Septumization of honeycomb sandwiches

1. A method of producing an acoustic liner having a honeycomb core comprising cells, the method comprising:

forming an inner facesheet comprising perforations:

forming a septa insert comprising an array of septum in a sheet comprising a porous material, the septa insert comprising integrally formed, one-piece unitary construction containing the array of septum, each septum comprising sides angling, relative to sound waves propagating into the honeycomb core from the perforations in the inner facesheet, and every side of each septum joining at a tip of the each septum;

nesting, in at least one septum in the array of septum, a nested septum comprising perforated sides angling, relative to sound waves propagating into the honeycomb core from the perforations in the inner facesheet, every side of the nested septum joining at a tip of the nested septum, and a cross-sectional shape different than a cross-sectional shape of the at least one septum; and

septumizing the honeycomb core via inserting the septa insert, tips first, into the cells of the honeycomb core, such that each cell of the cells of the honeycomb core receives a septum of the septa insert; and

adhering the inner facesheet to the septa insert.

2. The method of claim 1 , wherein forming the septa insert is performed by one of:

injection molding a plastic; and

thermo-forming a sheet of plastic.

3. The method of claim 1 , wherein inserting the septa insert is performed by inserting the septa insert substantially simultaneously into the cells of the honeycomb core.

4. The method of claim 1 , wherein inserting the septa insert is performed by inserting the septa insert as a group through a top of the honeycomb core.

5. The method of claim 1 , wherein inserting the septa insert is performed by inserting the septa insert as a group through a bottom of the honeycomb core.

6. The method of claim 1 , wherein forming the septa insert includes:

forming a plurality of substantially hollow cones, and

selecting volumes for the hollow cones that form resonant cavities.

7. The method of claim 6 , further comprising:

bonding the septa insert to the honeycomb core by placing a reticulated film adhesive between the septa insert and edges of cells in the honeycomb core.

8. A method for attenuating sound in a honeycomb core comprising cells, the method comprising:

forming an inner facesheet comprising perforations:

adhering the inner facesheet across one side of the honeycomb core;

forming a single continuous septa sheet, comprising a porous material, the septa sheet comprising an array of septum, each septum comprising sides angling relative to sound waves propagating into the honeycomb core from the perforations in the inner facesheet, and every side of each septum joining at a tip of the each septum;

nesting, in at least one septum in the array of septum, a nested septum comprising perforated sides angling, relative to sound waves propagating into the honeycomb core from the perforations in the inner facesheet, every side of the nested septum joining at a tip of the nested septum, and a cross-sectional shape different than a cross-sectional shape of the at least one septum;

installing the septa sheet, tips first, into the honeycomb core from a side of the honeycomb core opposite the inner facesheet, such that each cell of the cells of the honeycomb core receives a septum of the septa sheet;

adhering an outer facesheet to the septa sheet.

9. The method of claim 8 , further comprising:

choosing a size and shape for each septum resulting in the each septum functioning as Helmholtz resonators.

10. The method of claim 8 , further comprising:

forming the sheet comprising a nested septum within at least one of the each septum, such that the nested septum comprises a perforated material selected from at least one of: a plastic sheet, and a metal sheet, that differs from the porous material and the cross-sectional shape of the at least one of the each septum.

11. The method of claim 8 , further comprising:

using the each septum to form multiple acoustic cell inserts based on acoustic requirements and geometric cell tolerances of the honeycomb core.

12. The method of claim 8 , further comprising:

forming the each septum with substantially uniform heights.

13. The method of claim 8 , further comprising:

forming the each septum with non-uniform heights to adjust acoustic performance based on characteristics of a noise source.

14. The method of claim 8 , further comprising:

providing a sheet of porous material; and

forming the each septum into the sheet.

15. A method of septumizing a honeycomb core, the method comprising:

attaching a porous inner facesheet to the honeycomb core comprising cells comprising polygon shapes;

installing a sheet comprising an array of septum into the honeycomb core, such that each cell of the cells of the honeycomb core receives a septum of the sheet; the sheet comprising a porous material such that a size, shape, depth, and porosity of each septum in the array of septum vary depending upon a desired tuning attenuation desired respectively for each cell in the honeycomb core occupied respectively by each septum in the array of septum, each septum comprising sides angling relative to sound waves propagating into the honeycomb core from perforations in the porous inner facesheet, and every side of each septum joining at a tip of the each septum, and at least one septum in the array of septum comprising a nested septum comprising perforated sides angling, relative to sound waves propagating into the honeycomb core from the perforations in the inner facesheet, every side of the nested septum joining at a tip of the nested septum, within the at least one septum.

16. The method of claim 15 , wherein installing the sheet includes adhesively bonding the sheet to the honeycomb core.

17. The method of claim 16 , wherein adhesively bonding the sheet to the honeycomb core includes placing a reticulated film adhesive between edges of the cells of the honeycomb core and the sheet.

18. The method of claim 15 , wherein installing the sheet includes inserting the septum respectively into the cells of the honeycomb core.