G.R.A.S. 40BH 1/4" Ext. Polarized Pressure Microphone, High Pressure

Freq range: 10 Hz to 20 kHz
Dyn range: 54 dB(A) to 193 dB
Sensitivity: 0.4 mV/Pa


The 40BH is an IEC 61094 WS3P ¼" externally polarized high-pressure microphone with rear-venting.

40BH is a high-precision condenser microphone made according to IEC 61094-4 requirements. Its very low sensitivity and wide frequency response make it ideal for measuring very high sound pressure levels of up to 194 dB. It is extremely robust and reliable and can handle acoustic impulse measurements in frequencies of up to 20 kHz.

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

Typical applications and use

40BH is typically used for sound pressure, very high level measurements, and impulse-sound measurements. It is suitable for general purpose acoustic measurements in couplers and at boundaries.

The 40BH is a very versatile microphone when connected to the RA0086 Transmitter Adapter for ¼" Microphones. The 40BH becomes a high-impedance sound source when the RA0086 takes a calibration signal directly from the signal generator and makes the microphone behave like an electrostatic loudspeaker. When used for calibrating an acoustic coupler, this gives a frequency response that is as good as when the 40BH behaves like a microphone.


The 40BH requires a standardized ½" or ¼" LEMO preamplifier and an input module that supports this technology with a 7-pin LEMO 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.


When leaving the factory, all G.R.A.S. microphones have been calibrated in a controlled laboratory environment using traceable calibration equipment. Depending on the use, measurement environment and internal quality control programs we recommend that the microphone is recalibrated at least once a year.

We offer two kinds of calibration as an optional after-sales service: G.R.A.S. Traceable Calibration and G.R.A.S. Accredited Calibration.

G.R.A.S. Traceable Calibration is a traceable calibration performed by trained personnel under controlled conditions according to established procedures and standards. This is identical to the rigorous calibration that all G.R.A.S. microphones are subjected to as an integral part of our quality assurance.

G.R.A.S. Accredited Calibration is performed by the G.R.A.S. Accredited Calibration Laboratory that has been accredited in accordance with ISO 17025 by DANAK, the Danish Accreditation Fund.

If you want a new microphone set delivered with an accredited calibration in stead of the default factory calibration, specify this when ordering.

Learn more at gras/calib.

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.

Frequency range (±2 dB) Hz 10 to 20 k
Dynamic range lower limit (microphone thermal noise) dB(A) 54
Dynamic range lower limit with G.R.A.S. preamplifier dB(A) 62
Dynamic range upper limit dB 194
Dynamic range upper limit with G.R.A.S. preamplifier @ +28 V / ±14 V power supply dB 181
Dynamic range upper limit with G.R.A.S. preamplifier @ +120 V / ±60 V power supply dB 193
Open-circuit sensitivity @ 250 Hz (±2 dB) mV/Pa 0.4
Open-circuit sensitivity @ 250 Hz (±2 dB) dB re 1V/Pa -68
Microphone cartridge capacitance, typ. pF 6
Microphone venting Rear
IEC 61094-4 Compliance WS3P
Temperature range, operation °C / °F -40 to 150 / -40 to 302
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 -0.01
Humidity range non condensing % RH 0 to 100
Humidity coefficient @250 Hz dB/% RH -0.001
CE/RoHS compliant/WEEE registered Yes / Yes, Yes
Weight g / oz 1.5 / 0.053

Typical frequency response (without protection grid)

Free-field corrections for different angles of incidence

Optional items

G.R.A.S. RA0086

Transmitter adapter for ¼” microphones

G.R.A.S. CA0001

Traceable Calibration of Microphone

G.R.A.S. CA2001

Accredited Calibration of Microphone