June 09, 2021
Other than the speaker, the microphone is arguably the most important piece in the recording and sound reinforcement chain. It’s also the piece that can affect the quality of your sound the most. With that in mind, it seems wise to know how microphones are built – at least at a basic level.
There are three basic types of microphones: dynamic mics, ribbon mics, and condenser mics. Each type is constructed slightly differently, but they all share some common parts:
The windscreen is simply some device that keeps random moving air from getting picked up. Nearly every microphone has some kind of built-in windscreen.
The diaphragm, conductive material, and magnet/backplate are sometimes referred to as the “capsule” - they work together to convert sound waves into electrical signal.
The body is simply the body; the outer casing that protects the goodies inside.
Finally, the output connector connects to a mic cable, which connects to your audio gear. Nowadays, microphone outputs are standardized to be 3-pronged XLR connections - although this wasn’t always the case and there are a few mics out there which use 4 or 5 pin connectors. Read on for the specific differences between microphone types.
Dynamics such as Carvin Audio’s M68 dynamic vocal mic are also known as “moving coil” mics and technically that is the better term, because ribbon mics are also dynamic mics. Usually, though, moving coil mics are simply referred to as “dynamics” and ribbons as “ribbons.”
Dynamic mics create electrical signal using electromagnetism when a conductive material moves within a magnetic field.
Moving coil mics (or “dynamics”) are quite similar to speakers. They consist of a membrane (or diaphragm) with conductive wire (usually copper) attached to its back. This contraption is surrounded by a strong magnetic field. Sound waves move the membrane, which in turn moves the coil, changing its position inside the field. This induces a variable voltage into the coil, which changes as the sound waves move the membrane.
This kind of moving coil construction is the most robust kind of construction, as the membrane is relatively heavy compared to other mic styles. This is why dynamics are usually preferred for stage applications and some high-volume recording like drums.
As mentioned above, ribbon mics are technically dynamic mics, although they’re rarely referred to that way. Ribbons work on the same principle – conductive material is positioned inside a magnetic field and sound waves cause it to move inside that field, inducing voltage.
The difference is that instead of a two-part contraption inside, there’s a very thin aluminum strip. Basically, the membrane and the coil are combined in ribbons mics. The strip itself is moved by sound waves and induces voltage when it changes position inside the magnetic field (this strip is also known as the transducer).
Since the “ribbon” strip is lighter, it responds more accurately to delicate sound information. It’s also more delicate. In addition, this strip has a much lower output level because there’s less conductive material than in a moving coil design, which uses a whole coil of wire.
Because of this low output level, ribbon mics also incorporate a step-up transformer, which multiplies this output voltage.
Since the transducer is a two-sided strip, ribbon mics have a figure-8 pickup pattern by nature (ie: they pick up sound from the front and back – not the sides). Ribbons tend to have limited high-end response, and they’re quite delicate so their uses are more specialized. That said, they’re great for smooth recordings, and can be quite beautiful on overly bright instruments or instruments where extended treble response isn’t necessary, like guitar cabinets (just watch out for high sound pressure levels).
Condenser mics are the go-to choice in studio recording, because of all the types of mic, they have the widest frequency response and best transient response. They also tend to have higher sensitivity and lower output noise than other types.
Condensers work on a different principle than ribbons and moving coil mics. They work with capacitance. In case you skipped high-school physics – a capacitor is basically two metal plates close to each other which acts as an electrical charge storage device. The closer the plates are to each other, the higher their capacitance.
Condensers, therefore, employ a thin membrane (or diaphragm) which is electrically conductive (usually gold sputtered mylar or sometimes thin foil) close to a solid metal backplate.
Sound waves move the diaphragm, which changes the distance between the two pieces, thus changing the capacitance. This creates the electrical signal which is analogous to the sound wave.
The problem in this scenario, though, is that while this output voltage is high, there’s very little current, since the little capacitor stores so little energy. So, condensers employ an impedance converter, which increases the signal by boosting the current. Because of this process, condenser mics require a power source (other types of mics do not).
Conveniently, virtually every condenser employs phantom power, which is delivered through the same mic cable you’re already using and is provided by your mixer or pre-amp. Look for the button or switch labeled “phantom power” or “48V”. Just remember to never flip that switch on a channel connected to a ribbon microphone. You’ll know if phantom power is off when your condenser isn’t picking up any sound!
There you have it: basic microphone anatomy. Hopefully you now have a bit better understanding of what’s under the hood in these crucial pieces your audio arsenal.
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