Abstract
Pipe laggings are used as a means of inhibiting the transmission of sound radiated from pipes. They are usually formed of porous jackets such as fibreglass or rockwool blankets and impervious jackets such as cladding sheets. Sometimes air spaces are used to separate these jackets from the pipe and each other. Papers in the readily available literature relating to the acoustic performance of pipe laggings are generally concerned with presenting experimental results such as frequency dependent insertion losses. The authors have developed a model to calculate the insertion losses produced by such laggings when the lagged pipes are vibrating in their low order structural modes. The results of the model indicate that negative insertion lossess are not unexpected with conventional pipe laggings, particularly at low frequencies.