Abstract: A damping treatment for bodies where the temperature may rise above 150.degree. C. consists of a number of stand-off cantilever, sandwich type dampers (1), consisting of a layer of viso-elastic material (3) sandwich between two rigid metal plates (4, 5), which are attached to a support (2) that can be attached to the body (7). The support (2) is thermally isolated from the body (7) and is positioned at a position of high amplitude of a radiating frequency that is to be reduced.

Abstract: This invention provides an improved method and apparatus for attenuating the sound of flowing fluid. The apparatus of this invention includes at least two attenuating areas, preferably particle-filled containers arranged serially within a housing. One of the attenuating areas has a central void into which a portion of the fluid may flow on its way through the muffler. The muffler may also include a mechanism for permitting one of the attenuating devices to move in order to accommodate changes in fluid pressure.

Abstract: The present invention relates to a novel installation of a sound attenuating laminate. More particularly, the invention relates to the installation of a simpler, lighter, and more effective noise attenuating laminate which is made up of seven layers of material. The laminate includes a duct liner, a moisture barrier, a first protecting layer, a screen, acoustic attenuating material, a second protecting layer, and a solid backing sheet. The laminate is readily incorporated into various sections of a jet engine compartment in order to attenuate the sound produced by the jet engine. Hollow rivets are used to conduct acoustical energy to the intermediary layers of the laminate. This novel means for conducting the acoustical energy to the intermediary layers of the laminate also allows for an improved anti-icing system, for more efficient jet engine operation, and for more efficient dissipation of acoustic energy.

Abstract: Toilet bowls made of porcelain are conventionally disposed directly on the floor and/or attached thereto through rigid connections. When the toilet is used, acoustic vibratons are therefore transmitted from the bowl to the floor and spread all over the dwelling. In the case of a multiple unit residential building, the acoustic vibrations even reach the surrounding residential units and disturb their occupants. To overcome this drawback, the acoustically insulating method proposes to insert a strip of rubber foam between the base of the bowl and the floor and to attach the toilet bowl to the floor through a pair of fasteners each including a rubber link, whereby no acoustic short circuit is established between the bowl and floor to thereby considerably reduce the transmission of acoustic vibrations to the floor.

Abstract: Method of reducing the overflying noise of airplanes having a propeller den by a piston engine. The propeller is arranged on the engine shaft in such a way that positive components of the engine sound pressure fall on negative components of the propeller sound pressure. It is preferable to use an engine/propeller combination in which the number of engine ignitions per revolution of the propeller shaft divided by the number of the propeller blades is an integer, preferably being equal to 1.

Abstract: The present invention discloses a ported reflex speaker enclosure for use in the automotive audio systems industry. The ported reflex speaker enclosure is a design that factors the audio and thermal design considerations as found in the automotive operating environment as well as factoring the audio and mechanical mounting considerations as found in the automobile audio systems. The ported reflex speaker enclosure is primarily intended for six (6) by nine (9) inch standard speaker chassis used in automotive audio systems that typically are found as non-enclosed suspended speakers in the trunk compartment of automobiles.

Abstract: A sound reproducing apparatus for use in a vehicle having a speaker system constituted by at least one acoustic duct and a speaker unit disposed at a throat of the acoustic duct, an opening formed at the other end of the acoustic duct facing the passenger compartment of a vehicle. The apparatus is arranged such that, F0 and Fs are substantially equal to each other. Where Fs is the lowest frequency in a frequency range within which the imaginary part of the acoustic impedance at the sound radiating surface of the speaker system in the direction of the space within the passsenger compartment is zero and F0 is the low-range resonance frequency of the speaker system itself in the free space.

Abstract: A light weight exhaust muffler is provided comprising a pair of formed external shells and a pair of pipes disposed therein. The external shells are formed to include peripheral portions and chambers extending from the peripheral portions. The chambers are separated from one another by baffle creases unitary with the respective external shells. Portions of the baffle creases of one external shell are secured in face-to-face contact with corresponding portions of the baffle creases in the other external shell. The baffle creases comprise arcuate portions corresponding to the shape of the pipes passing between the chambers separated by the baffle creases.

Abstract: A post and panel wall system for use as sound barriers and the like utilizes a precast post which is disposed upon a foundation having a tensioning cable extending upwardly therefrom and recesses into which depending anchoring rods on the posts are placed. The tensioning cable is tensioned and then the recesses in the foundation are filled with a cementitious mixture or grout to thoroughly bond the anchoring rods into the foundation. The posts have channels in which the vertical edges of the wall panels are seated, and desirably the wall panels have reduced thickness end portions with arcuate edges to permit some adjustment within the channels. The posts and panels may be erected seriatim, or the posts may initially erected and the panels then lowered into place.

Abstract: A noise attenuating assembly for use in conjuction with an air conditioning unit having a sloped discharge opening is disclosed. The assembly includes a front wall and a pair of side walls forming a flow path for the conditioned air which is discharged to the space containing the unit. The assembly has a layer of sound attenuating material attached to the inside surface of the walls so that the assembly deflects and absorbs line-of-sight sound produced by the unit fan, thus reducing the noise level of the unit.

Abstract: A concrete post assembly and method of mounting same. The post assembly is supported in upright position by an inground pier in which a plurality of anchor bolts are embedded with a portion of each bolt extending upwardly above the upper surface of the pier. The post assembly includes a concrete post and a base plate rigidly secured to the bottom of the post, the base plate having a plurality of holes located so as to register with upwardly extending anchor bolts. A nut is threaded onto each anchor bolt and the post assembly is mounted on the bolts with its base plate resting on the nuts which can then be adjusted to level the plate. A second set of nuts are threaded onto the anchor bolts and tightened against the upper surface of the base plate to lock the post assembly in mounted position.

Abstract: Acoustic damping is provided by a dimensionally-recoverable article, either in single layer or constrained-layer form. The single layer, or the damping layer of a constrained-layer article, comprises a mixture of a damping component (generally having a high tangent delta value) and a hold-out component (generally having a significant crystallinity).

Abstract: A kit includes a self-contained muffler which attaches to the output exhaust system of a small two-cycle engine, such as a model engine that is in the range of 0.15 to 1.25 cubic inches displacement. The kit provides a low cost adaptation of existing engine manifolds to meet required sound reduction guidelines of below 90 Db at nine feed from the engine. The kit is easily adapted and installed on a wide variety of manifold-muffler adaptations, for example model engines using a mounting bolt which clamps the kit muffler to a portion of the existing engine muffler.

Abstract: A system is provided for existing three-engine jet aircraft to reduce the noise levels at take-off and landing in order to meet governmental noise regulations. The system is particularly suitable for 727-200 aircraft having three JT8D engines. A hush kit is formed of the modified components for installation in existing airplanes.

Abstract: A compact, sound-attenuating muffler for an internal combustion engine is disclosed in which the muffler includes a stream dividing partition positioned proximate the inlet of the muffler to divide the incoming exhaust gases into two streams of substantially equal volume. The stream dividing partition directs the streams laterally of the inlet in directions diverging from each other, and the muffler sound-attenuating assembly further includes corridor defining partitions receiving the streams from the stream dividing partition and maintaining the streams in corridors as coherent substantially eddy-free streams. The corridor defining partitions further direct the streams laterally to converge towards each other for discharge of the coherent streams against each other from opposed directions in a common volume inside the muffler casing. Further sound attenuation is accomplished by a common channel receiving the streams after they are intersected or discharged against each other.

Abstract: A compact turbine engine exhaust gas noise suppressor has a housing having a first chamber, a second chamber having an outlet and communicating with the first chamber through a transfer passage, and a third chamber communicating with the first chamber through a perforated dividing wall and having a resonant sound attenuator positioned therein. A sound absorbing member is positioned in the second chamber to create therein a serpentine flow path extending between the transfer passage and the outlet. The exhaust gas noise is attenuated by flowing the exhaust gas into the first chamber through a duct into which ambient cooling air is educted, and then forcing the exhaust gas outwardly through the serpentine flow path.

Abstract: An apparatus and method for changing the optical and/or physical properties of a fluid composition employ an electric field applied across the fluid for controlling the fluid properties. The fluid consists of a dielectric liquid and an electrically conductive, elongated, fibrous particulate material. The fibrous material has a length between approximately 1000 angstroms and five millimeters, a diameter less than about 700 angstroms, and an aspect ratio of length to diameter greater than about five. The particulate material is in colloidal suspension in the liquid. Generally, when the particles are dispersed in the liquid by Brownian movement forces, the fluid composition has an average separation between particles of approximately three to ten or more times the average length of the particulate material.

Abstract: A basic new method and devices for treating flowing substances such as subdivided solids, colloids, gels, liquids and gases, under varying temperatures, pressure and velocity conditions is disclosed. The method is characterized by forming three concentric types of non-turbulent and unobstructed streams flowing essentially in one direction but differing in velocity from one another, the outermost of which is accelerated to become a surrounding jetstream flowing tangentially past reduced openings interconnecting with the other two types of streams, reducing fluid pressure in them until suction-effect at origin point results, and by final recombination of flows to produce a helically spinning accelerated vortical exiting thrust, to insure either virtually silent atmospheric gaseous discharge or energy-efficient pumping and optimally frictionless travel of liquids or flowing solids through extended conduit, for which devices are supplied by this invention.

Abstract: An exhaust silencer has an inlet opening and an outlet opening spaced axially from the inlet opening and includes a cylindrical shell. A core inside the shell defines at least one axial passage and has at least one helical baffle defining a helical flow passage around the axial flow passage within the shell. The axial flow passage has a barrier at its downstream end and has an upstream opening aligned with the silencer inlet opening. It also has an outlet axially spaced from the axial passage inlet opening, the said outlet being directed transversely outwardly into the downstream half of the helical flow passage, at a region upstream from the barrier.

Abstract: A sound dampening panel comprises a corrugated center barrier sandwiched between fibrous sound dampening material which is covered with fabric. The fibrous material fills the spaces between corrugations and forms a layer over the corrugations. In one form of panel the fibrous material is thermally fused under pressure such that it is rigidly formed with a relatively low density in the spaces between the corrugations and with a relatively high density in the layer over the corrugations. The fibrous material is also thermally bonded to the center barrier. In another form of panel, inserts of one density are placed in the spaces between corrugatins and those inserts are covered by a layer of greater density which is glued to ridges of the corrugations.

Abstract: A pressure modifying device and method which utilizes a gas or vapor and an adsorbent material to reduce the amplitude of pressure variations in gas or vapor. The technique is applicable to loudspeaker assemblies having a box (2), low frequency loudspeaker (16) and a mass (20) of activated charcoal in the box. Excursions of the cone (18) of the loudspeaker in the range 20 to 100 Hz cause pressure fluctuations in the air in the box but the size of those pressure fluctuations is comparatively small owing to increased air adsorption on the activated charcoal leading to increased efficiency.

Abstract: The present invention is an acoustic panel having a porous layer and a generally rigid layer affixed to each other. The generally rigid layer includes at least one passageway opening on one side of the rigid layer and extending through the rigid layer to the porous layer. The porous layer is a fibrous material. The rigid layer is a concrete-type material, such as vermiculite-cement plaster. This acoustic panel further comprises a generally rigid planar surface positioned adjacent to the porous layer. This generally rigid planar surface can comprise an insulating layer affixed to the other side of the porous layer and a structural layer fastened to the insulating layer. The insulating layer is a polyurethane foam board. The structural layer is a particle board.

Abstract: Sound transmission from an equipment room via the air conditioning ductwork must be reduced so as to permit the full use of adjacent areas. The ductwork located within the equipment room is made of a lighter gauge material to facilitate radiation of sound back into the equipment room. The flow is divided into a plurality of duct passages within the duct to achieve sufficient attenuation. Each of the duct passages is lined on all sides so that there is a double thickness of acoustic insulation between adjacent duct passages.

Abstract: In order to subject sound-emitting surfaces of motor vehicles to localized interference with the sound field, for example, sound obstruction and attenuation, it is already known to insulate the region of the sound sources against noise by cladding the passenger space from within at the relevant point of the wall to be insulated by application of a heavy layer and of a resilient layer which, if necessary, is impregnated with a sound-attenuating material. However, limits are imposed on a sound-insulating cladding of this kind even when further sound-reducing materials are applied, as the transmission of sound energy to the interior space of the motor vehicle then takes place in other ways.In order to remedy this, at least one sound sink is subjected to intensified sound absorption by providing on the wall (2,3) a sound-insulating cladding (6/7). Specifically this cladding comprises a resilient layer (6) preferably made of foam material or fleece which is covered by a heavy layer (7).

Abstract: Acoustic pulsations in fluid transmission systems such as gas pipelines, engine exhaust systems and compressed air networks are suppressed by an acoustic filter comprising an enlarged pressure vessel with inlet and outlet conduits arranged such that conduit inlet and outlet openings are at the pressure node of standing pressure waves of the pressure vessel length resonant frequency and odd or even harmonics of the fundamental frequency. The inlet and outlet conduit openings are arranged such that the direction of convection flow and acoustic pulsation modulating flow is transverse to the instantaneous particle velocity of fluid resulting from acoustic pulsations existing in or excitable in the pressure vessel. Inlet and outlet conduits preferably open into the pressure vessel in a generally radial direction with respect to the central longitudinal axis of the vessel.

Abstract: A combination convergent jet engine aircraft nozzle (86, 142, 146) and a ventilation tube (88, 136, 144) are fixed in place and have no moving parts. Ambient air is entrained through duct inlets (96, 140, 154, 160), through the nozzle walls, through hollow struts (90, 138), the struts supporting and being connected to a hollow central tube (102, 144) or a plurality of tubes (136), to adjacent the downstream end of the nozzle to mix at takeoff with the jet forming gas exhaust. The ducts (102, 136, 144) are positioned with respect to the nozzle exhaust so that entrained ambient air flows into the gas exhaust during takeoff and so that the ambient air flow is substantially restricted or shut off during cruise flight.

Abstract: A method of absorbing sound generated within a clean-room environment and the sound-absorbing panel for carrying out that method, wherein said sound absorbing panel comprises a fibrous core material enclosed in a non-porous membrane, said membrane being attached to at least one of the extensive surfaces of said fiberglass core in a series of closed geometric figures. The membrane occupying the central portion of each of said geometric figures defines a diaphragm, the dimensions of the diaphragm being configured such that the lower order natural frequencies of vibration of each of the independent diaphragms correspond substantially to the frequency range of sound to be absorbed.

Abstract: A space divider and method for making same, the space divider comprising a peripheral frame, having at least two portions lying in different planes and a fabric sleeve stretched over and entirely covering the peripheral frame, forming at least two double-curvilinear surfaces. The peripheral frame may comprise side rail members and a plurality of braces connecting the rail members. The fabric sleeve may be impregnated with a resinous material, thereby providing a substantially rigid omni-directional sound reflecting and dispersing surface, or left soft, with fill or padding optionally disposed between opposite surfaces of the fabric sleeve, thereby providing a omni-directional sound absorbing surface. The fabric sleeve may be a one-piece, two-way stretch member, such as different types of knitted materials or a non-stretch member of different types of woven materials.

Abstract: A technique for reducing noise generated by transverse vibrations in elongated members comprises the application of a friction element on a surface of the member. The friction element is forced against one or more surfaces of the member by a selected normal force and is provided in a vicinity of maximum distortion of the member when the member undergoes vibrations. A differential movement between the inner surface of the friction element and the outer surface of the member causes heat to be generated which dissipates the energy of such transverse vibrations.

Abstract: An acoustical device for reducing sound pressure levels and the potential for noise induced hearing loss comprising an arched shaped acoustic pad having an interior or frontal concave sound absorption panel and an exterior or rear convex sound shield supported by an interior frame member. Sound attenuation is accomplished by enclosing the frame with at least one layer of resilient material having a high sound absorption coefficient. The acoustic pad is affixed to the back of a musician's chair by means of a mounting device which provides a high degree of flexibility in positioning for optimal directional protection of the performer.

Abstract: An ejector and method of reducing jet engine noise are disclosed wherein the primary combustion gas stream of the jet engine is ejected into a mixing section or zone of the ejector and into which a secondary gas stream is also injected at a velocity sufficient to create a choked or Mach 1.0 mixed flow condition, resulting in rapid mixing of the primary and secondary gas streams in the mixing zone. A diffuser is connected to the ejector downstream from the mixing zone for pulling the mixed gas stream through the mixing zone. The diffuser has an exit area greater than the area of the mixing zone. The ejector is provided with means for adjusting the area of the mixing section or zone and diffusion section to match engine operating conditions so as to create proper conditions within the mixing zone for noise suppression. Noise suppression by the method and means disclosed occurs at all frequencies with a minimal loss of thrust, and possibly a slight gain.

Abstract: A method of manufacturing a damped resonator acoustical panel in which a porous acoustical damping fabric and a resin impregnated open weave fabric are laid up and subjected to moulding by the application of heat and pressure thereto to cause a portion of the resin from the open weave fabric to impregnate the abutting portions of the acoustical damping fabric and bond the fabrics together. A film of an adhesive is then applied to the open weave fabric and heated by a hot gas stream until it reticulates. The bonded fabrics are then bonded to the edges of an open honeycomb core by means of the reticulated adhesive. A solid sheet is bonded to the other side of the honeycomb core in order to close the cells thereof.

Abstract: A system for determining optimal selection and positioning of transducers (e.g., loudspeakers or microphones) in an acoustical environment, and relating an acoustic environment to any sound source. The system determines the acoustical dispersion pattern, and the sensitivity or power requirements for transducers or sound sources.The system involves mapping acoustical environment, as viewed from a specific location, in true angles and with attenuation information, onto the surface of a sphere. The transducer or sound source is related to this mapped environment by mapping its angular sensitivity or radiating pattern onto an overlay which is manipulated over the surface of the sphere.A system light source permits the information depicted on the sphere to be projected onto a scale model. Final documentation of all interrelationships may be viewed on the system sphere, or photographed from a system screen.

Abstract: An arrangement for attenuating noise in an air handling unit having a forwardly curved centrifugal fan and dampers downstream of the fan for varying the volume rate of air flow. The dampers are located downstream of the fan a distance L which is about 30 inches so that the critical acoustical frequency f=C/4L is relatively high (125 Hz). The discharge section of the air handling unit between the fan and the dampers is lined on the sides with acoustical panels that are effective in absorbing sound at the critical frequency.

Abstract: Methods and apparatus for attenuating sound levels characterized by a muffler utilizing the splitting of exhaust gas flows followed by recombining of these split flows in mutually opposed relationship. Sequentially alternating expansion and contraction of the exhaust gas is caused to occur, during which increments of exhaust gas exit sequentially along the exhaust gas flow from the muffler.

Abstract: A method for optimizing the design of finite noise barriers by using an extension of the Biot-Tolstoy rigorous closed form impulse solution for diffraction of an acoustic pressure pulse by an infinite rigid wedge. An initial finite barrier is defined and then a calculation made of the impulse signal transmitted on one side of the barrier and received on the other side by adapting the Biot-Tolstoy solution to a digital computer. The integrals of the acoustic pressure impulse are calculated for each source/receiver path for each segment of the barrier. The integrals are then compared and the segments are adjusted and new calculations made until all integral contributions are equal. The integrals are then digitally Fourier transformed to determine attenuation at the desired frequencies. After comparison with the desired attenuation, all segments are proportionately adjusted and the entire computational process reiterated until the optimal attenuation is achieved.

Abstract: A space divider and method for making same, the space divider comprising a peripheral frame, having at least two portions lying in different planes and a fabric sleeve stretched over and entirely covering the peripheral frame, forming at least two double-curvilinear surfaces. The peripheral frame may comprise side rail members and a plurality of braces connecting the rail members. The fabric sleeve may be impregnated with a resinous material, thereby providing a substantially rigid omni-directional sound reflecting and dispersing surface, or left soft, with fill or padding optionally disposed between opposite surfaces of the fabric sleeve, thereby providing a omni-directional sound absorbing surface. The fabric sleeve may be a one-piece, two-way stretch member, such as different types of knitted materials or a non-stretch member of different types of woven materials.

Abstract: A hermetic compressor housing formed from sheet metal as two housing halves which when joined form a generally ellipsoidal inner surface having a maximum radius of curvature of about one order of magnitude greater than the minimum radius of curvature and deviating from the generally ellipsoidal shape only where necessary for supporting a compressor-motor assembly therein and for joining the housing halves is disclosed and provides a housing of relatively uniform rigidity to reduce the level of sounds radiated thereby. In one specific embodiment all of the audible natural resonant frequencies of the housing are above 3500 Hz.

Abstract: Both an improved loudspeaker enclosure and an improved acoustical process for generating sound radiation in a room is herein disclosed. Basically, the walls of the improved enclosure include a loudspeaker, and a sound transmission port for transmitting sound generated by the back of the loudspeaker cone into the room. The interior of the enclosure includes a tuned acoustical chamber for absorbing the even and odd harmonics of the system resonance frequency, and a compression chamber acoustically coupled at one end to the back of the loudspeaker cone. The compression chamber is acoustically coupled to both the tuned acoustical chamber and the transmission port of the enclosure walls by means of an acoustical coupling.

Abstract: A method for preparing a resistive screen for underwater sound absorption consisting of a metallic honeycomb structure, adding a thermosetting plastic material to the cells within said structure, heating said structure under pressure and forming small apertures within said thermosetting plastic material.

Abstract: A novel method of producing a vibration damping and sound absorbing coating on a rigid substrate is provided in which method a first coating of a viscoelastic material having after gelling a modulus of elasticity of 5.times.10.sup.6 to 5.times.10.sup.8 dynes/cm.sup.2 is sprayed onto the substrate whereafter there is sprayed onto said first coating a second coating of a viscoelastic material having after gelling a modulus of elasticity of 5.times.10.sup.7 to 5.times.10.sup.9 dynes/cm.sup.2, the modulus of elasticity of said second outer coating being at least 10 times greater than that of said first coating.

Abstract: The acoustical radiation from handling empty cans and containers is reduced to sound levels which decrease the risk of hearing damage for exposed personnel by this invention. The invention comprises the temporary use of damping end-caps comprised of viscoelastic material which eliminates metal to metal contact between containers, guides, and cables and which also dissipates vibratory and airborne acoustical energy in the containers, thereby reducing the acoustical radiation.The invention is applicable in particular to canneries and canning operations.

Abstract: A muffler construction, particularly for exhaust gases of air-operated tools, comprises, a tubular sleeve having a passage therethrough, an exhaust gas pipe connected into the sleeve and defining a constricted flow passage with the sleeve, first and second opposed cylindrical coaxial shell sections, each having a closed end wall at their respective outer ends and facing in opposite directions engaged with the exhaust gas pipe, and sidewalls spaced radially outwardly from the sleeve. The exhaust gas pipe has a gas pipe discharge and there are partition walls in the shell sections defining a first expansion chamber and at least one additional expansion chamber. A constricted flow passage is defined between the first expansion chamber and the at least one additional expansion chamber with sealing and enclosing members closing the sidewalls of the first and second shell sections so as to define the first expansion chamber and at least one additional expansion chamber within the shell sections.

Abstract: A sound deadening coating is provided on an article, such as an engine cover, by applying a polysulphide, silicone or polyurethane rubber layer to the surface of the article and applying a layer of zinc, aluminium or ferrous metal or their alloys to the rubber layer. Preferably, polysulphide rubber and zinc metal are used. The metal or alloy may be applied to the rubber layer when the latter is only partly cured. Preferably, the rubber and metal layers are sprayed.

Abstract: A method of reducing noise during the throttling of vapor and gas streams by supercritical expansion, followed by dividing the streams during deceleration.

Abstract: Method of making attenuation sandwich panels having a cellular core positioned between and bonded to an imperforate facing sheet on one surface thereof and a perforate sheet with an outer layer of porous fabric material adhered to the other surface. The combined perforate facing sheet and porous fibrous material have a predetermined open surface area prior to its adherence to the cellular core. A coating of adhesive is applied to either the facing sheets or to the faying surface of the cellular core. The sheets are then properly positioned with respect to the cellular core. The porous fabric surface of the combined perforate sheet and porous fibrous material is positioned against a perforated plate. The opposite surface of the perforated plate is positioned against a bonding tool that has a plurality of longitudinal grooves on its perforated plate adjacent surface.

Abstract: A method and apparatus for reducing acoustic noise associated with the release of gases from a submerged device, such as a sea water battery. A flat piece of material, preferably polyurethane, is mounted onto the top of the device. The piece of material is provided with an outwardly extending lip on the lower surface thereof adjacent an outlet port through which the gases issue. The lower surface of the lip is preferably curved upwardly and outwardly away from the outlet port and is disposed immediately at the upper edge of the outlet port. Gas emitted from the outlet port immediately forms bubbles on the lower surface of the lip, and the bubbles so formed pass outwardly and upwardly along the lower surface and subsequently escape into the free water.

Abstract: Method of fabricating attenuation sandwich panels having a central cellular core positioned between and bonded to an imperforate facing sheet on one surface thereof and a perforate facing sheet with an outer layer of porous fibrous material adhered to the other surface. The combined perforate sheet and porous fibrous material have a predetermined open surface area prior to attenuation panel fabrication. The perforation exposed surface of the combined perforate sheet and porous fibrous material is covered with a maskant material which covers the surface only. The porous fibrous surface is then saturated with a liquidous anti-wetting solution which coats substantially all of the fibers. The solution is allowed to dry and the maskant is then removed from the opposite surface. The components making up the panel are then assembled and bonded together to form the attenuation panel.

Abstract: A porous acoustic element is disclosed having a configuration comprised of individual cross-wound porous layers of widely varying porosity, with transition plenum layers interposed therebetween having a configuration so as to prevent formation of blockages and small area openings which would be created by a direct overlay winding of differing pitch. The porosity of each wound layer increases in successive layers to compensate for expansion of the gas as it flows through the element. The resulting porous element allows gaseous flow therethrough, with maximum pressure energy dissipation and controlled velocity to minimize aerodynamic noise created by flow through valves and other flow restrictions. A specific embodiment is disclosed in which the porous layers are created by variable pitch wire ribbon cross windings and the transition layers are provided by wire mesh having relatively large openings.

Abstract: A method of making a panel for installation in the high velocity air flow region of an engine nacelle and other applications requiring sound absorbing material and increased air frame strength. The panel utilizes a single layer of either a metallic or nonmetallic cellular core with a solid or perforated septum disposed internally therein. The septum may have a planar or nonplanar configuration within the individual cells of the core thereby providing means for reducing the noise level of various sound frequencies created by a jet engine or any other sound producing devices for that matter. The planar or nonplanar septum provides structural stabilization and/or vibration dampening to a bonded sandwich assembly. The panel may also be used in strengthening air frame construction and other applications besides sound attenuating panels.