Induct dissipative bar-silencer design.

The aim of this project was to investigate the performance of bar-silencers in ventilation ducts, with and without mean flow. The goal of which was to determine a product which could be used on its own or in conjunction with current traditional methods for induct sound attenuation. A literature review was conducted on induct sound attenuation and bar-silencers. A test facility was established in the Department of Mechanical Engineering, University of Canterbury. Modifications were made to an existing fan and duct rig to align it with ISO 7235 (1991) - Measurement procedures for ducted silencers - Insertion loss, flow noise and total pressure loss. A number of bar-silencers were tested in the test facility to determine both their insertion loss and pressure loss characteristics. Bar-silencers which varied in thickness, (such as, triangular shaped silencers) were confirmed to have an insertion loss across a greater range of frequencies, but lower peak absorption than ducting lined on two sides. It was found that the bar-silencers would not be a cost effective method of sound attenuation on their own, due to less effective noise absorption, higher material costs and higher pressure losses, than traditionally lined sections of ducting. However, the bar-silencers could be used in conjunction with traditional methods of sound attenuation to increase the attenuation or in low flow velocity ventilation exits where pressure losses are reduced