  The success of models of coupled two-leg spin ladders in describing the
magnetic excitation spectrum of La_[2-x]Ba_xCuO_4 has been widely interpreted
as evidence for bond-centered stripes. Here, we determine the magnetic coupling
induced by the charge stripes between bond- or site-centered spin stripes
modeled by two- or three-leg ladders, respectively. We find that only the
site-centered models order. We further report excellent agreement of a fully
consistent analysis of coupled three-leg ladders using a spin wave theory of
bond operators with the experiment.
