  As an extension to our previous work, we study the transport properties of
the Witten-Sakai-Sugimoto model in the black D4-brane background with smeared
D0-branes (D0-D4/D8 system). Because of the presence of the D0-branes, in the
bubble configuration this model is holographically dual to 4d QCD or Yang-Mills
theory with a Chern-Simons term. And the number density of the D0-branes
corresponds to the coupling constant ($\theta$ angle) of the Chern-Simons term
in the dual field theory. In this paper, we accordingly focus on small number
density of the D0-branes to study the sound mode in the black D0-D4 brane
system since the coupling of the Chern-Simons term should be quite weak in QCD.
Then we derive its 5d effective theory and analytically compute the speed of
sound and the sound wave attenuation in the approach of Gauge/Gravity duality.
Our result shows the speed of sound and the sound wave attenuation is modified
by the presence of the D0-branes. Thus they depend on the $\theta$ angle or
chiral potential in this holographic description.
