| 摘要 |
PURPOSE:To improve the workability for wiring and assembling process by using a sound pressure test type detecting element as a means to detect the movement of a speaker diaphragm and providing a polarity inversion switching means into a feedback loop. CONSTITUTION:When a selection switch S1 is opened, a speed component corresponding to the movement of a diaphragm of a speaker 23 is fed back to a main amplifier 22 through an adder circuit 21 to drop the Q value of the speaker 23. While a positive feedback is carried out when the mobile contact of a selection switch S2 is set at a fixed contact (a). Thus the effect of reduction of the minimum resonance frequency fO is obtained. Then the mobile contact of the S2 is set at a fixed contact (b), and therefore an amplitude component having its phase inverted by a phase inverting circuit 38 is fed back to obtain the effect of rise of the frequency fO. As a result, the frequency fO of an auxiliary speaker device 17 can be selected between low and high states by switching the switch S2. |
