Patent US3887031A successfully refreshed from Google Patents.
US3887031A
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Dual-range sound absorber
Assignee: Lockheed Martin Corp
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Filing: 1973-06-11
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Granted: 1975-06-03
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Expires: 1993-06-11
Abstract
Abstract A dual-range sound absorber, comprising a cavity, a horn located within the cavity and having its larger end (mouth) communicating with the exterior of the cavity, and a permeable facing over the mouth of the horn. At a given frequency below the cutoff frequency of the horn, the inertia of the air in the horn is just compensated by the stiffness of the air in the enclosing cavity causing a helmholtz resonance to occur. This resonance is heavily damped due to the permeable facing across the mouth of the horn. Above the cutoff frequency, the horn freely propagates incoming acoustic waves but the discontinuity in area at the junction of the horn throat and the air cavity causes a reflection to occur. Thus, above the cutoff frequency the device behaves much in the manner of a conventional laminar sound absorber. By proper selection of horn, facing, and cavity parameters, the low frequency absorption zone and the high frequency absorption zone may be made to exhibit a dual characteristic so as to function well at low frequencies, without requiring excessively large volume, while still having comparable absorption efficiency at high frequencies. The functional operation of the device is relatively independent of the materials from which it is made and may, for example, be fabricated from metal, plastic, ceramic, or other materials. It is particularly suitable for sound attenuation in engines, vehicles, factories, and other applications having adverse environmental conditions.
Inventors
- 👤 Leslie S Wirt
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 17:40
CPC Classifications
G; G10; G10K; G10K11/00; G10K11/16; G10K11/172; E; E04; E04B; E04B1/00; E04B1/62; E04B1/74; E04B1/82; E04B1/84; E04B1/86; E04B2001/742; E04B2001/748; E04B2001/8423; E04B2001/8428; Y; Y10; Y10T; Y10T428/00; Y10T428/24; Y10T428/24628; Y10T428/24661
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
194 words
Wide-range apparatus for the absorption of an ambient sound field, comprising: means defining a sound-confining chamber; and, an acoustical horn having a predetermined cutoff frequency and having a sound-receiving mouth at one end and a smaller throat at the other end of the horn path, said path being characterized by a continuously changing cross-sectional area along its length, said horn being nested within said chamber so as to have said mouth acoustically coupled to the exterior of said chamber and said throat acoustically coupled to the interior of said chamber, the internal volume defined by said chamber and said horn comprising a damped helmholtz resonator whereby incoming sound above said cutoff frequency will be propagated from said mouth towards said throat whereupon said sound will be reflected back toward said mouth due to the discontinuity at the junction of said throat and said chamber, thereby causing destructive cancellation between incoming and reflected sound waves, and whereby the inertia of the air mass in said horn resulting from incoming sound below said cutoff frequency is just compensated by the air confined in said chamber so as to cause helmholtz resonance to occur within said chamber.
Claim 2
Dependent Claim
194 words
Wide-range apparatus for the absorption of an ambient sound field, comprising: means defining a sound-confining chamber; and, an acoustical horn having a predetermined cutoff frequency and having a sound-receiving mouth at one end and a smaller throat at the other end of the horn path, said path being characterized by a continuously changing cross-sectional area along its length, said horn being nested within said chamber so as to have said mouth acoustically coupled to the exterior of said chamber and said throat acoustically coupled to the interior of said chamber, the internal volume defined by said chamber and said horn comprising a damped helmholtz resonator whereby incoming sound above said cutoff frequency will be propagated from said mouth towards said throat whereupon said sound will be reflected back toward said mouth due to the discontinuity at the junction of said throat and said chamber, thereby causing destructive cancellation between incoming and reflected sound waves, and whereby the inertia of the air mass in said horn resulting from incoming sound below said cutoff frequency is just compensated by the air confined in said chamber so as to cause helmholtz resonance to occur within said chamber.
Claim 3
Dependent Claim
194 words
Wide-range apparatus for the absorption of an ambient sound field, comprising: means defining a sound-confining chamber; and, an acoustical horn having a predetermined cutoff frequency and having a sound-receiving mouth at one end and a smaller throat at the other end of the horn path, said path being characterized by a continuously changing cross-sectional area along its length, said horn being nested within said chamber so as to have said mouth acoustically coupled to the exterior of said chamber and said throat acoustically coupled to the interior of said chamber, the internal volume defined by said chamber and said horn comprising a damped helmholtz resonator whereby incoming sound above said cutoff frequency will be propagated from said mouth towards said throat whereupon said sound will be reflected back toward said mouth due to the discontinuity at the junction of said throat and said chamber, thereby causing destructive cancellation between incoming and reflected sound waves, and whereby the inertia of the air mass in said horn resulting from incoming sound below said cutoff frequency is just compensated by the air confined in said chamber so as to cause helmholtz resonance to occur within said chamber.
Claim 4
Dependent Claim
194 words
Wide-range apparatus for the absorption of an ambient sound field, comprising: means defining a sound-confining chamber; and, an acoustical horn having a predetermined cutoff frequency and having a sound-receiving mouth at one end and a smaller throat at the other end of the horn path, said path being characterized by a continuously changing cross-sectional area along its length, said horn being nested within said chamber so as to have said mouth acoustically coupled to the exterior of said chamber and said throat acoustically coupled to the interior of said chamber, the internal volume defined by said chamber and said horn comprising a damped helmholtz resonator whereby incoming sound above said cutoff frequency will be propagated from said mouth towards said throat whereupon said sound will be reflected back toward said mouth due to the discontinuity at the junction of said throat and said chamber, thereby causing destructive cancellation between incoming and reflected sound waves, and whereby the inertia of the air mass in said horn resulting from incoming sound below said cutoff frequency is just compensated by the air confined in said chamber so as to cause helmholtz resonance to occur within said chamber.
Claim 5
Dependent Claim
45 words
Apparatus as defined in claim 1 including: a permeable flow-resistive element plAced in series, acoustically, with said mouth and the ambient sound field, the flow resistance of said element being sufficient to heavily damp the resonance of said chamber at frequencies below said cutoff frequency.
Claim 6
Dependent Claim
36 words
Apparatus as defined in claim 1 wherein said chamber defining means comprises: a cylinder closed at one end by a sound-confining end wall and closed at the other end by the mouth of said acoustical horn.
Claim 7
Dependent Claim
31 words
Apparatus as defined in claim 1 wherein said throat of said horn is acoustically coupled to the interior of said chamber via an aperture in the side wall of said horn.
Claim 8
Dependent Claim
27 words
Apparatus as defined in claim 1 wherein said horn has a continous exponential taper and said mouth thereof is contiguous with the outer surface of said chamber.
Claim 9
Dependent Claim
17 words
Apparatus as defined in claim 2 wherein said flow-resistive element extends across the mouth of said horn.
Claim 10
Dependent Claim
46 words
Apparatus as defined in claim 6 wherein said flow resistive element has a flow-resistance of the order of 1 Rho c where Rho is the density of the fluid medium through which the sound is propagated and c is the velocity of sound in said medium.
Claim 11
Dependent Claim
180 words
A wide-range sound absorber, comprising: a parallel array of tuned helmholtz resonator compartments; and, a plurality of acoustical horns each having a sound-receiving mouth at one end and a smaller open throat at the other end of the horn path, each of said horns being nested within corresponding compartments so as to have the mouths thereof acoustically coupled to the exterior of said array and the throats thereof acoustically coupled to the interior of corresponding compartments, said horns being characterized by a continuously-diminishing cross-sectional area between said mouths and said throats, whereby incoming sound above said cutoff frequency will be propagated from said mouths towards said throats whereupon said sound will be reflected back toward said mouths due to the discontinuity of the junctions of said throats and said compartments, thereby causing destructive cancellation between incoming and reflected sound waves, and whereby the inertia of the air masses in said horns, resulting from incoming sound below said cutoff frequency, is just compensated by the air confined in said compartments so as to cause helmholtz resonance to occur within said compartments.
Claim 12
Dependent Claim
180 words
A wide-range sound absorber, comprising: a parallel array of tuned helmholtz resonator compartments; and, a plurality of acoustical horns each having a sound-receiving mouth at one end and a smaller open throat at the other end of the horn path, each of said horns being nested within corresponding compartments so as to have the mouths thereof acoustically coupled to the exterior of said array and the throats thereof acoustically coupled to the interior of corresponding compartments, said horns being characterized by a continuously-diminishing cross-sectional area between said mouths and said throats, whereby incoming sound above said cutoff frequency will be propagated from said mouths towards said throats whereupon said sound will be reflected back toward said mouths due to the discontinuity of the junctions of said throats and said compartments, thereby causing destructive cancellation between incoming and reflected sound waves, and whereby the inertia of the air masses in said horns, resulting from incoming sound below said cutoff frequency, is just compensated by the air confined in said compartments so as to cause helmholtz resonance to occur within said compartments.
Claim 13
Dependent Claim
29 words
A wide-range sound absorber as defined in claim 8 including: permeable flow resistance means placed in series, acoustically, with said mouths and the ambient sound field to be absorbed.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-06-02 | 1978-12-02 | 1979-06-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-06-02 | 1982-12-02 | 1983-06-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-06-02 | 1986-12-02 | 1987-06-03 | $7700.00 | Window Closed / Lapsed |