US3913702A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Cellular sound absorptive structure
Assignee: Lockheed Martin Corp
•
Filing: 1974-04-08
•
Granted: 1975-10-21
•
Expires: 1994-04-08
Abstract
Abstract A sound absorbing structure comprising an orthogonal array of like cells, wherein each cell comprises a bundle of parallel, terminated, acoustical waveguides. The bundle of waveguides is cut obliquely so that individual waveguides vary substantially in length along the cut. The total admittance of acoustical energy to each absorber cell is the sum of the individual admittances of the waveguides comprising the bundle. The cell (unit bundle) structure is repeated throughout the array. A sound wave arriving at the open end of any cell in the array will encounter at least one waveguide which is effectively resonant at the frequency of the arriving wave. The admittance for the resonant waveguide will be large; the rest of the waveguides will not be resonant to that frequency (admittance is small). The local resonance serves to absorb acoustic energy at its frequency from an area up to about lambda 2/ pi , where lambda is the wavelength of the sound to be absorbed. Operation of the structure is relatively independent of the materials from which it is made and is particularly suitable for sound attenuation in jet engines, high-velocity gas flow ducts, and other applications having similar adverse environmental conditions.
Inventors
- 👤 Leslie S Wirt
- 👤 Duane L Morrow
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 06:21
CPC Classifications
G; G10; G10K; G10K11/00; G10K11/16; G10K11/172; B; B64; B64D; B64D33/00; B64D33/04; B64D33/06; Y; Y10; Y10T; Y10T428/00; Y10T428/24; Y10T428/24149; Y10T428/24165
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
131 words
A sound absorbing panel comprising: first and second spaced-apart waveguide arrays each comprising a plurality of side-by-side acoustical waveguides of non-uniform length and having adjacent open ends defining the soundreceiving end of the array, the sound receiving end of like waveguides in each of said arrays being spaced from each other by a distance not more than approximately the wavelength of the highest frequency to be absorbed divided by the square root of pi; and a plurality of waveguide terminating means each of which is disposed with respect to a corresponding one of said waveguides at the end thereof opposite said open end so as to result in that one waveguide having a resonant frequency that is different from the resonant frequencies of those waveguides having different lengths, comprising said array.
Claim 2
Dependent Claim
131 words
A sound absorbing panel comprising: first and second spaced-apart waveguide arrays each comprising a plurality of side-by-side acoustical waveguides of non-uniform length and having adjacent open ends defining the soundreceiving end of the array, the sound receiving end of like waveguides in each of said arrays being spaced from each other by a distance not more than approximately the wavelength of the highest frequency to be absorbed divided by the square root of pi; and a plurality of waveguide terminating means each of which is disposed with respect to a corresponding one of said waveguides at the end thereof opposite said open end so as to result in that one waveguide having a resonant frequency that is different from the resonant frequencies of those waveguides having different lengths, comprising said array.
Claim 3
Dependent Claim
25 words
A sound absorbing panel as defined in claim 1 including: an impermeable backing sheet disposed adjacent the ends of said waveguides opposite said open ends.
Claim 4
Dependent Claim
22 words
A sound absorbing panel as defined in claim 1 including: a relatively sound-transparent facing sheet overlying the sound-receiving ends of said arrays.
Claim 5
Dependent Claim
27 words
A sound absorbing panel as defined in claim 1 including: a permeable, flow-resistive, facing sheet spaced apart from and extending across the sound-receiving ends of said arrays.
Claim 6
Dependent Claim
18 words
A sound absorbing panel as defineD in claim 1 wherein each of said waveguides has an hexagonal cross-section.
Claim 7
Dependent Claim
18 words
A sound absorbing panel as defined in claim 1 wherein each of said arrays has a square cross-section.
Claim 8
Dependent Claim
27 words
A sound absorbing panel as defined in claim 1 wherein said terminating means comprises: a planar impermeable sheet closing like ends of the waveguides comprising each array.
Claim 9
Dependent Claim
34 words
A sound absorbing panel as defined in claim 7 wherein said planar impermeable sheet is disposed at an angle, with respect to said sound-receiving end of the array, which is > or = 30*.
Claim 10
Dependent Claim
172 words
A sound absorbing structure, comprising: a plurality of acoustical waveguides having dissimilar lengths such that ln (l-n Delta )lo, where lo is equal to the length of the longest of said waveguides ln is the length of the nth waveguide and n is an index number 0,1,2,3, and Delta is the decrement of length, said waveguides having their sound-receiving ends in mutual proximity; and, a plurality of terminating means, equal in number to the number of said waveguides, each of which acoustically terminates a corresponding one of said waveguides at the end thereof away from the sound-receiving end, said plurality of waveguides being disposed with respect to each other in such a way that for any one waveguide of a first given length other than the shortest of said wave guides there is another waveguide approximately half as long as said first given length with its sound-receiving end disposed with respect to the sound-receiving end of said one waveguide, at a center-to-center distance which is not greater than said first given length.
Claim 11
Dependent Claim
172 words
A sound absorbing structure, comprising: a plurality of acoustical waveguides having dissimilar lengths such that ln (l-n Delta )lo, where lo is equal to the length of the longest of said waveguides ln is the length of the nth waveguide and n is an index number 0,1,2,3, and Delta is the decrement of length, said waveguides having their sound-receiving ends in mutual proximity; and, a plurality of terminating means, equal in number to the number of said waveguides, each of which acoustically terminates a corresponding one of said waveguides at the end thereof away from the sound-receiving end, said plurality of waveguides being disposed with respect to each other in such a way that for any one waveguide of a first given length other than the shortest of said wave guides there is another waveguide approximately half as long as said first given length with its sound-receiving end disposed with respect to the sound-receiving end of said one waveguide, at a center-to-center distance which is not greater than said first given length.
Claim 12
Dependent Claim
25 words
A sound absorbing structure as defined in claim 9 including: a relatively sound-transparent, flow resistive, sheet covering said sound-receiving ends of said plurality of waveguides.
Claim 13
Dependent Claim
16 words
A sound absorbing structure as defined in claim 9 wherein said waveguides comprise contiguous honeycomb cells.
Claim 14
Dependent Claim
33 words
A sound absorbing structure as defined in claim 11 including: an impermeable backing sheet; and, honeycomb cell support means interposed between, and abutting, said plurality of end closing means and said backing sheet.
References Cited (Backward Citations)
US1878409A
Cited
US2916101A
Cited
US2975853A
Cited
US3177970A
Cited
US3180448A
Cited
US3144913A
Cited
US3353626A
Cited
US3439774A
Cited
US3437173A
Cited
US3481427A
Cited
US3734234A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-10-20 | 1979-04-21 | 1979-10-21 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-10-20 | 1983-04-21 | 1983-10-21 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-10-20 | 1987-04-21 | 1987-10-21 | $7700.00 | Window Closed / Lapsed |