JPH0761192B2 - In-vehicle sound reproduction device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle-mounted sound reproducing device having improved vehicle interior acoustic characteristics.

2. Description of the Related Art In recent years, a vehicle-mounted sound reproducing device using a loudness circuit and a graphic equalizer circuit has been used as a method for correcting a vehicle interior acoustic characteristic lacking high-pitched sound, but means for changing the amplitude characteristic has not been considered so much. The current situation is not. The conventional vehicle-mounted sound reproducing device will be described below. FIG. 7 is a block diagram showing an example of a conventional vehicle-mounted sound reproducing device. Reference numeral 1 is an audio signal source such as a car radio, car tape deck, or car compact disc player, 2 is an equalizer circuit in which a resonance circuit is composed of a semiconductor inductor, 3 is a power amplifier, and 4 is a speaker.

Figure 8 shows a semiconductor inductor 5, two amplifiers 6 and 7, resistors
FIG. 9 is a circuit diagram of the equalizer circuit 2 including 8, 9, 10, 11 and the capacitor 12, and FIG. 9 is an amplitude characteristic diagram of the equalizer circuit 2.

Regarding the in-vehicle sound reproduction device configured as described above,
The operation will be described below.

First, the signal sent from the acoustic signal source 1 is emphasized by the equalizer circuit 2 shown in FIG. 8 in the high frequency range of the amplitude characteristic as shown in FIG. 9, and amplified by the power amplifier 3, It is reproduced by the speaker 4. As a result, the high frequency sound which is lacking in the conventional reproduction apparatus without the high frequency correction apparatus is corrected and reproduced, so that it is balanced with the middle and low frequency sounds and a flat vehicle interior acoustic characteristic is obtained.

However, in the above-described conventional configuration, in order to emphasize the high frequency range of the amplitude characteristic in the equalizer circuit 2 having the resonance circuit formed of the semiconductor inductor 5, the amplifier 6 is used as shown in FIG. There is a problem in that the circuit configuration becomes complicated because at least two are required.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a vehicle-mounted sound reproducing device having a simple circuit configuration in which the amplitude changing means for emphasizing high frequencies is realized by a single amplifier. is there.

Means for Solving the Problem In order to solve this problem, the on-vehicle sound reproducing device of the present invention uses at least two or more active low-pass filters in which the amplitude changing means is composed of a resistor, a capacitor, and one amplifier. Q of this active low-pass filter
Is set to 1.0 or higher, an active low-pass filter that emphasizes the high frequency range of the amplitude characteristic, a power amplifier that amplifies the output of this active low-pass filter, and a speaker that reproduces the output of the power amplifier. It is something.

Operation With this configuration, the amplitude characteristic in which the high frequency band is emphasized can be realized by the second or higher-order active low-pass filter configured by one amplifier.

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

FIG. 1 is a block diagram showing the configuration of an on-vehicle sound reproducing device according to an embodiment of the present invention. In FIG. 1, 13 is a sound source such as a car radio, a car tape deck, and a car compact disc player, 14 is a positive feedback low-pass filter composed of a resistor, a capacitor and one operational amplifier, 15
Is a power amplifier and 16 is a speaker.

FIG. 2 is a circuit diagram of the positive feedback type low pass filter 14.

FIG. 3 is an amplitude characteristic diagram of the positive feedback type low pass filter 14.

Regarding the vehicle-mounted sound reproducing device configured as described above,
The operation will be described below.

First, the output of the acoustic signal source 13 is a positive feedback low-pass filter.
Entered in 14. As shown in FIG. 2, the positive feedback low-pass filter 14 includes resistors 19, 20, 21, 22 and capacitors 17, 18
And one operational amplifier 23, and the transfer function is expressed by the following equation.

The high cutoff frequency of the positive feedback low-pass filter 14 and Q indicating the sharpness of resonance are expressed by the following equations.

However, ωc = 2 · π · Fc where Q is 2.4, the cutoff frequency is 10 KHz, the resistor 21 is 2.7 KΩ, the resistor 22 is 2.7 KΩ, and the capacitor 17 is
0.027μF, capacitor 18 0.012μF, resistor 19 0.1K
If you set constants for Ω and resistance 20 to 1.0 KΩ respectively,
As shown in the figure, the amplitude characteristic can have a peak near the high cutoff frequency, and the level difference between the mid and low frequencies below 5 KHz can be secured by about 10 dB. In other words, the amplitude characteristic of the positive feedback type low-pass filter 14 emphasizes high frequencies. When the output that has passed through the positive feedback low-pass filter 14 is reproduced by the speaker 16 in addition to the power amplifier 15,
Same as the on-vehicle sound reproduction device that consists of an equalizer circuit that requires two amplifiers in the past, it corrects the lacking high frequency sound, so it is balanced with the mid and low frequency sound, and a flat interior acoustic characteristic is obtained. To be

As described above, according to the present embodiment, the amplitude changing means is composed of the positive feedback low-pass filter 14 using a resistor and a capacitor and one operational amplifier, and the constants of the resistor and the capacitor are adjusted to adjust the positive feedback low-pass filter. By setting the Q of 14 to 2.4, the amplitude characteristic in which the high frequency band is emphasized can be realized with one amplifier.

In the above embodiment, the positive feedback type low pass filter 14
Other constants may be used for the resistors and capacitors to determine the Q and the cutoff frequency. As shown in FIG.
To set Q to 2.3, set resistor 21 to 15.0 KΩ and resistor 22 to 1
5.0KΩ, capacitor 17 0.0012μF, capacitor 18 0.
It is assumed that the resistance 19 is 10.0 KΩ and the resistor 20 is 10.0 KΩ. At this time, the high range of about 6 dB can be emphasized at 10 KHz. Similarly,
When Q is set to 1.0, about 1dB high range can be emphasized. Also,
As shown in FIG. 5, in order to increase the cutoff frequency without changing Q, the constants of the resistors 21 and 22 should be decreased, and to decrease the cutoff frequency, the resistor 21 and the resistor 22 should be decreased.
Increase the constant of 22.

Moreover, as shown in FIG. 6, the resistance 21 is set to 12.0 KΩ and the resistance 22
12.0KΩ, capacitor 17 0.001μF, capacitor 18
If 0.0018μF, resistance 19 is 39.0KΩ and resistance 20 is 13.0KΩ, the gain is 12d over the entire frequency band with Q set to 2.2.
B can have. In this case, the load on the voltage amplifier circuit of the power amplifier 15 connected behind is lightened.

In addition, resistors 21 and 22, capacitor 17 and capacitor 18
When the values are equal to each other, Q can be determined by the ratio of the resistance 19 and the resistance 20, so that the constant can be easily set. In the above embodiment, the low-pass filter is the positive feedback low-pass filter 14, but the positive feedback low-pass filter 14 is
A multi-feedback low-pass filter may be used.

As described above, according to the present invention, the amplitude changing means is composed of a low-pass filter using a resistor, a capacitor, and one amplifier,
By adjusting the constants of the resistors and capacitors and setting the Q of the low-pass filter to 1.0 or more and changing the cutoff frequency, it is possible to configure an amplitude characteristic that arbitrarily and efficiently emphasizes the high frequency band of the signal. It is possible to realize an excellent vehicle-mounted sound reproducing device.

[Brief description of drawings]

FIG. 1 is a block diagram of an on-vehicle sound reproducing device in one embodiment of the present invention, FIG. 2 is a circuit diagram of the low-pass filter of FIG. 1, FIG. 3 is an amplitude characteristic diagram of the low-pass filter of FIG. FIG. 4 is an amplitude characteristic diagram when Q of the low pass filter of FIG. 1 is changed, FIG. 5 is an amplitude characteristic diagram when Q of the low pass filter of FIG. 1 is constant, and FIG. 6 is FIG. FIG. 7 is an amplitude characteristic diagram when the gain of the low-pass filter is changed, FIG. 7 is a block diagram of a conventional vehicle-mounted sound reproducing device,
8 is a circuit diagram of the equalizer circuit of FIG. 7, and FIG. 9 is an amplitude characteristic diagram of the equalizer circuit of FIG. 13 ... Acoustic signal source, 14 ... Low-pass filter, 15 ... Power amplifier, 16 ... Speaker, 17, 18 ... Capacitor, 19
~ 22 …… resistor, 23 …… operational amplifier.

Claims (1)

[Claims] 1. An active low-pass filter of at least a second order or more is used as amplitude changing means for changing the amplitude of a signal from an acoustic signal source for generating an acoustoelectric signal, and the Q of the active low-pass filter is set to 1.0 or more. In-vehicle sound reproduction consisting of an active low-pass filter configured to emphasize the high-frequency range of the signal amplitude characteristic, a power amplifier that amplifies the output of this active low-pass filter, and a speaker that reproduces the output of the power amplifier. apparatus.