To broaden the resonant band gap in locally resonant sonic metamaterials (LRSMs), coupled resonance was introduced through a stacked structure. Stacked-structure LRSMs are formed by orthogonally stacking square coated-steel rods and embedding them layer by layer in an epoxy matrix. Calculations suggest that stacked-structure LRSMs have wider band gaps, which are adaptable to all types of vibration polarizations. Using vibration modes and a mass spring model, strong coupling was confirmed between the orthogonal resonances at the upper edge of the band gap, providing a wider bandwidth. Moreover, the effects of the rod width, thickness of coating material and viscoelastic damping on the band gap were investigated. The close relationship of the bandwidth with the strength of coupling between resonances was thereby demonstrated. (C) 2016 Elsevier B.V. All rights reserved.