Types of Microphones
In today’s audio world, there are three main types of microphones which are used in studios every day:
– Dynamic
– Condenser
– Ribbon
Each of these mics works differently and as a result, they each yield different sounds. Each has a purpose and a situation when it gives great results and very rarely is there one type of mic (or one mic of any type) that’s perfect for every situation.
Often, it’s the old favorites that we go to every day that get the most use for the common situations. But what do you grab when the common situation become an uncommon one?
Let’s explore the types of mics, how they work and what we think we can expect from them.
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The Dynamic Microphone
The dynamic mic is one of the most common types of microphones and is very versatile.
Most clubs and live sound venues have a solid collection of them and for a good reason—dynamic mics can take a beating.
The basic principle of the dynamic mic is an electrical principle called inductance.
It’s the same principle that electrical generators use in river dams and turbines.
The basic principle is that when a powerful magnet is wrapped in wire (or a voice coil), an electrical current is created (induced)
as the magnetic field around it moves. In turbines, the change is created by its spin.
The Condenser Microphone
It is ironic that the dynamic mic is actually not as dynamic as its condenser mic counterpart.
The reason for this difference is due to the technology that drives the functionality of the mics.
In condenser mics, the electrical principle being utilized is called capacitance.
Capacitance works differently than inductance, although both rely on voltage being created by a moving diaphragm.
In dynamic mics, the diaphragm moves the voice coil through a magnetic field, creating a voltage out of the electro-magnetic field already there.
In condenser mics, a voltage already exists within the capsule and the diaphragm movement causes another voltage to be created.
Tech-Speak: Capacitance
Capacitance is the measure of a device’s ability to store electrical charge, or the measure of an electrical charge that is already stored in a device. A battery, for example, is a capacitor and a 9V battery’s capacitance is 9 volts.
The secret of the condenser mic? Its diaphragm is placed in front of a metal “backplate,” which holds a charge, as shown in the image above.
The diaphragm is coated with a conductive material (often gold dust) and the center of the diaphragm has a wire that’s connected to the output of the microphone.
The gold dust is sputtered (evenly sprayed) onto the diaphragm, so it evenly coats the surface.
As the gold-sputtered diaphragm moves closer and further from the charged backplate, a voltage is created in accordance with the movement of the diaphragm.
As there’s a charge held at the backplate, the capacitance in this case, is the difference between the diaphragm’s regular position and the fluctuating distance to/from the backplate.
As the diaphragm gets closer, a positive voltage is created, and as it gets further away, a negative voltage is created.
If it moves very close, a higher voltage is created, corresponding to the energy used to move it. Therefore louder sounds move the diaphragm more, which puts it closer to the backplate, creating a higher voltage.
Similarly, a quieter sound will also move the diaphragm, but not as much (and therefore not as close to the backplate), creating a smaller voltage.
In this way, the movement of the diaphragm corresponds to the volume (SPL) of the incoming signal, much like the dynamic mics.
The Ribbon Microphone
Ribbon mics are a type of dynamic microphones in that they consist of an extremely thin (and quite fragile) aluminum or other metal strip suspended between two poles of a strong magnetic field as shown in the image below.
The suspended ribbon reacts to the velocity of air particles (rather than the pressure, as in the case of dynamic mics.
This motion within the magnetic flux field generates a small AC voltage proportional to this velocity.
This slight movement creates a fairly small electrical signal (even smaller than that of dynamic mics), so the ribbon mics tend to have a very low output compared to condenser and dynamic mics.
With this in mind, ribbon mics typically require a preamp with a substantial amount of gain.
Many ribbon mics are fragile, like condensers, and are easily damaged by bumps, drops, bangs and even extreme wind or breath blasts.
And placing a ribbon mic in a high air velocity location—such as inside a kick drum—can permanently distort or deform the ribbon element.
Additionally, many will be damaged or destroyed by the activation of +48V, unlike their cousin the dynamic mic!
Some ribbon manufacturers are now making ribbons that are +48V safe but their older counterparts are not so lucky.
Always refer to the manual of the ribbon mic manufacturer (or the internet) before plugging in the mic and always refer to the above list of safety tips before activating +48V.
The image below shows a diagram showing operation of a typical ribbon mic and the bidirectional field created by the ribbon element (Graphic courtesy Mix magazine; used by permission.)
COACH’S CORNER:
Ribbons have become en vogue recently, as they tend to have a warmer and darker sound to them.
Ribbon mics lend warmth to the source, which can help smooth out some of the harsh and edgy quality of digital audio.
While today’s digital signals are much smoother than some of the early CD quality recordings, some people still claim that digital imparts a “coldness” to the audio quality.
Keeping with our “there seems to be an exception for everything” theme, I should mention a new breed of ribbon microphones with on-board pre-amplification circuits that boost a ribbon mic element’s normally-low output to a level comparable to that of condenser or dynamic mics.
Such “active” electronic designs—available from manufacturers such as Royer (who also offer standard, non-active ribbon mics without onboard electronics) may even require phantom power to operate!
These active ribbon models are less commonly encountered than passive ribbon mics, however; here’s another case for reading manuals before using unfamiliar products.
