battery as mic preamp?

[paradox]

well,i was reading the biography of steve jobs by walter isaacson,and in it was one example when someone used a simple carbon mic,a speaker,and a battery,without any preamp for mic.i pretty much confused young steve,and me too.i mean,how is it possible to not use a preamp and still get it going?thanks in advance!!!

 

[duke37]

A carbon microphone cosists of a pack of carbon granules which are conductive. Sound vibrations alters the connections between the particles so altering the current. The output electrical power is therefore higher than the sound input power.
This is the system used in early telephones.