We study existence of localized waves that can propagate in an acoustic medium bounded by two thin semi-infinite
elastic membranes along their common edge.
The membranes terminate an infinite wedge that is filled by the medium, and are rigidly connected at the points of their common edge.
The acoustic pressure of the medium in the wedge satisfies
the Helmholtz equation and the third-order boundary conditions on the bounding membranes as well as the other appropriate
conditions like contact conditions at the edge. The existence of such localized waves is equivalent to existence of
the discrete spectrum of a semi-bounded self-adjoint operator attributed to this problem.

In order to compute the eigenvalues and eigenfunctions, we make use of an integral representation
(of the Sommerfeld type) for the
solutions and reduce the problem to
functional equations. Their non-trivial solutions from a relevant class of functions exist only for some
values of the spectral parameter. The asymptotics of the solutions
(eigenfunctions) is also addressed.
The far-zone asymptotics contains exponentially vanishing terms. The corresponding solutions
exist only for some specific range of physical and geometrical parameters of the problem at hand.