G.R.A.S. 40BD-FV 1/4" Prepolarized Pressure Microphone, Front Vented

Freq range: 4 Hz to 70 kHz
Dyn range: 44 dB(A) to 174 dB
Sensitivity: 1.6 mV/Pa


The 40BD-FV is an IEC 61094 WS3P ¼" prepolarized pressure microphone with front venting. Read about the externally polarized equivalent [ G.R.A.S. 40BP-FV]

It is a high-precision condenser microphone made according to IEC 61094-4 requirements. Its low sensitivity makes it ideal for sound measurements at high frequencies and high sound pressure levels of up to 174 dB. Its small size reduces the effects of diffraction and reflections around the microphone, resulting in a frequency range that extends up to 70 kHz.

40BD-FV is individually factory-calibrated and delivered with a calibration chart stating its specific open-circuit sensitivity and pressure frequency response.

Typical applications and use

The 40BD-FV is ideal for sound pressure measurements, as well as high frequency and high level pressure measurements. It is suitable for general purpose acoustic measurements in couplers and at boundaries. 40BD-FV is included in the G.R.A.S. 46BD-FV ¼" Pressure microphone set.


The 40BD-FV requires a standardized ½" or ¼" CCP preamplifier and an input module that supports this technology with a BNC, SMB, or Microdot connector.

System verification

For daily verification and check of your measurement setup, we recommend using a calibrator like G.R.A.S. Sound Level Calibrator 42AB.

For proper sensitivity calibration, we recommend using a pistonphone like G.R.A.S. Intelligent Pistonphone 42AP.

Quality and warranty

All G.R.A.S. microphones are made of high-quality materials that will ensure life-long stability and robustness. The microphones are all assembled in verified clean-room environments by skilled and dedicated operators with many years of expertise in this field.

The microphone diaphragm, body, and improved protection grid are made of high-grade stainless steel, which makes the microphone resistant to physical damage, as well as corrosion caused by aggressive air or gasses.

This, combined with the reinforced gold-plated microphone terminal which guarantees a highly reliable connection, enables G.R.A.S. to offer 5 years warranty against defective materials and workmanship.


If you accidentally damage the diaphragm on a G.R.A.S. microphone, we can—in most cases—replace it at a very reasonable cost and with a short turn-around time. This not only protects your investment, but also pleases your quality assurance department because you don't have to worry about new serial numbers, etc.


Before leaving the factory, all G.R.A.S. microphones are calibrated in a controlled laboratory environment using traceable calibration equipment.

Depending on the use, measurement environment, and internal quality control programs, we recommend recalibrating the microphone at least once a year.

Frequency range (±1 dB) Hz 10 to 25 k
Frequency range (±2 dB) Hz 4 to 70 k
Dynamic range lower limit (microphone thermal noise) dB(A) 34
Dynamic range lower limit with G.R.A.S. preamplifier dB(A) 44
Dynamic range upper limit with G.R.A.S. preamplifier @ +28 V / ±14 V power supply dB 166
Dynamic range upper limit with G.R.A.S. preamplifier @ +120 V / ±60 V power supply dB 174
Dynamic range upper limit with G.R.A.S. CCP preamplifier dB 166
Open-circuit sensitivity @ 250 Hz (±3 dB) mV/Pa 1.6
Open-circuit sensitivity @ 250 Hz (±3 dB) dB re 1V/Pa -56
Resonance frequency kHz 50
Microphone cartridge capacitance, typ. pF 7
Microphone venting Front
Temperature range, operation °C / °F -40 to 120 / -40 to 248
Temperature range, storage °C / °F -40 to 85 / -40 to 185
Temperature coefficient @250 Hz dB/°C / dB/°F -0.01 / -0.006
Static pressure coefficient @250 Hz dB/kPa -0.008
Humidity range non condensing % RH 0 to 100
Humidity coefficient @250 Hz dB/% RH -0.001
Influence of axial vibration @1 m/s² dB re 20 µPa 55
CE/RoHS compliant/WEEE registered Yes / Yes, Yes
Weight g / oz 1.5 / 0.053

Typical frequency response (without protection grid)