GRAS 40AU-1 1/2" Ext. Polarized Reference Pressure Microphone

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The 40AU-1 is an IEC 61094 LS2aP ½" externally polarized reference microphone that is rear-vented.

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GRAS 40AU-1 1/2" Ext. Polarized Reference Pressure Microphone


The 40AU-1 is an IEC 61094 LS2aP ½" externally polarized reference microphone that is rear-vented.

It is a ½" laboratory-standard pressure microphone that is ideal for precision sound pressure measurements. It has a front cavity as specified in IEC 61094-1 and is supplied with a protective dust cap.

40AU-1 is individually calibrated (accredited calibration) and delivered with a calibration chart stating its specific open-circuit sensitivity and pressure frequency response.

A 1/2" Electrostatic Actuator especially designed to fit the 40AU-1 is part of the delivery.

Typical applications and use

The 40AU-1 can be used for precision sound pressure measurements, calibrations at high frequencies, laboratory reference measurements, and measurements in couplers and ear simulators.

The 40AU-1 can be used in couplers, ear simulators, enclosures, and at boundaries.


The 40AU-1 requires a standardized ½" 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.

For frequency calibration, the special electrostatic actuator that is part of the delivery must be used, the RA0014-S1.


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.

40AU-1 is delivered with an accredited calibration.

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.