Microphone Basics: Type, Frequency Response, and Polar Patterns

I’m Peyton Haynie from Bay City, Tx. This is for week 2 of Introduction to Music Production at coursera.org. I will be talking about microphone basics.

Type

Dynamic Microphones: Dynamic microphones fall into two categories; moving coil and ribbon.

In a moving coil microphone a diaphragm is attached to a coil of thin wire. When sound pressure moves the diaphragm it passes the coil to a thin magnet which generates voltage at the output and can then be amplified by the microphone pre-amp of the mixer.

A ribbon microphone uses a metal ribbon suspended in a magnet. When sound pressure causes the ribbon to move in the magnetic field, voltage is generated at the microphones output.

Since dynamic microphones are generally unidirectional and end addressed they are less likely to pick up unwanted sounds, making them a better choice for stage use.

Condenser Microphones: A condenser (or capacitor) microphone uses an electrically charged flexible diaphragm and a hard plate charged with an opposite polarity. When the diaphragm moves, a small charge is generated and is amplified by an internal transformer in the microphone. Condenser microphones require an outside source of power, the most common of which is phantom power and is provided by the mixer.

Electret condenser microphones are similar to capacitor microphones. The difference is the plate and diaphragm of the electret condenser are charged at the factory and the power is usually provided by a double A battery. While the plates tend to lose their charge resulting in a lower voltage at the microphones output over time, they are generally cheaper than phantom powered condenser microphones.

Since they are omnidirectional and usually side addressed, condenser microphones are more likely to pick up background noise and cause feedback, making them a better choice for the recording studio.

Frequency Response

The frequency response is the output level or sensitivity of a microphone over its operating range.

A flat frequency response means that the microphone is equally sensitive on all sides. No frequencies would be boosted or attenuated, resulting in a more accurate representation of the sound. Condenser microphones usually have flatter frequency responses than dynamic microphones.

A tailored frequency response means the microphone is more sensitive to certain frequencies, making them better for specific usage. For instance, a microphone with a peak range of 2-8 kHz would increase intelligibility of live vocals, while a peak range of 20 Hz -10 kHz would boost bass.

Polar Patterns

A microphone’s polar pattern is a graph of the sensitivity to frequencies coming from a full 360 degrees. The front of the microphone is 0 and 360 degrees on-axis; the back is 180 degrees off-axis; and the sides are 90 degrees off-axis.

An omnidirectional polar pattern depicts a microphone that is equally sensitive to frequencies coming from all sides. Being highly susceptible to feedback it is not recommended for live sound.

Unidirectional microphones are more sensitive to frequencies coming from the front. Being less susceptible to sounds from the sides and back, it is mostly used in sound reinforcement.

Cardioid is a type of unidirectional polar pattern. The greatest rejection is directly off-axis ( the back of the microphone). Rejecting sound from stage monitors, it is highly recommended for live sound.

A bidirectional (or figure eight) polar pattern is equally sensitive in the front and back with the greatest rejection at the 90 and 270 degree points. Because of this, bidirectional microphones are usually used in recording studios.

To summarize: there are many types of microphones, frequency responses and polar patterns. It is recommended to use dynamic microphones with a tailored frequency response and a unidirectional or cardioid polar pattern for live sound. For a recording studio, a condenser microphone with a flat frequency response and an omnidirectional or figure eight polar pattern would be best.

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