  To observe the Weyl phonon (WP) with the maximum charge and to design a
realistic material structure containing only single-pair-WPs have long been
considered two challenges in the field of topology physics. Here we have
successfully designed an acoustic crystal to realize the single-pair-WPs with
the maximum charge for the first time. Our theoretical simulations on acoustic
band dispersions demonstrate that protected by the time-reversal symmetry
($\cal T$) and the point group symmetries, a WP with the charge -4
($\mathcal{C}=-4$) and another WP with $\mathcal{C}=+4$ are located at the
high-symmetry point $\Gamma$ and R, respectively, with the absence of any other
kinds of WPs. Moreover, the singe-pair-WPs obtained here are designed by the
simplest two-band mode, and the related quadruple-helicoid Fermi acrs can be
observed clearly in experiments, since they aren't covered by any bulk bands
and hybridized by other kinds of WPs. Our theoretical results provide a
reliable acoustic crystal to study the topological properties of the
single-pair-WPs with the maximum charge for experimentalists in this field.
