Intensity Microphone Kit 1/4″ GRAS 40BI

Introduction

• The 40BI is an IEC 61043-compliant 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 GRAS 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.

Compatibility

• The 40BI requires a standardized ¼” LEMO preamplifier and an input module that supports this technology. We recommend GRAS 26AA preamplifier.