JPS6235320B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low frequency correction circuit for a speaker, and when it compensates for the lack of low frequency response of a speaker,
The purpose is to prevent low-frequency signals from exceeding the permissible low-frequency input of the speaker.

Generally, the relationship between the input signal frequency and the response of a speaker decreases rapidly below the low resonant frequency _O , as shown in FIG.

Since this low-frequency resonance frequency _O is within the normal audible range, there were complaints that the low-frequency range was unsatisfactory.
Especially when the speaker box volume is small,
Since this _O tends to be high, there is a strong feeling that there is a lack of low frequencies, so there was a desire for a speaker system that could produce low frequencies even with a small speaker box.

As a way to meet these demands, conventional
A third low frequency enhancement means having the characteristics shown in the figure is used.
As shown in the figure, the low-frequency characteristics of the speaker are equivalently improved by connecting it to the front stage of the power amplifier. In Fig. 3, 1 is an input terminal, 2 is a low frequency enhancement means, 3 is a power amplifier,
4 is a speaker.

By the way, the permissible input level of the speaker is the fourth level.
As shown in the figure, it is often lower in the low range. In FIG. 4, a is the allowable input level regulated by the allowable amount of amplitude of the diaphragm, b is the allowable input level regulated by the allowable amount of heat generation of the voice coil, and c is the total allowable input level.

When the input level of the speaker exceeds the level a, the voice coil may jump out of the magnetic field, the edges or damper may become loose, or the diaphragm may become wrinkled, immediately producing a harsh and abnormal sound.

On the other hand, if the input level exceeds the level b and continues for a long time, the temperature of the voice coil will rise and be damaged, but even large inputs can be tolerated for a short period of time. In the case of normal music signals, the time for the input signal to reach a large amplitude is very short, so even if a fairly large input is applied, the voice coil will not be damaged.

However, since the input signal usually does not have many low-frequency components, in reality, the low permissible low-frequency input has not been much of a problem.

However, as in the previous example, when the low frequency components of the input signal are enhanced, the low frequency permissible input is affected.
A problem arose in which abnormal noises were generated during large inputs.

The present invention provides a low frequency correction circuit that solves these problems. An embodiment of the present invention will be described below with reference to FIG.

In FIG. 5, 1 to 4 correspond to the same numbers in FIG. 3, 5 is an amplitude limiting means, 6 is a low pass filter, 7 is a high pass filter, and 8 is an adding means.

The operation of the embodiment shown in FIG. 5 will be explained. first,
The input signal applied to the input terminal 1 has its low frequency band enhanced by a low frequency enhancement circuit 2, its output amplitude is limited by an amplitude limiting means 5, and its high frequency band is cut off by a low pass filter 6. On the other hand, the input signal has its low frequency cut off by a high-pass filter 7, is added to the output of the low-pass filter by an adding means 8, is amplified by a power amplifier 3, and is supplied to a speaker 4.

In the embodiment shown in FIG. 5, the amplitude of the enhanced low-frequency signal is limited by the amplitude limiting means 5 to below the permissible input of the speaker shown in FIG. 4a. Therefore, even in response to a large input in the low range, the speaker does not generate abnormal sound due to excessive diaphragm amplitude.

However, when the amplitude is limited by the amplitude limiting means 5, a new problem arises in that harmonic distortion components are generated and the sound becomes muddy. Therefore, in order to remove this harmonic distortion component, the signal is passed through a low-pass filter 6.

However, by passing the signal through the low-pass filter 6, the high frequency components of the signal are also attenuated. Therefore,
By adding the signal obtained by passing the input signal through the high-pass filter 7 to the above signal, only the harmonic distortion components can be removed without attenuating the high frequency components of the signal.

Next, specific circuit examples of this low frequency correction circuit are shown in FIGS. 6 to 8.

6 to 8, 1 to 4 correspond to the same numbers in FIG. 5, 9 is an operational amplifier, 1
0 to 14 are feedback circuits forming the bridge T circuit;
15 to 17 are diode limiters, 18 and 19 are frequency division circuits, and 20 is an input resistor of the power amplifier 3.

In FIGS. 6 to 8, the operational amplifier 9 and the feedback circuits 10 to 13 constitute the low frequency enhancement means 2, the diode limiters 15 to 17 constitute the amplitude limiting means 5, and the frequency division circuits 18, 19 A low-pass filter 6, a high-pass filter 7, and an adding means 8 are constructed. Further, the resistor 14 is provided to compensate for the lowering of the low frequency level due to the input resistor 20 of the power amplifier.

In Figures 6 and 7, the diode limiter is
Although it is composed of an L-shaped circuit including a resistor 15 and diodes 16 and 17, in FIG. 8, the diodes 16 and 17 are inserted into the feedback circuit of the operational amplifier 9.

In addition, in Figures 6 to 8, the low frequency enhancement is performed in a partial frequency width of the low frequency range.By enhancing the components below the audible frequency, it is possible to increase the frequency range more than necessary. Increase the level of low-frequency boost output,
This is to make the low frequency signal more susceptible to amplitude limitation and thereby to prevent the low frequency signal from being subjected to cross modulation by the very low frequency signal.

In addition, the frequency division circuits 18, 1 in FIGS. 6 to 8
9 has a very simple configuration and is characterized by three functions: low-pass, high-pass, and addition.

As described above, according to the present invention, by enhancing the low frequency range, it is possible to improve the low frequency characteristics of the speaker, and to ensure that the low frequency signal exceeds the permissible low frequency input of the speaker. It can be prevented.

In addition, the amplitude of the enhanced low-frequency signal is softly limited by a diode limiter, so there is little distortion, and harmonic distortion components caused by amplitude limitation are suppressed without affecting the high-frequency components of the signal. Can be removed.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram of a typical speaker, Figure 2 is a characteristic diagram of a typical low frequency enhancement circuit, Figure 3 is a block diagram of a conventional low frequency correction circuit, and Figure 4 is a typical speaker diagram. FIG. 5 is a block diagram of an embodiment of the present invention, and FIGS. 6 to 8 are circuit diagrams showing specific circuits thereof. 1...Input terminal, 2...Low frequency enhancement means, 4...
Speaker, 5... Amplitude limiting means, 6... Low pass filter, 7... High pass filter, 8... Adding means.

Claims (1)

[Scope of Claims] 1. A low frequency correction circuit that corrects the low frequency range of an input signal that drives a speaker having a low resonance frequency _O , the low frequency enhancement means that enhances the frequency band of the input signal below the above _O. and an amplitude limiting means for limiting the amplitude of the output signal of the low frequency enhancement means, a low pass filter for cutting out the band above _O of the output signal of _the amplitude limiting means, and
A low-frequency correction circuit comprising a high-pass filter that cuts the following bands, and means for adding the outputs of the low-pass filter and the high-pass filter. 2. The low frequency correction circuit according to claim 1, characterized in that the amplitude limiting operation is a soft clip. 3 In claim 1, the low frequency enhancement is
A low frequency correction circuit characterized in that it is performed for input signals in a partial band of _O or less. 4. The low frequency correction circuit according to claim 1, wherein the low frequency enhancement means is constituted by an operational amplifier having a bridge T circuit as a feedback circuit. 5. The low frequency correction circuit according to claim 1, wherein the amplitude limiting means is comprised of a resistor and a diode connected in antiparallel. 6. The low frequency correction circuit according to claim 1, wherein the amplitude limiting means is constituted by an operational amplifier having a diode connected in antiparallel between the output and the feedback input. 7. In claim 1, the low-pass filter, the high-pass filter, and the means for adding their outputs include a resistor having one end connected to the output of the amplitude limiting means and a capacitor having one end connected to the input end. A low frequency correction circuit comprising: the resistor and the capacitor having their respective other ends connected to each other to form an output end.