Abstract: To design the novel forbidden-noise material, the compound lattice may reduce the structure symmetry and open the low-frequency bandgaps, a phononic crystal composed of (4.8²) lattice array of circular steel rods in water was investigated and has four "atoms" per unit cell. The experimental transmission spectra of directed bandgaps were tested as the acoustic waves propagate through the phononic crystal along the ΓX and ΓM directions. Further, the eigenmodes of complete bandgap edges and acoustic wave energy were discussed comprehensively. Results of complete bandgaps agree well with the theoretical values by the flnite element method.