Emf Pppres

7/28/2019 Emf Pppres

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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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