| 摘要 |
<p>PURPOSE:To make a feedback coil and an amplifier for driving it needless by multiplying and feeding back a voltage corresponding to difference between output voltages of upper-side and lower-side magnetic flux detection coils and a voltage proportional to the current flowed to a voice coil. CONSTITUTION:When current I is flowed to voice coil 5, coil 5 is driven in the axis direction between center pole 1 and plate 3, and the diaphragm connected to bobbine 4 is driven according to the drive above. At this time, upper-side and lower-side magnetic flux detection coils 6 and 7 detect magnetic fluxes across the upper end and the lower end of coil 5 respectively, and output voltages are supplied to amplifier 10. amplifier 10 amplifies difference between these input voltages and inputs the result to multiplier 12. Meanwhile, a voltage proportional to current I which is obtained at both ends of resistance 11 is inputted to the other input end of multiplier 12, and the output obtained by multiplying these inputs is fed back to voice coil driving amplifier 13. Here, if amplifier 13 is constituted by a constant- current amplifier, distortion components of the current flowed to coil 5 are regarded as almost zero, so that distortion components of the driving power for coil 5 can be made zero.</p> |
