The fault that the series resistor has high value can be avoided by using the constant current amplifier , and the fault that the dividing resistor reduces the working voltage of the speaker can be avoided by using the constant voltage amplifier 使用恒流功放,可以避免传统方法中串联电阻取值过大的缺点;使用恒压功放,可以消除分压电阻降低扬声器工作电压的不足。