Patent ID: 6988057

Claim:
A method of designing a chamber for attachment of a duct to reduce noise in said duct, said chamber having a peripheral chamber height h c to reduce noise in a duct having a height h by, said duct being separated from said chamber by a membrane having a tension Tand membrane length L, including the steps of: a) setting the chamber height h c , the membrane length L, and tension T to predetermined values; b) setting incident wave frequency ƒ such that angular frequency ω=2πƒ, c 0 =speed of sound; c) determining the radiation pressure acting on the upper surface of the membrane facing away from the chamber, p +rad caused by a unit modal amplitude; d) determining the radiation pressure acting on the lower surface of the membrane facing towards the chamber, p +rad caused by a unit modal amplitude; e) determining the radiation pressure by reflection of the radiated waves into the cavity by the walls of the chamber, p −ref caused by a unit modal amplitude; f) calculating vibration amplitude of the jth in-vacuo mode V j using the modal impedance yielded from p +rad , p −rad , and p −ref , g) calculating transmitted wave p t using calculated vibration amplitude V j from step f); h) calculating transmission loss TL forf, i) repeating steps b) to h) by varying wave frequency ƒ to calculate transmission loss TL for different ƒ, and j) determine a frequency range ƒ 1 and ƒ 2 from the transmission loss TL versusf spectrum such that transmission loss TL within ƒ 1 to ƒ 2 is higher than or equal to a threshold transmission loss TL cr and wherein at the one of the chamber height h c , membrane length L or tension Tare varied and steps a) to j) are repeated to obtain an optimized noise-reduction spectrum for said duct.