There have been concerns about the differences between underwater sound fields in a temporary fiberglass‐reinforced plastic (FRP) pool and in a conventional reinforced concrete (RC) pool. A temporary FRP pool was to be used for competitions at the World Swimming Championships in Fukuoka. We considered three items as key factors for a swimming pool used for synchronized swimming: (1) the sound source itself (output level, fluctuations in frequency characteristics); (2) the effect of materials used in pool construction upon sound source installation conditions; and (3) the effect of the mth mode low‐frequency cutoff in ‘‘shallow water.’’ To improve basic problems related to the first factor, we developed a new actuator‐driven underwater sound system (YALAS), which can eliminate the effect of installation conditions for underwater speakers in the FRP pool. This new underwater system has now seen practical use in competitions. The report summarizes this new underwater sound system and compares the system with conventional systems in terms of its acoustic characteristics. The system can offer music with sufficient audibility in water. We gained a good reputation with competitors because the system showed superior performance to conventional systems in sound volume and quality, and in uniformity of sound distribution.