US Patent 11869473 Hollow structure and resonant sound reducing body

A hollow structure has a hollow body with an annular first space and at least one resonator. In the resonator there is formed an elongated second space with a pair of openings at two ends thereof. Each of the pair of openings opens inwardly toward the interior of the first space. The ratio of the length of a centerline of the second space to the length of a centerline of the first space is within a range of from 0.45 to 0.55. The second space is disposed in a curve along a circumferential surface of the first space and is shaped such that one of the two ends of the second space is folded back toward the other end.