The Telephone Museum of New Mexico had some models of "Liquid Transmitter" that Alexander Graham Bell and Mr. Watson used for first telephone call. Wire from Battery negative terminal connects to brass rod suspended in small tank of conductive liquid. The "T' looking thing at top is membrane that vibrates from sound. downward part of "T" is wire suspended just above conductive liquid in liquid holding cup connections at right go to computer amplifier speakers to increase sound. Critical is wire height attached to membrane above conductive liquid.
A DIY build and demo of this at:
http://www.pcbheaven.com/opendir/index.php?show=893jc3780gm0e99d60e
