I bought a bargain external speaker and mic for an iPOD. I wanted to
play a tape recorder device direct into the speaker by plugging the
speaker + mic into the 3.5mm (1/8 inch) output of a tape recorder.

It wouldn't work even when changed some of the connections after I
had checked the pinout for the four connectors on the 3.5mm plug and

When I opened up the external speaker + mic there was circuit board.
What does the circuit board do?

http://tinypic.com/view.php?pic=2j31sue&s=4

And why does the speaker have four connections ???