Transcript Diapositiva 1 - News | ISTITUTO MARCONI

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 WORK
A 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.
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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 MIC
In 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
SPECIFICATIONS
The 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.
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SENSITIVITY
OVERLOAD CHARACTERISTICS
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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.
NOISE
Microphones 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-DIRECTIONAL
BI-DIRECTIONAL (OR HEIGHT FIGURE)
CARDIOID
HYPER-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.
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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.
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