Microphones Are Cool
After signal flow logic, understanding microphones is one of the most important things you can learn about audio. A good understanding about microphone design and construction, along with the knowledge of what is available in the marketplace will be indispensable to your job as a sound technician.
A microphone is a transducer. A transducer converts energy from one medium into another. The job of the mic is to convert acoustical energy (sound) into mechanical energy, and then into electrical energy. The better the job of conversion, the more natural the reproduced sound will be.
Microphones are available in a variety of designs and price ranges. As with so many things, the better-sounding mics typically carry a higher price tab, right? Careful. Your warning light should have gone off with that comment. Who's to say what sounds better? While it is true that most engineers will use a higher quality mic in most applications, a good engineer will not succumb to price, perceived value, or tradition in favor of the right sound. In fact, he/she may be found using a very common, relatively inexpensive mic to deliver the sound they're after. It's the sound and what is right for your ears- that is important.
Terminology
There are a few terms that we should be familiar with which will help us to understand how microphones work and how to tell the difference between them just by looking. You should also compare the sound of the mics that you have at your disposal with what the accompanying literature has to say about them. The terms we'll discuss are type, pickup pattern, frequency response, off-axis coloration, sensitivity, proximity effect, impedance and handling noise.
Types
There are two basic types of microphones used in professional audio today - dynamic and condenser. A dynamic mic is constructed of a coil of wire attached to a diaphragm. The coil of wire is suspended in a magnetic field. As sound strikes the diaphragm, it wiggles back and forth, and the coil of wire goes along for the ride. This action causes the coil of wire to cut the lines of magnetic flux, which thanks to God's laws of physics, induces a flow of current in the wire.
A condenser mic works in a similar fashion. It is constructed of a thin conductive diaphragm, placed very close to a fixed, electrically polarized, perforated back plate. As sound strikes the diaphragm, it moves back and forth causing a corresponding change in the capacitance created between the two plates. This action results in a flow of current, which is then fed to the console.
The choice of using a dynamic mic or a condenser mic is very much a matter of application and personal taste. A few general comments can be made about the difference between the two types. Typically, a dynamic mic is considered to be more physically rugged or durable. By contrast, a condenser mic is much more sensitive and reproduces transient peaks better than a dynamic mic. Transients are found in the attack of a percussive sound, such as a piano, drum, or guitar. The ability of a mic to reproduce those transients has a great deal to do with the faithful reproduction of the original sound.
Most sound engineers prefer the sound of condenser mics for recording orchestras, especially strings. The same could be said for miking drums or acoustic piano. With the same breath though, some engineers prefer to use dynamic mics for miking drums, especially for touring sound reinforcement systems since traveling can be hard on all audio gear.
Next issue we will look at other important microphone characteristics.
Curt Taipale
Curt@ChurchSoundcheck.com
http://www.ChurchSoundcheck.com
