1. Directivity (Polar Pattern)
Directivity refers to a microphone's sensitivity to sound coming from different directions. It is often represented using a polar pattern diagram. Common types include:
- Omnidirectional – Picks up sound equally from all directions.
- Unidirectional (Cardioid) – Most sensitive to sound from the front, less from the sides and rear.
- Bidirectional (Figure-8) – Sensitive to sounds from the front and rear, but not the sides.
- Supercardioid – A narrower pickup pattern than cardioid, with slightly more sensitivity at the rear.
2. Sensitivity
Sensitivity indicates how efficiently a microphone converts acoustic pressure (sound) into an electrical signal. It is typically measured in millivolts per Pascal (mV/Pa).
Reference sound pressure: 1 Pascal (Pa) = 94 dB SPL. Sensitivity example: A microphone with a sensitivity of -44 dB means it outputs a relatively low signal and may need more amplification.
3. Signal-to-Noise Ratio (SNR)
SNR represents the ratio of the desired audio signal to background noise produced by the microphone itself. Higher SNR values (e.g., 68 dB) indicate cleaner, clearer audio.
4. Total Harmonic Distortion (THD)
THD measures the distortion caused when the microphone reproduces sound. It is defined as the ratio of harmonic components (unwanted additional frequencies) to the original signal. Lower THD values indicate better fidelity.
5. Equivalent Input Noise (EIN)
EIN reflects the inherent self-noise level of a microphone, typically expressed in dB-A. It is the noise output of the microphone when no sound is present, referenced to a standard input.
6. Power Supply Rejection Ratio (PSRR)
PSRR indicates how well a microphone or internal amplifier can suppress power supply noise. A higher PSRR value means less interference from power fluctuations.
7. Output Impedance
Output impedance refers to the internal resistance of the microphone's output signal. It must match or be lower than the input impedance of the connected device for optimal signal transfer. Common values are 680Ω, 2.2KΩ, etc.
