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WPI Technical Theatre Handbook: Converting Sound to Electricity
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Converting Sound to Electricity

Dynamic microphones are among the simplest types of microphones. They consist of a diaphragm that is attached to a small coil of wire. This coil of wire is mounted such that it is surrounded by a magnet. The diaphragm is arranged such that it will move when it is exposed to sound pressure. This, in turn, moves the coil, creating an electric current in it, due to the magnet. The current produced is an electrical representation of the sound that moved the diaphragm. Dynamic microphones are durable, reasonably inexpensive, and usually have good sonic characteristics. Their applications in theatre are numerous; everything from wireless mic transmitters to intercom systems can use dynamic microphones. They are also especially useful in situations where a production calls for an actor's ``disembodied'' voice to play a role, as dynamic mics are an excellent choice for speech and singing. Two common, favorable types of dynamic microphones are Shure models SM-57 and SM-58. These durable mics are suited to a wide variety of tasks, and are quite affordable. The microphone resting on top of the case in figure 6.2 is a Shure SM-58, while the microphone directly below that is an SM-57.

Figure 6.2: A variety of microphones in a microphone road case.

Condenser microphones and electret condenser microphones vary in design considerably from dynamic microphones. A full dissertation on the operating characteristics of condenser mics will not be given here; suffice it to say that they use properties of capacitance to produce a very small signal proportional to the sound wave entering the microphone. This signal is amplified with a small transistor amplifier mounted inside of the mic. Because of this, condenser microphones require some sort of power, either from a battery or what is known as phantom power (the powering of microphones remotely from the sound board). Condensers are very sensitive, and offer excellent sonic capabilities. For this reason, they can be useful in theatre applications where a sound needs to be picked up from some distance away from its source. A favorite condenser microphone for many applications is the Shure model SM-81.

There are many other methods for converting sound energy to electrical engergy. Carbon, piezoelectric and ribbon are also common types of microphones, though less so than dynamic and condenser types. It is not within the scope of this book to provide an in-depth description of all types of microphones, so further reading elsewhere is recommended for those with an interest in the subject.

next up previous contents index
Next: Directionality Up: Microphones Previous: Microphones   Contents   Index
Steve Richardson 2000-07-06

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