Microphone heads (MIC) have various technical specifications that are crucial to their performance. These specifications include consumption current, sensitivity, output impedance, directional characteristics, frequency response, and more. Here's a breakdown of the primary parameters:
1. Current Consumption
The working current of a microphone head is primarily the current when the FET (Field-Effect Transistor) is at VSG = 0. Based on the FET class, microphones can be designed for different working currents. In cases of low working voltage and high load resistance, strict requirements for current flow are necessary. The relationship can be expressed as:
ID = (VS - VSD) / RL
Where:
- ID is the current of FET at VSG = 0,
- RL is the load resistance,
- VSD is the voltage drop between the Source (S) and Drain (D),
- VS is the standard working voltage.
The general current range is 100μA < IDS < 500μA.
2. Sensitivity
Sensitivity refers to the ability to generate voltage under a unit sound pressure level. It is often expressed as:
- V/Pa or dBV/Pa,
- Some companies use dBV/μBar.
For example:
- -40 dBV/Pa = -60 dBV/μBar
- 0 dBV/Pa = 1V/Pa
The sound pressure unit is Pa = 1N/m².
3. Output Impedance
The output impedance is typically equivalent to the load resistance, RL, and can range between 1% and 70%.
4. Directional Characteristics & Frequency Response
Microphones can have various directional characteristics:
- Omnidirectional (Non-directional): The microphone sensitivity is equal in all directions at the same distance. These microphones are sealed on the PCB, so sound pressure enters only from the microphone hole, making them pressure-based transducers.
- Unidirectional (Cardioid, Supercardioid, Hypercardioid): These microphones exhibit directionality, where the sensitivity is highest at 0° (when the microphone is directly facing the sound source) and lowest at 180° (opposite direction). The structure differs from omnidirectional mics, as sound can enter through both the microphone hole and openings in the PCB. The internal sound-absorbing material makes them a hybrid between pressure and pressure-difference transducers.
- Bidirectional (Noise Cancelling): These microphones are pressure-difference microphones and have an 8-shaped directional response. Unlike unidirectional microphones, they do not have sound-absorbing materials inside.
5. Frequency Range
- Omnidirectional: 50 ~ 12000Hz to 20 ~ 16000Hz
- Unidirectional: 100 ~ 12000Hz to 100 ~ 16000Hz
- Noise Cancelling: 100 ~ 10000Hz
6. Maximum Sound Pressure Level
The maximum sound pressure level is defined as the sound pressure level at which the distortion reaches 3%. The sound pressure level is defined as 20μPa = 0dBSPL. The maximum SPL should be greater than 115 dBSPL (A-weighted SPL).
7. Signal-to-Noise Ratio (S/N)
S/N refers to the ratio of the microphone's sensitivity to the inherent noise generated by the microphone under the same conditions. The noise is primarily due to the FET itself. Refer to the product manual for detailed noise levels.
