Localization of Noise Sources in an Outdoor HVAC Unit by using the Arbitrary Source Location Method in combination with Wideband Acoustical Holograpahy

An outdoor heating, ventilating, and air conditioning (HVAC) unit has multiple noise sources which contribute to its overall acoustical signature, such as fan blade passage noise, compressor noise, aeroacoustic noise from vortex shedding off the grille, and structure-borne radiated noise. The identification of each noise source's strength and frequency content is key to giving the designer the ability to shape the HVAC unit's sound quality. In the present work, a two-dimensional microphone array was used to localize noise sources by using one of the commonly available acoustical holography methods, Wideband Acoustical Holography (WBH). It has previously been found that WBH holography results are very sensitive to the initial estimate of the equivalent source strengths, particularly at low frequencies. Here, a procedure referred to as the Arbitrary Source Location (ASL) model is introduced to provide the initial estimate of the principal source locations. It will be shown that when the latter procedure is combined with WBH, good sound field reconstructions and source visualizations may be achieved at relatively low frequencies, and that closely-spaced sources may be distinguished. The combined procedures will be illustrated through an application to noise source identification in an outdoor HVAC unit.