History of Microphones
The word "microphone" has been around since Sir Charles Wheatstone coined it in 1827, but functional microphones weren't invented until Emile Berliner of Germany came up with the details while working with Alexander Graham Bell on the first Bell telephones. The 25-year-old inventor sold his microphone design to the Bell Telephone Company in 1875 for $50,000. His microphone worked by translating sound waves into electrical current using two metal disks separated by granules of carbon. Sound waves changed the pressure between the disks, which correspondingly changed the electrical resistance. When direct current passed through both plates, the current varied according to the resistance, allowing sound to be transmitted electrically.
Today there are several different designs for microphones for you to choose from, and they vary both by the way they convert audio into electricity and by the application for which they were designed. This article covers two of the most common types: the dynamic microphone and the condenser microphone.
Dynamic Microphones
Dynamic microphones are designed for environments like live shows, where they are durable enough to survive rough handling but don't pick up vocals with the clarity you would expect on a professional recording. A dynamic mic consists of a thin plastic diaphragm that is attached to a coil of wire. Either surrounding or in the center of the coil is a magnet. When you talk or sing into a dynamic mic, the sound waves of your voice make the diaphragm vibrate, which in turn vibrate the coil and move it in relation to the magnet. This causes current to travel through the coil and out to a speaker or amplifier. This type of microphone is "velocity sensitive," meaning the amount of current is determined by the speed of the vibration of the diaphragm and coil.
Condenser Microphones
Condenser microphones are much more sensitive than dynamic microphones. The term "condenser" is actually an old word for "capacitor," which refers to an electronic component that is able to store energy and release it very quickly, much faster than a battery. Like dynamic microphones, the condenser mic uses a diaphragm to capture sound waves. The diaphragm is attached very close to (but not touching) a rigid metal plate. A battery or power supply is connected to both the diaphragm and the metal plate, which creates electric potential between them --- i.e., the assembly can hold a certain specific amount of current depending on the distance between them. When the diaphragm vibrates, it moves in relation to the metal plate, and the amount of current the assembly can hold (called its "capacitance") changes. When the plates are closer together, they can hold more energy (the capacitance increases) and so the assembly draws current from the power source. When the plates are further apart, they can hold less energy (the capacitance decreases) and the assembly discharges, or releases, current that it can't store. By measuring the amount of power drawn or discharged, a condenser mic converts sound waves into electrical energy that can be transmitted to speakers or recording equipment.
Because they are so much more sensitive, condenser microphones are preferred for recording and for getting all the nuances of vocal performances. They are so sensitive, however, that higher-volume sounds can be distorted. You're more likely to find a condenser mic in a recording studio, and a dynamic mic at a live rock show.
Tags: amount current, metal plate, sound waves, assembly hold, between them, energy capacitance, into electrical