of the output impedance of the circuit shown in fig3 note that in the circuit shown in fig3 when the lpf 33a and the hpf 33c have different gains the absolute value of the positive impedance can be different from that of the negative impedance for example when the gain of the hpf 33c is set to be larger than that of the lpf 33a as shown in fig3 the absolute value of the positive impedance can be set to be larger than that of the negative impedance as shown in fig3 in this manner the gain of the hpf 33c is set to be larger than that of the lpf 33a so that the output impedance z o is set to be a negative impedance of z o lt r vc in a low frequency range and to be a positive impedance of z lvc lt lt z o with respect to an impedance z lvc of the inductance l vc of the voice coil as shown in fig3 as a result a damping force for the speaker 32 is increased near the resonance frequency f o of the speaker 32 and the influence of the inductance l vc of the voice coil i e.