  We implement the concept of complete local symmetry in lossy acoustic
waveguides. Despite the presence of losses, the existence of a spatially
invariant current is shown theoretically and observed experimentally. We
demonstrate how this invariant current leads to the generalization of the Bloch
and parity theorems for lossy systems defining a mapping of the pressure field
between symmetry related spatial domains. Using experimental data we verify
this mapping with remarkable accuracy. For the performed experiment we employ a
construction technique based on local symmetries which allows the design of
setups with prescribed perfect transmission resonances in the lossless case.
Our results reveal the fundamental role of symmetries in restricted spatial
domains and clearly indicate that completely locally symmetric devices
constitute a promising class of setups, regarding the manipulation of wave
propagation.
