JPH0722436B2 - Sound reproduction device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound reproducing device used for a car stereo or the like.

2. Description of the Related Art Generally, in a sound reproducing device, there are two methods for improving the reproduction capability of low-pitched sound: acoustic control and electric control.

Looking at the acoustic system, heavy bass can be played by installing a large-diameter bass speaker (woofer) in a large-capacity box, but such a large box requires a large space for installation. Therefore, there are few problems for home audio, but it is not practical for a portable system or a car audio installed in a car. That is, the speaker box installed in the car has a limited space and must be small. The low frequency reproduction capability of a small speaker system is low,
For example, if a speaker with a diameter of 12 cm is put in a box of 1.5, o (minimum resonance frequency) is as shown in Fig. 4.
It rises to about 150-180Hz. So in a small system
It is difficult to raise the sound pressure below 100Hz, so it becomes necessary to electrically correct it.

As a function of electrically correcting, there are conventional low-frequency boost by tone control and loudness control. The loudness control is aimed at this correction because the low range becomes difficult to hear when the volume becomes low due to the characteristics of the human ear (equal loudness curve such as Fletcher-Munson). This loudness control is 50
There are many things that excite the band below 0Hz, but when you enliven up to 500Hz, the voice (human voice) also changes the timbre, and it is often not used because it becomes a thick and thick voice.

It is possible to correct the low range to some extent with conventional tone control and loudness control, but that is when the output power of the amplifier is large, and when the power supply voltage is as low as 6 to 12 V, such as in portable systems and car audio systems. It cannot be corrected due to insufficient output power. For example, the output of a power amplifier used for car audio is usually 18 to 20 W, but if the power supply voltage is increased by using a DC-DC converter, the output is large, but there are problems of cost and mounting space. It is not used except for some parts. In order to correct the low range with the amplifier, for example, in the example of Fig. 4, the output sound pressure level of 70Hz is 150H.
+12 dB at 70 Hz to equalize the output sound pressure level of z
The above amplification degree is necessary. Furthermore, if loudness correction is added, a total amplification of 20 dB or more is required,
It is impossible to amplify this much because the output of the amplifier is limited. In other words, the peak level of the music source is higher than the average level by more than +6 dB, so if the amplifier is amplifying more than 20 dB, the output of the power amplifier will clip even if the gain is increased a little, and an abnormal sound is produced and the speaker May be destroyed.

Problems to be Solved by the Invention In a speaker system using a small box such as a portable system or a car audio system, sufficient bass at both high and low volumes under conditions where the output of the amplifier is limited. In addition, a sound reproducing device which reproduces the above-mentioned sound, and has no amplifier clip even at the time of a large input, that is, has no abnormal sound, has not been realized in the past due to the above problems.

Means for Solving the Problems The present invention solves the above problems and reproduces a sufficient bass in a small speaker system. Therefore, an amplifier circuit is incorporated in a speaker box, and an auto loudness control function is provided in the amplifier circuit. Further, it has a limiter function for suppressing an abnormal sound at the time of a large input.

Operation With such a configuration, the amplifier circuit divides the input signal into the bass range and the mid-high range, inserts a logarithmic compression type amplification circuit in the low range, and then mixes the low range and the mid-high range. Then, power amplification is performed as one signal. For this reason, when comparing the amplification levels of the bass and mid-high range parts, the change in the level of the bass range is 1/2 that of the mid-to-high range part, and the loudness is corrected by this. Further, since the degree of compression is very large for a large input, the input to the power amplifier is limited and the amplifier does not clip.

Examples Hereinafter, the sound reproducing device of the present invention will be described with reference to examples.

One embodiment of the present invention is shown in FIG.

First, the high-pass filter (HPF) 1 and the band-pass filter (BPF) 2 divide the input signal into a low sound range part and a mid-high range part. The logarithmic compression amplifier 3 is an amplifier that logarithmically compresses an input signal, and has an input / output gain of 1 when the input is slightly lower than the maximum input. Low-pass filter (LP
F) 4 has fc (cutoff frequency) of 150 Hz. The mixing circuit 6 is a circuit for mixing the low-pitched sound range portion and the mid-high-pitched sound range portion. First, the input signal is amplified by the bandpass filter 2 by 6 dB. The band and amplification factor of the bandpass filter 2 are determined by the capacity of the speaker or box used, the mounting position, and the like. Next, the dynamic range of the signal is compressed by the logarithmic compression amplifier 3. That is, a signal below the reference level (a level at which the input / output gain is 1) operates so that the amplification degree becomes relatively higher as the level becomes lower, and conversely, a signal above the reference level operates at that level. Operates so that the higher the value becomes, the lower the amplification degree becomes. By the logarithmic compression amplifier 3, the output dynamic range is logarithmically halved with respect to the input dynamic range. The input / output characteristics of the logarithmic compression amplifier 3 are shown in FIG. When the level lower than the maximum input is set as the reference level, it operates as a limiter for the input higher than that.

Due to the non-linearity of the input / output characteristics of the bass range, the bass volume becomes relatively loud when the signal level is low, and when the input signal becomes loud and near full power, the bass and mid-treble volumes are loud. Are on the same level. That is, the auditory sense can be corrected. Since the fc of this circuit is 150 Hz, problems such as unnatural voice sound caused by conventional loudness control do not occur. In stereo playback, the sense of direction of the sound almost disappears at low frequencies below 150 Hz, so even if the bass levels of 150 Hz or below are boosted and the left and right bass levels approach, the stereo feeling is not lost. Further, since the center frequency becomes faster and the limiter works due to the boost frequency and the boost amount of the bandpass filter 2, at the time of low level output, the sound pressure frequency characteristic has a triangular shape, but the output level becomes high. As the mountains are compressed, they gradually become trapezoidal. This is a power amplifier with limited output, which solves the problem that the bass dynamic range is narrow due to the large boost amount at low output, so by expanding the range to boost at high output, the bass increased in hearing. This is because the control is performed so that it feels like.

Using the circuit of the present invention, a speaker unit having a diameter of 12 cm is 1.5
FIG. 3 shows the acoustic characteristics of the sound reproducing device attached to the box of FIG. As you can see from this figure, the low-pitched sound rises up to nearly 20 dB when the volume is low, and it has flat characteristics over the entire band when full power.

EFFECTS OF THE INVENTION As described above, the present invention solves the shortage of heavy bass, which is a problem in the case of a small speaker system using a power amplifier with limited output such as a portable system or an in-vehicle system, and it is possible to solve the problem of human beings. It is possible to realize a small-sized, high-performance sound reproducing device at a low cost, which can simultaneously obtain an auto-loudness control function that very naturally corrects the audibility of the ear and a limiter function that controls the generation of abnormal sound.

[Brief description of drawings]

FIG. 1 is a block diagram of an amplifier circuit according to an embodiment of the sound reproducing apparatus of the present invention, FIG. 2 is an input / output characteristic diagram of a logarithmic compression circuit used in the present invention, and FIG. 3 is an output of the sound reproducing apparatus of the present invention. FIG. 4 is a sound pressure frequency characteristic diagram, and FIG. 4 is an output sound pressure frequency characteristic diagram of a small speaker system as a conventional example. 1 ... High-pass filter (HPF), 2 ... Band-pass filter (BPF), 3 ... Logarithmic compression amplifier, 4 ... Low-pass filter (LPF), 5 ... Linear amplifier, 6 ...
… Mixed circuit.

Claims (1)

[Claims] 1. A circuit having a built-in speaker and a voice band amplifier, said voice band amplifier dividing an input signal into a bass range part and a middle and high range part, and a non-linear system connected to an output of said bass range part. , A logarithmic compression amplifier, a low-pass filter connected to the output of the logarithmic compression amplifier, and a mixing circuit for synthesizing the output of the low-pass filter and the output of the mid-high range part. apparatus.