GRAS 40AD 1/2" Prepolarized Pressure Microphone, High Sensitivity

Freq range: 3.15 Hz to 10 kHz
Dyn range: 16 dB(A) to 148 dB
Sensitivity: 50 mV/Pa

GRAS 40AD 1/2" Prepolarized Pressure Microphone, High Sensitivity



GRAS 40AD a high-precision condenser microphone made according to IEC 61094-4 requirements and is ideal for coupler measurements in both laboratory and production environments. It is extremely robust and reliable and can measure sound pressure levels up to 148 dB and down to 16 dB(A) in the range of 3.15 Hz to 10 kHz. The presence of the 40AD in a sound field at low frequencies is minimal due to its small size compared to the large wavelengths.

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

A front-vented version is available, 40AD-FV 1/2" Prepolarized Pressure Microphone, High Sens. Front Vented.

Typical applications and use

It is the ideal partner for testing headsets, headphones, and earphones, as well as hearing aids, in coupler setups. The small size makes it well suited for making flush (boundary) measurements.

The 40AD is a very versatile microphone when connected to the RA0067 Transmitter Adapter for ½" Microphones. The 40AD becomes a high-impedance sound source when the RA0067 takes a calibration signal directly from the signal generator and makes the microphone behave like an electrostatic loudspeaker. In a coupler, this gives a frequency response that is as good as when the 40AD behaves like a microphone.

40AD can be used in

Other coupler systems can be configured with the 40AD and a CCP preamplifier on request


The 40AD 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 42AG Multifunction Sound Level Calibrator.

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


When leaving the factory, all GRAS 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: GRAS Traceable Calibration and GRAS Accredited Calibration.

GRAS 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 GRAS microphones are subjected to as an integral part of our quality assurance.

GRAS Accredited Calibration is performed by the GRAS 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 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 5 years 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.


0 V / CCP
Frequency range (±1 dB)
12.5 to 7.5 k
Frequency range (±2 dB)
3.15 to 10 k
Dynamic range lower limit (microphone thermal noise)
Dynamic range lower limit with GRAS preamplifier
Dynamic range upper limit
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 (±2 dB)
Open-circuit sensitivity @ 250 Hz (±2 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
9 / 0,317


Typical frequency response


Free-field corrections for different angles of incidence

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






Ordering info


40AD 1/2" Prepolarized Pressure Microphone, High Sens. This  is the rear vented "standard" version.


40AD-FV 1/2" Prepolarized Pressure Microphone, High Sens., Front Vented. Identical to 40AD, but front vented.


Traceable Calibration of Microphone


Accredited Calibration of Microphone

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

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