Welcome to part one of our microphone crash guide.

In part 1 we are looking at one of the most common microphone types you will come across in studios, live sound and location recording: the dynamic microphone.

Strictly speaking, the type we are covering here is a moving-coil dynamic microphone. Ribbon microphones are technically dynamic microphones as well because they also work through electromagnetic induction, but in everyday studio language, ‘dynamic microphone’ usually means the moving-coil type. We will look at ribbon microphones later.

Before we start: microphone type and polar pattern are not the same thing

The type of microphone describes the transducer principle: how the microphone converts sound energy into an electrical signal.

The polar pattern describes the direction, or directions, from which the microphone picks up sound.

The two can influence each other through the acoustic and mechanical design of the microphone, but one does not automatically determine the other.

A dynamic microphone is therefore not automatically cardioid, just as a ribbon microphone is not automatically figure-of-eight. Different microphone constructions can be designed with different polar patterns.

So keep these two questions separate:

A little history

Although practical versions of the moving-coil principle go back to around 1877, when Werner von Siemens filed an early patent, dynamic microphones appeared only much later.

Early microphone technology initially included carbon microphones, followed by condenser, moving-coil and finally ribbon designs. Practically usable moving-coil microphones began to appear in the 1920s, around the same period in which ribbon microphone technology was also developed. By the 1930s and 1940s, moving-coil microphones had become increasingly important in broadcasting, public-address systems and in live sound.

One particularly significant example is the Shure Unidyne Model 55 which was introduced in 1939. While early moving-coil microphones were commonly omnidirectional, the Unidyne achieved a cardioid response from a single moving-coil element and became one of the most recognisable microphone designs of the twentieth century.

From there, moving-coil dynamic microphones became increasingly common in recording and live sound—particularly because they were robust, reliable and able to cope well with demanding conditions.

How does a dynamic microphone work?

A dynamic microphone converts sound energy into electrical energy through electromagnetic induction.

The basic process is:

sound wave → diaphragm moves → coil moves inside magnetic field → electrical voltage is generated

1. Incoming sound waves move a thin diaphragm inside the microphone.

2. Attached to the diaphragm is a small coil of wire, usually called the voice coil.

3. This coil sits inside the magnetic field of a permanent magnet.

4. When the diaphragm moves, the coil moves with it through the magnetic field. This movement generates a small electrical voltage that follows the movement of the original sound wave.

The electrical signal can then be amplified, recorded or processed.

What does this construction mean when recording?

The diaphragm and coil together have more physical mass than the rather light diaphragm used in condenser microphones.

This matters because the moving assembly has more inertia. The sound wave therefore needs more energy to move the coil. As a result, the microphone does not respond quite as easily to very small or very fast changes in air pressure and usually produces a lower electrical output. The preamplifier therefore needs to provide more gain.

Eventually, dynamic microphones are less sensitive than condenser microphones.

On the bright side, the same construction means that dynamic microphones are extremely robust and can tolerate rather high sound-pressure levels, rough handling or demanding live environments really well. For these reasons they can be seen everywhere on stages.

Advantages and disadvantages

This means that the lower sensitivity is neither automatically good nor bad. Instead, using—or not using—a dynamic microphone depends on what is being recorded.

Where would we use a dynamic microphone?

Given their attributes, dynamic microphones are extremely common for loud or close-miked sources such as:

• live vocals or other loud vocal sources

• spoken voice

• broadcast and podcast recording

• drum set

• percussion

• guitar amplifiers

• brass instruments

• ... and more.

A famous dynamic microphone is the Shure SM58, which was specifically designed as a vocal microphone. Its grille includes pop filtering and its cardioid pattern helps reduce unwanted sound arriving from other directions. Shure describes it as suitable for both live sound reinforcement and studio vocal recording.

A close relative of the Shure SM58 is the Shure SM57. With a different grille design, the SM57 is commonly used as an instrument microphone since the smaller grille allows it to be positioned closer to the source. On a directional microphone this closer placement can also increase the proximity effect and change the frequency response.

The important principle to keep in mind is not that ‘dynamic microphones are for loud sounds’, but that their construction often makes them particularly suitable for close placement, high sound-pressure levels and situations where robustness matters.

Always check if the behaviour of the microphone suits the source, the environment and the sound you are trying to achieve!

Distance matters

Dynamic microphones are often used relatively close to the sound source. This is partly because their sensitivity is lower and hence moving the microphone closer increases the level of the direct sound compared with the indirect sound from the surrounding room.

With directional microphones, distance can also affect the frequency response. Cardioid microphones exhibit proximity effect. This means that low frequencies become stronger as the microphone moves closer to the sound source.

This can be useful to make a voice sound fuller or warmer (think radio presenter sound). But too much proximity effect can also make speech or vocals sound boomy or muddy.

This is when the distance of a microphone relative to the sound source turns into part of the sound design. Hence, do not simply put the microphone as close as possible. Listen to what happens when you change its position.

Some well-known dynamic microphones

Microphone	Typical use
	A classic general-purpose studio and live microphone, particularly associated with guitar amplifiers, snare drums and other instruments.
	One of the most widely used live vocal microphones. Its grille, built-in pop filtering and robust construction are designed specifically with vocal performance in mind.
	Strongly associated with broadcasting, voice-over and studio vocals, and now also widely used for podcasting. It comes from the same Unidyne III design lineage as the SM57 and SM58, although its acoustic design is different.
	A classic choice for radio broadcasting, spoken voice, voice-over and studio recording. Its Variable-D design is particularly useful because it reduces proximity-effect changes as the source moves closer to the microphone.
	A versatile studio microphone widely used on drums, guitar amplifiers, brass and speech. Just make sure you point it the right way!

Well-known dynamic microphones and their most common applications

I hope you enjoyed this short introduction to dynamic microphones. If you have any questions, drop me an email.

In the next episode, we will look at condenser microphones: how they work, why they are generally more sensitive and when and why we might want to use those instead.