Time Domain Acoustical Holography and Its Applications

SOUND AND VIBRATION/FEBRUARY 2001 This article describes Time Domain Acoustical Holography, its implementation in Brüel & Kjær’s Non-Stationary Spatial Transformation of Sound Fields (NS-STSF) system and its application to solve a few noise source location problems in the automotive industry. Essentially, Time Domain Holography provides spatial mapping of a radiated sound field with a time resolution as short as the sampling interval of the A/D-converter used for the acquisition. The use of Envelope Intensity to view the time history of noise radiation is explained and verified. Three application examples are outlined. The first concerns localization of brake squeal noise sources. The second example deals with engine knocking noise (where and when noise is radiated as a function of crankshaft angle). In the third application, an engine run-up measurement is analyzed and selected engine orders are mapped to localize the origin of strong order-related noise components. A wealth of different analyses can be performed on a single fast time history recording taken with a microphone array and a tacho probe.