Microphones convert sound waves into electrical voltages.
They were first used with early telephones and then radio transmitters and have evolved through a number of major changes to the high quality instruments of today. Collecting microphones can be very interesting and some representative microphones are included in this web page along with a reference to an excellent article on early microphones. This is Bell's original liquid transmitter from a set of Bell Laboratories photographs in the Ron Christianson Telephone Collection. Many reproductions of Bell's original Liquid Transmitter have been made. Since it is a simple design, it is very hard to tell the difference between the original and the reproductions as you can see from these photographs.