Note: Descriptions are shown in the official language in which they were submitted.
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ACOUSTICAL WALL BOARD AND WALL SYSTEM
FIELD OF THE INVENTION
The invention is generally directed toward the field of wallboard, and more
particularly to the fields of composite wallboard and acoustical wallboard
composition,
and is also directed toward the field of Acoustical Wall Systems.
BACKGROUND OF THE INVENTION
In the art of sound attenuation, it is known to use resilient channel to
decouple
plasterboard (also known as drywall) from the stud wall to which it is
attached. This is
depicted in Fig. 1, where a stud wall 102 is formed of a base plate 104 to
which are
attached vertical studs 106. A header (not depicted) is typically found at the
top of the
studs 106 in a position opposite to the base plate 104. Typically, the base
plate, studs and
header are formed of "2x4" material, made either of wood or steel. Strips of
resilient
(steel) channel 108 are mounted perpendicularly to the studs 106. A sheet of
drywall 110
is attached to the strips of resilient channel 108.
Fig. 2 depicts a cross-section of Fig. 1 along the view line II-II'. The
resilient
channel 108 has feet portions 204 and a center section 202. Screws 112 are
used to attach
2o the feet portions 204 to the studs 106. Screws 112 are also used to attach
the plasterboard
110 to the center section 202 of the resilient channel 108.
The resilient channel succeeds in attaching the plasterboard 110 to the studs
106
while decoupling the plasterboard 110 from the studs 106. Depending upon the
degree of
its resiliency, the channel 108 can provide varying levels of decoupling
between the
plasterboard 110 and the studs 106. This can reduce the amount of vibration
transmitted
from the plasterboard 110 to the studs 106, and vice-versa.
A disadvantage of the use of resilient channel is that the resilient channel
108 must
be attached to the studs 106 before the plasterboard 110 is attached to the
resilient channel
108. Moreover, the resilient channel 108 must be attached carefully in a
periodic manner
so that it will be easy to locate the center sections 202 when attaching the
plasterboard
110. Thus, a person using resilient channel to attenuate sound transmission
must obtain
not only plasterboard but also a supply of resilient channel, then that person
faces a two
step process to attach the plasterboard 110 to the studs 106 via the resilient
channel 108.
In contrast, attaching plasterboard 110 directly to the studs 106 is a single-
step process.
In other words, the resilient-channel technique is much more labor-intensive.
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SUMMARY OF THE INVENTION
The invention, in part, provides an acoustical isolation wall system that can
be
assembled in one-step rather than in two-steps. An advantage of the invention
is that it
substantially decouples the stud wall from the plasterboard. Decoupled is used
here to
mean that the wallboard does not physically touch the stud.
Another advantage of the invention is that is provides tunable lo~~ frequency
sound absorption via the use of Helmholtz resonators.
The invention, in part, provides a composite wall board comprising: a
plasterboard layer; an insulation layer; and a perforated board layer. Such an
insulation
layer attaches said plasterboard layer to said perforated board layer while
decoupling said
plasterboard layer from said perforated board layer.
The invention also provides, in part, a wall system comprising: an existing
wall;
and a composite wall board attached to said stud wall; said composite wall
board
including a plasterboard layer; a insulation layer; and a perforated board
layer; wherein
said insulation layer attaches said plasterboard layer to said perforated
board layer while
decoupling said plasterboard layer from said perforated board layer.
The invention also provides, in part, a method of constructing a wall system
in a
room having at least one subject wall, the method comprising:
2o providing a composite wallboard that includes a plasterboard layer; a
insulation
layer; and a perforated board layer; and attaching said composite wallboard to
said subject
wall.
The foregoing and other objectives of the present invention will become more
apparent from the detailed description given hereinafter. However, it should
be understood
that the detailed description and specific examples, while indicating
preferred embodiments
of the invention, are given by way of illustration only, since various changes
and
modifications within the spirit and scope of the invention will become
apparent to those
skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed
description given hereinbelow and the accompanying drawings which are given by
way of
illustration only, and thus do not limit the present invention.
Fig. 1 is a three-quarter perspective depiction of a background wall system.
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Fig. 2 is a cross-sectional view of Fig. 1 taken along the view line II-II'.
Fig. 3 is a three-quarter perspective depiction of a first embodiment of the
composite wallboard according to the invention.
Fig. 4 is a three-quarter perspective depiction of an embodiment of a wall
system
according to the invention that incorporates the embodiment of Fig. 3.
Fig. ~ is a cross-sectional view of the embodiment of Fig. 4 taken along the
view
line V-V' .
Fig. 6 is a schematic depiction of a basic Helmholtz resonator. And,
Fig. 7 is cross-sectional view of a second embodiment of the composite
wallboard
l0 according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 3 is a three-quarter perspective depiction of a first embodiment of a
composite wallboard 300 according to the invention. The composite wallboard
300
includes a perforated, rigid board 302, insulation material 306 and
plasterboard 308.
Examples of the insulation layer 306 are board fiberglass (approximate density
of 3-12
lbs/ft3 (48.03 - 192.12 kg/m3)), open-cell melamine foam (approximate density
of 0.7
lbs/ft3 (11.21 kg/m3)) or mineral wool board (approximate density of 3-5
lbs/ft3 (48.03 -
80.05 kg/m3)). Commercial examples of the insulation layer 306 include a board
formed
2o of compressed fiberglass insulation such as the Type 703 model of semi-
rigid glass fiber
insulation board sold by Owens Corning and a board formed of open cell
melamine foam
such as is sold under the brand name of BASOTECT V 3012 Melamine Foam marketed
by the BASF Corporation. Preferably, the insulation is in the range of'/z
(1.27) to 1'/2
(3.81 ) inches (cm) thick.
The perforated board 302 is preferably a synthetic board or a particle board,
e.g.,
oriented-strand board (OSB) or a material that is similar to that from which
peg board is
made, or even plywood. Typically, the perforated board 302 will be between
about 1/8
inch ( .3175 cm) and 1/4 inch (.635 cm) thick. Alternatively, the board 302
need not be
perforated, though not having the holes forfeits the advantages of the
Helmholtz
3o resonators discussed below.
The holes 304 in the perforated board 302 are preferably of varying diameters
and
are preferably randomly distributed. Alternatively, the holes can be of the
same diameter
and distributed in a pattern. The sizing and distribution of the holes will be
discussed
more below.
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The plasterboard 308 is preferably a board made of several plies of
fiberboard,
paper or felt bonded to a hardened gypsum plaster core. Alternatively, the
plasterboard
308 could be replaced with paneling or a cement-based backer board. The
thickness of
the plasterboard 308 is preferably in the range of'/4 inch (.635 cm) to 5/8
inch (1.59 cm).
The 5/8 inch (1.59 cm) size represents the largest commercially available
plasterboard
and is preferred because it exhibits the best sound attenuation properties.
Fig. 4 is a three-quarter perspective depiction of a sound attenuation wall
system
400 according to the invention. In Fig. 4, the composite wallboard 300 is
attached to a
stud wall 102. Fig. 5 is a cross-section of the wall system 400 taken along
the view line
V-V'. In Fig. 5, screws 112 are used to attach the perforated board 302 to the
studs 106.
As noted above, the perforated board 302 is attached to the front surface 310
of
the stud wall 102. When a covering material 504 (Fig. 5) is attached to the
back surface
312 of the stud wall 102, a cavity is defined by the studs 106, the base plate
104 and the
header plate (not depicted), the covering material 504 and the perforated
board 302. The
holes 304 in the perforated board 302 act to define Helmholtz resonators
within the
cavities. The diameter of the holes is related to the frequency desired to be
absorbed by
the Helmholtz resonator. Thus, the diameter of the holes will depend upon the
circumstances to which the invention is applied.
The theory and physics of Helmholtz resonators are known. Thus, only a brief
discussion of the theory and physics will be provided in regard to Figure 6. A
cross-
sectional view of a basic Helmholtz resonator 600 is illustrated in Figure 6.
The volume,
V, of air in the chamber 602 of the Helmholtz resonator 600 is linked to the
environment
612 (containing a sound source) outside the resonator 600 via an aperture 606
in the body
604. The aperture 606 has a cross-sectional area, S, and a length, L,
indicated via items
608 and 610, respectively, in Figure 6.
When sound impinges on the aperture 606, the air in the neck of aperture will
be
induced to vibrate. In turn, this causes the volume of air in the cavity to
undergo periodic
compression and expansion. The friction between the air particles in the
aperture 606, and
the resistance to air flow associated with the neck itself, cause the energy
in sound waves
to be absorbed. The efficiency of this absorption is at a maximum when
resonance occurs,
with the efficiency diminishing at frequencies above and below the resonant
frequency.
The general equation governing the performance of a Helmholtz resonator is:
4
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c
° zII ~v
where fo = resonant frequency (Hz)
C = velocity of sound (m/sec)
L = depth of hole (m)
S = cross-sectional area of hole (m2)
V = volume of chamber (m3)
D = diameter of hole (m) (assumed circular).
By appropriately selecting V, L and S, the resonant frequency of the Helmholtz
resonator can be controlled.
1o The composite wallboard, and the wall system incorporating such a composite
wallboard, according to the invention operate as diaphragmatic absorber that
converts
acoustical energy, especially low frequency acoustical energy, into mechanical
vibrations.
The resilency of the insulation layer 306 makes it possible for the acoustical
energy to be
transformed into mechanical vibration. This prevents the transmission of the
acoustical
energy through the composite wallboard or the wall system that incorporates
it.
An alternative embodiment 700 of the composite wallboard according to the
invention is depicted in Fig. 7. In the cross-sectional view of Fig. 7, an
insulation layer
702 is sandwiched between the plasterboard layer 308 and the perforated board
layer 302.
The insulation layer 702 has a non-uniform distribution. The portions 704
completely fill
2o the distance 706 between the perforated board 302 and the plasterboard 308.
The portions
708 and 712 only span distances 710 and 714, respectively, i.e., they
incompletely fill the
distance 706 between the perforated board 302 and the plaster board 308. Such
non-
uniform distribution of the insulation layer can be used to tune the sound
absorbing
qualities of the composite wallboard 700. If viewed from the front of the
composite
wallboard 700, i.e., from a perspective normal to (and looking through) the
plasterboard
308, the insulation layer 702 would appear to be a stripped pattern and/or a
checker board
pattern.
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The composite wallboard according to the invention is preferably installed by
screwing (or nailing) through the plasterboard 308 and into the perforated
board 302 such
that the screws (or nails) only contact the perforated board 302. The
screw/nail holes, as
well as the seams between the composite wallboards, are then finished in the
typical
manner associated with plasterboard. Alternatively, the perforated board 302
could
simply be glued to the studs 106. An advantage of the composite wallboard
according to
the invention is that no nail pops can occur in the plasterboard 308.
Alternatively, the plasterboard 308 could be attached to the studs 106,
resulting in
the perforated board 302 facing into the room. This would cause the composite
wallboard
1o to act as a mid-range and high frequency sound absorbing surface. To make
this surface
more attractive, it could be covered with an acoustically transparent fabric
such as that
used in the Acoustic Room System marketed by Owens Corning.
Alternatively, the insulation layer 702 could be replaced by a known honeycomb
material (not depicted), such as in any one of U.S. Patent Nos. 4,496,024;
4,522,284; and
4,084,367. It is also commercially available from the Tenneco Packaging
company. The
honeycomb material is typically made of paper and optionally can be
impregnated with
resin, and is available in a variety of sizes and paper weights. Such a
honeycomb material
would enhance the sound attenuation effect of the Helmholtz resonators, but
would not
decouple as well as the insulation layer 702.
2o Again, it is an advantage of the invention that is provides a composite
wallboard
that attaches to an existing wall and yet is decoupled from that wall so as to
attenuate
sound transmission through the wall. Moreover, this composite wallboard can be
installed in one-step, which represents a considerable savings in labor
relative to the
resilient-channel technique of the Background Art.
The invention being thus described, it will be obvious that the same may be
varied in
many ways. Such variations are not to be regarded as a departure from the
spirit and scope
of the invention, and all such modifications as would be obvious to one
skilled in the art are
intended to be included within the scope of the following claims.
