  An experimental study of Ion Acoustic (IA) wave propagation is performed to
investigate the effect of neutral density for argon plasma in an unmagnetized
linear plasma device. The neutral density is varied by changing the neutral
pressure, which in turn allows the change in ion-neutral, and electron-neutral
collision mean free path. The collisions of plasma species with neutrals are
found to modify the IA wave characteristics such as the wave amplitude,
velocity, and propagation length. Unlike the earlier reported work where
neutrals tend to heavily damp IA wave in the frequency regime {\omega}<{\nu}_in
(where {\omega} is ion-acoustic mode frequency and {\nu}_in is ion-neutral
collision frequency), the experimental study of IA wave presented in this paper
suggests that the collisions support the wave to propagate for longer distances
as the neutral pressure increases. A simple analytical model is shown to
qualitatively support the experimental findings.
