The discretized Helmholtz and equivalence integral equations yield the
impedance representation of a generalized network formulation for aco
ustic scattering. Trans- and self-impedances relate the ensonification
, the scattered field, and the pressure and velocity on the scatterer'
s surface, S; the scatterer's dry impedance loads S. This formulation
suggests applying analysis tools from electrical circuit theory: netwo
rk element abstraction and change of field-variable basis. The scatter
er's wet admittance (impedance) corresponds to the augmented driving p
oint admittance (impedance) from electrical network theory. The lower-
branch modes of the scattering from a submerged spherical shell occur
when the reactance looking into the fluid from S negates that looking
into the shell. Change of basis on S transforms the impedance represen
tation into the admittance, arbitrary-reference, and network-scatterin
g representations. The impedance, admittance, and arbitrary-reference
representations naturally separate hard, soft, and intermediate backgr
ound scattering, respectively. Scattering from passive objects with li
mited vibrational degrees of freedom is bounded: the lower-branch mode
s of the submerged spherical shell approach this bound. No bound exist
s when the vibrational degrees of freedom are unlimited. (C) 1997 Acou
stical Society of America.