PURPOSE: To vary an acoustic characteristic irradiated from a speaker corresponding to an output voltage by adjusting a signal obtained from an acceleration MFB (motional feedback) circuit and a signal obtained from an amplifier output terminal interlocking with a variable attenuator adjusting sound volume.

CONSTITUTION: Since a variable attenustor 12 in interlocking with a variable attenuator 2 is turned near ground position when a slider of the variable attenuator 2 is placed near the ground position, a resistance value of a voltage controlled attenuator 14 is a maximum value. Thus, a signal divided by resistors R1, R2 and fed back negatively is small, and a signal having a large level from the MFB feedback circuit 13 is fed back to an input terminal and a voltage shown in A is obtained at an output terminal. When the slider of the variable attenuator 2 is at a maximum position next, a voltage applied to the voltage controlled attenuator 14 through the variable attenuator 12 becomes maximum and its resistance value becomes a minimum value. Thus, the signal divided by the resistors R1, R2 and applied to the input terminal is maximized, the signal form the MFB feedback circuit 13 is minimized and a voltage shown in B is obtained.