Noise suppressor

Claim 1

An apparatus for reducing the level of sound traveling through a duct comprising in combination: a plurality of acoustically-absorbent annular elements disposed in a face-to-face adjacent relationship such that an integral unit is formed having a continuous duct therethrough, each of said elements having a uniform inner diameter with selected ones of said elements having dissimilar backing depth dimensions; means mounted in each of said elements for developing a sound wave traveling therethrough into a characteristic mode which is incompatible with the mode developed by the same means in the next adjacent element such that at the interface therebetween the traveling wave is partially reflected back into the element through which it was originally traveling and is partially transmitted into the next adjacent element, wherein the sound wave is partially absorbed while traveling through each of said plurality of elements into which it has been transmitted and in addition is partially absorbed while traveling through each of said plurality of elements into which it has been reflected, thereby reducing the level of sound traveling through the duct by the continuous alternating cycle of transmission-absorption and reflection-absorption.

Claim 2

An apparatus for reducing the level of sound traveling through a duct comprising in combination: a plurality of acoustically-absorbent annular elements disposed in a face-to-face adjacent relationship such that an integral unit is formed having a continuous duct therethrough, each of said elements having a uniform inner diameter with selected ones of said elements having dissimilar backing depth dimensions; means mounted in each of said elements for developing a sound wave traveling therethrough into a characteristic mode which is incompatible with the mode developed by the same means in the next adjacent element such that at the interface therebetween the traveling wave is partially reflected back into the element through which it was originally traveling and is partially transmitted into the next adjacent element, wherein the sound wave is partially absorbed while traveling through each of said plurality of elements into which it has been transmitted and in addition is partially absorbed while traveling through each of said plurality of elements into which it has been reflected, thereby reducing the level of sound traveling through the duct by the continuous alternating cycle of transmission-absorption and reflection-absorption.

Claim 9

An apparatus for reducing the level of sound traveling in ducts through utilization of sound wave incompatibility reflection and transmission comprising: first, second and third acoustically-absorbent annular elements, each of sAid elements having identical inner diameter dimensions; said first and third elements having an identical backing depth dimension dissimilar from that of said second element; means mounted in said first and third elements for developing a sound wave traveling therethrough into a mode characteristic of said first and third elements; means mounted in said second element for developing a sound wave traveling therethrough into a mode characteristic of said second element and incompatible with the mode characteristic of said first and third elements; first, second and third annular casings, each having an inner diameter and backing depth of a dimension corresponding to that of said first, second and third elements; said first, second and third casings containing, respectively, said first, second and third elements and being connected in a face-to-face relationship such that an integral unit having a uniform duct therethrough is formed, whereby a sound wave traveling through each of said first, second and third elements will be partially transmitted into the next adjacent element and partially absorbed therein and whereby that same sound wave traveling through each of said first, second and third elements will be reflected at the interface therebetween back into the element through which it was traveling and be partially absorbed therein.

Claim 10

An apparatus for reducing the level of sound traveling in ducts through utilization of sound wave incompatibility reflection and transmission comprising: first, second and third acoustically-absorbent annular elements, each of sAid elements having identical inner diameter dimensions; said first and third elements having an identical backing depth dimension dissimilar from that of said second element; means mounted in said first and third elements for developing a sound wave traveling therethrough into a mode characteristic of said first and third elements; means mounted in said second element for developing a sound wave traveling therethrough into a mode characteristic of said second element and incompatible with the mode characteristic of said first and third elements; first, second and third annular casings, each having an inner diameter and backing depth of a dimension corresponding to that of said first, second and third elements; said first, second and third casings containing, respectively, said first, second and third elements and being connected in a face-to-face relationship such that an integral unit having a uniform duct therethrough is formed, whereby a sound wave traveling through each of said first, second and third elements will be partially transmitted into the next adjacent element and partially absorbed therein and whereby that same sound wave traveling through each of said first, second and third elements will be reflected at the interface therebetween back into the element through which it was traveling and be partially absorbed therein.

Claim 13

A method for reducing the level of sound of a sound wave travelling through a duct, including the steps of: providing a travelling sound wave; providing a plurality of peripheral acoustically-absorbent elements having uniform inner diameter dimensions and having alternating first and second backing depth dimensions such that the characteristic mode of the sound wave travelling through said elements having backing depths of the first dimension is incompatible with the characteristic mode of the sound wave travelling through said elements having backing depths of said second dimension; disposing the elements in an alternating face-to-face relationship such that an integral unit having a uniform duct formed therethrough is formed; introducing said travelling sound wave into the integral unit, whereby the sound wave travels through the first element and is partially absorbed therein; and at the interface between the first and second elements it is partially reflected back into the first element being further absorbed therein and is partially transmitted into the second element wherein it is further absorbed and at the interface between the second and third elements it is again partially reflected and partially transmitted into the second and third elements, respectively, and further absorbed therein and wherein that portion of the wave transmitted into the third element is emitted from the integral unit at a reduced level of sound and wherein that portion of the wave reflected back into the second element is partially reflected and transmitted at each element interface and is further absorbed.

Claim 14

A method for reducing the level of sound of a sound wave travelling through a duct, including the steps of: providing a travelling sound wave; providing a plurality of peripheral acoustically-absorbent elements having uniform inner diameter dimensions and having alternating first and second backing depth dimensions such that the characteristic mode of the sound wave travelling through said elements having backing depths of the first dimension is incompatible with the characteristic mode of the sound wave travelling through said elements having backing depths of said second dimension; disposing the elements in an alternating face-to-face relationship such that an integral unit having a uniform duct formed therethrough is formed; introducing said travelling sound wave into the integral unit, whereby the sound wave travels through the first element and is partially absorbed therein; and at the interface between the first and second elements it is partially reflected back into the first element being further absorbed therein and is partially transmitted into the second element wherein it is further absorbed and at the interface between the second and third elements it is again partially reflected and partially transmitted into the second and third elements, respectively, and further absorbed therein and wherein that portion of the wave transmitted into the third element is emitted from the integral unit at a reduced level of sound and wherein that portion of the wave reflected back into the second element is partially reflected and transmitted at each element interface and is further absorbed.