 37, has a 12 dB/
0ct (level decreases by 12dB when frequency doubles)
This constitutes an active low-pass filter 15'. Each circuit constant is set so that the cut-off frequency of this low-pass filter 15' matches the turnover frequency of the low-frequency boost circuit A'.

Figure 12a shows the frequency characteristics of the speaker drive voltage level when a small speaker system with a cabinet volume of 10 is driven by the speaker drive device according to the present invention, and Figure 12b shows the frequency characteristics of the output sound pressure level from the speaker. The characteristics are shown using speaker drive power as a parameter.

The characteristics shown in these figures are the characteristics obtained when a 100W power amplifier 4 is used. When the average power during reading is 1W,
A significant bass boost has been implemented to significantly expand the bass reproduction frequency range, and the speaker can be driven up to the maximum output (100W) without reducing the power amplifier's dynamic range. One thing can be gleaned from these figures.

〔Effect of the invention〕

As explained above, according to the present invention, the speaker drive device has a configuration in which the amount of low-frequency boost can be automatically varied depending on the low-frequency input signal level, so that the dynamic range of the power amplifier can be changed without reducing the dynamic range of the power amplifier. This has the effect of significantly expanding the reproduction frequency range toward lower frequencies. Further, the low frequency characteristics realized by the present invention are not unnatural to the human ear, considering the loudness characteristics of human hearing, and are sufficiently usable for practical use.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an example of a boost circuit used in a conventional speaker drive device, and Figure 2a is a graph showing frequency characteristics in a conventional speaker drive device with and without low-range boosting. , Fig. 2b is a graph showing the frequency characteristics to show the drawbacks when low frequency boost is implemented in a conventional speaker drive device, and Fig. 3a is a graph showing the frequency characteristics when implementing the present invention at voltage level. Figure 3b is a graph showing how the frequency characteristics of the reproduced sound change with the sound pressure level.
Fig. 4 is a block diagram showing an embodiment of the present invention, Fig. 5 is a graph showing changes in the amount of low-frequency boost when the gain of the VCA 16 is changed in the circuit shown in Fig. 4, and Fig. 6 a. is a graph showing the relationship between control voltage and gain in VCA16, No. 6
Figure b is a graph showing the relationship of each part signal to the input signal amplitude in the control voltage generation circuit S of Figure 4, and Figure 7 shows a specific circuit example of the embodiment shown in the block diagram in Figure 4. The circuit diagram, FIG. 8 is a block diagram showing another embodiment of the present invention, and FIG.
A circuit diagram showing a specific circuit example of the embodiment shown in the block diagram in the figure, Figure 10 is a VCR in Figure 9.
Graph showing the relationship between the resistance value exhibited by No. 33 and the amount of low-range boost of the low-range boost circuit A', Fig. 11a
is a graph showing the relationship between the control voltage V _k in the VCR33 and its relative resistance value, and Figure 11b is
FIG. 12a is a graph showing the relationship between the control voltage V _k applied to the VCR 33 and the input signal amplitude, and FIG. 12b is a graph showing the frequency characteristics of the speaker drive voltage level when the present invention is implemented. It is also a graph showing the frequency characteristics of the output sound pressure level from the speaker. Symbol explanation, 1...Input terminal, 2...Output terminal,
3, A ₁ , A ₂ , A ₃ , A ₄ , A ₅ , A ₆ ... operational amplifier,
4... Power amplifier, 5... Speaker, 6... Variable resistor, 7, 24, 29, 34, 35... Capacitor, 8, 23, 27, 30, 36, 37...
Resistor, 9, 9', 13, 13', 13''...Speaker output sound pressure characteristics, 10, 10', 10'', 12,
12', 12''...Speaker drive voltage characteristics, 11...
...Power amplifier saturation voltage level, 14...Adder, 15, 15'...Low pass filter, 16...
...VCA (voltage control amplifier), 17...rectifier circuit,
18...Limiter circuit, 19...Integrator circuit, 20
...Inversion circuit, 21 ...Level shift circuit, 2
2, 22', 22''...VCA control voltage, 25,
26, 31... Diode, 28, 32... Constant voltage source, 33... VCR (voltage control resistor), A,
A'...Low frequency boost circuit, 38, 38'...VCR
control voltage.

Claims (1)

[Claims] 1. Means for extracting a low frequency component from an original signal to drive a speaker, means for amplifying the extracted low frequency component, and adding the amplified output from the amplifying means to the original signal. means for driving a speaker with the added output from the adding means;
A speaker driving device comprising: when the amplifying means comprises a voltage controlled amplifier;
The gain in the amplification means is set so that the higher the level of the original signal, the lower the gain, and the lower the level of the original signal, the higher the gain.
As a means for variable control depending on the level of the original signal, a rectifier circuit that rectifies the low frequency component extracted from the original signal, an integrator circuit that integrates the output of the rectifier circuit, and a DC output from the integrator circuit are used. a level shift circuit that shifts the level; an inversion circuit that inverts the level-shifted DC output from the integrating circuit; and an inversion circuit that limits the upper limit of the level of the output of the inversion circuit and then supplies it as a control voltage to the voltage control amplifier. 1. A speaker drive device comprising means for adding a limiter circuit. 2. Means for extracting a low frequency component from the original signal to drive a speaker, means for amplifying the extracted low frequency component, means for adding the amplified output from the amplifying means to the original signal, and the addition. means for driving a speaker by the addition output from the means;
When the amplifying means comprises an amplifier whose gain is controlled by a variable resistance value of a voltage-controlled resistor, the gain in the amplifying means is lowered as the level of the original signal becomes higher, and lowered as the level of the original signal becomes higher. As a means for variable control depending on the level of the original signal so that the lower frequency component becomes higher as a level shift circuit that level-shifts the DC output from the integration circuit; and a limiter circuit that limits the level-shifted output from the integration circuit to a lower limit and then applies it to the voltage control resistor as a control voltage. What is claimed is: 1. A speaker driving device characterized by comprising means for: