GRAS 40PM EQset™ Miniature Production Line Microphone

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The GRAS 40PM Miniature Production Line Microphone is the world's first microphone to incorporate EQset technology.

EQset incorporation in a microphone removes all of the traditional hassle associated with installing, setting up, and replacing microphones in a production line setting. EQset microphones all have flat response curves and fixed sensitivity. Sensitivity variation between individual microphones varies less than 0.2 dB from nominal sensitivity. The flat frequency response is less than 0.5 dB up to 10 kHz, another huge improvement over traditional production line microphnes' ±3 dB across the full frequency range. This provides a number of immediate benefits. 

  • Cost efficiency—low microphone entry cost, no special hardware needed, and fully backwards compatible with CCP setups.
  • Ease of use—a uniformly flat frequency response fixed sensitivity (or gain) for each EQset microphone makes GRAS 40PM microphones plug and play in any 48 V phantom power or CCP-based setup.
  • Reduced risk—the extremely narrow pressure response spread (±0.5 dB) greatly reduces the risk of false passes and false failures, which greatly reduces the risk of bad units reaching the customer and the risk of good units being scrapped or recycled.
  • High environmental stability—the unique design of the GRAS 40PM provides this range of microphones with unmatched environmental stability. Deviation on a typical production line is less than ±0.3 dB, so there is no need for corrections due to temperature or humidity.

Freq range: 20 Hz to 20 kHz
Dyn range: 30 dB(A) to 120 dB
Sensitivity: 25 mV/Pa


GRAS 40PM with EQset™

GRAS 40PM with EQset is designed for use in production line environments, and it provides many benefits over traditional production line- or array-style microphones. Designed to be cost-effective, easy to use, resistant to errors, and environmentally stable, GRAS 40PM is the best production line microphone option on the market. Each GRAS 40PM microphone has a flat response curve and fixed sensitivity. The tolerance for individual microphone sensitivities is less than ±0.2 dB, and frequency-response variation is less than ±0.5 dB up to 10 kHz. And because GRAS 40PM is dimensionally identical to the traditional production line microphones, it can easily replace them in existing setups. 

EQset technology

EQset microphones all have a uniformly fixed sensitivity and flat curve. This reduces measurement uncertainty and greatly simplifies microphone setup, monitoring, replacement, and corrections. EQset means that everything can happen quickly and easily without any individual microphone adjustments or corrections. The simplification of setup and other tasks saves both time in the setup itself and time in operator training. There is, however, one additional benefit that outshines the time savings: EQset almost completely eliminates the inherent risk of false passes on production lines or correction error for frequencies outside the calibrated frequency in R&D—common issues with other microphones in the market. 

Another benefit of the uniformly fixed sensitivity and flat response curve of each EQset microphone is that there is no need to make individual corrections for each microphone. There is, therefore, no need to store that correction information on the microphones via TEDS. This enables EQset microphones to be used effectively with systems based on audio sound cards using 48 V phantom power as well as any CCP-based system already in use, so there is no need for price-prohibitive new equipment or retooling of existing CCP-based systems.

For more on EQset technology, see:   EQset Landing Page QR code or

Environmental stability

The unique design of the GRAS 40PM provides this range of microphones with unmatched environmental stability. The sensitivity deviation on a typical production line* is less than ±0.3 dB, so there is no need for corrections due to temperature or humidity over the course of a normal day in a typical production-line environment.

*Typical environmental conditions on a production line are defined by temperature varying between 13 and 35°C (55 to 95°F), static pressure varying between 983 and 1043 hPa, and non-condensing humidity. 

Typical applications and use

  • Production-line testing of audio devices such as drivers, receivers, micro-speakers, and miniature microphones
  • Measurements in confined spaces

When starting up, these microphones have a settling time of approximately 5 seconds for accuracy better than 0.1 dB or 1 minute for full accuracy.


The GRAS 40PM  is a robust, cost-effective microphone designed for use in production line testing of loudspeakers and acoustic transducers. It has a wide frequency range, from 20 Hz to 20 kHz, and a dynamic range from 30 dB (A) to 120 dB.

The cost-effectiveness of the GRAS 40PM is a key consideration when setting up multiple production lines. Each GRAS 40PM is interchangeable with any other GRAS 40PM without the need for recalibration or additional corrections.

GRAS 40PM is a 34 mm long ¼ microphone that can be used in space-challenged setups where larger microphones would not fit or provide difficulties in testing. Additionally, its small aperture provides an advantage in testing micro-speakers, or miniature microphones. It is good practice to use a microphone with a diameter similar to or smaller than the device to be measured.


This range of microphones is fully compatible with 48 V phantom power setups and CCP-based setups. As such the GRAS 40PM can be used in new cost-saving production-line setups or as replacements for less accurate TEDS-based microphones in existing CCP setups. 

Using a phantom power setup along with an analyzer such as the APx500 Flex Audio Analyzer will create a budget-friendly setup that can be expanded or upgraded easily as need arises. 

Calibration—measurement chain 

GRAS 40PM microphones can be calibrated to ensure that down-stream equipment (such as a sound card) is correctly set up using a pistonphone like GRAS 42AP or a hand-held calibrator like the GRAS 42AG Multifunction Sound Calibrator.

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. 

Thanks to the high quality, our warranty against defective materials and workmanship is two years.


0 V / CCP
Dynamic range lower limit with GRAS preamplifier
Dynamic range upper limit
Power supply (Constant Current Power)
4 to 10 (min. to max.)
Microphone venting
Output impedance
Temperature range, operation
°C / °F
-10 to 55 / 14 to 131
Temperature range, storage
°C / °F
-25 to 70 / -13 to 158
Humidity range non condensing
% RH
0 to 90
Connector type
CE/RoHS compliant/WEEE registered
g / oz
3.5 / 0.12346

Sensitivity (250 Hz; ±0.2 dB)

mv/Pa 25

Sensitivity (250 Hz; ±0.2 dB)

dB re
1 V/Pa

Pressure response (±0.5 dB)

Hz 20 - 10k

Pressure response (±2 dB)

Hz 10k - 20k

Output DC bias voltage

V 13.7 ±0.5 

Max cable length

m 10 (@ 4 mA)


EQ 40PM typical pressure responseTypical pressure response

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


Dimensions in millimeters:

Length (incl. connector): 34 
Diameter: 7 

EQ 40PM OutLine drawing



Ordering info

Optional items


3 m SMB - BNC Cable


10 m SMB - BNC Cable


3 m SMB angled - BNC Cable


Adapter for CCP preamplifier to 48V phantom power (BNC to XLR)


7 mm Microphone Holder, POM


Multifunction Sound Calibrator, Class 1


Intelligent Pistonphone, Class 0

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

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