  Recently, intense efforts have been devoted to realizing classical analogues
of various topological phases of matter. In this Letter, we explore the
intriguing Weyl physics by a simple one-dimensional sonic crystal, in which two
extra structural parameters are combined to construct a synthetic
three-dimensional space. Based on our underwater ultrasonic experiments, we
have not only observed the synthetic Weyl points directly, but also probed the
novel reflection phase singularity that connects inherently with the
topological robustness of Weyl points. As a smoking gun evidence of the
topological states of matter, the presence of nontrivial interface modes has
been demonstrated further. All experimental data agree well with our full-wave
simulations. As the first realization of topological acoustics in synthetic
space, our study exhibits great potential of probing high-dimensional
topological phenomena by such easily-fabricated and -detected low-dimension
acoustic systems.
