Condenser microphones are commonly found in recording studios but not often on stages because of the different way in which they pick up sound. Condenser microphones use a diaphragm, just as the dynamic microphone does, but instead of sitting in front of a wrap of coil (the voice coil), the diaphragm sits in front of a stationary plate of metal called the back plate. The diaphragm in a condenser microphone is always made of thin metal or metal-coated plastic. Both the diaphragm and the back plate have polarized voltage applied to them. As the diaphragm moves back and forth in relation to the stationary back plate, a very small current is produced, which is the signal. Figure 9-3 shows a large diaphragm condenser microphone.
Condenser microphones are often classified by the diameter of their diaphragms. Obviously, large-diaphragm microphones are larger in size than small-diaphragm microphones. Large diaphragms are more sensitive to low-level sounds than small diaphragms. Small diaphragms can handle louder overall sounds, however. Condenser microphones can range from $100 to many thousands of dollars. The good news is that you don't have to spend a lot to get one that sounds good.
Condenser microphones are used for everything that dynamic microphones can't do. Condensers are more delicate and more expensive than dynamic microphones, but they are also more accurate. Condensers usually have a flat and wide frequency response, are sensitive to all frequencies, and tend not to boost or lower any particular frequency. This is why condensers are the microphones of choice for acoustic instruments such as piano, winds, strings (including guitar and bass), drum overheads, and vocals.
Figure 9-3: An M-Audio Luna II condenser microphone Courtesy of Avid Technology, Inc.