In this note, we are going to talk about Capacitor Microphone or Condenser Microphone and its Construction, Working Principle, 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 Capacitor Microphone or Condenser Microphone?
A microphone that employs a capacitor to transform sound waves into electrical impulses is called a capacitor microphone, sometimes referred to as a condenser microphone. It is composed of a thin, usually plastic or metal diaphragm that is positioned next to a backplate. As one plate and the other as the backplate, the diaphragm and the backplate together constitute a capacitor.
Condenser microphones are widely used in broadcasting, studio recording, and other professional audio applications because of their reputation for sensitivity and accuracy in sound capture. In order to function, they need power, which can be supplied by batteries, phantom power from a mixer or preamplifier, or, in some more recent models, USB connections.
Construction
The figure below shows a capacitor microphone. It is composed of a permanent metal back plate and a lightweight metal diaphragm, usually made of aluminum, hanged above it.
A few picofarads of capacitance are formed by the fixed metal plate and metal diaphragm coming close to each other. A constant DC voltage, ranging from 50 to 100 volts, is supplied between the movable diaphragm plate and the backplate. The diaphragm is in stretched condition as it remains attached to the supporting fixtures with the help of spider springs. There is insulation between the two plates. This microphone has a capacitance of roughly 30 pF.
Working Principle
A capacitor microphone, sometimes referred to as a condenser microphone, functions by detecting variations in capacitance. It is made up of a charged capacitor, a backplate, and a diaphragm. The diaphragm moves in response to sound waves, which modifies the distance between it and the backplate and, in turn, the capacitance. The microphone’s output is then created by converting these fluctuations in capacitance into electrical impulses.
The capacitance ( C ) of a capacitor microphone can be expressed using the equation:
C = εA/d
Where:
- C is the capacitance,
- ε is the permittivity of the dielectric material between the diaphragm and the backplate,
- A is the area of overlap between the diaphragm and the backplate, and
- d is the distance between the diaphragm and the backplate.
The capacitance (C) changes in proportion to the distance (d) changes as a result of sound waves vibrating the diaphragm. An electrical signal is then created from this variation in capacitance.
Characteristics
- Sensitivity: The output is very low.
- Signal to Noise Ratio: High, about 40 dB.
- Frequency Response: Excellent, around 40 Hz to 15 kHz for ±1 dB.
- Distortion: Low, about 1%.
- Directivity: Omnidirectional.
- Output Impedance: High, about 100 Megaohm.
Advantages
- Distortion is Low.
- Frequency response is high.
- Noise is quite low.
Disadvantages
- This microphone needs external dc power supply.
- It is costly.
Applications
- Used as a standard microphone.
- Used in sound level meters.
- Used in professional recording.