Just The Basics of Microphones

Microphones are transducers. They turn acoustical energy into electrical energy. They consist of several components: diaphragm, chasis, connector, and sometimes phantom power or dc power and frequency dropoff controls.

There are 5 types of mic's used in the sound reinforcement field. Of which only two concern us the live taper.

1st) Carbon microphones are similar to those found in telephones. While being rugged, they do not have frequency responce.

2nd) Crystal microphones are composed of piezoelectric material that when compressed produces electrical current. They produce high impedance outputs. An example is the pickups on some guitars.

3rd) Ribbon microphones are perhaps the best mics, however they are often too fragile for most touring situations. Perfect for Studio applications. Frequency response ranges from 40 - 18,000 hertz.

4th) Dynamic microphones are in popular use on the road. A diaphragm connected to a coil moves up and down on a magnet thereby producing current. Common brand names include Shure SM-58 and SM-57, Sennheiser MD-421, AKG D330-BT and The Audio Technica ATM-41.

5th) Condenser microphones are on the rise due to DAT and smaller sized mics. They operate on the principle of a capacitor. Electron discharge between two plates (diaphragm and coil) causes current flow. Some popular condensers are AKG C-414EB, Audio Technica ATM-11, and the crown PZM.

All microphones have some form of directivity. Omnidirectional mics pick up sound from all sides of the diaphragm. Bidirectional mics pick up sound in a figure eight shape in front and behind the diaphragm. Directional mics, also known as cardioid and unidirectional, pick up sounds in a heart shaped area around the diaphragm. The bass responce of cardioids increases within two feet of the mic. This is known as the "proximity effect". The hypercardioid is a variation of the cardioid with slightly more directivity and sensitivity in the back.

Microphones produce small voltages in the order between .0775 mV to 77.5 mV depending on the loudness of the sound source. Low impedance levels range from about 50 to 600 ohms. This is the most common range for dynamic microphones. High impedance levels range from 50,000 to 2,000,000 ohms. This is thew most common range for condenser microphones. It is important to match impedance outputs with inputs so that distortion is avoided.