Moving Coil Microphone

1. Moving Coil
Microphone
By Prof. Hitesh Dholakiya
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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 µP
❖ It uses the principle of Electromagnetic Induction
❖ sound pressure – moves coil placed in magnetic field – change
in flux – emf is produced – forms output of µP
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4. Structure of Moving Coil Microphone
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5. Elements
❖ Magnet :
❑ permanent POT Type
❑ gives uniform magnetic field in the gap
❖ Diaphragm :
❑ thin circular sheet of nonmagnetic material
❑ It is of light weight
❑ slightly domed for extra rigidity
❑ fixed with the help of springs
❖ Springs :
❑ provides compliance to the motion of diaphragm
❖ Mass of the diaphragm and coil assembly :
❑ provide inductive effect
❖ Protective cover :
❑ metal grill
❑ To save delicate diaphragm and coil assembly from being mishandled
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6. Working
❑ Sound strikes the diaphragm – coil moves in and out in magnetic field –
changes flux through the coil – results in emf being produced in coil
❑ value of emf depends on the rate of change of flux and hence on the motion
of coil
❑ displacement of coil depends on sound pressure – ‘Pressure Microphone’
❑ B : flux density in tesla (or Wb/m2) | l : length of coil in meters | v : velocity of
diaphragm in m/s | Then induced voltage :
𝒆 =
𝒅∅
𝒅𝒕
= 𝑩 × 𝒍 × 𝒗
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7. Directivity
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8. Characteristics
❖ Sensitivity : 30 µV 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
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9. Features
❑ magnet is quite heavy – heavy protective case – very
robust and reliable
❑ does not need external bias
❑ can be spoken into from distance of 25 cm
❑ cost is not high – lower cost than ribbon and capacitor –
higher than crystal and carbon
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10. Applications
❑ Suitable for PA systems
❑ Broadcast studios
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