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An electret microphone is a widely used small capacitor microphone found in many electronic devices. It contains a permanently charged electret material that maintains an electric field between capacitor plates without the need for external polarization voltage, greatly simplifying microphone design and integration.
Known for its stable performance and cost-effectiveness, the electret microphone remains a popular choice in lavalier and headset microphones, two-way radios, surveillance equipment, and measurement instruments.
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Electret Microphone vs. Traditional Condenser Microphone
Both electret microphones and traditional condenser microphones work on the principle of variable capacitance caused by diaphragm vibration. However, the key difference lies in how the capacitor is polarized:
- Traditional condenser microphones require an external high-voltage power supply (phantom power or dedicated bias voltage) to polarize the capacitor.
- Electret microphones use a permanently charged electret material embedded in the diaphragm or backplate, eliminating the need for external polarization voltage.
This makes electret microphones smaller, more cost-effective, and easier to integrate into consumer devices. In recent years, electret condenser microphones have advanced significantly and are increasingly used in many professional recording scenarios, though traditional condenser microphones remain preferred for certain high-end applications.
Do Electret Microphones Need Power?
Although the electret microphone contains a permanently polarized layer, the built-in Field Effect Transistor (FET) amplifier requires a DC bias voltage to operate. Typical supply voltage ranges from 1.5V to 4.5V, commonly around 2V.
Different models may require different voltages. Excessively high or low voltage can affect the microphone’s performance and lifespan. Therefore, it’s essential to follow the datasheet specifications.
How Does an Electret Microphone Work?
Electret microphones operate based on the capacitor principle. Inside the microphone, the diaphragm and electret electrode form a capacitor. Sound waves cause the diaphragm to vibrate, changing the capacitance. The built-in FET amplifier converts these capacitance changes into electrical signals.
There are two main types of electret structures: front electret and back electret. The front electret design embeds the charged material on the diaphragm itself, while the back electret places it on the backplate behind the diaphragm.
Nowadays, most electret microphones use the back electret structure because it offers improved stability, reduced noise, and better frequency response compared to the older front electret type.
Because the electret material is permanently charged, the microphone does not require an external polarization voltage, which distinguishes it from traditional condenser microphones.
How to Use and Wire an Electret Microphone?
Electret microphones usually have two leads: positive (power) and negative (ground).
Correct wiring is critical to ensure proper microphone operation. Typically, connect the positive lead to the specified voltage supply (e.g., 2V), and the negative lead to ground.
It is recommended to follow the electrical parameters and wiring diagrams provided in the microphone’s datasheet to avoid damaging the component.
How to Identify Electret Microphone Polarity?
| Step | Method | Positive Lead | Negative Lead | Notes |
|---|---|---|---|---|
| 1 | Visual Inspection | Marked with “+” symbol | Marked with “−” symbol | Check symbols first for highest accuracy |
| 2 | Observe PCB Pad | Pad fully surrounded by green or blue solder mask | Pad connected directly to metal casing, no solder mask | Use a magnifier for better judgment |
| 3 | Multimeter Measurement | Resistance to casing between 2.2kΩ and 10kΩ | Resistance to casing less than 5Ω | Use 2kΩ resistance setting on multimeter |
| * | Check Datasheet | Labeled as “+” terminal | Labeled as “−” terminal | Most authoritative method, applicable for all models |
Standard Operating Voltage for Electret Microphones
The typical operating voltage for electret microphones ranges from 1.5V to 4.5V. Common voltages include 1.5V, 2V, 2.1V, 2.2V, 3V, and 4.5V.
Supply voltage greatly affects microphone performance; excessive voltage can cause distortion, while too low voltage results in weak signal, reduced sensitivity, and poor signal-to-noise ratio.
It is advised to strictly follow the voltage specifications provided in the microphone datasheet.
History: When Was the Electret Microphone Invented?
The electret microphone was invented in 1962 by James West and Gerhard Sessler at Bell Labs. Its simple structure, low cost, and stable performance rapidly made it the dominant microphone technology in the market.
How to Test an Electret Microphone?
Testing an electret microphone generally involves using a multimeter to measure resistance and voltage to ensure proper power supply and output signal.
For more detailed testing, use an oscilloscope and audio testing equipment to evaluate signal quality according to the microphone’s technical datasheet.
Abschluss
Electret microphones are widely adopted for their cost-effectiveness and reliable performance. Understanding their working principles, polarity identification, power requirements, and correct wiring is crucial for designing and using these microphones effectively.
