GRAS 40BD 1/4" Prepolarized Pressure Microphone
Freq range: 4 Hz to 70 kHz
Dyn range: 44 dB(A) to 174 dB
Sensitivity: 1.6 mV/Pa
The 40BD is an IEC 61094 WS3P ¼" prepolarized pressure microphone with rear-venting. Read about the externally polarized equivalent [40BP]
It is a high-precision condenser microphone made according to IEC 61094-4 requirements. Its low sensitivity makes it ideal for sound measurements at high frequencies and high sound pressure levels of up to 174 dB. Its small size reduces the effects of diffraction and reflections around the microphone, resulting in a frequency range that extends up to 70 kHz.
40BD 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 40BD is ideal for sound pressure measurements, as well as high frequency and high level pressure measurements. It is suitable for general purpose acoustic measurements in couplers and at boundaries. 40BD is included in the GRAS 46BD ¼" Pressure microphone set.
The 40BD requires a standardized ½" or ¼" CCP preamplifier and an input module that supports this technology with a BNC, SMB, or Microdot connector.
For daily verification and check of your measurement setup, we recommend using a calibrator like GRAS Multifunction 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.
Traceable Calibration of Microphone
Accredited Calibration of Microphone
GRAS Sound & Vibration reserves the right to change accessories without notice.