What Is a Dynamic Microphone and What Can It Be Used for?
A dynamic microphone is the type of microphone often used by performing vocalists and musicians. But when you go from live shows to recording in the studio can a dynamic microphone still be used, and if so, what for?
We’ll start by looking at what a dynamic microphone is and how it works. Then we’ll move on to look at some of the ways that dynamic microphones can be used in live and recording settings.
Here’s a quick summary of what you’ll find in the rest of this article.
Dynamic microphones capture sound using a plastic diaphragm that makes a coil move in a magnetic field. This produces an electric current that carries the audio signal. Dynamic microphones are particularly suitable in live performance, both vocals and instruments. They can also be used for specific purposes in a recording studio.
There are different types of microphone, and the various designs make them suitable for different purposes. You can read about types of microphone for home studio recording in another article on our website. Here, we’re going to try to make sense of dynamic microphones and what they can be used for.
What Is a Dynamic Microphone?
Microphone manufacturers like Neumann define a dynamic microphone as one that convert sound into an electrical signal by means of electromagnetism.
They include two main types of microphone in the “dynamic” category: moving coil microphones and ribbon microphones.
Ribbon microphones are very expensive and easily damaged. Although Neumann include them in the dynamic microphone category, dynamic usually means moving coil microphones.
This is what people normally think of they are talking about dynamic microphones and this is what we will be talking about here.
Singers on Stage and TV Use Dynamic Microphones
A dynamic microphone is the type that you will have seen vocalists singing into in a live performance. You may also have seen microphones pointing at musical instruments in a live setting, which are probably dynamic microphones too.
This type of microphone usually has a cylindrical shape with a little wire mesh, or grille, at the end you sing (or play) into, and a wire coming out of the other end that connects to an amplifier.
Two popular examples of dynamic microphones, that you will have seen, are the Shure SM57 and Shure SM58 (see these microphones on Amazon using the links), which we’ll talk about more here.
How Does a Dynamic Microphone Capture Sound Waves?
Underneath the wire mesh (or grille) there is a thin plastic film, which is the diaphragm. Sound waves from a vocalist or musical instrument enter through the mesh and cause the diaphragm to vibrate in the same way as the incoming sound waves.
The plastic diaphragm has a coil of wire attached to it, which vibrates along with the diaphragm. The coil of wire forms a cylinder that surrounds a cylindrical magnet.
As the coil vibrates together with the diaphragm it moves in the magnetic field. This movement induces (produces) a voltage in the coil, which causes a current to flow in the wire.
The current flowing in the wire carries the audio signal that represents the sound waves that caused the diaphragm to vibrate at the start of this process.
This electrical audio signal will be sent to an amplifier to boost the level of the signal so that it can be recorded or played directly through speakers.
The diagram above (image from WikiMedia) shows the sound capture mechanism in a dynamic microphone. The parts of the microphone that the numbers refer to are outlined below.
- This shows the sound waves coming into the microphone.
- The diaphragm that is made to vibrate by the incoming sound waves.
- Wire coil attached to the diaphragm, which moves with the diaphragm
- Magnet surrounded by the wire coil, which moves in the magnetic field.
- The electric current generated in the wire coil is carried out of the microphone for amplification.
Dynamic Microphones Are Best for Live Performance
Dynamic microphones are usually the best choice for live performance. There are a few reasons for this, some of which are outlined below.
Dynamic Microphones Aren’t Damaged Easily
The design and construction of dynamic microphones makes them very robust. This means that they can withstand a lot of punishment in a live setting.
For example, a microphone is easily dropped during a performance and any microphone used in a live setting needs to be able to withstand this.
Live performance gear often has to be unpacked and packed up again very quickly, and the equipment isn’t always treated with care. This is another point at which delicate equipment could be damaged easily.
Dynamic Microphones Are Cheaper
Dynamic microphones are usually less expensive than other types of microphone. Even the dynamic microphones used by professional vocalists are pretty inexpensive, making them affordable for many of us.
For example, two of the most popular and highly regarded dynamic microphones, the Shure SM57 and SM58, can be bought for around $100 each.
This means that there’s less likely to be a problem buying spare microphones, or getting a replacement, to deal with any damage that might happen.
Cardioid Polar Pattern Makes Dynamic Microphones Unidirectional
Looking beyond durability and affordability, dynamic microphones have some advantages in the way they respond to sound.
The way that microphones respond to sound is often represented in a “polar pattern”. This is a circle that show how sensitive the microphone is to sound all around the circle.
Dynamic microphones are usually described as having a “cardioid” polar pattern.
Cardioid Polar Pattern
The image on the left (image from WikiMedia) shows the cardioid polar pattern of a dynamic microphone. This is what makes dynamic microphones “unidirectional”.
Each circle from outside to inside represents the reduction in the level of sound captured by the microphone (from 0dB to -25dB).
Audio capture is greatest for sound coming straight into the microphone (top). Less sound is captured from the sides, and very little from “behind” the microphone.
The cardioid pattern means it is most sensitive to sound coming directly into the end of the cylinder, less sensitive to sound coming from the side, and not at all sensitive to sound coming from the end where the wire is.
This pattern is sometimes called “unidirectional”, meaning that the sound is only picked up from one direction, i.e. sound coming straight into the top of the cylinder.
This makes it perfect for live performance situations, where there may be a lot of noise from the audience, and other instruments like drums in the background.
If the vocalist’s microphone was equally sensitive to sound coming from every direction these other sound sources could be picked up and amplified, which probably isn’t ideal.
Dynamic Microphones Are Less Sensitive to Low Level Sound
One of the things that makes different types of microphone suitable for different situations is sensitivity.
This refers to the level of audio signal produced by a particular sound source, and dynamic microphones are at the lower end of the sensitivity range.
This is mostly because the wire coil attached to the plastic diaphragm adds weight, which resists the development of vibrations in response to sound vibrations.
Microphone manufacturers usually measure sensitivity by the amount of voltage produced by a particular sound wave pressure. The units for this are mV/Pa.
mV means “millivolt(s)”, which is a thousandth of a volt – the voltages produced inside a microphone are very small. Pa is “Pascal(s)” – a unit of pressure measurement.
Since dynamic microphones produce a weaker audio signal for a particular level of sound, the signal often needs to be amplified to a greater extent that with other types of microphone.
A live amplification system or audio interface will normally have a “pre-amplifier” that increases the level of the audio signal ready for further processing.
In a live setting this would take it up to the point where an amplifier can boost it to the level needed to drive speakers.
In a recording setting the audio interface would raise the level of the signal so that it can be captured by recording equipment.
This additional amplification can also increase the level of any unwanted background noise or audio interference. This noise can creep in, even with the cardioid polar pattern that we looked at earlier.
In a live setting it might not be noticeable, but this unwanted noise could be a real problem when recording.
Recording With Dynamic Microphones
Since we’re focusing on a home recording studio setting here, we’ll look at the inexpensive dynamic microphones that people may already have, or could obtain without breaking the bank.
I’ll use the two popular Shure microphones I mentioned earlier, the SM57 and SM58, as typical examples. Other manufacturers produce similar microphones, but we’ll used these here as typical examples.
Dynamic Microphones for Recording Instruments
Dynamic microphones are often used to record instruments, even in a studio setting.
Of the two Shure microphones I mentioned earlier, the SM57 is the one that is often used for record instruments. On the Shure website it’a actually described as a “dynamic instrument microphone”.
Since dynamic microphones aren’t very sensitive, the SM57 is normally used to record instruments that produce quite a loud, dynamic sound.
This is because this type of sound is needed to make the dynamic microphone produce a good level of audio signal.
The low sensitivity of dynamic microphones like the SM57 means that they are unlikely to be overloaded by loud sounds produced by amplified instruments like guitars.
Problems might result if more sensitive microphones were used with this type of sound.
The Shure website says that the SM57 is suitable for recording drums, guitars and woodwinds.
Drums would produce the type of intense sound that works well with a dynamic microphone.
Guitar playing would need to be quite loud or percussive too, so strong rhythm playing or an amplified guitar would be suitable. It might not work for recording light fingerpicking.
Woodwind instruments like the saxophone, clarinet or flute (and brass instruments like the trumpet) could produce enough sound pressure to make a dynamic microphone produce a high level audio signal.
Microphone Placement Is Important
The SM57 guidelines on the Shure website state that the microphone needs to be placed close to the sound source.
The distances from the instrument mentioned range from 1 inch to 3 inches for drums.
For guitar, only the suggested distance from an amplifier is outlined. The distances range from 1 inch to 3 feet from the speaker, with the amount of bass sound captured being reduced as the distance increases.
There is no mention of recording acoustic guitars, but the microphone would probably need to be placed a few inches from the guitar body.
You can see the information on SM57 microphone placement on the Shure website.
We’ll look at microphone placement for recording in more detail in another article, but as you may know, the way the microphone is pointed at the instrument or speaker also makes a difference to the sound captured.
Although the SM57 is promoted as an instrument microphone, the placement guidelines include information for using it for vocals.
The suggested distance vocals is less than 6 inches, or your lips actually touching the “windscreen” – the grille where the sound goes in.
Shure say this produces a robust sound, emphasized bass, with maximum isolation for other sources. This fits with what we have already talked about in relation to dynamic microphones.
Can You Record Vocals Using a Dynamic Microphone?
Although Shure say that the SM57 can be used for vocals, it’s their SM58 microphone that is really intended for vocal use. The SM58 has design features that make it more suitable for vocals.
The microphone has a built-in spherical filter to reduce breath noises, particularly the loud “popping” that can result from “plosive” sounds from words that include letters like “b” and especially “p”.
Like all dynamic microphones the SM58 has a unidirectional cardioid polar pattern. Also, like other dynamic microphones a vocalist needs to place the microphone very close to the mouth and pointing directly at it.
Microphone Design and Close Placement Isolates Vocals
The microphone design and placement helps to ensure that only the vocalist’s voice is picked up by the microphone. In a live setting this prevents unwanted external noise from the audience and other instruments being picked up and amplified.
Close placement of the microphone and its unidirectional properties help to avoid feedback too. This is where the amplified sound of the vocalist is picked up by the microphone and sent through the amplifier again, to be picked up by the microphone and amplified again, and so on.
This is a feedback loop, which you have probably heard where microphones and amplifiers are used. It produces an unpleasant squealing sound that continues until the loop is broken, usually by turning the amplifier down or isolating the microphone so that it can no longer pick up the amplified sound.
The SM58 placement guidelines on the Shure website state that the microphone should be placed less than 6 inches or lips touching the “windscreen”. As before, the microphone should be pointing straight at the vocalist’s mouth, or “on axis to microphone” as Shure put it.
As with the SM57 they say that this close placement captures a robust sound, with an emphasis in the bass frequencies, and isolates the vocal from other sounds.
The microphone can also be moved further away for less intense “natural” sound. This includes a reduction in sibilance (excessive “s” sounds) with slightly off-center placement.
Recording Vocals With a Dynamic Microphone
In any recording that includes vocals it is usually the vocal element that is the main focus of the track. This is why music producers take a lot of care in choosing microphones to capture the vocal performance.
The lack of sensitivity to subtle changes in air pressure outlined above means that dynamic microphones aren’t able to capture up a lot of the detail in a vocal performance.
This is one of the reasons why other types of microphone are normally used for recording. The main type of microphone used for recording vocal performances is the condenser microphone.
You can read more about types of microphone for home studio recording in another article on our website.
Sometimes a Duller Sound Is What You Need
I have heard that when a vocalist has a lot of harmonic variation in their voice it can be difficult to capture a balanced recording. This is one situation where it could be helpful to use a dynamic microphone to record vocals.
In this case the dynamic microphone can help you to capture the basic sound, although it is likely to sound a bit duller than with other types of microphone.
However, this might be just what you need if the performance started off a bit too harsh due to lots of harmonic content.
You may have heard it said that vocals recorded with a dynamic microphone can have a “nasal quality”. It’s probably the way that dynamic microphones capture a duller sound that is responsible for this.
If the vocalists performance isn’t very bright and edgy to begin with, then the dynamic microphone is likely to make it even less bright.
I don’t really want to end this section on a negative, but we do need to be aware of the limitations of the equipment that we have available.
So, What Can Dynamic Microphones Be Used For?
Dynamic microphones are comparatively inexpensive, are very durable and can withstand a lot of punishment. They respond well to loud, punchy sounds and can be used in a live setting or a recording studio.
In most cases there will be better options for recording vocals, but dynamic microphones have their uses for this too.
I normally use a condenser microphone connected to an audio interface with an XLR cable for recording vocals. I have a USB condenser microphone to capture ideas when songwriting.
Writing this has made me want to dig out the couple of dynamic microphones that I don’t use very often any more (haven’t played live for a long time) and try them out again.
