The Basics
- mics are a type of transducer: devise that converts energy from one form to another.
- convert acoustical energy/sound waves into electrical energy (the audio signal)
- different mics have different ways of converting energy
- very common...the diaphragm.....very thin material like paper, plastic, aluminum
- vibrates when struck by sound waves
- makes other components vibrate.Vibrations converted into an electrical current and forms into audio signal
- other end of audio chain....the loudspeaker is also transducer- converts the electrical energy into acoustical energy

different types of mics
- type of technology they use
-- most common technologies are dynamic, condenser, ribbon, and crystal.

- the application they are designed for
- characteristics to look for: directional properties, frequency response and impedance

MIC LEVEL AND LINE LEVEL
- mic level or electrical current is small. measured in millivolts. Signal needs to be amplified, usually to line leverl (0.5- 2 V).
- line level is the standard signal strength used by audio processing equipment and common domestic equipment such as CD players, tape machines etc....

Amplification:
-some mics have tiny built-in amplifiers...boost signal to a high mic level/line level
- mic can be fed through a small boosting amplifier...line amp
- sound mixers have small amplifiers in each channel. Attenuators can accommodate mics of varying levels and adjust them all to an even line level.
- audio signal is fed to a power amplifier-- a specialized amp that boosts signal enough to be fed to loudspeakers. audio signals is fed to power amplifier-- specialized amp that boosts the signal enough to be fed through loudspeakers

DYNAMIC MICS
- versatile and ideal for general purpose. simple. ad sturdy
- handle high volume levels, have no internal amp and don't require batteries or external power

how they work
- uses a wire coil and magnet to create the audio signal
- diaphragm attached to coil. when vibrates in response to incoming sound waves, coil moves backwards and forwards past the magnet...creates a current in the coil which is channeled from mic along wires.
- its a loudspeaker in reverse.
- dynamics do not often have the same flat frequency response as condensers. they have tailored frequency responses for certain apps
- Neodymium magnets more powerful than conventional magnets, can be smaller with more linear frequency and higher output level

Condenser Mics
- means capacitor, an electronic component that stores energy in the form of an electrostatic field.
- uses a capacitor to convert acoustical energy into electrical energy
-require battery or external source. stronger signal than from dynamic
- more sensitive and responsive than dynamics
- subtle nuances in a sound...not ideal for high-volume work, prone to distort

how they work
-2 plates with a voltage between them. one made of light material and acts as diaphragm. vibrates when struck by sound waves, changing distance between the plates, changing the capacitance, when plates are close...capacitance increases and charge current occurs
- when further, capacitance decreases discharge current occurs
-voltage in capacitor needed to work

ELECTRET CONDENSER MIC
- uses special type of capacitor (has a permanent voltage built in during manufacture)
- like permanent magnet, doesn't require external power to work
- often include pre- amp which does still require power

DIRECTIONAL PROPERTIES
- each mic has property known as directionality.....describes mics sensitivity to sound from various directions.
- 3 main categories:

  1. Omnidirectional
    Picks up sound evenly from all directions (omni means "all" or "every").
  2. Unidirectional
    Picks up sound predominantly from one direction. This includes cardioid and hypercardioid microphones (see below).
  3. Bidirectional
    Picks up sound from two opposite directions.


Omnidirectional:
uses: capture ambient noise. sound from all directions. mic position must remain fixed while the sound source is moving
very general and unfocused - if you are trying to get sound from particular subject it is likely to be overwhelmed by other noise

Cardioid:
- "hear-shaped". type of pick up pattern these mics use . Sound picked up from front, but to a lesser extent the sides as well.
Emphasizes sound from the direction the mic is pointed whilst leaving some latitude for mic movement and ambient noise
- versatile, general use, handheld mics
- many variations of cardioid patern (like hypercardioid)

Hypercardioid:
-exagerated version of cardioid pattern. direction and eliminates most sound from sides and rear. sometimes shotgun mics
- isolates sound from a subject when theres a lot of ambient noise, picking up sound from subject at a distance

  • By removing all the ambient noise, unidirectional sound can sometimes be a little unnatural. It may help to add a discreet audio bed from another mic (i.e. constant background noise at a low level).
  • You need to be careful to keep the sound consistent. If the mic doesn't stay pointed at the subject you will lose the audio.
  • Shotguns can have an area of increased sensitivity directly to the rear.

Bidirectional

mic-polarpattern-bi.gif
mic-polarpattern-bi.gif

Uses a figure-of-eight pattern and picks up sound equally from two opposite directions.
Uses: As you can imagine, there aren't a lot of situations which require this polar pattern. One possibility would be an interview with two people facing each other (with the mic between them).


Variable Directionality

Some microphones allow you to vary the directional characteristics by selecting omni, cardioid or shotgun patterns.This feature is sometimes found on video camera microphones, with the idea that you can adjust the directionality to suit the angle of zoom, e.g. have a shotgun mic for long zooms. Some models can even automatically follow the lens zoom angle so the directionality changes from cardioid to shotgun as you zoom in.Although this seems like a good idea (and can sometimes be handy), variable zoom microphones don't perform particularly well and they often make a noise while zooming. Using different mics will usually produce better results.


Line level- high impedance
mic level- low impedance
spl- sound pressure level