I. Overview
The MegaSig M 645+A 835 is a 1/4-inch prepolarized free-field microphone assembly that conforms to the IEC 61094-4 WS3F standard .
Before introducing the specifications, it’s necessary to explain “why we need to use a 1/4-inch (miniaturized) microphone?” This is mainly based on two key trade-offs in acoustic physics:
- High Frequency Extension: The smaller the microphone size, the less diffraction and interference it causes to high-frequency sound waves. A 1/2-inch microphone is typically limited to 20kHz to 40kHz, while the 1/4-inch M 645 can extend the frequency response to 100kHz , which is crucial for capturing ultrasonic signals.
- High SPL Handling: The smaller diaphragm area means lower sensitivity (5mV/Pa for this product), which sacrifices some noise floor performance but in exchange for extremely high overload resistance. It can withstand sound pressure levels up to 155 dB without significant distortion, a level that ordinary microphones cannot achieve.
II. Core Functions and Technological Advantages of the Product
The M 645+A 835 integrates a measurement-grade cartridge and a preamplifier, and features the following core technologies:
1. Ultra-wideband and free-field sound response
- Frequency range: Supports 10 Hz to 100 kHz (±3dB), with the error controlled within ±2dB in the key frequency band of 20 Hz to 50 kHz.
- Free-field design: Designed specifically for anechoic chambers or open spaces, it can compensate for the interference of microphones on high-frequency sound waves after they are placed in the sound field, restoring the true sound pressure level “before the microphone was placed”.
2. Dynamic range optimized for high sound pressure levels.
- Maximum sound pressure level: can withstand sound pressure levels up to 155 dB (distortion < 3% at 1 kHz).
- Background noise: Thermal noise is about 37 dBA, which is a natural characteristic of reduced physical size (compared to about 15-20 dBA for a 1/2-inch microphone), so it is more suitable for “loud” rather than “very quiet” measurement scenarios.
3. TEDS Intelligent Recognition and Industrial-Grade Interface
- TEDS Support: Built-in chip compliant with IEEE 1451.4 v1.0 standard, the measurement system can automatically read microphone model, serial number and sensitivity, avoiding human input errors.
- Microdot Interface: Employs an L5 (Microdot) connector, which is standard on 1/4-inch microphones to maintain a miniaturized size and ensure stable high-frequency signal transmission.
- IEPE power supply: Uses a standard 4mA constant current source for driving, eliminating the need for expensive traditional 200V polarized power supplies.
III. Usage Scenarios
Based on its “high frequency, high voltage, free field” characteristics, the M 645+A 835 is suitable for the following demanding engineering applications:
- Ultrasonic and high-resolution audio measurements: Used to measure devices with frequencies exceeding 20kHz, such as industrial ultrasonic cleaners, reversing radar sensors, or to verify the high-frequency response characteristics of Hi-Res Audio products.
- Blast & Impulse Noise: Withstanding high sound pressure levels of up to 155 dB, it is ideal for measuring the instantaneous pulse sound pressure of airbag explosions, gunshot noises, or blasting operations.
- High-precision scale model wind tunnel testing: In scale model testing, frequencies are often increased proportionally (e.g., for a 1/10 model, the frequency becomes 10 times). In this case, a 1/4-inch microphone must be used to capture the correct high-frequency aerodynamic noise.
IV. Specifications
| Sound field type | Free field |
| Polarization voltage | 0V (pre-polarization) |
| Frequency response (Hz) | 10 – 100k ± 3dB 20 – 50k ± 2dB |
| Dynamic range | 37dB(A) – 155dB (1000 Hz distortion <3%) |
| Background noise | 37dB(A) |
| Sensitivity (mV/Pa, dBV/Pa) | 5mV (-46.0dB) ± 2dB |
| Maximum output voltage | 5.6V |
| Output impedance | <50Ω |
| Power supply | 2mA – 10mA (typical 4mA) |
| Equalization method | Post-equalization pressure |
| Interface type | Micordot(L5) |
| Operating temperature range | -20℃ to 60℃ |
| Storage conditions | Temperature: 25℃±5℃, Humidity: 50%±15%RH (to ensure long-term stability of the sensor) |
| Relative humidity | 20-90% non-condensing |
| Relative humidity coefficient | <0.003dB (250Hz, reference temperature 40℃, reference RH 50%) |
V. Conclusion
The MegaSig M 645+A 835 is a tool designed to explore the limits of sound pressure.
If your test subject has a very loud sound (>140dB) or a very high frequency response (>20kHz), a standard 1/2-inch microphone will not be sufficient. In this case, the M 645+A 835, with its 100kHz bandwidth and 155dB handling capacity , is an essential investment for obtaining accurate, distortion-free data. It is particularly suitable for use in acoustic laboratories, the defense industry, and the research and verification of high-end automotive components.
Need further planning consultation for your project? Feel free to contact us anytime for technical discussions.