MICROPHONES:

Basic transducer for changing air pressure to electricity.
   Voltage levels tend to be very low:
     .001 volt range

Prototype microphone: the Ear
Has a mechanical collector: the outer ear
A diaphram to detect sound waves
A transducer to convert the sound into electricity: the choclea.

Microphones have analoguous parts:
A case,  diaphram or similar detector, and a pickup element/transducer.
Mics used for reinforcement and for creation of sound effects.
PA or Public address:  used for amplifying live voices.
Three determining factors as to type:
	* Generating element
	* Pickup pattern
	* Impedance
These factors are interrelated, but variations occur within any given type.

GENERATING ELEMENT:
All mics consist of a diaphram and a generating element.
	* Diaphram- detects sound
	* Element- converts sound into electricity

Obsolete types simplest but useful for principles:
* Crystal mic- Diaphram connected to piezoelectric crystal
   Example of mic that generates current.
   Pressure makes current.
   Unsuitable for most uses- poor quality and very high impedance. 
   Only advantage is low cost.
* Carbon Mics: voice activated resistor.
   Another low cost mic.
   Varies rather that creates current.
Requires pure DC source, e.g. battery.
Mic, battery, speaker all in series.
Speakers don't react to DC, only AC fluctuations are reproduced.
Durable, low cost, but poor quality
Used mostly in telephones and cheap headsets.
Example of a mic that regulates voltage.

PROFESSIONAL MICS:
High quality mics fall into three categories:
--Ribbon or Ribbon Velocity mics
--Dynamic or Moving Coil mics
--Condensor mics

RIBBON MIC: True voltage generator.
Flexible foil strip or ribbon suspended in magnetic field.
True voltage generator.

Voice vibrates ribbon, which acts as moving conductor in a magnetic field.
Also called ribbon velocity mic:
Reacts to velocity of sound rather pressure of the sound.
Quality is generally very good- was standard broadcast mic for many years.
   Nice warm sound.

Drawbacks:  easily damaged by dropping or loud close sound.
   Blowing into mic can damage or destroy it.
Tend to be large and somewhat clunky.
Has a bi-polar pick-up pattern.

DYNAMIC MICS: Most popular and versital of mics.
Like ribbon,a true voltage generator

Element is a small coil attached to a diaphram.
Coil placed inside a magnetic core.
Reacts to sound pressure from any direction.
Pressure of sound rather than velocity affects the diaphram, 
also called a Pressure/Dynamic mic.

Element tends to be omni-directional; picks up equally from all sides.
Widely used for laveliers and conference work.
	* Have excellent fidelity and sensitivity.
	* Extemely durable, probably most common theatre mic.
	* Pickup pattern can be varied by case design.
   Holes and vents in back of element tends to cancel sound from rear, 
   creating a cartioid or uni-directional pattern, or even 
   a hypercartioid pattern.

CONDENSOR MICS: uses a capacitor as the pickup element.
Once rare and expensive, but invention of electret condensor 
makes price similar to equiv. dynamic mic.

For many uses, electret condensors have replaced all other types.
-Voice activated variable capacitor in series with resistor and battery.
-Battery needed to charge plate & resistor.
-Resistor converts minute current changes on plate into relatively large 
 voltage across the resistor.

Actual voltage variance still very small;
   Preamp often built into case to boost output enough to reach system preamps.

Electret similar in principle, differs in detail.
Plates permanently charged, DC power source not needed to charge plates.
-However-
DC source is still needed to run internal preamp, often an internal battery.
Older mics needed 100 VDC to charge plates.
Currently as little as 3 v. used in some designs for preamp.

Professional condensors use apprx. 48 vdc.
   Phantom power; often built into mixer.
	* Fidelity of condensor mics best available.
	* Best S-N ratio of any mic.
	* Comparably priced with equiv. dynamics.
Only drawback: not quite as rugged , but usually good enough.

PICKUP PATTERNS:
Shape of area where mics pick up best.
Exact pattern varies with frequency.
Low freqs tend to be more omni-directional.
Hi's tends to be more directional.

Omni-directional:  
Basic pattern of carbon mics, dynamic and condensor mics.
Picks up equally well from all directions.
Omnis not always suitable, as they pick up everything.
More subject to feedback, as more easily picks up own speakers.

Bidirectional:  
Two pickup areas front and back of mic, almost none to sides.
Characteristic of ribbon mics: Two pick-up areas.
Not often used on stage because picks up audience as well as talent.
   Ideal for two talents facing each other
     while sideways to audience.

Cartioid pattern: 
Heartshape pickup pattern.
Most sensitive in front, as much as -20 dB rolloff to rear.
Most condensors and dynamics use selective venting of elements 
     to create pattern.
Omnis: no vents, sound from back wraps around front.

Cartioid: with vents.
With vents, rear sound also enters from back, cancelling rear 
     sound entering from front.
Vents are small; little front sound enters rear to cancel front sound.

Hypercartioid: so-called shotgun mic.
Additional vents extend cartioid pattern; add lobes.

IMPEDANCE
Affects not just mics, but all elements of sound chain.

Impedance: total opposition to current flow of Alternating Current 
     in a circuit.
Output Impendance: how easily current flows OUT of a device.
Input impedance: how easily current flows INTO a device, 
     i.e. how much current a device pulls from upstream device.

Impedance Matching:
Power most completely transfered when impedances match.
RULE OF THUMB: impedances can be connected up, not down.
Input impedance should be 10 times output impedance of its feed device.
BUT:
MICROPHONES SHOULD BE MATCHED MORE CLOSELY!
Low-Z mic to low-Z input, high-Z mic to high-Z input!

Impedance and Frequency transmission
High-Z mics: put out much higher voltage, so less affected by external noise;
BUT more affected by cable capacitance, w/ severe high frequency roll-off.
Low-Z mics: low voltage output, so more affected by external noise;
BUT less affected by cable capacitance, little high freq. rolloff w/ long cable.