GRAS 246AO 1/2'' CCP Pressure Standard SysCheck2™ Microphone Set

246AO SysCheck2 Commercial Overlay 1814x407 px

Ensuring reliable and consistent data in each measurement setup can be challenging. Test and production engineers need to minimize testing time and the risk of errors, while maintaining data accuracy. GRAS has therefore introduced SysCheck2-enabled microphones that allow remote-controlled, fast and precise self-verification of the entire measurement chain (microphones, channel gain and cable integrity). GRAS currently offers two microphone sets with SysCheck2TM: GRAS 246AE for general use and GRAS 246AO for audiology. 

Both ½ʺ CCP microphone sets are improved versions of GRAS 46AE and GRAS 46AO – with the added SysCheck2TM functionality. The verifications are made on each SysCheck2-enabled microphone connected to a CCP power module with transducer electronic data sheet (TEDS) support and measurement software with a single click. GRAS 246AE and GRAS 246AO can be accessed with many data acquisition systems and offer seamless plug-and-play operation with Audio Precision’s APx data acquisition and Siemens Simcenter Testlab software. Both microphone sets also provide on-demand environmental data: Temperature, barometric pressure and humidity.

SysCheck dots2GRAS 246AO with SysCheck2TM - Helps Improved Productivity

The GRAS 246AO builds on the renowned GRAS 46AO and has undergone the same strict highly accelerated life tests (HALT) designed to ensure the high quality that GRAS microphone users have come to expect and trust. It is suitable for laboratory work and ideal for production line testing in coupler setups for hearing aids, earphones, headphones, and headsets. GRAS 246AO is particularly convenient when the microphones are placed where physical verification is time consuming or hazardous—for example, if the microphones are hidden in complex mechanical structures, such as couplers / ear simulators or specialized test boxes on production lines. 

For more information about SysCheck2TM, click here.

SysCheck dots2Explore the Benefits

> Remote-controlled verification of the entire measurement chain
> Rapid check of all channels with a single click
> Monitoring of environmental data (temperature, humidity and barometric pressure)
> No physical interaction with microphones required
> Plug n' Play with Audio Precision and Siemens platforms
> An intelligent microphone with self-test capability
> Detects variation in sensitivity greater than 0.3 dB
> Detects temperature change greater than 2°C / 3.6°F
> RGB LEDs to locate microphones easily
> CCP compatible-no need for expensive cabling

Freq range: 3.15 Hz to 20 kHz
Dyn range: 25 dB(A) to 150 dB
Sensitivity: 12 mV/Pa
Use: For acoustic testing—
SysCheck2-enabled measurement chains



GRAS 246AO with SysCheck2™ is a ½ high-precision microphone suitable for laboratory work and ideal for production line testing in coupler setups for test of hearing aids, earphones, headphones, and headsets.

GRAS 246AO is a variant of 46AO that contains SysCheck2 functionality that can be accessed with many data acquisition systems, but offers seamless plug-and-play operation with Audio Precision's APx data acquisition software. 

SysCheck2 and TEDS

Verification with SysCheck2*
SysCheck2 is a GRAS patented technology for verifying measurement chain integrity. This verification tool performs remote health check on microphones, channel gain and cable integrity. The verifications are made on each SysCheck2-enabled microphone connected to a CCP power module with transducer electronic data sheet (TEDS) support and measurement software with one click.. SysCheck2-enabled microphones also provide on-demand environmental data (temperature, barometric pressure and humidity). SysCheck2 functionality is particularly convenient when the microphones are placed where physical verification is a risk (for example, if the microphones are hidden in complex mechanical structures, such as couplers or specialized test boxes on production lines), the locations are difficult or dangerous to reach, or if used in a distributed measurement where there are many microphones spread out over a large area.

SysCheck2 microphones are equipped with an ultra-low power microcontroller located in the microphone preamplifier. This microcontroller is able to produce a reference signal that SysCheck2 compares to a reference measurement to determine the measurement chain status. Changes in microphone or cable capacitance, channel gain or the unexpected use of a filter will result in a measurement deviation and will be reflected in a change in the output from the measurement channel. Once detected, the problem can be examined and then rectified.

The microphone can be set to display visual cues to the health of the measurement chain and can be used for the easy identification of specific microphones. In the evaluation of measurement-chain health, SysCheck2 can detect microphone sensitivity or channel gain changes greater than 0.3 dB. Additionally, the microphone acquires data on local environmental conditons, including temperature, pressure and humidity. This data can help with the tracability of acquired data and help refine testing to reduce the number of erroneous pass-fail results on a production line.

Full SysCheck2 functionality is ready for use out of the box when connected to  APx 500 Measurement Software with GRAS 12BA, 12BB or 12BE power modules and an Audio Precision APx series analyzer or with an Audio Precision APx series analyzer with CCP and TEDS read/write capabiliy.

However, all features are accessible with a suitable CCP-based power module, analyzer and data acquisition system after setup with the GRAS-supplied software developement kit (SDK) or application programming interface (API), depending on your system. 

For example, Siemens Simcenter Testlab Signature Acquisition (as of release 2021.1) has integrated SysCheck2 for use with GRAS 246AE microphones with a dedicated remote check procedure, allowing it to smoothly check the validity of a calibration previously performed in the field. After initial calibration of the system, their system enables a remote check to be performed in a dedicated tab. All 246AE SysCheck2 microphones present in the field can be checked with one click, and each microphone’s measured value is stored in that microphone’s TEDS as a reference value.

System verification with TEDS
TEDS is very useful to determine which microphone is connected to which input channel and contains relevant information needed by SysCheck2 and other tools used for measurement setup and verification. However, it is not by itself a check of whether the microphone is within specifications or not.


GRAS 246AO is a high-performance standard microphone set. The set is assembled and sealed with a label in our clean-room environment. 

The microphone cartridge is the high-quality IEC  61094 WS2P standardized GRAS 40AO 1/2" Prepolarized Pressure Microphone, designed for long-term reliability in multiple environments.

The preamplifier is based on the GRAS 26CA ½ CCP Standard Preamplifier. This preamplifier unites SysCheck2 functionality with our well-known circuit-board substrates. In the industry, these circuit-board substrates are famous for their low self-noise, wide frequency range and excellent slew rate performance.


To perform as specified the GRAS 246AO microphone set requires a constant current input module that can deliver 4 mA and 24 V unloaded CCP voltage supply. If the constant current supply is lower, the capability of driving long cables is reduced and consequently the upper frequency is reduced. If the voltage supply is lower it will influence the upper dynamic range.

The microphone set is terminated with a BNC connector. Ready to use coax cable assemblies of various types and lengths are available in standard as well as customized lengths.

The 246AO is IEEE 1451.4 TEDS v. 1.0 compliant. If your measurement platform is TEDS compatable, you will be able to read and write data such as properties and calibration data.


Should you by mistake damage the diaphragm on a GRAS microphone we will in most cases be able to exchange it at a very reasonable cost and short turn-around time. This not only protects your investment but also meets your quality assurance department since you do not have to worry about new serial numbers etc.


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.

For subsequent, needed acoustic verification and checks of your measurement setup, we recommend using a sound source like the GRAS 42AG Sound Calibrator. For sensitivity calibration we recommend using a reference sound source like the GRAS 42AP Intelligent Pistonphone.

Learn more at calibration.

Quality and warranty

GRAS microphone sets are made of components from our proven standard portfolio and are all manufactured of high-quality material and branded parts that were chosen and processed to ensure life-long stability and robustness.

All parts are manufactured and assembled at the factory in Denmark by skilled and dedicated operators in a verified clean-room environment. The microphone diaphragm, body and unique protection grid are made of high-grade stainless steel and make the microphone set resistant to physical damage as well as corrosion caused by aggressive air or gasses.

This, together with the enforced gold-plated microphone terminal guarantees a highly reliable connection. Thanks to the high quality, our warranty against defective materials and workmanship is five years.

* NOTE: SysCheck2 is a verification tool, not a calibration tool. SysCheck2 cannot be used to correct microphone sensitivity. While SysCheck2 has the ability to detect small variations in the complete measurement chain from the acquisition hardware to the microphone diaphragm, it cannot detect unexpected physical changes in the vicinity of the microphone (like a forgotten calibrator covering the microphone cartridge). SysCheck2 cannot detect errors due to unlikely scenarios with errors coming from multiple sources that add up and cancel each other out. Jump back to footnote * in the text.↩


0 V / CCP
Frequency range (±1 dB)
5 to 12.5 k
Frequency range (±2 dB)
3.15 to 20 k
Dynamic range lower limit with GRAS preamplifier
Dynamic range upper limit with GRAS CCP preamplifier
Set sensitivity @ 250 Hz (±3 dB)
Set sensitivity @ 250 Hz (±3 dB)
dB re 1V/Pa
Output impedance
Output Voltage Swing, min. @ 24-28 V CCP voltage supply
Power supply min. to max.
2 to 20*
DC bias voltage, typ.
Microphone venting
IEC 61094-4 Designation
Temperature range, operation
°C / °F
-30 to 85 / -22 to 185†‡
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
10 to 90
Humidity coefficient @250 Hz
dB/% RH
-0.001 (10–90%)
Influence of axial vibration @1 m/s²
dB re 20 µPa
Connector type
CE/RoHS compliant/WEEE registered
g / oz
30.15 / 1.064

SysCheck2 resolution** 

dB 0.3

 *  At temperatures below −10°C / 14°F use at least 4 mA for full functionality of SysCheck2.
 †  If used at temperatures higher than 70°C / 158°F, use high-temperature cables.
 ‡  SysCheck2 functional temperature range is between −20°C / -4°F and 65°C / 149°F.
** Requires an ambient noise level less than 85 dBSPL.

GRAS HALT Test Parameters††

Humidity 90%

@50°C / 122°F 48 hours

Drop―horizontal orientation of microphone, attached to 2 kg load

m 1

Drop―vertical, grid downwards

m 1

Vibration―horizontal and vertical

@8 g 15 hours

†† For a short introduction to HALT, see the section "GRAS HALT" above.

Environmental sensor data accuracy (operational from –40 to 85°C / –40 to 185‡‡

  Accuracy Range for given Accuracy


±2°C / 3.6°F  from 0 to 65°C / 32 to 149°F

Pressure, static

 ±1.5 hPa from 0 to 65°C / 32 to 149°F and 300 to 1100 hPa

Relative humidity

 ±4%   from 0 to 65°C / 32 to 149°F

‡‡ This temperature range is solely for the functionality of the environmental data acquisition. This table provides the temperature ranges where the stated accuracy is guaranteed. For example, if the SysCheck2-stated temperature falls below the microphones operational temperarure limit, it may not have the stated accuracy but should still be confirmed.

Temperature: 20°C / 64°F
Pressure: 760 mm

Typical frequency response.

Free-field corrections for different angles of incidence

246AO Self noise bar graph

Typical noise floor in dB shown in 1/3-octave bands—linear and A-weighted.

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


GS1005 RevC Salg

Ordering info


1/2" CCP Pressure Standard SysCheck2 Microphone Set

Optional items


3 m BNC - BNC Cable


Customized length BNC - BNC Cable


½ Microphone Holder, POM


½ Microphone Holder, Stainless Steel


Swivel head




Windscreen for ½ Microphones


½ Rain protection cap


1-Channel CCP Power Module with TEDS Support


4-Channel CCP Power Module with TEDS Support


Multifunction Sound Calibrator, Class 1


Intelligent Pistonphone, Class 0


Traceable Calibration of Microphone Set


Accredited Calibration of Microphone Set

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

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