They all do one thing
Microphones appear in an almost endless variety of shapes, sizes and design types. Their purpose is same: to convert acoustic vibrations to electrical energy so it can be amplified or recorded. Most achieve this by the action of the air vibrating a diaphragm connected to something that either creates or allows a small electron flow. Recording, sound reinforcement, broadcast, telecommunications, all have specialist microphones that have evolved over the years to suit particular intended purposes. One purpose is studio recording and a common product is the condenser microphone.

The Studio Condenser
There are many types of studio condensers but they can be narrowed down to two basic types: cardioid and omni-directional. Some of the more complex studio condensers have variable pattern control and have multiple patterns that can be selected to manipulate its pick up characteristics

How it works?
Imagine the classic “studio Mic”. You may have seen pictures of the gold disc capsule often with a wire screwed into the centre on one side and the gold plate with little holes on the other. Inside the mic will be some electronics and a power supply. Some microphones have the power supply in a separate box. The gold discs represent two electrically charged plates, one that can move and one that is fixed. This is in effect, a capacitor with a positively and negatively charged electrode, and an air space between.

A pressure gradient device?
The cardioid condenser microphone is a pressure gradient device, responding to the differences in sound pressure on each side of the diaphragm. In operation, sound passes the diaphragm depressing it and causing a change in the spacing between it and a charged metal back plate. The electrostatic attraction between the plates increases. This change in capacitance and distance between it and the back plate causes a change in voltage potential that can be amplified to a recordable level. To boost this small variation in voltage, originally a vacuum tube and later FET transistors were employed. This is why a battery or phantom power is needed to charge the plates and also to run the pre amp.

The directional effect
The directional effect of the cardioid microphone is achieved by adding little holes in the back plate. The holes create a sound entrance and delay network. The object is to delay the arrival of sound at the rear of the diaphragm to coincide with the same sound at the front. This way the sound is cancelled out. The size and position of the holes determines the frequencies that will be cancelled. The Mann microphone capsule has a second diaphragm at the back, but more about that later.

The multi pattern microphone
Another type of condenser microphone is the Multi pattern condenser type. This design is generally composed of a single plate between two diaphragms. A variable resistor set between the two diaphragms and the plate determine how much signal from each diaphragm is fed to the pre amp. In this system the rear diaphragm in conjunction with the holes that run through the plate become part of the phase shift when the unit is selected to a cardioid pattern. As a result, this microphone can have selectable patterns ranging from a tight cardioid through to a figure eight and finally to full omni directional.