ON THE COMPLETENESS AND ORTHOGONALITY OF THE ACOUSTIC MODES OF AN OPEN CAVITY
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Acoustics 2015 Hunter Valley 15-18 November 2015Abstract: The modal representation of closed acoustical systems such as rooms and enclosures is well known
and is commonly used to find the forced response at a given frequency as the superposition of the
modes. In open systems such as parallel noise barriers, open enclosures or reactive type duct mufflers,
the modal representation may be incomplete due to radiation losses encompassed by the imaginary part
of the eigensolution. This has been declared as an open problem in the literature, with sound field
predictions being found accurate only at the resonant frequencies. In the present study, the
completeness and orthogonality of the quasinormal modes is investigated using the example of a twodimensional
open cavity system.
The modal representation of closed acoustical systems such as rooms and enclosures is well known
and is commonly used to find the forced response at a given frequency as the superposition of the
modes. In open systems such as parallel noise barriers, open enclosures or reactive type duct mufflers,
the modal representation may be incomplete due to radiation losses encompassed by the imaginary part
of the eigensolution. This has been declared as an open problem in the literature, with sound field
predictions being found accurate only at the resonant frequencies. In the present study, the
completeness and orthogonality of the quasinormal modes is investigated using the example of a twodimensional
open cavity system.