MICROPHONES

The precision of German engineering; the delicate elegance of British design; the rugged reliability of an American touring machine. Are we speaking of fine sports cars? No. But no subject in audio evokes passions similar to those of a classic car collector like the subject of microphones. Whether a classic German Telefunken tube mic, a Coles ribbon mic with its British flair or an American standard for touring from Shure, you can’t capture your sound without the assistance of these delightfully eclectic little devices.

Microphones come in all shapes and sizes to fit all purposes and personalities. The number and variety of microphones manufactured, both past and present, could certainly fill a tome or two. However different they may appear, the thing they share in common is a transducer. A transducer is a device that transforms one kind of energy into another. A microphone converts acoustic energy to electrical energy, and a speaker converts electrical energy back to acoustic energy.

There are two basic classifications of microphones, based on their method of transduction: dynamic and condenser. Dynamic mics, including moving coil and ribbon microphones, work on the principle of electromagnetic induction. A moving coil microphone’s diaphragm is attached to a coil of wire, which is suspended in a magnetic field. As sound encompasses the thin, light membrane of the diaphragm, it vibrates, moving the coil of wire within the magnetic field, creating a flow of electrons and current along a wire. Ribbon mics function similarly; however, they use a delicate rectangular diaphragm, similar in appearance to piece of ribbon, instead of a coil. The rectangular diaphragm moves within the magnetic field to create the current.

Condenser mics, sometimes called capacitor mics, work on the principle of variable capacitance. A capacitor is a device capable of holding a charge. In the capsule, there is a fixed back plate and a front plate, the diaphragm, which vibrates back and forth in response to sound pressure. The changing distance of the front plate varies the capacitance, which creates a small current. This signal is so small that there must be a small amplifier, or pre-amp, in the microphone. To charge the capsule and power the amplifier, an external power source is necessary for a condenser mic to work. This is usually supplied in the form of phantom power, which applies 48-volt power from the mixing console or mic-preamp through one of the wires in the mic cable to power the internal electronics. Some condenser mics use a tube for the amplification stage, and when their power requirements exceed what the phantom power from the console can provide, they will use an external power supply box.

The most popular dynamic mic of all is probably the affordable Shure SM-57. This moving coil mic stands up to rough use and high sound pressure levels. It is a first choice for snare drum, and also very popular on electric guitar amplifiers, among other things. The AKG D112 is a popular choice for bass drum. Small diaphragm condenser mics like the Audio Technica 4051 are often used for drum overheads or on acoustic stringed instruments. Large diaphragm condensers like the classic Neumann U87 are standard fare for vocals.

Whether laying down the next Sgt. Pepper’s or thrashing around in the basement, mic choice is an important component to your sound. Choose your tools wisely.

-Jay Frigoletto

Question for Jay? Visit him online at www.promastering.com or www.myspace.com/sslmixer.

Starting a Mic Collection

(Below, l-r)

Audio technica 4051: $499

Shure SM-57: $99

AKG D-112: $199

Neumann U87: $2,600