Elnady T., Åbom M.

Low frequency sound generation and propagation in duct systems can be applied to different applications. The applications range from ventilation systems to IC-engine exhaust and inlet systems. Several codes were developed by universities to simulate this problem. The most famous are: Davies, Lamps, and SID. Plane wave two-port theory is used to describe the sound transmission along the system. Based on the experience of using these codes for many years, a new user-friendly software was developed to meet the engineering needs. The new code is based on the old SID 3.0 developed at MWL/KTH. It is now MATLAB based with available access to the source code. This gives the user a flexibility to do other calculations than those already defined and further post-process the data. SIDLAB includes typical elements for many applications such as: Pipes, horns, quarter-wave and Helmholtz resonators, expansion chambers, catalytic converters, diesel particulate filters, area expansions and contractions lined ducts, and perforates. At each connection point (node) between the two-port elements, it is possible to introduce active one-ports with predefined source strength and impedance, such as a constant or user-defined source, an open and, and a reflection free termination. There is no limitation to the number of elements and they can be connected together in any arbitrary scheme. By introducing the one-ports, the network can handle several inlets and outlets. SIDLAB can simulate passive results, such as transmission loss and transfer matrices between arbitrary nodes in the network. It can also simulate active results, such as pressure and sound power at each node in the network. An example of a complex muffler system is presented and the SIDLAB simulation result is compared with measurements.