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By Jorge Molina
&
Rodrigo Chvez
SPEAKERS, MICROPHONES, NOISE
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SPEAKERS
Uses Electromagnetic Motor
A current is fed to the ends of the coil which creates a
magnetic field.
The coil vibrates when
the magnets field
interacts with the
coils field. The cone amplifies
the sound waves.
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MICROPHONE
1) Sound waves created by your voice.
2) Diaphragm
3) Voice Coil4) Permanent Magnet
5) Electric Current
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FARADAYS LAW OF INDUCTION
The electromotive force induced on the coil may becalculated with the following formula:
=
, =
Where:
N = Number of turns
= Magnetic flux density
B = Magnetic Field
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MAGNETIC FIELD IN THE COIL
Knowing the current I that goes through the coil, we
may calculate the magnetic field on the coil with the
following formula:
= 2
Where:
0 = Permeability. r = radius of the coil.
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THE CURRENT INDUCED
It is important to know that a current in a conductor
generates a magnetic field.
Likewise, a magnetic field that changes in time
generates a current in a conductor.
The Right-Hand Rule can be used to determine the
direction of the current.
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ELECTROMAGNETIC ENERGY
A current going through a coil has an Electromagnetic
Energy which may be calculated with the following
formula.
= 12
2 ()
W = Energy Stored (J)
L = Inductance
I = Current
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INDUCTANCE
The Inductance (L) from the Electromagnetic Energy
may be calculated with the following formula:
=
0.393
9+10 Where:
a = Radius of the coil
b = lenghtn = Number of turns
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MATERIALS TONAL CHARACTER
Cone Paper, aluminum, titanium, polypropylene, or
ceramic (to name a few).
Voice-Coil Former Aluminum, Kapton, Nomex or
paper.
Voice-Coil Cover paper or aluminum.
Magnet AlNiCo (Aluminum-Nickel-Cobalt) or Ceramic
(Strontium Ferrite).
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NOISE
What is noise?
It is undesired sound that distorts the reproduction of
any audio signal.
This noise may come from a badly tuned radio or from
outside noise while listening to your headphones.
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PASSIVE NOISE REDUCTION (HEADPHONES)
The On-Ear Headphones apply a certain pressure to
your ear so that no sound enters your ear while
listening to any recording.
This is also called noise isolation because it isolatesthe listener from outside noise.
This is only a physical method of noise reduction.
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ACTIVE NOISE REDUCTION (HEADPHONES)
There is a microphone outside of the headphones that
captures the outside noise and inverts it.
This inverted signal cancels out with the sound that
inevitably goes through your headphones.
Sound wave
Sound wave Inverted
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ACTIVE NOISE REDUCTION (MICROPHONE)
There is an additional microphone placed on the back
of the main input.
This additional microphone captures a sound which is
then inverted and added to the sound wave that themain input captures.
The inverted signal will cancel out with the main input
signal leaving only the desired signal without noise.
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POP FILTERS
These are placed in front of the microphone.
This serves for two reasons:
To reduce certain input noise from the signal going intothe microphone.
And to reduce the amount of saliva that may build up
on the
microphone.
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