The G.R.A.S. 40AZ 1/2" free-field microphone is a precision condenser microphone for low-frequency (including infra-sound) measurements in open acoustic fields.
As a free-field microphone, 40AZ is designed essentially to measure the sound pressure as it would appear if the microphone were not present, the sound field pointing towards the microphone.
At low frequencies, the disturbing effects of its presence in the sound field are minimal (large wavelengths compared to the size of the microphone).
At higher frequencies (>1 kHz), the effects of diffractions generally cause microphones to measure sound pressure levels increasing with frequency. In a free-field microphone, the effects of diffraction are compensated for to provide a flat frequency response in a free-field for 0º incidence.
The G.R.A.S. 26CG 1/4" high impedance preamplifier is available for use with 40AZ. The mounting thread (11.7 mm - 60 UNS-2) is compatible with microphone preamplifiers for WS2P/F microphones.
Typical applications and use
The low-frequency property combined with its high sensitivity and robust design make 40AZ the obvious choice for infra-sound measurements - a fast growing discipline following the need for monitoring and reducing low-frequency noise from, for example, power and production plants and the increasing number of wind turbines.
The 40AZ requires a standardized 1/2" or 1/4" CCP preamplifier and an input module that supports this technology with a BNC, SMB, or Microdot connector.
To benefit from 40AZ’s low frequency capabilities, it is important that the microphone preamplifier, analyzer input module, or sound level meter is designed to match 40AZ.
For daily verification and check of your measurement setup, we recommend using a calibrator like G.R.A.S. 42AB Sound Level Calibrator .
For proper sensitivity calibration, we recommend using a pistonphone like G.R.A.S. 42AP Intelligent Pistonphone.
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.
Before leaving the factory, all G.R.A.S. microphones are calibrated in a controlled laboratory environment using traceable calibration equipment.
Depending on the use, measurement environment, and internal quality control programs, we recommend recalibrating the microphone at least once a year.
|TYPE (Microphone features)||FF|
|Frequency range (±1 dB)||Hz||1 to 10 k|
|Frequency range (±2 dB)||Hz||0.5 to 20 k|
|Dynamic range lower limit (microphone thermal noise)||dB(A)||14|
|Dynamic range lower limit with G.R.A.S. preamplifier||dB(A)||17|
|Dynamic range upper limit||dB||148|
|Dynamic range upper limit with G.R.A.S. preamplifier @ +28 V / ±14 V power supply||dB||142|
|Dynamic range upper limit with G.R.A.S. preamplifier @ +120 V / ±60 V power supply||dB||148|
|Dynamic range upper limit with G.R.A.S. CCP preamplifier||dB||138|
|Open-circuit sensitivity @ 250 Hz (±2 dB)||mV/Pa||50|
|Open-circuit sensitivity @ 250 Hz (±2 dB)||dB re 1V/Pa||-26|
|Microphone cartridge capacitance, typ.||pF||20|
|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||-0,008|
|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||62|
|CE/RoHS compliant/WEEE registered||Yes / Yes, Yes|
|Weight||g / oz||9 / 0,317|
Typical frequency response
Free-field corrections for different angles of incidence