1. Types of Microphone Elements
1.1 Dynamic Microphones
A dynamic microphone operates based on electromagnetic induction. It consists of a diaphragm, a coil, and a permanent magnet. When sound waves hit the diaphragm, it vibrates, causing the coil attached to it to move within the magnetic field and generate an induced current (per Faraday's law).
Features: Durable and cost-effective, but less sensitive and limited in high-frequency response. Known for a warm, natural sound, often used for vocal capture.
Applications: KTV, live performances, public address systems.
1.2 Condenser Microphones
These microphones work by converting sound into electrical signals using capacitance changes between two plates - a diaphragm and a backplate. When sound waves cause the diaphragm to move, the capacitance changes and generates a signal.
Features: High sensitivity and frequency response; ideal for high-fidelity audio capture.
Applications: Studio recording, broadcasting, high-end audio devices.
1.3 Ribbon Microphones
Ribbon microphones use a thin metal ribbon suspended within a magnetic field. The ribbon vibrates in response to sound waves and induces an electrical signal.
1.4 Carbon Microphones
Carbon microphones use carbon granules whose resistance changes under pressure from sound waves, generating a signal. They are mostly obsolete today but historically used in early telephones.
2. ECM vs MEMS Microphones
2.1 Electret Condenser Microphone (ECM)
ECMs use electret material that permanently holds an electrical charge, eliminating the need for external bias voltage. However, the internal preamplifier still requires power.
Advantages: Mature technology, low cost.
Disadvantages: Larger size, not suitable for SMT assembly, more susceptible to signal loss and production inconsistencies.
2.2 MEMS Microphone
MEMS (Micro-Electro-Mechanical Systems) microphones are built on silicon wafers using microfabrication technology. Many MEMS microphones integrate an ASIC and may even include analog-to-digital conversion for direct digital output.
Advantages: Compact size, SMT-compatible, stable and consistent performance.
Disadvantages: Higher cost compared to ECM.
Note: A MEMS microphone with an integrated amplifier or ADC is often referred to as a pickup module.
3. Key Microphone Parameters
3.1 Directivity
Describes how sensitive a microphone is to sounds from different directions. Common polar patterns include omnidirectional, unidirectional (cardioid), bidirectional (figure-8), etc.
3.2 Sensitivity
Indicates how much electrical output a microphone produces for a given sound pressure level. Usually measured in mV/Pa or expressed in dB relative to 1V/Pa.
3.3 Signal-to-Noise Ratio (SNR)
The ratio of useful audio signal to the noise produced by the microphone itself. A higher SNR means cleaner audio.
3.4 Total Harmonic Distortion (THD)
THD measures how much unwanted harmonic content is present in the output signal, caused by non-linearities in the microphone response.
3.5 Equivalent Input Noise (EIN)
Represents the noise level the microphone generates when no external sound is present. Measured in dB SPL.
3.6 Power Supply Rejection Ratio (PSRR)
PSRR indicates how well the microphone's internal circuits suppress fluctuations in the power supply voltage.
3.7 Output Impedance
Indicates how much resistance the microphone presents to the output signal. Important for matching with preamps or input stages of other devices.
