G.R.A.S. 40DD 1/8" Prepolarized Pressure Microphone

Freq range: 6.5 Hz to 70 kHz
Dyn range: 40 dB(A) to 175 dB
Sensitivity: 0.9 mV/Pa


The 40DD is an IEC 61094 1/8" prepolarized pressure microphone with rear-venting. Read about the externally polarized equivalent.G.R.A.S. 40DP

It is a high-precision condenser microphone made according to IEC 61094-4 requirements. Its tiny size allows it to be used for measuring very high frequency sounds without disturbing the sound field. It can measure sound pressure levels up to 174 dB in the range of 6 Hz to 140 kHz.

40DD 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 40DD has a low sensitivity making it perfect for sound measurements at high frequencies and very high level pressure, as well as impulse noises.

The 40DD is included in the 67SB Blast Probe Microphone because of its wide-frequency response.


The 40DD must be used with an adapter for mounting a 1/8" microphone onto a 1/4" preamplifier.

System verification

For daily verification and check of your measurement setup, we recommend using a calibrator like G.R.A.S. G.R.A.S. 42AG Multifunction Sound Level Calibrator.

For proper sensitivity calibration, we recommend using a pistonphone like G.R.A.S. Intelligent Pistonphone G.R.A.S. 42AP.


When leaving the factory, all G.R.A.S. 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: G.R.A.S. Traceable Calibration and G.R.A.S. Accredited Calibration.

G.R.A.S. 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 G.R.A.S. microphones are subjected to as an integral part of our quality assurance.

G.R.A.S. Accredited Calibration is performed by the G.R.A.S. 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 G.R.A.S. 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 G.R.A.S. to offer 5 years warranty against defective materials and workmanship.


If you accidentally damage the diaphragm on a G.R.A.S. 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.

Frequency range (±1 dB) Hz 10 to 25 k
Frequency range (±2 dB) Hz 6.5 to 70 k
Frequency range (±3 dB) Hz 6.5 to 140 k
Dynamic range lower limit (microphone thermal noise) dB(A) 40
Dynamic range lower limit with G.R.A.S. preamplifier dB(A) 47
Dynamic range upper limit dB 175
Dynamic range upper limit with G.R.A.S. preamplifier @ +28 V / ±14 V power supply dB 175
Dynamic range upper limit with G.R.A.S. preamplifier @ +120 V / ±60 V power supply dB 175
Dynamic range upper limit with G.R.A.S. CCP preamplifier dB 175
Open-circuit sensitivity @ 250 Hz (±3 dB) mV/Pa 0.9
Open-circuit sensitivity @ 250 Hz (±4 dB) dB re 1V/Pa
Resonance frequency kHz 160
Microphone cartridge capacitance, typ. pF 3.5
Microphone venting Rear
Temperature range, operation °C / °F -40 to 120 / -40 to 248
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 dB/kPa -0.014
Humidity range non condensing % RH 0 to 100
Humidity coefficient @250 Hz dB/% RH -0.001
Influence of axial vibration @1 m/s² dB re 20 µPa 59
CE/RoHS compliant/WEEE registered Yes / Yes, Yes
Weight g / oz 1.5 / 0.053

G.R.A.S. Sound & Vibration reserves the right to change specifications without notice.

Typical frequency response (without protection grid).

G.R.A.S. CA0001

Traceable Calibration of Microphone

G.R.A.S. CA2001

Accredited Calibration of Microphone

G.R.A.S. Sound & Vibration reserves the right to change accessories without notice.