Lined ducts are used in a wide range of applications, including ventilation ducts, sound mufflers and electroacoustics applications such as transmission-line loudspeakers. Knowledge and understanding of sound propagation within acoustically treated ducts is therefore essential in order to be able to create and analyse designs for the intended applications.
Transmission-line loudspeaker cabinets consist of a long, acoustically-lined, folded duct attached to the rear of a loudspeaker driver. The acoustic load on the driver and the sound radiated from the end of the duct both depend upon the propagation of sound through the duct. Transmission-Line Cabinets are aimed to extend the low-frequency response of the loudspeakers.
This project investigates the characteristics of sound propagation through a variety of lined ducts at low frequencies. In this research dissipative mufflers that consist of ducts lined on the inside with an acoustically absorptive material have being considered. The impedance mismatch and acoustic dissipation between the sound absorbing layer and the free propagation within the duct is being been modelled analytically, and the resulting models have been compared to numerical models. Within the framework of this project, the numerical method has been benchmarked against analytical results.