  Based on the many-boson system structure factor, which takes into account
three- and four-particle direct correlations, there was found the first sound
velocity temperature behaviour in liquid $^4$He in the post-RPA approximation.
The expression received for the sound velocity matches with the well-known
results in both low and high temperature limits. The results of this paper can
be used to analyze the contributions of three- and four-particle correlations
into thermodynamic and structural features of liquid $^4$He.
