In the circuit shown let the rectangular box on the left represent the (high-impedance) output of an audio amplifier, with . Let represent the (low-impedance) coil of a loud speaker. We have to match the impedances by using a suitable transformer.

Solution:             Click For PDF Version

For impedance matching we need a transformer with primary and secondary turns and suitably fixed such that

In our problem the low-impedance to be matched is the resistance of the loud speaker coil, , with the high-impedance of the audio amplifier, . Therefore,

For impedance matching we need a transformer with

.