Patent Application
20060179760
1. Field of the Invention
This invention relates to methods and structures for constructing walls which have specific acoustic characteristics, such as theater and auditorium walls.
2. Background of the Invention
The primary function of interior walls and partitions is to divide building space into separate, private spaces. Many other factors, however, must be considered by designers and builders, one of which is sound control. In hotels, for example, the prevention of sounds originating in one room from passing through walls and into adjacent rooms is of major concern. This consideration is extremely important in the design and construction of multi-screen movie theaters or home media rooms.
Conventional wall construction techniques tend to rely on a stud frame interior with wall covering panels comprised of gypsum board, plywood or other largely modular panels. Interior walls in offices, hotels and the like are typically made by erecting a frame that includes vertical studs, either wood or steel, on a 12″ or 16″ spacing, lining each side with gypsum board (sheet rock) panels, then finishing the wall surfaces with a variety of textures and paint. When additional thermal and/or acoustic insulation is needed, insulation medium such as fiberglass, rock wool or mineral wool will commonly be placed to fill the interior space between vertical studs and gypsum board panels. Sound transmission through walls can be reduced by widening the wall and staggering the studs such that no stud spans the full width of the wall. Sound transmission is often further reduced by surface or exterior treatments such as the application of light, resilient materials like carpeting, folded or layered upholstery, or the like.
Sound transmission through walls is typically expressed according to one of two single-number rating systems—Sound Transmission Class (STC) and Weighted Sound Reduction Index (Rw). Both are single-figure ratings schemes intended to rate the acoustical performance of a partition element under typical conditions involving office or dwelling separation. The higher the value of either rating, the better the sound insulation. The rating is intended to correlate with subjective impressions of the sound insulation provided against the sound of speech, radio, television, music, office machines and similar sources of sound characteristic of offices and dwellings.
The first rating system is called Sound Transmission Class (STC). STC is defined by the American Society for Testing Materials (ASTM) standard E 413. To assign an STC rating to a barrier separating two rooms, a sound is generated in one of the rooms, the sound power is measured on both sides of the barrier, and the ratio between the two measurements (the transmission loss) is stated in decibels. Sixteen measurements are made in each room, at ⅓ octave intervals from 125 Hz to 4000 Hz. The higher the STC rating, the greater the sound transmission loss. The E413 standard specifies a transmission loss curve having 16 points on the same ⅓ octave intervals. From 125 to 40 Hz, the curve slopes 9 dB per octave; from 400 Hz to 1250 Hz, 3 dB per octave, and it is flat from 1250 Hz to 4000 Hz. The curve is moved up and down until the sum of all 16 differences between the curve's value and the measured values for the barrier is less than 32 dB (providing no single difference is more than 8 dB). The rating is then expressed as the curve's loss in decibels at 500 Hz.
The second rating system is called Weighted Sound Reduction Index (Rw) and is defined by International Standards Organization standard ISO 717. Test procedure for Rw are similar to STC except the frequency range for Rw spans 100-3150 Hz whereas, as indicated supra, STC covers a frequency range of 125-4000 Hz. STC and Rw correlate very well. For architectural elements such as doors, windows and walls, differences in STC and Rw are typically less than 1%.
When sound waves strike a surface, some of the energy is usually reflected while some is transmitted through the surface. A typical objective in reducing sound transmission through a structure is to isolate the source from the structure before the energy can be transmitted to the structure, causing the structure to vibrate. The primary ways to reduce sound transmission through multi-component structures is to add mass and to decouple or isolate individual components so that vibrations cannot be passed from one component to the next.
Decoupling can be done in many ways and is the subject of much development. Typically, decoupling is done by means of soft, resilient and/or generally bulky materials. Isolated or still air is an effective decoupler and there are many applications wherein the insulation of sound and heat are accomplished analogously. Decoupling can be enhanced by the use of viscoelastic materials, typically high molecular weight polymers, to isolate components and reduce contact between larger or more rigid components. The viscoelastic materials, in effect, allow the larger and/or more rigid components to vibrate independently and, more importantly, act to dampen the vibration of the components.
Viscoelastic materials, as the name implies, exhibit both elastic and viscous properties and are generally modeled using a combination of springs and dashpots. Springs simulate elastic behavior while dashpots simulate viscous behavior. When a viscoelastic material is made to vibrate, a complex strain is generated on the material thereby generating a complex stress. The elastic modulus (E) is known to be the ratio of stress (s) and strain (e) in a material and can be described as the amount of strain resulting from an applied stress (E=s/e). In a viscoelastic material, the elastic modulus is comprised of two components, a storage elastic modulus (ES) which results from the elastic properties of the material, and a loss elastic modulus (EL) resulting from the viscous properties of the material. The ratio of loss modulus to storage modulus is called loss tangent (tan d) and is the mathematic ratio between the two (tan d=EL/ES). The loss modulus component corresponds to a materials ability to convert dynamic energy to electric or thermal energy, thus an ability to dampen vibrations. It follows that as a materials tan d increases, so does that materials ability to dampen vibrations.
Decoupling can also be achieved by means of resilient channel members used as part of a wall construction. Resilient channels, typically transversely mounted, act to absorb vibrational energy instead of transmitting the energy from one wall component to the next. Historically, however, less than optimum construction and installation practices effectively lead to acoustic short circuits around resilient channels negating their full effect.
Another technology often employed is the use of panels comprised of a honeycomb core. In some cases, the cells of the honeycomb core effectively trap dead air which is a relatively poor acoustic conductor. In more sophisticated applications, the individual honeycomb cells may be designed as interconnected Helmholtz resonators which dissipate acoustic energy by allowing the viscous laminar flow of air between resonators.
It is known that sound insulation is best obtained from multi-shell components wherein both the mass and the resiliency of the components are factors, thus a best combination of weight and bulk is typically sought New materials, namely novel viscoelastic polymers included as part of layered panels or are finding use in high STC wall construction, but these materials tend to be expensive and remain largely unproven.
The present invention includes a structure and a method for building the structure for a sound insulating wall. The sound insulating wall is useful for improving acoustics in commercial buildings, theaters. It has a multi-layer construction formed from at least three compressed strawboard panels in adjacent and generally parallel planar alignment and defining spaces in between which can be hollow or filled with insulating medium. Each panel is held in place by opposed edge bracket assemblies positioned to clasp the ends of each panel. The bracket assemblies include a resilient material acting to isolate or decouple each panel. The strawboard panels are positioned so that horizontal panel to panel joints in each layer are offset to eliminate easy burn through areas. Edge brackets are generally mounted to vertical I-beams and can be adapted for use with a variety of beam types.
The present invention should be more fully understood when the written description is considered in conjunction with the drawings contained herein, wherein:
a-4i show isometric views of the progressive steps followed to erect a wall according to subject embodiments;
The improved construction disclosed herein includes a number of individual components, but is generally designed around a compressed straw panel. In the preferred embodiment, compressed straw panels such as those manufactured by Durra Building Systems of Texas are used. Each compressed straw panel is composed of highly compressed straw, typically wheat, rice, oat or other recovered agricultural straw lined on all exterior sides by paper or paperboard. Compressed straw panels are typically made through a dry extrusion process wherein straw is compressed into a substantially flat continuous web, normally between 1″ and 3″ thick and between 30″ and 65″ wide. As previously mentions, the continuous web is lined on all sides by paper or paperboard. The continuous web is then cut into rectangular panels of various lengths.
The acoustic and combustion properties of the compressed straw panels are of particular importance to the embodiments disclosed herein. A typical 2¼″ thick panel has a Class A flame spread rating (FSI=10, SDI=45) as tested and rated according to ASTM E-84, and an STC and Rw rating of 36 as tested and rated according to ASTM E90-99, E413-87, E1132-90, and ISO 717. Further, the preferred compressed straw panels disclosed herein each provide a one hour fire rating on both sides as tested and rated according to ASTM E-119.
The desirable acoustic properties of compressed strawboard panels is not fully understood, but it is asserted that two primary factors are involved. First, straw is a cellulosic material, thus when dried, is comprised of many substantially hollow cells. Further, a significant amount of dead air is trapped in small spaces between individual straw fibers within a panel. Second, the individual straw fibers within a panel are not glued or otherwise bonded together, thus it is plausible that a quasi-viscous flow can occur within a panel.
Continuing with
Center strawboard panel 4 is situated along the centerline of the wall and spans the distance between the web sections of said I-beams 1. Center strawboard panel 4 is held in place along a first vertical edge by means of a channel bracket 6, with said channel bracket being attached to the web of an I-beam 1 by means of a plurality of tapping screws 10. Each tapping screw 10 penetrates through said channel bracket 6 and makes a rigid attachment to the web of an I-beam 1. Center strawboard panel 4 is held along a second vertical edge my means of a pair of angles brackets 5 in opposed relative arrangement so as to sandwich the edge of center panel 4 there between. As illustrated, each angle bracket 5 is attached to I-beam 1 by means of a plurality of tapping screws 10, each of which penetrate through said angle bracket 5 and then form a rigid attachment to the web of an I-beam 1. The vertical edges of center panel 4 are separated from either channel bracket 6 or angle brackets 5 by means of an edge decoupling pad 8. Said decoupling pads 8, each act to decouple the center panel 4 from channel bracket 6 and angle brackets 5 respectively by effectively dampening and absorbing vibrational energy. Tapping screws 10 represent the preferred connector for attaching angle brackets 5 and channels brackets 6, but alternative connectors such as rivets, bolts, welds or the like can be used as well.
Retainer plate 9 is sized such that upon installation, flange decoupling pad 7 is in solid contact with a panel 2,3 and said retainer plate 9, but remains in a substantially non-compressed state. This is critical when flange decoupling pad 7 is made of a viscoelastic material as permanent non-elastic deformation will result. Likewise, channel bracket 6 is sized and angle brackets 5 positioned such that solid contact is made with edge decoupling pad 8, yet said edge decoupling pad 8 remains in a substantially non-compressed state. This is particularly critical when edge decoupling pad 8 is made of a viscoelastic material as permanent non-elastic deformation will result.
With continued reference to
In the preferred embodiment, strawboard panel 2,3,4 will be comprised of compressed recovered wheat straw held within a paperboard liner comprised of kraft or recycled paper having a basis weight greater that 69 lbs./msf., and the overall panel dimension will be approximately 4 ft×8 ft×2½″. I-beams 1, retainer plates 9, angle brackets 5, and channel brackets 6, will be made from a metal or metal alloy. Flange decoupling pads 7 and edge decoupling pads 8 will be made from a soft resilient material, preferably a viscoelastic material, and more preferably a viscoelastic material having a loss tangent (tan d)>0.5. Retainer plates 9, angle brackets 5 and channel brackets 6 can easily be made from alternative materials such as polymers, but will preferably be made from materials with melting or combustion temperatures higher than that of mild steel.
a-4i illustrate the typical steps followed to construct a wall according to the preferred embodiment. The figures illustrate the very important characteristic of the present embodiment wherein the horizontal edge to edge joints between adjacent panels in the center are offset from those in the front and rear. This important characteristic eliminates the presence of an easy burn through route for a fire. As previously stated, each strawboard panel possesses a Class A flame spread rating, thus a composite wall comprising three layers of panels represents a formidable obstacle for fires.
a shows two adjacent I-beams 1 erected along a wall line and a first section of angle bracket 5 precut to size. Further, the flange sections of said I-beams 1 are each wrapped by a flange decoupling pad 7.
c, then show the components from
d shows the components of
e shows the components of
g shows the wall construction of
h then shows the wall construction of
The subject embodiments are especially adaptable to structures such as theaters wherein the floor is sloped.
Though the subject invention is illustrated herein using compressed strawboard panels exclusively, any modular panel that can be suitably attached to the subject beams and brackets, and more importantly, possesses the desired acoustical properties can be used in accordance with the subject embodiments disclosed herein.
The dimensions of the walls including the panels, beams, angle and channel brackets and various connectors shown herein were selected for illustrative purposes only. The actual dimensions of each element may vary and is largely subject to the needs of each individual application. Further, The embodiments shown and described above are exemplary.
Even though numerous characteristics and advantages of the present embodiments have been described in the drawings and accompanying text, the description is illustrative only, and changes may be made in the detail, especially in matters of shape, size, and arrangement of the parts within the spirit and scope of the present invention, as determined by the following claims.
