  A new class of solutions for Bose crystals with a simple cubic lattice
consisting of N atoms is found. The wave function (WF) of the ground state
takes the form \Psi_0=e^{S_{w}^{l}+S_{b}}*\prod_j
[\sin{k_{l_x}x_{j}}\sin{k_{l_y}y_{j}}\sin{k_{l_z}z_{j}}], where e^{S_{b}} is
the ground-state WF of a fluid, and \textbf{k}_l=(\pi/a_l, \pi/a_l, \pi/a_l)
(a_l is the lattice constant). The state with a single longitudinal acoustic
phonon is described by the WF \Psi_k=[\rho_{-k}+corrections + 7
permutations]\Psi_0, where the permutations give the terms with different signs
of components of vector k. The structure of \Psi_k is such that the excitation
corresponds, in fact, to the replacement of \textbf{k}_l in some triple of
sines from \Psi_0 by \textbf{k}. Such a structure of \Psi_0 and \Psi_k means
that the crystal is created by sound: the ground state of a cubic crystal is
formed by N identical three-dimensional standing waves similar to a
longitudinal sound. It is also shown that the crystal in the ground state has a
condensate of atoms with \textbf{k}=\textbf{k}_l. The nonclassical inertia
moment observed in crystals He-4 can be related to the synchronous tunneling of
condensate atoms.
