G.R.A.S. Sound & Vibration
Sound-intensity Probe Type 50AI - Page 14
* According to the investigations of Jacobsen, Keith, and Krishnappa, diffraction effects at the intensity probe com-
pensate for the insufficiencies of the finite difference approximation. The frequency range of intensity measure
-
ments may therefore be extended to frequencies up to 10kHz using ½″ probes with a 12 mm spacer.
1. Mount one of the microphones on the Right-angled adapter RA0001 and the other micro-
phone on either the other Right-angle adapter for a symmetrical probe or on the Straight
adapter RA0003 for a straight-probe configuration.
Remove the yellow protection caps from the two Preamplifiers Type 26AA and mount the
microphone-adapter assemblies on the preamplifiers. Screw the Spacer cup GR0040
onto the protection grid of one of the microphones. Select an appropriate spacer (see
Fig. 5.1 for working frequency ranges) from the four supplied and screw this onto the
protection grid of the other microphone. In many cases, the 12 mm spacer RA0266 will
be appropriate and will cover the frequency range from 100 Hz to 6.3 kHz *.
Fig. 4.1 Straight setup using the 25-mm spacer
Fig. 4.2 Symmetrical setup using the 12-mm spacer
