U.S. patent number 3,881,569 [Application Number 05/394,833] was granted by the patent office on 1975-05-06 for soundproofing panel construction.
Invention is credited to William O. Evans, Jr..
United States Patent |
3,881,569 |
Evans, Jr. |
May 6, 1975 |
SOUNDPROOFING PANEL CONSTRUCTION
Abstract
A soundproofing panel particularly suited for use in a sound
control cabinet for machinery. In its preferred form, the panel
comprises in respective laminations a relatively rigid,
sound-admitting, perforate wall formed of a matrix of large
apertures for mechanical strength and a matrix of small apertures
for blocking penetration by small or relatively pointed objects, an
acoustically transparent membrane for excluding foreign material, a
void layer of sound-absorbing material, and an acoustically limp,
imperforate wall of high mass-per-unit area for preventing
transmission of residual sound through the imperforate wall from
the sound-absorbing material.
Inventors: |
Evans, Jr.; William O. (Hudson,
OH) |
Family
ID: |
23560600 |
Appl.
No.: |
05/394,833 |
Filed: |
September 6, 1973 |
Current U.S.
Class: |
181/200;
428/137 |
Current CPC
Class: |
G10K
11/16 (20130101); B32B 27/40 (20130101); B32B
27/065 (20130101); B32B 27/08 (20130101); E04B
1/8218 (20130101); E04B 2001/8452 (20130101); B32B
2307/10 (20130101); B32B 2311/24 (20130101); E04B
2001/8433 (20130101); A47B 2220/13 (20130101); Y10T
428/24322 (20150115) |
Current International
Class: |
E04B
1/82 (20060101); G10K 11/00 (20060101); G10K
11/16 (20060101); E04B 1/84 (20060101); E04b
001/86 () |
Field of
Search: |
;181/33G,33GA,33GB,63,72
;161/41,116,68 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
US. Pat. No. 3,770,560, Nov. 6, 1973, filed 10/21/71, Elder et
al.,.
|
Primary Examiner: Wilkinson; Richard B.
Assistant Examiner: Miska; Vit W.
Attorney, Agent or Firm: McNenny, Farrington, Pearne &
Gordon
Claims
What is claimed is:
1. A soundproofing panel for covering machinery comprising, in
successive laminations, a relatively rigid perforate wall, a thin
sound-transmitting membrane, a relatively thick layer of low
density void sound-absorbing material, and a layer of acoustically
limp material of substantially greater density than said void
sound-absorbing material, said membrane being formed of an
imperforate, nonporous material that is chemically inert and
substantially unaffected by fluids normally encountered in
machinery environments, said perforate wall having an effective
open area for sound transmission to said sound-absorbing material
of at least 30 percent of its total area and having a mechanical
strength sufficient to protect the membrane from puncture when
struck by inadvertent blows from rigid objects, said membrane
preventing passage of machinery fluids through said perforate wall
into said void material and thereby avoiding contamination and loss
of the sound-absorbing performance of said material.
2. A panel as set forth in claim 1, wherein said perforate wall
comprises a first sheet having relatively small apertures and a
second sheet having relatively large apertures.
3. A panel as set forth in claim 2, wherein said sheet of small
apertures is arranged between said sheet of large apertures and
said membrane.
4. A soundproofing panel for covering machinery comprising a
substantially rigid perforate wall and a layer of void relatively
non-rigid sound-absorbing material adjacent to and substantially
coextensive with said perforate wall, said perforate wall having an
open area of at least 30 percent of its total area, said perforate
wall having a set of large openings therein at a first plane and a
set of small openings at a second plane, said large openings having
dimensions of the same order of magnitude as the thickness of the
panel, said small openings having dimensions of at least one order
of magnitude smaller than the thickness of the panel, a
sound-transmitting membrane between said perforate wall and said
sound-absorbing material, said membrane being formed of a material
substantially impervious to fluids normally found in machinery
operations.
5. A panel as set forth in claim 4, wherein said plane of small
openings is between said plane of large openings and said
sound-absorbing material.
6. A panel as set forth in claim 4, wherein said rigid wall
comprises a pair of separately formed apertured sheets, one of said
sheets providing said large openings and the other sheet providing
the small openings.
7. A panel as set forth in claim 6, wherein said other sheet is
disposed between said one sheet and said sound-absorbing
material.
8. A panel as set forth in claim 7, wherein said one sheet
comprises expanded sheet metal stock.
9. A panel as set forth in claim 8, wherein said other sheet
comprises wire fabric.
10. A panel as set forth in claim 9, wherein said sheets are both
formed of aluminum.
11. A panel as set forth in claim 4, wherein said panel includes an
acoustically limp imperforate wall on a side of said
sound-absorbing material opposite said rigid perforate wall.
12. A soundproofing panel comprising in successive, substantially
coextensive laminations, a perforate rigid wall having an effective
open area of at least 30 percent of its total area to reduce its
acoustical reflecting and dampening properties, a layer of void
sound-absorbing material, and an imperforate high acousitcal
transmission loss wall, said imperforate wall including
nonstructural high density material of the order of at least 1
pound per square foot, said perforate wall having substantially
less mass-per-unit area than said imperforate wall, while providing
substantially more rigidity to the panel per-unit-mass than said
perforate wall, a sound-transmitting imperforate membrane adjacent
said perforate wall to prevent entrance of foreign material into
said sound-absorbing material, said membrane being substantially
chemically inert whereby it is impervious to fluids normally
encountered in machinery operations.
13. A panel as set forth in claim 12, wherein said membrane is
disposed between said perforate wall and said sound-absorbing
material, whereby said membrane is protected from puncture by said
perforate wall.
14. A panel as set forth in claim 13, wherein said perforate wall
comprises a first matrix having apertures of relatively large size
and a second matrix superimposed over the apertures of the first
matrix and having apertures of relatively small size, the first
matrix providing the major portion of the rigidity of the perforate
wall.
15. A panel as set forth in claim 14, wherein said matrices are
arranged in separate planes.
16. A panel as set forth in claim 15, wherein the plane of the
second matrix is between the plane of the first matrix and said
membrane.
17. In combination, a rectangular rigid framework adapted to be
positioned over a machine, a plurality of self-supporting
soundproofing panels on the framework, said panels including an
inner perforate wall, an imperforate outer wall spaced from the
inner perforate wall, a relatively thick layer of low density void
sound-absorbing material between said walls, said perforate wall
being formed of two separately formed perforate laminae, one of
said perforate laminae being relatively rigid and having relatively
large apertures, the other of said perforate laminae having
relatively small apertures and being disposed between said one
perforate lamina and said sound-absorbing material, an acoustically
transparent, substantially chemically inert membrane between said
other lamina and said sound-absorbing material, said membrane
preventing entrance of foreign material into said sound-absorbing
material, said perforate wall protecting said membrane from
physical damage, said imperforate wall being acoustically limp as a
result of a relatively high mass-per-unit area and relatively low
rigidity, the stiffness to mass-per-unit area ratio of said
perforate wall being substantially greater than the corresponding
ratio of stiffness to mass-per-unit area of said imperforate
wall.
18. The combination of claim 17 in which said imperforate outer
wall comprises two separately formed imperforate laminae, one being
a relatively thin inner limina of sheet lead and the other being a
relatively thicker, non-metallic, outer lamina of substantially
greater stiffness than the sheet lead for supporting and protecting
the sheet lead against physical damage.
19. The combination of claim 17 in which said imperforate outer
wall comprises two separately formed imperforate laminae, one being
a relatively thin inner lamina of sheet lead and the other being a
relatively thicker, outer lamina of substantially greater stiffness
than the sheet lead for supporting and protecting the sheet lead
against physical damage.
Description
BACKGROUND OF THE INVENTION
The invention relates to sound-absorbing panels and, more
specifically, to a panel construction particularly adapted for
control of machinery-generated noise in industrial and commercial
environments.
DESCRIPTION OF THE PRIOR ART
Medical and social awareness of the permanent, destructive effect
of noise on human hearing has resulted in growing legislation and
social pressure directed to abatement of excessive machine-based
noise. Technical and economic factors often favor arrangements for
absorbing or muffling machine-generated noise rather than or in
combination with efforts to eliminate the actual noise sources.
A known technique for controlling excessive noise is the provision
of an acoustic cover or jacket over a machine or critical portion
of a machine to absorb the noise generated by it. The interior of
the enclosure is thus acoustically isolated from the surrounding
personnel space. Various panel constructions have been proposed for
use in these applications, such as illustrated in U.S. Pat. Nos.
3,322,233 and 3,478,958.
Besides providing adequate sound control, it is important that an
acoustic panel be suitable for its intended environment. Prior
panel arrangements have exhibited varying degrees of
sound-absorbing effectiveness but have not always been equal to the
rigors of industrial and commercial service. Panels have often been
susceptible to both immediate and cumulative loss of efficiency as
the result of exposure to dirt-laden atmospheres and to fluids,
such as water or water vapor, lubricants, detergents, and other
chemicals, which in one manner or another come into contact with
the sound-absorbing material of the panel and, by saturating it,
greatly diminish its performance.
SUMMARY OF THE INVENTION
The invention provides an integrated, self-supporting panel
structure having a plurality of laminations each producing an
acoustic or structural function, or both. The elements comprising
the various panel layers, and their respective arrangement, provide
an efficient combination for maximum sound control and structural
integrity. The acoustic panel, in accordance with the invention,
comprises a pair of spaced walls, one perforate and the other
imperforate, and an intermediate body of sound energy-absorbing
material. When assembled as a machine enclosure, the perforate wall
faces the interior of the enclosure or cabinet, while the
imperforate wall provides the exterior cabinet surface.
The inner perforate wall permits substantially free passage of
sound into the sound-absorbing medium, contributes a large portion
of the stiffness of the self-supporting panel, and protects the
interior of the panel from physical damage. The imperforate wall,
normally forming the visible exterior of a cabinet, is an
"acoustically limp"structure characterized by a relatively high
sound transmission loss factor such that it reflects a substantial
portion of the sound energy which reaches it back into the
sound-absorbing medium. Such a wall should have a sound
transmission class value in the range from about 20 to about 40.
The sound energy-absorbing material sandwiched between the
perforate wall on one side of the panel and the imperforate wall on
the other side of the panel should be a high-void material having a
noise reduction coefficient ("NRC") in the range of about 0.70 to
about 0.90.
In the preferred embodiment, the perforate wall includes two
superimposed matrices each presenting a different aperture size.
The first matrix is preferably a sheet of expanded sheet metal
having relatively large apertures and of sufficient gauge and body
to provide requisite panel stiffness and physical protection for
the panel interior. The second matrix, interior of the expanded
metal matrix, is formed of wire cloth having an opening size
substantially less than that of the expanded metal matrix. The wire
cloth is adapted to complement the protection afforded by the
expanded metal by blocking the latter's larger apertures to objects
of measurable size, while maintaining sufficient open area for
passage of sound into the sound-absorbing material.
The interior of the panel contains sound-absorbing material,
typically a hollow or unfilled mass of cellular, fibrous, or
granular structure, such as sound-absorbing polyurethane foam. A
sound-transmitting membrane, ideally a film of chemically inert
plastic film, is positioned between the perforate wall and the
sound-absorbing material. The membrane is acoustically transparent
but prevents entrance of solid and fluid contaminants into the
sound-absorbing material, which, by its unfilled nature, is
generally pervious to such contaminants.
The imperforate outer wall has a relatively high mass and low
stiffness to provide a sound-reflecting layer by which
substantially more energy is reflected back into the sound absorber
than is transmitted into surrounding space. In the disclosed
embodiment, the imperforate wall is composed of an inner sheet of
lead and an adjacent outer sheet of high density plastic material
that is relatively stiff compared to the lead sheet for supporting
and protecting the lead sheet against physical damage, but soft
enough to have substantial sound-reflecting properties. Thus, the
sheets of lead and plastic material, together, provide a high mass
for the imperforate wall, while the plastic sheet additionally
provides exterior protection against physical damage and an
attractive appearance at the exterior surface of the panel, and may
be colored and/or decoratively embossed for the latter purpose. A
laminated panel constructed in accordance with the invention
provides a high degree of sound attenuation within practical limits
of overall weight and material cost, while providing a high
resistance to physical and chemical damage, an attractive
appearance, and good cleanability of both interior and exterior
surfaces.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a soundproofing cabinet assembly
for isolating and absorbing the noise produced by an enclosed
machine;
FIG. 2 is a perspective view of a typical self-supporting panel
constructed in accordance with the invention;
FIG. 3 is a perspective view, on an enlarged scale, of a
fragmentary section of the panel with various portions of its
elements broken away to reveal its constructional details; and
FIG. 4 is a fragmentary, cross sectional view, on an enlarged
scale, of a panel taken along the line 4--4 of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Noise generated by operation of machinery, such as a screw machine
10 or other machine tool, may be absorbed and isolated from a room
or other area in which it is operated by enclosing it with a
soundproof shell or cabinet, generally indicated at 11. As
illustrated, the cabinet assembly 11 comprises a rectangular,
rigid, skeletal frame 12 on which are mounted a plurality of
generally rectangular, planar panels 13. The frame 12 is formed of
lengths of angle iron 16 or other structural elements, welded or
otherwise secured into a three-dimensional, rectangular form large
enough to surround the machine 10. As in most instances, the
cabinet 11 does not include a separate horizontal floor panel, but
is arranged with its side panels closely adjacent the floor
supporting the machine 10 to prevent escape of noise energy from
the cabinet interior.
At least several of the panels 13a may be movably mounted on the
frame 12, such as by hinges 17, for access to the machine 10 for
adjustment, repair, etc. The specific details of the frame 12, its
configuration, and the manner of mounting the panels 13 thereon
form no part of the present invention except for generally
illustrating one manner of arranging the panels 13 in relationship
to a machine tool.
As shown in FIGS. 2 and 4, each panel 13 ideally includes a
perimeter frame 19 of U cross section. The perimeter frame 19 is
formed of aluminum or other structural metal, and may be fabricated
by welding or otherwise securing appropriate lengths of U stock at
its corners 21. The frame 19 contributes to the rigidity of the
panel 13 and sandwiches or holds together various layers or
laminations of the panel described below. Each panel 13 is
preferably self-supporting, either in a vertical or a horizontal
orientation, so that the panels 13 require no support at their
midportions or within the boundaries of the perimeter frame 19. The
panels 13 consequently may be mounted on the cabinet frame 12 by
suitable fasteners (not shown) without additional bridging to
otherwise prevent the panels from excessive flexing or sagging.
Referring now in particular to FIGS. 3 and 4, the main body of the
panel 13 comprises a plurality of coextensive layers in the form of
a perforate wall 26, a sound-absorbing layer or medium 27, and an
imperforate wall 28. With the panels 13 forming a machine enclosure
such as the cabinet 11, the perforate wall 26 faces the interior of
the cabinet. Ideally, the perforate wall 26 comprises two matrices,
here represented by separate sheets 31 and 32, defining apertures
of substantially different size. The outer sheet 31, in the
illustrated embodiment, is formed of expanded, flattened sheet
metal, with an open area of, for example, 60 percent of its total
area. The inner perforate sheet 32 is formed of an open weave
fabric, such as wire cloth commonly used for window screening.
Apertures 33 of the expanded metal 31 are preferably in the range
of 1/2 by 1 inch, for example, while the screen is about 16 mesh
per inch, so that the difference in aperture size between these
sheets is one or more orders of magnitude. The open area of the
screen 32 should not be less than 50 percent, and is preferably in
the range of 60 to 70 percent so that the total effective open area
of the perforate wall 26 is not less than 30 percent and,
preferably, is around 35 percent or more of its total area.
The sound-absorbing layer 27 is relatively thick in comparison with
the remaining layers of the panel 13, and comprises a low density
void material usually either cellular, fibrous, or granular in
structure. Such material, as is understood by those skilled in the
art, absorbs sound energy passing into it by converting it to heat.
Ideally, the material 27 is a semi-rigid foam having sufficient
compressive strength to maintain the opposed walls 26 and 28 apart
at least against their own weight when disposed in a horizontal
orientation without excessive compression of its overall
thickness.
A membrane 36 of chemically inert material, such as an inert
plastic film, is disposed between the sound-absorbing material 27
and the perforate wall 26. The membrane 36 may have a thickness in
the range of 0.5 to 4 mils, but is preferably about 1.5 mils thick.
Owing to its negligible mass, this membrane is acoustically
transparent and thereby transmits substantially all of the sound
energy impinging on it, with negligible reflection. The membrane 36
prevents entrance of foreign material normally encountered in
machinery operations, particularly fluids such as water, water
vapor, lubricating greases and oils, detergents and chemical
cleaners, into the sound-absorbing material. Permeation of such
materials into the sound-absorbing medium 27, by filling its voids,
greatly diminishes its sound-absorbing characteristics.
As illustrated, the outer imperforate wall 28 includes two separate
sheets or layers 38 and 39 of acoustically limp material. The inner
sheet 38 is formed of extremely high density, low rigidity
material, such as lead sheet stock having a density of
approximately 1 pound per square foot and an stc factor of about 22
to 23. The outer sheet 39 is formed of a high density plastic, and
preferably has an stc factor of about 15 or more. In combination,
the lead and plastic sheets 38 and 39 form a layer at which
substantially more sound energy is reflected back into the
sound-absorbing material 27 than is transmitted through the layer.
The zone or wall 28, owing to its relatively high-mass-per-unit
area and limited stiffness, as compared to a plain metal wall of
structural metal such as steel or aluminum, forms a high sound
transmission loss wall having an stc factor of about 30.
I have found that, in the interest of economy and simplicity of
construction, the sheet lead component of the imperforate wall 28
may be replaced by a high mass, vinyl-base sheet made from a vinyl
molding resin loaded with a dense, acoustically limp filler, such
as powdered lead, barium sulfate, or the like. Various high-mass
plastic sheet materials are available having stc factors in the
range of about 20 to about 30, in thicknesses of about one-eighth
to three-sixteenths inch weighing about 1 pound per square foot. A
one-eighth inch thick barium sulfate-loaded pvc panel weighing 1
pound per square foot has been found to be an equivalent substitute
for the sheet lead of the preferred embodiment of the invention
more specifically disclosed below, as far as sound attenuation is
concerned.
It is important that the materials and construction of the
imperforate wall 28 result in an acoustically limp structure, i.e.,
relatively high mass and relatively low stiffness, so that a
diaphragm or drum effect is not produced wherein the wall, by its
vibration, would become a secondary source of sound radiation to
the outside of the panel. In general, the sound transmission loss
of the wall 28 is proportional to its mass and inversely
proportional to its rigidity.
The expanded metal sheet 31 of the perforate wall 26, according to
the invention, provides a substantial portion of the overall panel
rigidity. The perforate wall 26 thus provides the two important
functions of protecting the interior of the panel and providing
stiffness to the panel without contributing to noise control
problems by producing a diaphragm or drum effect at the exterior of
the cabinet 11. The assembled panel 13 is thus characterized by a
pair of spaced walls in which the ratio of stiffness to
mass-per-unit area for the inner wall 26 is substantially greater
than the corresponding ratio of stiffness to mass-per-unit area at
the outer wall. It is contemplated that other equivalent
imperforate wall structures may be employed in place of the
two-layer wall 28, e.g., a single sheet of plastic filled with lead
or other high density material in particulate or pellet form.
By way of example, for panels ranging up to about 6 feet square and
a permissible thickness to about 11/4 inches, the following
construction may be used:
Expanded sheet metal (31)
Aluminum, 0.051 inch gauge, 1/2 .times. 1-inch openings, and about
60% open area
Screen (32)
Aluminum window screen having about 16 mesh/inch and about 65% open
area
Membrane (36)
1.5 mil "Tedlar" (a polyvinyl fluoride film manufactured by E. I.
DuPont de Nemours and Company)
Sound-absorbing medium (27)
Polyurethane, acoustical foam, 60 ppi (pores/inch)
Inner high transmission loss layer (38)
Sheet lead, about 1 pound/sq. foot
Outer high transmission loss layer (39)
One-eighth inch "Noryl" high density plastic sheet, about 0.75
pounds/sq. foot (a polyphenylene oxide sheet material manufactured
by General Electric Co.)
The bight section, designated 41, of the perimeter channel frame
19, is dimensioned with respect to the total thickness of the panel
layers to provide approximately one-eighth inch compression of the
sound-absorbing foam 27 along the edges thereof to maintain the
panel layers firmly together in the assembly.
The above-disclosed panel 13 is particularly suited for covering
machinery, since it is generally not susceptible to damage caused
by ordinary physical or chemical abuse. The perforate wall 26,
while allowing sufficient passage area for noise into the
sound-absorbing material 27, provides protection against
perforation of both the membrane 36 and sound-absorbing material.
The outer expanded metal matrix 31 affords protection against
inadvertent high energy blows from relatively large objects often
occurring in the handling of machinery, tools, material stock,
parts, or the panel 13 itself. The small aperture matrix 32, at the
same time, affords protection against penetration of the membrane
36 or sound-absorbing material 27 by small or relatively pointed
objects, e.g., a misdirected screwdriver, which may pass through an
aperture 33 of the expanded metal 31. The membrane 36 excludes
cutting and lubricating oils, and the like, from the
sound-absorbing material 27, and permits the expanded metal 31 and
mesh 32 to be periodically washed with detergents or chemical
cleaners without these fluids likewise contaminating the
sound-absorbing material.
Although a preferred embodiment of the invention is illustrated, it
is to be understood that various modifications and rearrangements
of parts may be resorted to without departing from the scope of the
invention disclosed and claimed herein.
* * * * *