We prepare a class of locally resonant (LR) sonic materials. The experiments demonstrate that the resonant frequency decreases with the increasing density of the scattering unit cores or with the reducing elastic constants of the silicone rubber coating. By combining three LR layers of different resonant frequencies and choosing 10 dB as the threshold of relative attenuation, we obtain an ultrawidebandgap (200-950Hz) sound material with an average transmission loss 22 dB lower than that dictated by mass density law.