The Complete Guide to Recording Studio Microphones
Some of the most famous recording studios in the world earned their renown through the quality of their recording rooms or the quality of their recording studio microphones. Studios like Abbey Road and Ocean Way used a combination of expert room design and vintage, multi-thousand dollar microphones to earn reputations as world-class studios.
In fact, the microphone is perhaps the most iconic symbol of recorded music. Microphones capture sound — anything from vocals to acoustic guitars to an entire live orchestra. So long as the instrument creates sound waves, microphones will transform it into electrical signals. Since your microphone sits at the very beginning of your signal chain, it can be the first point of failure for your recording quality.
This makes your choice of microphone in your recordings an important one.
Over time, three major microphone types have developed: the dynamic microphone, the ribbon microphone, and the condenser microphone. Within each category, you’ll find a wide range of mics at every budget level. Many studios have “microphone lockers” with a variety of microphones since the characteristics of one microphone may be better suited for a certain instrument or musical style than another.
The major three types of microphone are differentiated by their type of transducer. A transducer is a device that converts one form of energy to another — in this case, sound into electric voltage, which can be amplified and captured in a recording. What are those types, and what is each one best for?
Types of Microphones
1. The Dynamic Microphone
A dynamic microphone operates using electromagnetic induction. In essence, the dynamic mic contains three main components. The first is a stiff diaphragm, typically about .35 millimeters thick and made from Mylar (a type of polyester film). The second is the voice coil, which is a wrapped, fine wire, attached to the diaphragm, which is suspended precisely within a magnetic field. This magnetic field is supplied by a permanent magnet within the microphone. When sound waves hit the diaphragm, it causes the wire to move back and forth correspondingly, cutting across the lines of magnetic flux generated by the permanent magnet. This induces an electrical signal in the coil, which then passes out of the microphone and into your microphone preamp.
Dynamics are typically very durable, and you can find extremely cheap ones that are still studio quality (such as the ever-popular Shure SM57). They typically have a natural resonance in the 1kHz to 4kHz range, which determines voice intelligibility. This means that vocalists tend to like dynamic microphones, especially in live situations. Dynamic microphones also typically have bad high frequency response. The ability of a microphone to handle high frequency information is in large part determined by how heavy its moving parts are. Since both the diaphragm and voice coil are moving, a dynamic microphone is quite heavy compared to other microphone types. For this reason, they tend to fall off above 10kHz. However, they can handle much higher sound pressure levels than ribbon or condenser mics. Typically, they have a slow transient response, which means they output a more rough, inaccurate signal. Dynamic microphones often have a cardioid polar pattern.
2. The Ribbon Microphone
A ribbon microphone, like the dynamic microphone, operates using electromagnetic induction. However, rather than a voice coil, a ribbon mic uses an exceptionally thin aluminum strip that’s light enough to be moved by the air molecules of a sound wave – no separate diaphragm is necessary. This ribbon is suspended within a magnetic field. As sound waves move the aluminum, it cuts through the flux lines and generates a small voltage. This signal is very low – it’s generated by only one thin strip of metal, rather than a full coil of wire. For this reason, a step-up transformer is necessary to boost the output to a usable level.
Ribbon microphones are typically very fragile (though modern ribbons are becoming quite rugged). They’re also hard to find at the budget level, and you’ll be hard pressed to pick up a good ribbon for less than $300. They have less moving parts than a dynamic microphone, so they have a more extended frequency response up to 14kHz. They’re also much flatter along the range of frequencies, with natural resonance focused in low frequencies rather than the midrange (like dynamics) or the high frequencies (like condensers). This results in a very un-hyped response, one that’s very appealing in the digital era. They have a faster transient response than dynamic microphones but are still a bit inaccurate. Ribbon microphones typically have a bi-directional polar pattern.
3. The Condenser Microphone
Condenser microphones utilize the electrostatic principle rather than the electromagnetic principle found in the dynamic or ribbon microphone types. Inside a condenser microphone, you’ll find a pair of thin, electrically charged plates, called the diaphragm and backplate. This effectively forms a capacitor (or condenser, as it is still called in the UK). The diaphragm is unfixed and moves back and forth as sound waves hit it. The backplate is fixed; as the diaphragm moves, the distance between the two plates changes. The change in space between the plates creates a change in voltage potential, which can then be amplified to a usable level. For the microphone to work properly, a 48 volt DC source is required. In audio gear, this is called phantom power, which you’ll find in studio preamps and audio interfaces. Different polar patterns in a condenser microphone are created by punching small holes in the backplate.
Condenser microphones aren’t fragile in handling, like ribbon microphones, but they are much more susceptible to dust and dirt damage than the other microphone types. This is because they constantly generate a static charge, which attracts dust molecules from the air. They typically have a very clear and extended high-frequency response and can have a rich low-frequency response as well. Good condenser microphones will have a very flat response along their represented frequencies. A condenser’s natural resonance is in the upper midrange, the 8kHz to 12kHz range. They are very sensitive, picking up quiet sources more accurately than dynamic microphones but responding badly to very high sound pressure levels (which can actually overload the plates). Remember that these microphones require phantom power to operate! They have a very fast transient response, meaning they reproduce sound very, very accurately. Condenser microphones can have a variety of polar patterns.
There is more to a microphone than the way it captures audio. Each of the major microphone types I’ve mentioned can have different polar patterns, also called directional response.
The directional response of a microphone refers to how it responds to sound waves coming from different locations. For example, a cardioid directional response means the microphone picks up sound waves from the front well, but from the sides and back poorly.
This response is can be controlled by the design of a microphone’s casing, or by its transducer. Generally, a microphone’s directional response can be represented by a graph of sensitivity as it relates to 360° of direction. This graph is commonly called the microphone’s “polar pattern”. There are three basic categories of polar pattern: omnidirectional, bidirectional, and cardioid.
As the name suggests, an omnidirectional microphone picks up audio information equally from any direction. These microphones are ordinarily pressure-operated and react equally to sound waves at their surface regardless of the location of the sound source. Condenser microphones are often omnidirectional. However, some condensers contain a second capsule mounted on the sides of the backplate. Combining the two capsules in phase results in the standard omnidirectional response. Combining them out of phase results in a bidirectional or figure-8 response, while the in-betweens result in a cardioid response.
Bidirectional microphones respond equally to sound pressure from the front or back of the microphone. These are typically pressure-gradient devices. Information coming from the sides is almost completely rejected, so these microphones are especially useful in studio applications where side-rejection is necessary. Typically, the front side of the microphone has slightly better (and brighter) pickup than the back. Ribbon microphones are the quintessential bidirectional microphone, as the ribbon can only move forwards or backward.
A cardioid microphone features strong pickup to the front of the microphone, with light rejection to the sides and almost complete rejection to the back of the microphone. This creates a heart-shaped polar pattern; hence the name cardioid. This pattern is found in dynamic microphones, but can also be created in condenser or ribbon microphones. Other directional responses also feature “cardioid” in their names, such as supercardioid or hypercardioid. These polar patterns are in-between cardioid and bidirectional, as you can see in the pictures below.
While condenser and ribbon microphones must use complex electronics to create different polar patterns, dynamic microphones rely on changing the microphone’s casing. Cardioid dynamic microphones have a rear port, which delays the audio signal coming from behind the microphone. This delay puts the signal out of phase, and as it hits the diaphragm, the information from behind the microphone cancels out – resulting in little or no pickup.
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