1. What is a Microphone?
A microphone is a sound-to-electric energy conversion device (also known as a transducer or sensor). It serves as the input component in audio systems, while a speaker acts as the output. The microphone is often referred to as a transmitter, mic, or capsule.
2. Types of Microphones
2.1 Based on Operating Principle:
- Carbon-based microphones
- Dynamic microphones
- Electret microphones (primarily discussed here)
- Piezoelectric microphones
- Silicon-based microphones
2.2 Based on Size:
Electret microphones are available in various sizes:
- Φ9.7mm series
- Φ8mm series
- Φ6mm series
- Φ4.5mm series
- Φ4mm series
2.3 Based on Directionality:
- Omnidirectional
- Unidirectional
- Bidirectional (noise-canceling)
2.4 Based on Polarization Method:
- Diaphragm type
- Backplate type
- Frontplate type
2.5 Based on Connection Style:
- L-type solder points
- PIN connection (P-type)
- Concentric circle type (S-type)
3. Structure of an Electret Microphone
The key components of an omnidirectional electret microphone include:
- Dust-proof Mesh: Prevents dust accumulation and physical damage to the diaphragm.
- Housing: Provides support and electromagnetic shielding.
- Diaphragm: The key element that converts sound into electrical energy through vibration.
- Spacer: Maintains distance between diaphragm and backplate.
- Backplate: Works as the other electrode in the capacitive design.
- PCB: Hosts the field-effect transistor (FET) and other components.
4. Working Principle of Electret Microphones
Electret microphones operate based on changes in capacitance caused by sound pressure vibrations on the diaphragm. These changes are converted into electrical signals, which are amplified by a field-effect transistor (FET) and output for further processing.
5. Key Specifications of Microphones
- Current Consumption: Operating current determined by the FET.
- Sensitivity: Voltage generated under standard sound pressure (measured in dBV/Pa).
- Output Impedance: Typically matches the load resistor.
- Directionality: Defines sound pickup patterns (e.g., omnidirectional, unidirectional).
- Signal-to-Noise Ratio (S/N): The ratio of desired signal to background noise.
- Maximum Sound Pressure Level (SPL): The highest sound level the microphone can handle without distortion.
6. Testing Methods
Microphone performance can be evaluated through current measurements, sensitivity testing, and polar pattern analysis, often conducted using specialized testing equipment under standard conditions.
