Abstract: The boundary element method (BEM) is a flexible tool for modelling interior and exterior acoustics. However one of the prerequisites for this mathematical procedure to work is that the domain forms a proper volume. For example a sheet or a narrow slit would pose a problem. This so-called thin shape break-down effect can be over-come. The technique described here divides the acoustic domain into subdomains. Each subdomain should then be treatable by the boundary element method. The subdomain technique proofs to be robust and efficient. This paper demonstrates the subdomain technique for modelling a typical vented loudspeaker enclosure.