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Acoustically transparent duct

Fans are widely used for industrial as well as household applications. As their numbers increase, so does their effect on our comfort and health via noise pollution. In most instances, these fans are built into a ducted environment, and therefore acoustic investigations should also be carried out in a ducted environment in order to guarantee proper flow conditions. On the other hand, localizing noise sources in a ducted environment is a difficult task. A useful method for localizing noise sources is the beamforming of phased array microphone data, but building an array of microphones into a duct runs with many complications. This has provided motivation for the design of an acoustically transparent duct, which provides a means for using a microphone array located outside of the duct system for the investigation of fan noise sources within the duct. The acoustically transparent duct section provides an acoustic window for the microphone array while guaranteeing that the duct is hydrodynamically impenetrable. This investigation presents the design process as well as a case study of a low pressure fan in order to demonstrate the effectiveness of the design.