In this note, we are discussing about Moving Coil Microphone and its Construction, Operation, Characteristics, Advantages, Disadvantages, and Applications as well. Welcome to Poly Notes Hub, a leading destination for Diploma Engineering Notes for Polytechnic Students.
Author Name: Arun Paul.
What is Moving Coil Microphone ?
A moving coil microphone transforms sound waves into electrical signals using a diaphragm, a coil of wire, and a magnet. The diaphragm vibrates in response to sound waves, which causes the wire coil linked to it to move inside the magnetic field created by a magnet. This motion causes the coil to experience an electrical current, which is subsequently recorded as an analog signal. Moving coil microphones are a popular option for broadcasting, studio recording, and live performances because of their reputation for dependability, longevity, and capacity to withstand high sound pressure levels. They are frequently employed in many different contexts, such as speech amplification, instruments, and vocals.
Construction of Moving Coil Microphone
The main components of a moving coil microphone are a magnet, diaphragm and coil. The Construction of Moving Coil Microphone is shown in the Fig.
- Magnet: The magnet is a pot-style permanent magnet with a central and periphery pole component. In the space between the pole pieces, this kind of magnet produces a consistent magnetic field.
- Diaphragm: The diaphragm is a lightweight, thin, circular sheet made of non-magnetic material. It has a little dome to add more rigidity. With the aid of springs, it is secured to the magnet’s body. A diaphragm’s motion is conformed to by the springs. The inductive effect is produced by the diaphragm and coil assembly’s mass.
- Coil: A cardboard cylinder that is fastened to the diaphragm is wound with the coil. The coil is made of a thin, single-layered enameled wire.
- Protective Cover: The sensitive diaphragm and coil assembly are shielded from damage by a protective cover. The lower chamber is divided from the top chamber by a silk cloth partition. The lower chamber’s little tube provides access to the free atmosphere.
- Spring: The diaphragm’s mass limits the high-frequency output, while the compliance of the springs causes the stiffness that limits the low-frequency output.
Operation of Moving Coil Microphone
The diaphragm moves in response to sound, which causes the coil to move in and out of the magnetic field. Due to electromagnetic induction, this motion alters the flux through the coil, causing an EMF to be induced in the coil. This emf’s value is dependent on the coil’s motion and the pace at which flux changes. The pressure of the sound waves on the diaphragm determines the coil’s movement. It is a pressure microphone as a result. The equation below provides the induced voltage, or e, across the microphone coil.
If B is the flux density in Tesla or Wb/m^2, l is the length of the coil, v is the velocity of the diaphragm in m/s then
e = (dφ/dt)
= B x change of area per second
= B x length of conductor x distance moved per second
= B x l x v
thus, the induced emf is directly proportional to the velocity which in turn is proportional to the frequency of sound pressure vibration.
Characteristics of Moving Coil Microphone
- Sensitivity: 30 microvolts for sound pressure level of 0.1 Pa.
- Signal to Noise Ratio: 30 dB
- Frequency Response: 60 Hz to 8000 Hz for ±1 dB. It has a natural response between 3 and 4 kHz.
- Distortion: Less than 5%
- Directivity: Omni Directional.
- Output Impedance: Its output impedance is quite low and is about 25 Ohms.
Advantages of Moving Coil Microphone
- It does not need external bias source.
- Its cost is not so high.
- Suitable for wide range applications also.
Disadvantages of Moving Coil Microphone
- Limited frequency response.
- This microphone is quite heavy.
- Less sensitive than Condenser Microphone.
- It has a slower transient response.
Applications of Moving Coil Microphone
- Used in Public Address system,
- Used in Telephone Systems,
- Used in Broadcast Studios etc.