Moving Coil Microphone

Moving Coil Microphone

1. Moving Coil
Microphone

By Prof. Hitesh Dholakiya

2. Outlines
% Basics of Moving Coil Microphone
% Structure of Moving Coil Microphone
« Elements of Moving Coil Microphone
« Working of Moving Coil Microphone
«* Directivity of Moving Coil Microphone
*< Characteristics of Moving Coil Microphone
« Features of Moving Coil Microphone
< Applications of Moving Coil Microphone

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3. Basics
+ It is also called Dynamic UP
« It uses the principle of Electromagnetic Induction

“ sound pressure — moves coil placed in magnetic field — change
in flux — emf is produced — forms output of uP

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4. Structure of Moving Coil Microphone

Spring

Pole piece

5. Elements
“ Magnet:
Q permanent POT Type
Q gives uniform magnetic field in the gap
< Diaphragm :
Q thin circular sheet of nonmagnetic material
Q It is of light weight
Q slightly domed for extra rigidity
Q fixed with the help of springs
< Springs:
Q provides compliance to the motion of diaphragm
«* Mass of the diaphragm and coil assembly :
Q provide inductive effect
< Protective cover:
Q metal grill
Q To save delicate diaphragm and coil assembly from being mishandled

6. Working

Q Sound strikes the diaphragm — coil moves in and out in magnetic field —
changes flux through the coil — results in emf being produced in coil

Q value of emf depends on the rate of change of flux and hence on the motion
of coil

O displacement of coil depends on sound pressure — ‘Pressure Microphone’

OB: flux density in tesla (or Wb/m?) | | : length of coil in meters | v : velocity of
diaphragm in m/s | Then induced voltage :

do
es q -Bxixv

7. Directivity

8. Characteristics
Sensitivity : 30 uV for SPL of 0.1 Pa
“ SNR : 30 dB
< Freq Response : 60 Hz to 8000 Hz for +1dB
Distortion : less than 5%
“+ Directivity : basically Omni-directional
« O/P Impedance : quite low — about 25 ohm - to match line of

200 ohm - step up transformer of about 3:1 turns ratio is built

9. Features

U magnet is quite heavy — heavy protective case — very
robust and reliable

Q does not need external bias

Q can be spoken into from distance of 25 cm

Q cost is not high — lower cost than ribbon and capacitor —

higher than crystal and carbon

10. Applications
U Suitable for PA systems

Q Broadcast studios