Broadband sound absorber based on inhomogeneous-distributed Helmholtz resonators with extended necks

A sound absorber for noise reduction, comprising:

• a plurality of absorption units, each absorption unit of the plurality of absorption units comprising a cylindrical core disposed between an acoustically rigid back wall and a perforated plate extending in a radial direction of the cylindrical core, each absorption unit of the plurality of absorption units further comprising an extended neck attached to the perforated plate and extending from the perforated plate into the cylindrical core in an axial direction of the cylindrical core that is perpendicular to the radial direction,
• wherein the extended neck of each absorption unit of the plurality of absorption units is different from the extended neck of each laterally, non-diagonally adjacent absorption unit,
• wherein the perforated plate of each absorption unit of the plurality of absorption units comprises exactly one opening therein connecting an inside of the cylindrical core to an outside of the sound absorber,
• wherein the absorption units of the plurality of absorption units are disposed in a checkerboard fashion, where the extended neck of each absorption unit of the plurality of absorption units is the same as the extended neck of each diagonally adjacent absorption unit,
• wherein the plurality of absorption units comprise a first type of absorption unit with an extended neck with a first parameter value and a second type of absorption unit with a second parameter value different from the first parameter value, and
• wherein all absorption units of the plurality of absorption units are either the first type or the second type.