G.R.A.S. 40AC is a high-precision condenser microphone made according to IEC 61094-4 requirements. The 40AC’s design is based on the original reference 1/2" pressure microphone, but optimized for free-field measurements. This results in a doubling of the upper 3 dB frequency limit. All other parameters remain unchanged, making 40AC the perfect free-field complement to the original G.R.A.S. 40AG 1/2" Ext. Polarized Pressure Microphone.
The 40AC is individually factory-calibrated and delivered with a calibration chart stating its specific open-circuit sensitivity, pressure, and corrected free-field frequency responses.
Typical applications and use
The compact design and low sensitivity make 40AC extremely robust and stable. This, combined with its wide frequency range, makes it an all-round free-field microphone suitable for both field-work and precision laboratory measurements. It is also ideal as a working standard microphone in calibration laboratories that offer free-field calibration.
40AC requires a standardized 1/2" or 1/4" Lemo compatible preamplifier and an input module with a 7-pin Lemo connector that provides polarization and supply voltages for microphone and preamplifier.
For daily verification and check of your measurement setup, we recommend using a calibrator like G.R.A.S. 42AB Sound Calibrator, Class 1.
For proper sensitivity calibration, we recommend using a pistonphone like G.R.A.S. 42AP Intelligent Pistonphone, Class 0.
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.
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||5 to 16 k|
|Frequency range (±2 dB)||Hz||3.15 to 40 k|
|Dynamic range lower limit (microphone thermal noise)||dB(A)||20|
|Dynamic range lower limit with G.R.A.S. preamplifier||dB(A)||25|
|Dynamic range upper limit||dB||164|
|Dynamic range upper limit with G.R.A.S. preamplifier @ +28 V / ±14 V power supply||dB||153|
|Dynamic range upper limit with G.R.A.S. preamplifier @ +120 V / ±60 V power supply||dB||164|
|Open-circuit sensitivity @ 250 Hz (±2 dB)||mV/Pa||12.5|
|Open-circuit sensitivity @ 250 Hz (±2 dB)||dB re 1V/Pa||-38|
|Microphone cartridge capacitance, typ.||pF||18|
|IEC 61094-4 Compliance||WS2F|
|Temperature range, operation||°C / °F||-40 to 150 / -40 to 302|
|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||-0.01|
|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||60|
|CE/RoHS compliant/WEEE registered||Yes / Yes, Yes|
|Weight||g / oz||6.25 / 0.22|
Typical frequency response. Upper curve shows free-field response for 0°, lower curve shows pressure response
Free-field corrections for various degrees of incidence
Power Modules for Externally Polarized Ear Simulators and Microphones
|G.R.A.S. AF0008||Adapter for ¼” preamplifier and ½” microphone|
|G.R.A.S. GR0010||Adapter for ¼” preamplifier and ½” microphone|
|G.R.A.S. RA0001||Right-angled (90°) adapter for ½” microphone and ¼” preamplifier|
|G.R.A.S. RA0003||Adapter for ¼” preamplifier and ½” microphone|
|G.R.A.S. RA0016||20 dB Attenuator for externally polarized ½” microphones|