The state of the art sensor is the so called USP. The three dimensional ½ inchUSP regular probe consists of three orthogonally placed Microflown acousticparticle velocity sensors and a sound pressure microphone. The actual sensorconfiguration without its cap is less than 5×5×5mm! Any sound field isdescribed by two complementary acoustic quantities, the scalar value 'soundpressure' and the vector value 'particle velocity'. The Microflown is the onlysensor that can measure the acoustic particle velocity directly. Thanks to theunique properties of the USP probe all physical quantities, sound pressure andtri-axial particle velocity, can be measured directly, In order to get the 3DSound intensity vectors without any frequency limitations.