Understanding microphones

Let’s talk about microphones. Whether you are looking to buy one and don’t know where to start; or you want to know exactly how they work and the different parameters/ specialities each one has to enhance the type of recording you are carrying out… I hope this can help give you some guidance.

First, let’s start with what a microphone actually is.

“The one common thing that all mics do is respond to vibrations in the air (sound waves) that they convert into electrical energy (the audio signal) to be amplified” Paul White (2018).

So in other (and simpler) terms, they take in the sound and put it on your computer as a visible audio wave.

Mics can be broken down into a few different categories. The first way mics can be organised is into passive and active:

Passive mics require no external power supply.

Active mics on the other hand generally use phantom power, although some use batteries.

Let’s look at some other ways to categories mics…

Different types of microphones convert sound waves in different ways using a diaphragm (a very thin piece of material that vibrates when hit by sound waves). These are all types of microphones which do it in different ways:

Dynamic mics

This is the simplest mic in the studio, in technical terms. They are passive mics. Fisher (2005) writes “they work by connecting the vibrating diaphragm to a coil of wire. This wire surrounds a fixed magnet’. As the diaphragm vibrates, the coil moves through the magnetic field which generates a low power alternating current; as it is low, pre-amps are used to add gain, and sometimes colour to the sound. Dynamic mics are further split into two types:

Moving-coil dynamic mic:

• This microphone has a thin circular diaphragm.

• Most common in studios and great for live sound as they can withstand the ‘abuse’.

• Great for drums and guitar amps.

• They have a cardioid polar pattern (further explained below).

• Typically used with louder sound sources that have less high-end because the frequency response rolls off after 16kHz.

• An advantage is that they are cheaper than other mics, require no power and have high pressure levels so can withstand closer sound sources.

• A disadvantage however is the small output signal it has. A lot of amplification is needed to make it useable; this will also raise background noise picked up by the mic.

Ribbon mic:

• This microphone has a thin metal ribbon (usually aluminium) that is suspended between a U-shaped magnet.

• The ribbon is open to air on both sides giving a natural figure 8 polar pattern.

• They have a very natural sound.

• The frequency response, however, is no better than the moving coil but this can be used to your advantage when trying to smooth out frequencies. For example: The strident violin, the harsh guitar amp, cymbals and gives a great laid-back feel for lead vocal that could use it as a creative technique.

• There are unfortunately quite a few troubles that come with using this mic: It is expensive and very fragile as it is easily damaged by air, which is why pop-filters are a must. You also have to be wary with storing it; it must be kept upright otherwise the ribbon can stretch, affecting the tone and quality of the sound.

Capacitor mics

This is also known as a condenser mic. This involves two metal diaphragms spaced closely together with an insulating air between them. A positive voltage is sent to one plate and a negative voltage to the other so when a sound strikes the diaphragm, one plate, which can freely move, vibrates allowing it to move closer and then further to the other plate which is fixed. This changes the voltage creating a variable alternating current analogous to the sound waves striking it. Capacitor mics always contain an active circuitry for this reason, either in the form of an FET or valve, which divides this type of mic up into two types:

FET mic:

• Also known as a solid-state mic.

• They have great transient response allowing them to capture more precise transients. This makes them ideal for painting more of an honest picture when it comes to recording style.

• Runs on a lower power supply compared to valves, the standard is 48V phantom power. This make is ideal for touring musicians and engineers who are on the move and may not have access to a recording studio.
  

Valve mic:

• Also known as a tube mic.

• These mics are great at smoothing out the sound of an instrument creating a warm musical tonality. This makes them a great choice for vocals.

• In a blog by Soyuz Microphones (n.d.) “The tube can add an element of depth and resonance that makes instruments sound larger than life.”

Boundary mics

The final type of mic, and the least commonly used, is the boundary mic. These are sometimes referred to as Pressure Zone Mics or PZMs as they exploit the air pressure differences found at a room boundary, like the wall, floor or ceiling. When sound waves reach a boundary, the air molecules no longer move so the sound energy is converted into air pressure. Fixing a boundary mic to a ceiling is a good way to capture an overall drum kit, or you could place it on the floor by the kick drum to use as, or in addition to a close mic. White (2018), explains how he likes to put them on walls for acoustic guitar recordings and underneath grand pianos for a different, more unique sound.

So, I mentioned above something called Polar Patterns, what are these? This is how to illustrate the way a mic responds to a sound arriving from different directions. “It is essential to know polar patterns to get the perfect recording out of your microphone” (Thomas, 2016). There are three main groups of polar patterns which I have outlined in the table below:

There are mics available that are called variable pattern mics which can switch between the different polar patterns. This makes them a lot more flexible in the studio. It’s mostly capacitor models which can hold this feature. If you place two cardioids back-to-back, switching between different polar patterns means you have the full range of polar patterns.

The creative opportunities seem endless don't they?

...If you have an endless money supply anyway...

References

WHITE, P. (2018) The Producer’s Manual. Fourth Edition. Loughrigg: Jake Island Ltd.

FISHER, J. (2005) instant Surround Sound. San Francisco: CMP Books.

SOYUZ MICROPHONES. (n.d.) The Ultimate Showdown: TUBE vs FET Mics. [Online] Available at - https://soyuzmicrophones.com/articles/tube-vs-fet-mics. [Accessed: 11th November 2021]

K.T, T. (2016) Microphone polar patterns. [Online] August 16th, 2016. Available from - https://www.lewitt-audio.com/blog/polar-patterns. [Accessed: 12th November 2021]