The intensity-measurement technique is a powerful tool for locating sound sources, order rank them and determine the emitted sound power. The method is based on the simultaneous determination of sound pressure and particle velocity by two (or more) closely spaced microphones. The sound intensity probe must ensure a well-defined acoustic spacing between the microphones as well as minimise disturbances to the sound field.
 

To ensure maximum measurement accuracy, the spacing between the micro-phones must be optimised for the given measurement conditions. At low frequencies, in highly reverberant conditions, this spacing must be large, whereas for measurements at high frequencies, it must be small.
 

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Intensity Probes   : :   G.R.A.S. Sound & Vibration
	Type 50AI-xx   Microphone Pair:           Type 40AI    Preamplifiers:           2 x Type 26AA (with 4-pin LEMO FGG OB)    Frequency response & phase matching:           IEC 1043 Class 1    Comment:     Include pair of ½" intensity microphones     Type 40AI, spacers, adapters, a pair of     ¼" preamplifiers Type 26AA and a remote     control handle.     The remote control handle is available in a     number of different versions for connection to     a wide range of intensity analyzers.     Its remote-control capabilities give it complete     control of the data acquisition process via the     probe handle.   Type50AI-B:     Built-in remote-control facilities for direct     connection to, and control of, sound intensity     measuring systems from a wide range of     suppliers such as 01dB and Neutrix-Cortex.     It can also be used with the G.R.A.S.     Power Module Type 12AB.    Type 50AI-C:     Connect to any intensity analyzer with a     standard 7-pin LEMO connector or to G.R.A.S.     Power Modules Type 12AA or Type 12AB.     This version has no remote control facilities    Type 50AI-D:     Built-in remote-control facilities for direct     connection to, and control of, sound intensity     measuring systems from a wide range of     suppliers such as Müller-BBM and OROS.     It can also be used with the G.R.A.S.     Power Module Type 12AB.    Type 50AI-HP:     Built-in remote-control facilities for direct     connection to, and control of, Hewlett Packard     analyzers such as the Type HP 3569A    Type 50AI-LD:     Built-in remote-control facilities for direct     connection to, and control of, Larson Davis     analyzers Type LD2900 and LD3000		Type 50GI     CCP intensity probe   Microphone Pair:           Type 40GK    Preamplifiers:           2 x Type 26CB (phase matched)    Frequency response & phase matching:           IEC 1043 Class 1    Comment:     Type 50GI is a sound intensity probe for direct     connection to signal analyzers or data     acquisition devices with IEPE inputs.     The probe includes a pair of phase-matched     prepolarized precision microphones which     meet the requirements in IEC standard 61043     for a class-1 intensity probe.     The small rugged ¼ CCP preamplifiers ensure     minimum disturbance to the sound field for     accurate measurements in the full frequency     range.      The probe set includes solid interchangeable     spacers for microphone separations from     12 mm to 100 mm so that the probe can     cover the frequency range from 50 Hz to     10 kHz.

Special Intensity Probes   : :   G.R.A.S. Sound & Vibration
	Type 50VI   vector intensity probe   Microphone Pairs:           Type 40AI    Preamplifiers:           2 x Type 26AA (with 4-pin LEMO FGG OB)    Spacers:           3-D (and 2-D) 25 mm and 50 mm    Frequency response & phase matching:           IEC 1043 Class 1    Comment:     A flexible and adjustable, two or three-     dimensional sound-intensity probe.     The probe handle has marked inputs for     3 pairs of preamplifiers (a pair for each of     the mutually-perpendicular directions) and     a 24-pin LEMO output socket at its base for     connecting it to a suitable Power Module     (e.g. Type 12AC) or Power Modules (via     cable adapter).     The Type 50VI includes:       * Three pairs of phase-matched intensity          microphones Type 40AI.       * Three pairs of Type 26AA preamplifiers.       * 25mm and 50mm spacers to cover the           frequency range 80Hz to 6.3kHz.       * 6-channel probe handle.       * 10 m cable (24-core) with LEMO connectors           (for direct use with Type 12AC),       * Cable adapter for splitting the six           preamplifier channels into six separate           short leads (marked accordingly with           channel designations) each terminating           in a 7-pin LEMO connector.     Type 50VI-1   -   three-dimensional version.     Type 50VI-2   -   two-dimensional version.		Type 50VI-3   wide-band probe   Microphone Pairs:           2 x Type 40AI    Preamplifiers:           4 x Type 26AA (with 4-pin LEMO FGG OB)    Spacers:           25 mm and 60 mm wide-band spacer    Frequency response & phase matching:           IEC 1043 Class 1    Comment:     Flexible and adjustable four-channel     sound-intensity probe.     It enables sound intensity measurements     using two different microphone spacers     simultaneously to cover an extended     frequency range.     The spacers used with the Type 50VI-3 have     lengths of 25 mm and 60 mm to cover a     frequency range from 80 Hz to 6.3 kHz.     The remote control output can, for example,     be connected to an RS232 interface for     computer control of the process of data     acquisition.      The Wide-band Intensity Probe Type 50VI-3     comprises two pairs of phase matched     intensity microphones Type 40AI, two pairs     of preamplifiers Type 26AA, 25 mm and     60 mm spacers, a 6-channel probe handle     and a 5 m cable with LEMO connectors.		Type 50VX   X-Y-Z intensity probe   Microphone Pairs:           Type 40AI    Preamplifiers:           2 x Type 26AA (with 4-pin LEMO FGG OB)    Spacers:           12 mm, 25 mm, 50 mm and 100 mm    Frequency response & phase matching:           IEC 1043 Class 1    Comment:     A two-channel intensity probe for serially     measuring a three-dimensional sound intensity     vector in a stationary sound field.     It includes a pair of phase-matched intensity     microphones Type 40AI mounted on a pair     of Preamplifiers Type 26AA with adapters and     spacers. The whole assembly is mounted on     a swivel head that can be swivelled in three     mutually-perpendicular directions by means     of a pair of slider buttons on the probe handle.     The probe handle has inputs for 2     preamplifiers and a pair of LEDs for indicating     two states as well as a pair of push buttons     for interactive use with a remote-control     system. For example, the output socket     for remote control can be connected to the     RS232 interface of a computer which controls     the process of data acquisition.

 
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