In computational aero-acoustics, the lattice Boltzmann method (LBM) has demonstrated a number of advantages such as low dissipation and high scalability. To recover the thermal equation and energy transport in a physically consistent way, the fourth order moments of LBM distribution function must be accurately captured, which in turn demands a multispeed velocity set. Accurate and economic realization of various boundary conditions with multispeed velocities has been a challenge in LBM. Here we present a boundary condition for open boundaries with arbitrarily specifiable sound reflection properties by embedding the characteristic non/partially reflecting boundary condition of finite difference (FD) method into multispeed LBM. The local one-dimensional inviscid analysis for Euler equations is used to build boundary treatment method for FD, and distribution functions are reconstructed from FD solution at open outlets as inner-domain LBM's boundary condition. The numeric scheme is validated in a number of test cases, including one-dimensional (1D) and two-dimensional (2D) propagation of acoustic, entropy and vorticity waves, and sound generation in flow past a 2D cylinder. Results show our method can achieve desired reflecting coefficient and reduce non-physical reflecting waves to a satisfactory level.