Associate Professor of Voice, Shenandoah Conservatory Artistic Director of the CCM Vocal Pedagogy Institute
The late 1920s and early 1930s saw the emergence of “microphone singing.” Until the late twenties, singers performed acoustically and therefore had to train their voices to have “ring” and “power” in order to be heard in live performance. Bing Crosby was one of the first singers to make the microphone part of his instrument and exploit its potential. Soon others followed and a new style of singing called “crooning” became popular. Today, CCM singers will perform with a microphone 99% of the time and it is essential for them to understand the equipment they will be using during performances and recording sessions. This is the first of a three-part series on how microphones work and how to find the best microphone for each singer and situation. This is a complex topic and this is just an overview, but it will hopefully get you started. Be sure to follow the blog to receive notifications when parts two and three are posted.
What is a microphone?
Microphones are what electricians call “transducers.” Transducers transform one type of energy into another. In the case of a microphone, the acoustic sound waves of the voice are transformed into electrical impulses that can be enhanced and/or amplified by the sound engineer. The three most common microphone types singers will encounter are dynamic, condenser, and electret condenser.
Dynamic microphones consist of a dome-shaped Mylar diaphragm attached to a free moving copper wire coil that is positioned between two poles of a magnet (Campbell & Greated, 1987). The Mylar diaphragm moves in response to air pressure changes caused by sound waves. When the diaphragm moves, the magnetic coil that is attached to it also moves. As the magnetic coil moves up and down between the magnetic poles, it produces an electrical current that corresponds to the sound waves produced by the singer’s voice. That signal is then sent to the soundboard via the microphone cable (see figure 1).
Condenser microphones are constructed with two parallel plates: a rigid posterior plate and a thin flexible anterior plate. The anterior plate is constructed of either a thin sheet of metal or a piece of Mylar that is coated with a conductive metal. The plates are separated by air, which acts as a layer of insulation. In order to use a condenser microphone, it must be connected to a soundboard that supplies “Phantom Power” (see figure 2). A component of the soundboard, Phantom power sends a 48-volt power supply through the microphone cable to the microphone’s plates. When the plates are charged by the phantom power, they form a capacitor. As acoustic vibrations send the anterior plate into motion, the distance between the two plates varies, which causes the capacitor to release a small electric current. This current, which corresponds with the acoustic signal of the voice, travels through the microphone cable to the soundboard where it can be enhanced and amplified (Benson, 1988; Campbell & Greated, 1987; Turner & Gibilisco, 1985).
Electret condenser microphones are similar to condenser microphones, however they are designed to work without phantom power. The anterior plate of an electret microphone is made of a plastic film coated with a conductive metal that is electrically charged before being set into place opposite the posterior plate. The charge applied to the anterior plate will last for ten or more years and therefore eliminates the need for an exterior power source (Benson, 1988). Electret condenser microphones are often used in head-mounted (like those used on Broadway), lapel microphones, laptop computers, and smartphones.
Dynamic vs. Condenser
Dynamic microphones are most commonly used in live performance because their lower sensitivity rejects excess stage noise. Recording engineers often prefer using condenser microphones for recording applications due to their high level of sensitivity. You will occasionally find condenser microphones in some live performance venues for genres that do not have excessive stage noise. For example, hand-held microphones used by jazz and folk artists, and head-mounted microphones used in musical theatre.
While diaphragm type should be your first consideration, there are several other factors you need to consider when selecting a microphone including sensitivity, polar pattern, and frequency response. Those will be covered in parts two and three, so be sure to check back next week and the week after!
Benson, K. B. (1988). Audio engineering handbook. New York: McGraw-Hill.
Campbell, M., Greated, C. (1987). The musician’s guide to acoustics. New York: Schirmer Books.
Turner, R. P., Gibilisco, S. (1985). The illustrated dictionary of electronics, 3rd edition. Summit: TAB Books, Inc.