スピーカの駆動力歪の解析と低減法

抄録

The conventional distortion methods such as copper cap, laminated core can not satisfy the recently developed low distortion reproduction system like PCM. Corresponding to this situation, we tried to analyse the force distortion of loudspeaker and develop the new low distortion techniques. The driving force of loudspeaker is expressed as Bli, whereby Bl is called the force factor and i is voice coil current. To reduce the driving force distortion, the force factor must be constant and the voice coil current has to be linear. From our analysis, the condition for the constant force factor is that the magnetic flux variation across the voice coil must be zero. For this purpose, two techniques are proposed by the authers;one is the magetic flux feedback(MFFB) and another is the pushpull construction. MFFB is the feedback system which cancels the flux varition across the voice coil. 2nd HD is reduced to 0. 03% at 90dB/m. The pushpull construction has a symmetrical magnetic circuit with a voice coil pair, so 2nd HD is reduced. To reduce the voice coil current distotion, the constant current drive amplifier is used. By this amplifier, 3rd HD is reduced to 0. 01% at 1W.