G.R.A.S. 50VX Intensity Probe Type

Freq range: IEC 61043
Dyn range: 25 dB(A) to 152 dB
Sensitivity: 25 mV/Pa
  • 50VX Intensity probe

Typical applications and use

  • Sound-intensity vector measurements
  • Sound-source location
  • Sound-power measurements
  • IEC 61043 standard measurements
  • Sound-source ranking
  • Sound-intensity mapping


The G.R.A.S. 50VX complies fully with the requirements in IEC 61043, Electroacoustics - Instruments forthe Measurement of Sound Intensity - Measurements with Pairs of Pressure Sensing Microphones,1993 for Class 1 Sound-intensity probes and the draft document ISO/DIS 11205.2.

Sound intensity is a vector quantity which describes both the magnitude and direction of the ow of sound energy. A standard two-channel sound-intensity probe (e.g. G.R.A.S. 50AI) can measure a sound intensity vector in only one direction, i.e. along the axis of the probe. To describe a sound-intensity vector fully, sound intensity has to be measured in at least three mutually-perpendicular directions. Thiswill detect the three components of a sound-intensity vector in a system of orthogonal co-ordinates, and the resultant of these will fully describe the sound-intensity vector in three-dimensions.

The G.R.A.S. X-Y-Z Sound-intensity Probe Type50VX has a two-channel sound-intensity probe forserially measuring three-dimensional sound-intensity vectors in a stationary sound eld. It includes a pair of phase-matched intensity microphones, preampliers, adapters and spacers. These are assembled and mounted on a swivel head which can be manually swivelled in three mutually-perpendicular directions via a pair of slider buttons.

The small 1⁄4-inch diameter and 40 mm long microphone preampliers are housed in robust, stainless steel casings which enable novel probe designs that reduce disturbances to the sound eld otherwise brought about by the effects of shadows and diffraction. Symmetry of design enables reliable calibrations as described in the proposed standard (ISO/DIS 9614-2) for sound power measurements using sound-intensity measurements.

The X-Y-Z Sound-intensity Probe Type 50VX comprises G.R.A.S. 40AK Sound Intensity Microphone Pair, two 26AA Microphone Preampliers, four solid spacers of various lengths• Remote-control handle with a mechanism for swivelling the microphone pair in three mutually-perpendicular directions.

The microphones are high sensitivity, free-eld1⁄2-inch condenser microphones with a uniquely designed pressure equalization system that ensures extremely well dened phase characteristics. The microphones and preampliers are mounted on a swivel head on the arm of the Remote-control handle. To cover the full frequency range from 50 Hz to 10 kHz, the 50VX is delivered with four solid interchangeable spacers for spacing the microphones at 12 mm, 25 mm, 50 mm and 100 mm.

According to the investigations of Jacobsen, Keith,and Krishnappa, diffraction effects at the intensity probe compensate for the insufciencies of the nite difference approximation. The frequency range of intensity measurements may therefore be extended to frequencies up to 10 kHz using 1⁄2-inch probes with a 12 mm spacer.

The 50VX can also be supplied with a pair of phase-matched 1⁄4-inch microphones G.R.A.S. 40BI instead of the 1⁄2-inch pair G.R.A.S. 40AK mentioned above. The 40BI is for measuring very high intensity levels which lie above the dynamic range of the 40AK or in situations where the smaller size of the 40BI is necessary.

Frequency range (±2 dB) Hz IEC 61043 Class 1
Dynamic range lower limit (microphone thermal noise) dB(A) 25
Dynamic range upper limit dB 152
Set sensitivity @ 250 Hz (±2 dB) mV/Pa 25
Polarization voltage V 200
Microphone venting Rear
Temperature range, operation °C / °F 5 to 40 / 41 to 104
Temperature coefficient @250 Hz dB/°C / dB/°F -0.01
Humidity range non condensing % RH 0 - 100
Humidity coefficient @250 Hz dB/% RH -0.001
Influence of axial vibration @1 m/s² dB re 20 µPa 66
Connector type 24-pin LEMO
CE/RoHS compliant/WEEE registered Yes/Yes/Yes
Weight g / oz 450 / 15.873

Included items

G.R.A.S. AI0001 Windscreen