  In this paper, we use Dafermos-Rodnianski's new vector field method to study
the asymptotic pointwise decay properties for solutions of energy subcritical
defocusing semilinear wave equations in $\mathbb{R}^{1+3}$. We prove that the
solution decays as quickly as linear waves for $p>\frac{1+\sqrt{17}}{2}$,
covering part of the sub-conformal case, while for the range $2<p\leq
\frac{1+\sqrt{17}}{2}$, the solution still decays with rate at least
$t^{-\frac{1}{3}}$. As a consequence, the solution scatters in energy space
when $p>2.3542$. We also show that the solution is uniformly bounded when
$p>\frac{3}{2}$.
