  The apparent accelerating expansion of the Universe, determined from
observations of distant supernovae, and often taken to imply the existence of
dark energy, may alternatively be explained by the effects of a giant
underdense void if we relax the assumption of homogeneity on large scales.
Recent studies have made use of the spherically-symmetric,
radially-inhomogeneous Lemaitre-Tolman-Bondi (LTB) models to derive strong
constraints on this scenario, particularly from observations of the kinematic
Sunyaev-Zel'dovich (kSZ) effect which is sensitive to large scale
inhomogeneity. However, most of these previous studies explicitly set the LTB
'bang time' function to be constant, neglecting an important freedom of the
general solutions. Here we examine these models in full generality by relaxing
this assumption. We find that although the extra freedom allowed by varying the
bang time is sufficient to account for some observables individually, it is not
enough to simultaneously explain the supernovae observations, the small-angle
CMB, the local Hubble rate, and the kSZ effect. This set of observables is
strongly constraining, and effectively rules out simple LTB models as an
explanation of dark energy.
