Microphones are categorized by the way they transform sound energy into electrical energy. In acoustics terms, the process of changing energy from one type to another is called transduction. In this article we will explore the way a dynamic microphone transducer works and what that might mean for choosing the right microphone for your next project.
How Do They Work?
Some confusion about dynamic microphones exists because of the word dynamic. When dynamic is used to describe microphones, it is not referencing its ability to deal with a large dynamic range (as a musician might expect). It’s also not referring to dynamic in the sense of power. (In fact, one of the upsides to a dynamic microphone is that it does not require an external source of power.) Rather, dynamic as used here refers to motion. Dynamic microphones work on a principle of a moving coil. For this reason, many people call dynamic microphones moving-coil microphones to avoid the confusion.
The transducer part of the microphone—called the element or capsule—is usually protected by an outer casing of wire mesh. The element consists of a diaphragm (a thin sheet of material that can move back and forth with variations in air pressure), a coil, and a permanent magnet. The coil is glued to the back of the diaphragm so that when the diaphragm moves, the coil does too.
The coil—sometimes called a voice coil—moves back and for the within the ring of a fixed permanent magnet. Without going too deep into the physics of it, the motion of the coil inside the magnetic field of the permanent magnet generates changes in electrical current. This process is called electromagnetic induction. That’s how sound signals (oscillating changes in air pressure) are transformed into an electric signal (oscillating changes in the electrical current.) This is the same way most loudspeakers work, but with the process reversed.
Is a Dynamic Microphone Right for Me?
Overall, dynamic microphones are robust and generally inexpensive compared to other types of microphones. Unlike other types of microphones, dynamic microphones do not require an external power source. They also tend to be resistant to humidity and temperature changes, making them a good choice for many outdoor applications.
The membrane-coil transducer has more mass than other transducer types (such as the transducer of a condenser microphone), which gives the dynamic microphone certain characteristics. On one hand, the ‘heavier’ system of a dynamic microphone makes it have a slower transient response and a lower sensitivity than other microphones. On the other hand, dynamic mics tend to be resistant to overloading and, as a result, have high gain before feedback capabilities. This makes them great for applications where sound quality is not as important as durability.
Since dynamic microphone diaphragms do not respond linearly to all sound frequencies, many dynamic microphones specify the range over which they are designed to work best. High-end dynamic microphones sometimes use multiple diaphragms of different sizes to get a linear response out of a larger range of frequencies. These microphones use complex circuits to combine the signals from the various diaphragms before outputting a single signal.
Further information about specific dynamic microphones can be found on microphone manufacturers’ websites. Read more about condenser microphones here.