The G.R.A.S. 50AI Sound-intensity Probes Type builds on more than 20 years of theory and practical experience in sound-intensity measurements. It is adjustable, durable and fully complies with the requirements in IEC 61043, Electroacoustics- Instruments for the Measurement of Sound Intensity- Measurements with Pairs of Pressure Sensing Microphones, 1993 for Class 1 Sound-intensity probes.