WHAT IS THE SOUND?The sounds are generated by a generic generator G like the shoot of a gun or a clap of the hands.

When this generator is activated it triggers a vibratory phenomenon that swings the particles of material, in which it is immersed, from their state

of equilibrium. These molecules will vibrate against the others nearby. This phenomenon

continues until the energy isn’t all consumed. The displacement of the particles from their

equilibrium position gives rise to an increase or a decrease in density. At the equilibrium point, the

molecules form the zones of high and low pressure which are directly proportional to the

density.

This phenomenon is called “pressure wave”, which within certain limits of amplitude and frequency, relative to

medium atmospheric pressure, is perceived as sound by the human

ear. The waves described above are called sound waves and their speed of propagation is called “ speed of

sound”.

HOW THEY WORKA microphone is an example of a

transducer, a device that changes information from one form to another. Sound information exists as patterns

of air pressure; the microphone changes this information into patterns of electric current.

There are a hundreds of designs for microphone with thousands of

applications.

DYNAMIC MICROPHONE.

CONDENSER MICROPHONE.

SHOTGUN MIC.

A variety of mechanical techniques can be used in building microphones. The

two most commonly encountered in recording

studios are the:

The dynamic mic. The condenser mic.

THE DYNAMIC MICS.In the magneto-dynamic, commonly called dynamic

microphone, sound waves cause movement of a thin metallic diaphragm and an attached coil of wire. A magnet produces a magnetic field which surrounds the coil, and motion of the coil within

this field causes current to flow.

The principles are the same as those that produce electricity at the utility company, realized in a

pocket-sized scale.

It is important to remember that current is produced by the motion of the diaphragm, and that the

amount of current is determined by the speed of that motion. This kind of microphone is known as

velocity sensitive.

THE CONDENSER MICIn a condenser microphone, the diaphragm is

mounted close to, but not touching, a rigid backplate. A battery is connected to both pieces of

metal, which produces an electrical potential, or charge, between them. The amount of charge is

determined by the voltage of the battery, the area of the diaphragm and backplate, and the distance

between the two. This distance changes as the diaphragm moves in response to sound. When the distance changes, current flows in the wire as the battery maintains the correct charge. The amount

of current is essentially proportional to the displacement of the diaphragm, and is so small that it must be electrically amplified before it leaves the

microphone.

SPECIFICATIONSThe most important factor in choosing

a microphone is how it sounds in the required application. The following

specifics are the basic lines to make the right choise.

SENSITIVITY

OVERLOAD CHARACTERISTICS

NOISE

SENSITIVITY

This is a measure of how much electrical output is produced by a

given sound pressure. This is a vital specification if you are

trying to record very tiny sounds. More sensitivity equals less noise, but also means more

distortion at high level pressures.

OVERLOAD CHARACTERISTIC

Any microphone will produce distortion when it is overdriven by loud sounds (heavy air pressure). With a dynamic, the coil may be

pulled out of the magnetic field; in a condenser, the internal amplifier

might clip. Loud sounds are encountered more often than you might think, especially if you place the mic very close to instruments.

NOISEMicrophones produce a very small amount of current, which makes sense when you consider just how light the moving parts

must be to accurately follow sound waves. To be useful for recording or other

electronic processes, the signal must be amplified by a factor of over a thousand.

One of the most important characteristic to choose a mic is their signal to noise ratio specific. This specific directly

proportional to the efficiency of the mic.

POLAR PATTERNS

Another important characteristic of the Mics is the ability to capture sounds in a 3D

space.There are 5 principal polar patterns:

OMNI-DIRECTIONALBI-DIRECTIONAL (OR HEIGHT FIGURE)

CARDIOIDHYPER-CARDIOID

SHOTGUN

OMNI-DIRECTIONAL

maximum sensitivity at

360°

BI-DIRECTIONAL

maximum sensitivity

on axis 180°

CARDIOID

maximum sensitivity on

front 120°

HYPER-CARDIOID

90° on front

and

30° rear

SHOTGUN

50° on front,

30° rear

and

15° lateral

The knowing of those characteristics give us the

ability to make a right choice of the microphones

to use in a particular recording environment.

For example:We want to record a

classical string quartet.

At first we’ll analyse were the musicians are

positioned in the space.Second, the

characteristics of shape of sound outgoing from

their instruments.Third, were to place the

mics and at last their numbers.

the instruments are: two violins, one viola and one cello.

we need to capture every instrument in a separate channel

and we need also capture a stereo image of the surrounding sound

(ambience).we need four cardioid mics for

instruments and two omni-mics for ambience.

Another example could be a piano recording in a

concert hall.

we need two hyper-cardioid mics for the high and low frequencies of the

piano.we need two cardioid mics

pointing to the audience sits.

one omni mic on the stage for the early reflections of

the concert hall.