1. Field of the Invention
This invention relates to a bass compensation circuit for use in a sound reproduction device.
2. Description of the Related Art
First, a conventional sound reproduction device provided with a range correction circuit (namely, a tone control circuit or an equalizer) will be described hereinbelow by referring to the accompanying drawings. FIG. 3 is a circuit diagram for illustrating the configuration of the range correction circuit provided in the conventional sound reproduction device and adapted to change relative levels of amplitude (hereunder sometimes referred to simply as levels) at frequencies of middle and high frequency ranges and of a low frequency range correspondingly to change in sound volume. As shown in this figure, a variable resistance with a center tap is employed as a variable resistor 13 for volume control. Further, a time constant circuit comprised of resistances 16 and 17 and capacitors 14 and 15 is connected to the variable resistor 13. Circuit constants of this time constant circuit are determined in such a manner that the reactance of the capacitor 14 is sufficiently high but that of the capacitor 15 is low correspondingly to frequencies of a middle frequency range. Further, levels at frequencies of the middle frequency range can be changed only by regulating the variable resistor 13. Moreover, levels at frequencies of a high frequency range rise due to reduction in reactance of the capacitor 14. Furthermore, levels at frequencies of a low frequency range rise owing to increase in reactance of the capacitor 15. Additionally, the conventional sound reproduction device provided with this circuit employing a frequency response (namely, frequency characteristics), the graph of which is as illustrated in FIG. 4, in order to realize a well-known loudness contour.
As is seen from FIG. 4, the frequency response of the conventional sound reproduction device provided with the range correction circuit gently changes in a frequency range, the center frequency of which is 1 kilohertz (kHz). As the result, in case where sound volume is small, a listener has a feeling of indistinctness toward sounds of frequencies of middle and low frequency ranges. Especially, a listener feels as if a vocal part were turned down. Even if such a frequency response is improved and a rolloff frequency is regulated in such a manner to increase levels at frequencies of low and high frequency ranges, it is difficult to increase only levels at necessary frequencies, because of the fact that basically, the circuit has a first-order filter arrangement. The present invention is created to resolve such a problem of the conventional circuit.
It is, therefore, an object of the present invention to provide a bass compensation circuit for use in a sound reproduction device, which can compensate a frequency response at desired frequencies of a low frequency range, which are necessary for music reproduction in such a way that the compensated frequency response can change against change in sound volume in a natural manner.