  Several integral identities related to acoustic scattering are presented. In
each case the identity involves the integral over frequency of a physical
quantity. For instance, the integrated transmission loss, a measure of the
transmitted acoustic energy through an inhomogeneous layer, is shown to have a
simple expression in terms of spatially averaged physical quantities. Known
identities for the extinction cross section and for the acoustic energy loss in
a slab with a rigid backing, are shown to be special cases of a general
procedure for finding such integral identities.
