US3746114A - Sound attenuating structure - Google Patents

Sound attenuating structure Download PDF

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Publication number
US3746114A
US3746114A US00208227A US3746114DA US3746114A US 3746114 A US3746114 A US 3746114A US 00208227 A US00208227 A US 00208227A US 3746114D A US3746114D A US 3746114DA US 3746114 A US3746114 A US 3746114A
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US
United States
Prior art keywords
mat
shell
sound
attenuating structure
attenuated
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US00208227A
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English (en)
Inventor
S Sorber
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Volkswagen AG
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Volkswagen AG
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Publication date
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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
    • B60R13/00—Elements for body-finishing, identifying, or decorating; Arrangements or adaptations for advertising purposes
    • B60R13/08—Insulating elements, e.g. for sound insulation

Definitions

  • ABSTRACT A sound-attenuating structure includes a nonabsorbing shell and a mat of sound-absorbing material held parallel to and spaced from the shell a distance equal to one-quarter the wave length of the highest frequency to be attenuated.
  • the thickness of the mat of sound-absorbing material is defined by the expression:
  • This invention relates in general to sound-attenuating structures, and in particular, to an application in the automobile industry as a sound-attenuating fire wall between the engine and passenger compartments, and also as a fluid conduit such as an exhaust pipe.
  • a sound-absorbing wall having a non-absorbing shell and a sound-absorbing mat spaced from the non-absorbing shell a distance equal to one-quarter of the wave length of the highest frequency to be attenuated.
  • Another embodiment of the invention is a fluid conduit in which the non-absorbing shell forms the exterior casing of the conduit, and the spaced sound-absorbing mat is disposed interiorly of the shell and concentrically therewith, leaving an-interspatial zone between the shell and the mat for flow of fluid.
  • the thickness d of the mat of absorbent material may be calculated by the following relationship:
  • FIG. 1 is a cross section of a portion of a curved sound-absorbing wall constructed according to this invention
  • FIG. 2 is a graph in the solid curve showing the percentage of sound absorption at various frequencies for a given thickness of sound-absorbing material applied directly to a non-absorbent shell, and showing, in the broken curve, the corresponding percentage of sound absorption with the same thickness of absorbent material spaced from the non-absorbent wall according to the present invention;
  • FIG. 3 is a cross section of a conduit constructed according to the present invention.
  • FIG. 4 is a cross section of a second conduit constructed according to the present invention.
  • FIG. 5 is a cross section of a third conduit constructed according to this invention.
  • a sound-absorbing wall constructed according to the invention having a sheet metal shell 10 and a sound-absorbing acoustic panel or mat l2 spaced therefrom a uniform distance b by spacer webs 14.
  • the sound-absorbing mat 12 may be porous or open pored material, for example, or it may alsobe fibrous material. It may be compact homogeneous material or it also may be composite material formed of individual strands of sound absorbing material bound or adhering together and providing interstices or dead air spaces between the strands to con tribute to the sound absorbing properties of the material.
  • the shell 10 is typically sheet metal as in the usual construction of a fire wall between the passenger and engine compartments of an automobile. Shell 10, however, may be of any other suitable material such as plaster board or plywood as the requirements of different applications dictate.
  • the spacer webs 14 are preferably as few as possible and just enough to hold the acoustic mat 12 in position. The spacer webs 14 may take any known form and are shown schematically for purposes of illustration.
  • the interspatial dimension b between the inside face 16 of the acoustic mat l2 and the outside face 18 of the shell 10 is selected to coincide with one-quarter of the wave length of the highest frequency to be attenuated. For example, there is little utility in attenuating the frequencies that lie above the normal hearing range of a human being or frequencies which are within the hearing range but, because of the conditions in which the invention is used, are at low amplitudes or are otherwise not objectionable.
  • the acoustic particle velocity normal to the shell is zero so that sound absorbing material placed there, as it is in the prior art, does not contribute to sound absorption. This is because sound absorption is related to the acoustic velocity; the particle velocity at the particular location in the sound wave is attenuated by conversion into heat generated by viscous losses of the moving particles of the sound carrying medium within the capillary pores of the porous material, and by friction losses of the vibrating component parts of the material. Since the acoustic velocity adjacent the non-absorbing shell is zero, there is no contribution at that location to the sound attenuation. Accordingly, acoustic material placed at that location in the sound wave does not contribute to sound attenuation and merely represent wasted weight and expense.
  • the acoustic velocity is maximum at a distance from the shell 10 equal to one-fourth the wave length of the highest acoustic frequency to be absorbed.
  • the sound absorption material has the highest efficacy since that is the point of greatest amplitude of the oscillations of the particles in the sound carrying medium.
  • FIG. 2 is a graph of the relationship between the sound absorption value, measured in percent, and the acoustic frequency, measured in kilohertz for a given material.
  • The. curves reproduced have been plotted for a given static air pressure, a given air temperature and mean thickness of the sound-absorbing material.
  • the interspatial dimension b between the non-absorbing partition and the sound-absorbing panel serves to determine the highest acoustic frequency attenuated
  • the thickness of the sound-absorbing panel constitutes a further parameter which may be utilized to determine the acoustic frequency range to be absorbed.
  • the acoustic frequency range will be f -f wherein f constitutes the highest and f the lowest acoustic frequency to be attenuated.
  • the thickness d of the acoustic panel should be d i (f2 fl)]/ 'f1f2 where c is the sound propagation velocity in the ambient medium.
  • the medium present will be air; however, the invention may also be utilized in other fluid mediums having different values of c, in which case the thickness d will change proportionately.
  • the sound attenuating structure may also be constructed as a conduit wherein the shell forms the outside circumferential casing of the conduit and the mat is disposed coaxially within the shell and spaced from the interior surface thereof to leave an annular interspatial zone of uniform cross sectional width.
  • This annular interspatial zone may be used as the fluid flow zone to convey the fluid which flows in the conduit.
  • the acoustic mat disposed coaxially in the'conduit may take the form of a core 19 of solid cross section, as shown in FIG. 3.
  • the interspatial zone 24 between the interior surface 20 of the shell and the exterior surface 22 of the acoustic mat forms a free flow zone 24 for conveyance of fluid in the conduit.
  • Placement of the flow zone between the mat and the shell yields the advantage that the cross sectional area of the free flow zone 24 becomes larger than in known attenuation devices wherein the same thickness of the mat is applied directly to the shell.
  • the velocity of flow and the sound level become lower.
  • due to the concentration of the soundabsorbing material in the area of the conduit axis the effective thickness of the material is increased since it serves to absorb sound from both diametrical sides of the conduit and the exterior dimensions of the conduit remain the same while the quantity of material is reduced.
  • the sound absorbing material 19 may be subdivided axially by transversely extending partitions 23 held to the wall of conduit 10 and by means of webs 14.
  • the partitions 23 are for the purpose of preventing acoustic propagation within the absorbing material in the direction of the conduit axis and, in order not to adversely effect the free flow section 24, the web 14' is made narrow in the direction of the conduit axis.
  • the acoustic mat may take the form of an annulus 25 coaxially disposed with respect to the shell 10.
  • the cross sectional thickness d of the panel is defined by the same expression which defines the mat thickness of the sound attenuating wall shown in FIG. 1.
  • the axial zone 26 is used for conveyance of fluids through the conduit while the interspatial zone 24 may be used for fluid conveyance or may be divided into hollow chambers by partitions 23' which also divide the sound absorbing mat 25 into pieces to prevent sound propagation axially through the mat 25.
  • the dividers 23 will not extend out to the conduit wall 10 but will extend only through the mat 25 and will be connected to the conduit wall 10 by connecting webs similar to webs 14 in the embodiment of FIG. 3.
  • the mat 19' may extend laterally to contact the conduit 10 on diametrically opposite sides thereof.
  • the cross sectional area available for fluid flow is less than the embodiment of FIG. 3, but the mechanical strength of the arrangement and the simplicity of manufacturing techniques make this a desirable embodiment for some applications.
  • the embodiments of the invention disclosed herein provide sound attenuating structures which arrange the sound absorbing material to minimize weight, size and cost and make the formerly wasted space available for useful purposes.
  • the quantity of sound absorbing material used in these embodiments is less than that used in prior art structures, yet provides sound absorbing characteristics that are an improvement over the prior art.
  • a sound attenuating structure comprising;
  • a sound attenuating structure comprising:
  • a mat of sound absorbing material disposed adjacent to said shell and spaced therefrom a distance sub stantially equal to one-fourth of the wave length of the highest frequency to be attenuated, said mat having a thickness d having a value approximated by the expression:
  • f is the highest acoustic frequency to be attenuated
  • f is the lowest acoustic frequency to be attenuated
  • c is the sound propagation velocity in the ambient medium
  • a sound attenuating structure comprising:
  • a sound attenuating structure as defined in claim 3, wherein the lateral cross section of said mat comprises an annulus having an outside surface parallel to the inside surface of said shell and an inside surface defining a hollow interior of said mat.
  • f is the highest acoustic frequency to be attenu ated
  • f is the lowest acoustic frequency to be attenuated
  • c is the sound propagation velocity in the ambient medium
  • partition means extending through said mat and the annular interspatial zone between said shell and said mat and having means defining a centrally disposed opening to leave said axial passage open for fluid flow.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Building Environments (AREA)
US00208227A 1970-12-24 1971-12-15 Sound attenuating structure Expired - Lifetime US3746114A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19702063768 DE2063768A1 (de) 1970-12-24 1970-12-24 Anordnung nach Art eines Absorptionsschalldämpfers, insbesondere für Kraftfahrzeuge

Publications (1)

Publication Number Publication Date
US3746114A true US3746114A (en) 1973-07-17

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US00208227A Expired - Lifetime US3746114A (en) 1970-12-24 1971-12-15 Sound attenuating structure

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US (1) US3746114A (https=)
DE (1) DE2063768A1 (https=)
FR (1) FR2119683A5 (https=)
IT (1) IT945442B (https=)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2664418A1 (fr) * 1990-07-09 1992-01-10 Bertin & Cie Dispositif d'absorption d'energie acoustique emise a l'interieur d'une coque de navire et ecran acoustique modulaire formant partie d'un tel dispositif.
US20160185442A1 (en) * 2014-05-13 2016-06-30 The Boeing Company Method and apparatus for reducing structural vibration and noise

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4137706C2 (de) * 1991-11-15 1997-02-06 Bayerische Motoren Werke Ag Schallabsorbierende Wärmeisolierung

Citations (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US22283A (en) * 1858-12-14 fairfieli
US2017744A (en) * 1934-04-30 1935-10-15 Maxim Silencer Co Sound attenuating device
US2051515A (en) * 1935-10-07 1936-08-18 Maxim Silencer Co Sound attenuating device
US2056608A (en) * 1933-12-22 1936-10-06 C F Burges Lab Inc Silencer
US2059487A (en) * 1932-10-31 1936-11-03 Halsey W Taylor Company Muffler
US2271892A (en) * 1936-07-15 1942-02-03 Maxim Silencer Co Sound attenuating device
US2311676A (en) * 1941-07-02 1943-02-23 Maxim Silencer Co Silencer
US2326612A (en) * 1940-11-25 1943-08-10 Maxim Silencer Co Silencer
GB733329A (en) * 1952-11-12 1955-07-06 Lothar Cremer Improvements in or relating to ducts having sound-absorbing walls for the conductionof gaseous fluids
US2759556A (en) * 1952-08-04 1956-08-21 Bolt Beranek & Newman Acoustic method and system
FR1226438A (fr) * 1958-10-09 1960-07-11 Silencieux pour l'écoulement des fluides
US3113634A (en) * 1958-07-11 1963-12-10 Bolt Beranek & Newman Sound absorbing panel for lining a duct
US3353626A (en) * 1963-12-09 1967-11-21 Cremer Lothar Sound absorbing ventilation conduit with side branch chambers

Patent Citations (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US22283A (en) * 1858-12-14 fairfieli
US2059487A (en) * 1932-10-31 1936-11-03 Halsey W Taylor Company Muffler
US2056608A (en) * 1933-12-22 1936-10-06 C F Burges Lab Inc Silencer
US2017744A (en) * 1934-04-30 1935-10-15 Maxim Silencer Co Sound attenuating device
US2051515A (en) * 1935-10-07 1936-08-18 Maxim Silencer Co Sound attenuating device
US2271892A (en) * 1936-07-15 1942-02-03 Maxim Silencer Co Sound attenuating device
US2326612A (en) * 1940-11-25 1943-08-10 Maxim Silencer Co Silencer
US2311676A (en) * 1941-07-02 1943-02-23 Maxim Silencer Co Silencer
US2759556A (en) * 1952-08-04 1956-08-21 Bolt Beranek & Newman Acoustic method and system
GB733329A (en) * 1952-11-12 1955-07-06 Lothar Cremer Improvements in or relating to ducts having sound-absorbing walls for the conductionof gaseous fluids
US3113634A (en) * 1958-07-11 1963-12-10 Bolt Beranek & Newman Sound absorbing panel for lining a duct
FR1226438A (fr) * 1958-10-09 1960-07-11 Silencieux pour l'écoulement des fluides
US3353626A (en) * 1963-12-09 1967-11-21 Cremer Lothar Sound absorbing ventilation conduit with side branch chambers

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2664418A1 (fr) * 1990-07-09 1992-01-10 Bertin & Cie Dispositif d'absorption d'energie acoustique emise a l'interieur d'une coque de navire et ecran acoustique modulaire formant partie d'un tel dispositif.
WO1992000874A1 (fr) * 1990-07-09 1992-01-23 Societe Bertin & Cie Dispositif d'absorption d'energie acoustique emise a l'interieur d'une coque de navire et ecran acoustique modulaire formant partie d'un tel dispositif
US20160185442A1 (en) * 2014-05-13 2016-06-30 The Boeing Company Method and apparatus for reducing structural vibration and noise
US9725154B2 (en) * 2014-05-13 2017-08-08 The Boeing Company Method and apparatus for reducing structural vibration and noise

Also Published As

Publication number Publication date
DE2063768A1 (de) 1972-07-13
FR2119683A5 (https=) 1972-08-04
IT945442B (it) 1973-05-10

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