Microphones

A microphone is a transducer, which converts acoustic energy into electric energy. The element used in a mic names it.

• Magnetic Induction mics have a fixed magnet and a movable diaphragm.

1. Moving Coil, or Dynamic, mics have a small lightweight coil in the magnetic field that moves in response to the sound waves hitting the diaphragm and creates a voltage proportional to the sound pressure level.
2. Ribbon mics have a metal ribbon instead of a coil. The ribbon vibrates from the SPL and creates a voltage. Older ribbon mics used a vertical piece of metal, while newer ones use a horizontal ribbon which allows for the capsule to be smaller and lighter.
3. Active Ribbon use an amplifier system that requires Phantom Power - remotely powering along an audio cable. This allows for a higher output and sound sensitivity.

• Variable Capacitance mics transduce energy using voltage variation instead of magnetic

1. Capacitor mics have 2 parallel plates separated by a space . The front plate is a thin metalized plastic and the fixed back plate form a capacitor that holds charge. As sound hits the diaphragm, the capacitance changes and is translated into a relative level.
2. Tube mics use a tube circuit to sound more present and livelier than the standard mic.
3. Lavaliere mics use an electret diaphragm hat permanently holds a charge.

Moving Coil (Dynamic) mics are generally more rugged, with less self-noise, and higher SPL without distortion, as well as less expensive. However the transducing element has more mass and therefore has a slower response to transients (quick attacks).

Ribbon mics are good for voice and music recording, but are more expensive and delicate. The transient response is better than the Dynamic.

Capacitor mics have the best transient response, but are also most epensive. They are good for distance miking and have low noise.

Polar Response Pattern is the direction a mic will receive sound. It is NOT related to the transducer in the mic.
Omnidirectional - all around the mic
Bidirectional - front and back
Unidirectional - front only
Cardioid - heart shaped

For all patterns, higher frequencies result in a more directional pattern, while lower frequencies have a less directional pattern.

Mic Sound Responses depend on:

1. Frequency response - the range of frequencies that a mic will reproduce at an equal level with a margin of 3 dB. Essentially the "coloration" of the mic.
2. Overload - how well the mic handles the distortion if sound levels are too high. Ribbon mics are very sensitive to this and possibly damaged if overloaded.
3. Max SPL - the level where output starts to distort - harmonics are introduced by the audio system that are not in the original signal. 120 dB = good, 135 dB = very good, 150 dB = excellent
   
4. Sensitvity - measure the volltage the mic produces at SPL that indicates loudness. A capacitor has the loudest response, awhile ribbon has the quietest and requires more gain.
5. Self Noise - the SPL that creates the same voltage as inherant electrical noise. 40 dB = fair, 30 dB = good, 20 dB or less = excellent
6. Signal to Noise Ratio (SNR) - the difference between signal and noise levels in dB. [SPL/self noise] The larger the SNR, the less noise in the signal. 64dB = fair, 74 dB= good, 84 dB = excellent
7. Proximity effect - bass frequencies increase when close to microphone. Pressure is raised at lower frequences, so Bass Roll Off is used to attenuate the bass frequencies and negate the effect.
8. Hum - stray Alternating Current at 50-60 Hz occurs especially in dynamic mics. Use balanced cables to reduce this. Humbucking cancels induced hum with a 50/60Hz component.