Archives of Acoustics, 34, 2, pp. 157–168, 2009

Computer modelling of coupled spaces: variations of eigenmodes frequency due to a change in coupling area

Mirosław MEISSNER
Institute of Fundamental Technological Research, Polish Academy of Sciences

Acoustically coupled spaces have recently been drawing
more and more attention in the architectural acoustics community, thus a
determination of shapes and frequencies of eigenmodes in these room systems from
computer-based models has become increasingly significant. In this
investigation, an eigenvalue problem was solved numerically for a simple room
system consisting of two connected rectangular spaces. In a numerical procedure,
the forced oscillator method with a finite difference algorithm was applied. In
order to determine the influence of irregularity of system shape on eigenmodes
frequency, a modal behaviour in the coupled spaces was studied for several sizes
of coupling area. Calculation results have shown that with the exception of a
fundamental mode, the changes in resonant frequencies were relatively small.
However, an increase in a system irregularity led to a coincidence of
frequencies of neighbouring modes and variations in a sequence of modes on a
frequency axis, which both contributed to a degeneration of eigenmodes.
Keywords: coupled spaces; modal analysis; degenerate modes; mode localization
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