Understanding Dynamic, Ribbon, and Condenser Mics

While all microphones are designed for the common purpose of converting variations in sound pressure to electronic signals, different technologies have their benefits depending upon the application. The three main types of microphones in common use today are dynamic, ribbon and condenser.

The dynamic or moving-coil microphone is the easiest to understand. It is the classic technology taught in grade school as the inverse of the common speaker. A plastic or metal diaphragm is attached to a copper coil that is, in turn, suspended in a magnetic field. Sound pressure waves hitting the diaphragm cause it to move, and with it, the coil within the magnetic field. The resulting magnetic fluctuations translate to electrical fluctuations generally corresponding to the physical fluctuations of the original sound wave.

Due to the requirement of attaching the coil directly to the diaphragm, dynamic diaphragms are thicker, and therefore less sensitive than the ribbon and condenser microphones discussed below. These same design considerations also give the mic the ability to take the greatest amount of sound pressure before distorting, as well as the greatest amount of physical abuse.

Dynamics are also the easiest and least expensive to make. Dynamics tend to color the sound in the range of about 5k to 10k, and start to sound thinner when more than about a foot away from the source.

For these reasons, dynamic mics are most often found in the average stage situation. After all, live performance environments are much more likely to subject mics to such torture as high volume, sweat, the elements, shock and being dropped. In the studio, dynamic mics are most often used to close-mic drums due to the possibility of wayward drum sticks. Large-diaphragm dynamics are often chosen for kick drums due to high sound pressure levels. The Shure SM57 and SM58 are common examples of dynamic microphones.

Ribbon mics are another form of dynamic microphone distinct from the moving-coil variety. A very thin metal ribbon is suspended between the poles of a magnet. Sound waves hitting the ribbon cause it to move, causing magnetic fluctuations that result in an analogous change in the flow of electrons. The extreme thinness of the ribbon makes this type of mic the most sensitive—both in terms of sound and abuse. Like moving-coil dynamics, they color the sound (although more warmly in comparison) and are best used in close-miking situations. They also tend to have very low output, thereby requiring more electronic gain—a factor that can add noise depending upon the quality of the preamp electronics.

This combination of attributes limits the practicality of ribbon mics in all but the most controlled environments. The Beyer M160 and M500 are common examples of ribbon microphones.

Condenser mics are, by far, the most common for studio use. A thin electrically conductive diaphragm is suspended over a back plate, forming a delicate flexible capacitor. When sound waves excite the diaphragm, the distance between the diaphragm and back plate changes—and with it the capacitance. This capacitance change, in turn, produces a voltage change. Associated circuitry converts these variations in voltage to a signal that is sent to the preamp. The power required by this design is serviced by the 48-volt phantom power commonly found on preamps and mixer inputs.

The diaphragms of condenser microphones are made of extremely thin metal or metalized plastic similar in thickness to kitchen plastic wrap. Their thinness makes condenser mics very accurate in frequency response and extremely sensitive to transients, such as the initial crack of a drum being struck. In addition to imparting the least sonic coloration of any microphone design, the sensitivity of condensers extends much further from the source than other mics, thereby allowing greater flexibility. This greater sensitivity also provides the engineer with the option of picking up more of the room ambience—a factor that can add a great deal of realism to a recording.

Condensers are more delicate than moving-coil dynamics, yet much more resilient than ribbons. Due to sensitivity to low-frequency handling noise and the delicacy of the diaphragm, condensers are invariably used in conjunction with a shock mount, and often with the addition of a pop filter. The sonic characteristics of condensers and their need for TLC make them more ideally suited for studio recording. That is not to say that condensers can’t be used for some tasks on stage—just that the environment should be controlled, such as in a professional show where cables are secured, mics are shock-mounted against vibration, and the stage is restricted to professional personnel.

Since condenser construction technology is much more labor-intensive and sophisticated compared to that of dynamics, good quality condensers tend to cost comparatively more money. Condensers are excellent choices for miking vocals, acoustic guitar, piano, orchestral instruments, saxophone, percussion and sound effects. The entire Groove Tubes microphone series is comprised of condenser models.

For more complete information on microphone technology and techniques, get a free copy of our "Record Now: Choosing and Using Microphones." It’s available via download, or at your local M-Audio dealer.