The 40BI is an IEC 61094-compliant, WS3F ¼" externally polarized sound-intensity microphone pair.
The 40BI microphone pair consists of two phase-matched free-field condenser microphones with extremely well-controlled phase characteristics for use in sound-intensity probes. Their standard mounting threads make them compatible with all the usual available makes of measurement-microphone preamplifiers.
The 40BI can be used in the G.R.A.S. 50AI Sound-Intensity Probe for high frequency sound-intensity measurements. The 50AI is delivered with ½" microphones, and the 40BI can be ordered as accessories so that you can cover a large frequency range for your sound-intensity measurements. Because the 40BI measures higher frequencies, smaller spacers - 6 mm, 12 mm, and 25 mm – are included with the 40BI kit.
40BI 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 40BI is designed for sound-intensity and sound-power measurements, as well as sound-source localization. Each 40BI microphone pair is phase matched according to the phase specifications for a Class 1 Sound Intensity Probe in accordance with international IEC 61043, Electroacoustics - Instruments for the Measurement of Sound Intensity - Measurements with Pairs of Pressure Sensing Microphones, 1993.
The quality of a sound intensity probe microphone is its ability to measure the real part of a complex sound intensity in highly reactive sound fields as well as in sound fields exposed to high levels of background noise. This ability depends largely on the phase responses of the microphone pair. The individual phase matching of each 40BI ensures that any differences in phase responses are extremely small.
The 40BI is also used for ranking of sound sources. When mounted in a sound-intensity probe such as the 50AI, the microphones can pinpoint the area generating the most noise, which may then require additional measurements, depending on the measurement procedures and processes used. The sound-intensity microphones reveal the weak and strong points when identifying noise sources. Sound-source ranking is useful as long as the background noise doesn't exceed the noise source.
The 40BI requires a standardized ¼" LEMO preamplifier and an input module that supports this technology. We recommend G.R.A.S. 26AA preamplifier.
For daily verification and check of your measurement setup, we recommend using a calibrator like G.R.A.S. 42AB Sound 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)||I|
|Frequency range (±1 dB)||Hz||IEC 60651 Type 0 IEC|
|Dynamic range lower limit (microphone thermal noise)||dB(A)||30|
|Dynamic range lower limit with G.R.A.S. preamplifier||dB(A)||35|
|Dynamic range upper limit||dB||172|
|Dynamic range upper limit with G.R.A.S. preamplifier @ +28 V / ±14 V power supply||dB||163|
|Dynamic range upper limit with G.R.A.S. preamplifier @ +120 V / ±60 V power supply||dB||172|
|Open-circuit sensitivity @ 250 Hz (±2 dB)||mV/Pa||4|
|Open-circuit sensitivity @ 250 Hz (±2 dB)||dB re 1V/Pa||-48|
|Microphone cartridge capacitance, typ.||pF||7|
|IEC 61094-4 Compliance||WS3F|
|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||-0.008|
|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||59|
|CE/RoHS compliant/WEEE registered||Yes / Yes, Yes|
|Weight||g / oz||1.5 / 0.053|
6 mm spacer
12 mm spacer
25 mm spacer
Straight adapter for ¼” microphone and ¼” preamplifier
Right-angled adapter for ¼” microphone and ¼” preamplifier (2 pcs)
Optional Accessories for 40BI:
Sound Intensity Calibrator