Free flow sound attenuating device and method of making

A device for attenuating the sound level in a fluid flowing therethrough, comprising:

• a conduit with one end an inlet and the other end the outlet and having a central foraminous portion;
• a layer of sound absorbing material surrounding the foraminous portion of the conduit to define a covered conduit, the sound absorbing material continuously increasing in thickness from the inlet to the outlet of the covered conduit;
• and,
• a housing surrounding the covered conduit and secured to the inlet and outlet to define a plurality of quarter-wave standing wave cavities in series after the inlet in operative association with the covered conduit.

A method of making a device for attenuating the sound level in a fluid flowing therethrough, comprising the steps of:

• providing a conduit with one end being the inlet and the other end the outlet, the conduit having a central foraminous portion between the inlet and outlet;
• applying a sound absorbing material on the periphery of the foraminous portion of the conduit to define a covered conduit, the sound absorbing material having a static flow resistance continuously increasing from the inlet to the outlet of the covered conduit;
• providing a housing around the covered conduit, the housing secured to the conduit at the inlet and outlet ends, the housing defining a space between the covered conduit and the housing;
• and,
• providing a plurality of plates in the space between the covered conduit and inner surface of the housing to define a plurality of quarter-wave standing wave cavities in series after the inlet end in operative association with the covered conduit.

A method of making a device for attenuating the sound level in a fluid flowing therethrough, comprising the steps of:

• providing a conduit with one end being the inlet and the other end the outlet, the conduit having a central foraminous portion between the inlet and outlet;
• applying a sound absorbing material on the periphery of the foraminous portion of the conduit to define a covered conduit;
• providing a housing around the covered conduit, the housing secured to the conduit at the inlet and outlet ends, the housing defining a space between the covered conduit and housing;
• compression rolling the sound absorbing material with increased pressure from the inlet to the outlet of the covered conduit, thereby increasing the density and static flow resistance of the material;
• and,
• providing a plurality of plates in the space between the covered conduit and inner surface of the housing to define a plurality of quarter-wave standing wave cavities in series after the inlet end in operative association with the covered conduit.

A method of making a device for attenuating the sound level in a fluid flowing therethrough, comprising the steps of:

• providing a conduit with one end being the inlet and the other end the outlet, the conduit having a central foraminous portion between the inlet and outlet.
• spirally winding a filamentary material in a back and forth overlapped fashion on the exterior surface of the foraminous portion of the conduit to form a sound absorbing layer covering the conduit and having a preselected static flow resistance;
• providing a housing around the covered conduit, and secured thereto at the inlet and outlet defining a space there between;
• and,
• providing a plurality of plates in the space between the covered conduit and the inner surface of the housing to define the plurality of quarter-wave standing wave cavities in operative association with the covered conduit