What is a Condenser Microphone?

Microphone Basics (2)

What is a Condenser Microphone?

What is a Condenser Microphone?

While dynamic microphones are popular for stage use, due to their rugged construction, condenser microphones have always been the preferred type for studio recording. Here’s why.

A condenser microphone capsule with a gold sputtered mylar diaphragm.
A condenser microphone capsule with a gold sputtered mylar diaphragm.
The backplate consists of solid brass with a hole pattern that must be drilled with extreme precision for consistent sound.
The backplate consists of solid brass with a hole pattern that must be drilled with extreme precision for consistent sound.

How a Condenser Microphone Works

The British call them “capacitor microphones” – and for a reason, too. You may remember from physics class that a capacitor is essentially two metal plates in close proximity. The closer they are, the higher the capacitance.

 

A condenser capsule is constructed similarly. It consists of a thin membrane in close proximity to a solid metal plate. The membrane or diaphragm, as it is often called, must be electrically conductive, at least on its surface. The most common material is gold-sputtered mylar, but some (mostly older) models employ an extremely thin metal foil.

 

When sound waves hit the diaphragm, it moves back and forth relative to the solid backplate. In other words, the distance between the two capacitor plates changes. As a result, the capacitance changes to the rhythm of the sound waves. Voilà, we have converted sound into an electrical signal.

 

The capsule signal itself, however, is much too “fragile” to be connected to other pieces of gear. The condenser capsule’s output voltage is actually quite high, but it produces almost no current, because so little energy is stored in this small capacitor. It requires what is called an “impedance converter”, a circuit that buffers between the capsule and the outside world. The impedance converter makes the signal more “sturdy” by making more signal current available.

 

Condenser microphones therefore require external power. This could be inconvenient in the old days, but today just about any microphone input offers P48 phantom power – a Neumann invention, which has become the international standard (see box “Powering Condenser Microphones”).

Due to their low-mass diaphragm, condenser microphones have superior transient response.
Due to their low-mass diaphragm, condenser microphones have superior transient response.

Superior Sound Quality

Due to its extremely low mass, the diaphragm of a condenser microphone can follow the sound waves more accurately than that of a dynamic microphone with a (relatively) heavy moving coil attached. Condenser microphones, therefore, offer superior sound quality. Of all microphone types, condensers have the widest frequency response and the best transient response (transients are fast bursts of energy, e.g. the attack of a drum   or the “pick” of an acoustic guitar). Also, condenser microphones usually offer much higher sensitivity (i.e. output) and lower noise than dynamic microphones.

 

However, keep in mind that these theoretical advantages only apply to well constructed specimens (such as Neumann’s, of course). A cheap $ 99 condenser microphone may be noisy and offer much lower sound quality than a top-of-the-line moving coil microphone (such as the Sennheiser MD 441).

Sound Samples:

Powering Condenser Microphones

Condenser microphones require external power for their internal electronics. Early specimens – Neumann has produced condenser mics since 1928! – had tube electronics, which were powered by an external PSU box the size of a brick. This was inconvenient in many ways, especially when many microphones were used at the same time, because each type required its own PSU box and a dedicated multipin cable.

 

When transistor technology took over in the late 1960s, Neumann invented a standardized scheme to power condenser microphones directly from the mixing desk, without the need for external PSU boxes and multipin cables. P48 phantom power works with 48 volts, supplied via the usual 3-pin microphone cable, and it does not affect dynamic microphones that do not require external power. Due to its convenience, P48 phantom power soon became a world standard.

 

More recently, tube technology has become popular again as a “vintage” sound alternative. Modern day tube condenser microphones, just like their ancestors, require an external power supply, because tubes consume more energy than phantom power is able to provide.