GRAS 40AP 1/2" Ext. Polarized Pressure Microphone, High Sensitivity

Freq range: 3.15 Hz to 10 kHz
Dyn range: 16 dBA to 149 dB
Sensitivity: 50 mV/Pa

GRAS 40AP 1/2" Ext. Polarized Pressure Microphone, High Sensitivity



The 40AP is an IEC 61094 WS2P ½" externally polarized pressure microphone with rear-venting. Read about the prepolarized equivalent [40AD]

It is a high-precision condenser microphone made according to IEC 61094-4 requirements and is ideal for coupler and boundary measurements in both laboratory and production environments. It is extremely robust and reliable and can measure sound pressure levels up to 160 dB within 3.15 Hz to 20 kHz. Because of its high sensitivity, it can also measure sound pressure levels down to 16 dB(A). If needed, the 40AP can also be used as a random-incidence microphone.

40AP 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 broad working range and reliability has made 40AP the preferred externally polarized microphone for coupler and ear simulator setups and is the natural supplement or replacement of existing solutions. The 40AP is especially suited for audiometer calibration when using a sound level meter / analyzer with a 200 V polarization feature.

It is used for production line testing in coupler setups for test of hearing aids, earphones, headphones, and headsets.

The KEMAR Manikin can also be configured with 40AP for wide-band binaural sound quality recordings.

40AP can be used in

  • RA0039 Ear Simulator according to IEC 60318-1
  • RA0038 ½" 2cc Coupler according to IEC 60318-5

Other coupler systems can be configured with 40AP and a GRAS LEMO preamplifier on request


The 40AP 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 GRAS Sound Level Calibrator 42AG.

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


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.


200 V / Traditional
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
Open-circuit sensitivity @ 250 Hz (±1 dB)
Open-circuit sensitivity @ 250 Hz (±1 dB)
dB re 1V/Pa
Resonance frequency
Microphone cartridge capacitance, typ.
Microphone venting
Temperature range, operation
°C / °F
-40 to 150 / -40 to 302
IEC 61094-4 Designation
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
Humidity range non condensing
% RH
0 to 90
Humidity coefficient @250 Hz
dB/% RH
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

Optional items


Adapter for ¼” preamplifier and ½” microphone


Adapter for ¼” preamplifier and ½” microphone


Right-angled (90°) adapter for ½” microphone and ¼” preamplifier


Adapter for ¼” preamplifier and ½” microphone


20 dB Attenuator for externally polarized ½” microphones


Traceable Calibration of Microphone


Accredited Calibration of Microphone

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

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