GRAS 40BD-FV 1/4" Prepolarized Pressure Microphone, Front Vented

Freq range: 5 Hz to 70 kHz
Dyn range: 44 dB(A) to 174 dB
Sensitivity: 1.6 mV/Pa

GRAS 40BD-FV 1/4" Prepolarized Pressure Microphone, Front Vented



The 40BD-FV is an IEC 61094 WS3P ¼ prepolarized pressure microphone with front venting. Read about the externally polarized equivalent [ GRAS 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.

NOTE:  At low frequencies, protection grids are acoustically transparent; however, around 20 kHz and above, protection grids can act as resonators and influence the frequency response. So for higher frequency measurements, ¼ and ⅛ microphones have been optimized for use without the protection grid. Please remove the protection grid when measuring.

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 GRAS 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 GRAS Sound Level Calibrator 42AG.

For proper sensitivity calibration, we recommend using a pistonphone like GRAS Intelligent Pistonphone 42AP.

Quality and warranty

All GRAS 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 GRAS to offer a five-year warranty against defective materials and workmanship.


If you accidentally damage the diaphragm on a GRAS 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 GRAS 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.


0 V / CCP
Frequency range (±1 dB)
10 to 25 k
Frequency range (±2 dB)
5 to 70 k
Dynamic range lower limit (microphone thermal noise)
Dynamic range lower limit with GRAS preamplifier
Dynamic range upper limit with GRAS preamplifier @ +28 V / ±14 V power supply
Dynamic range upper limit with GRAS preamplifier @ +120 V / ±60 V power supply
Dynamic range upper limit with GRAS CCP preamplifier
Open-circuit sensitivity @ 250 Hz (±3 dB)
Open-circuit sensitivity @ 250 Hz (±3 dB)
dB re 1V/Pa
Resonance frequency
Microphone cartridge capacitance, typ.
Microphone venting
Temperature range, operation
°C / °F
-40 to 120 / -40 to 248
IEC 61094-4 Designation
Temperature range, storage
°C / °F
-40 to 85 / -40 to 185
Humidity range non condensing
% RH
0 to 90
Temperature coefficient @250 Hz
dB/°C / dB/°F
-0.01 / -0.006
Humidity coefficient @250 Hz
dB/% RH
Static pressure coefficient @250 Hz
Influence of axial vibration @1 m/s²
dB re 20 µPa
CE/RoHS compliant/WEEE registered
Yes / Yes, Yes
g / oz
1.5 / 0.053


Typical frequency response (without protection grid)

GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.


Get Quote

I have read and accept the Privacy Policy.