Concrete with enhanced soundproofing in the low frequency range 100-200 Hz, and a novel test method to measure the sound transmission loss were developed. The concrete comprised short fibre-reinforced material containing lead balls of 15 mm diameter coated with a 2 mm thickness of silicone rubber. The balls were designed to resonate at the frequencies of interest, so absorbing incident sound energy. A measuring system consisting of a loudspeaker to generate a sound wave, and microphones placed either side of a test panel to measure the transmission loss, was used to compare the transmission loss of the experimental system with that of a plain concrete panel. The balls in the experimental system exhibited local resonance and enhanced transmission loss was observed. 8 refs.