US2350513A - Sound barrier wall or door construction - Google Patents

Description

4June 6, 1944. R. L LEADBE'TTER 2,350,513

SOUND BARRIER WALL OR DOOR CONSTRUCTION l Filed Dec. 30. 1940 2 Sheets-Sheet l aan @EEFF June 6, 1944. v RL, LEADBETTER 2,350,513

SOUND BARRIER WALL OR DOOR CONSTRUCTION Filed DSC. 30, 1940 2 Sheets-Sheet 2 Patented June 6, `1 944 soUNp BARRIER WALL on noon coNs'rnucrloN Ralph L. Leadbetter, Wheaton, Ill., assignor, by

mesne assignments, to Burgess-Manning Company, Chicago, Ill., a corporation of Illinois Application December 30, 1940; Serial No. V372,31()

9Claims.

This invention relates to building construction, more particularly to doors and partitions which form barriers to the passage of sound from orinto an enclosure such as a room or oice.

Sound is the sensation produced by vibrations of air particles at the organs of hearing. The waves which travel from the source of sound to the tympanic membrane consist of alternating zones of pressure (condensations) and partial vacuum (rarefaction). These pressure Waves, which are known as sound waves, possess appreciable kinetic energy and are capable of doing work.

Sound waves progressing in an elastic medium, such as air, and meeting an obstacle, such as the partition forming a wall of a room, are either reiiected. absorbed and dissipated in the form of heat, or transmitted to-structures connected with the obstacle or to the space adjacentthe further side of the obstacle. More accurately, such waves are generally reflected in part, and absorbed in part, the remaining energy being transmitted in the form of sound waves or vibrations. As a practical matter, no wall is 4fa perfect reflector of sound, nor is any partition known which will absorb all of the energy of the sound waves incident upon its surface.

It follows from the foregoing that in order to acoustically insuiate a room from the space surrounding it as, for example, to prevent the transmission of sounds from one room to an adjoining room through a common partition between them, the partition should be designed to reect and absorb as much of the energy of the sound waves impinging upon its surfaces as possible. Hdws ever, since it is generally desirable in such circumstances to minimize the sound level in one or both of the rooms, and since sound reflected from the partition would contribute to the maintenance of an elevated sound level, it is desirable in a sound barrier partition lto absorb as much as possible of the sound energy rather than to reflect the sound waves back into the source room.

The primary-object of this invention is to pro-4 vide a sound barrier or insulating partition which make up the sound waves may continue from one side of the partition through openings therein to the other side, transmission of sound through the partition must be the result of forced vibration of the structure caused by the alternating pressures of the sound waves on the incident side of the partition and resulting in the formation of corresponding alternating pressures on the further side of the partition which, in turn, are manifested as sound Waves. Thus, the acoustical energy of the sound waves is converted into mechanical energy of vibration of the structure, the latter being reconverted into acoustical energy by the generation of sound waves in the receiving room. Various devices whereby attempts have been made to minimize the amplitude of such structural vibrations by increasing the mass of the structure as, for example, by theuse of masonry walls, or by increasing the flexurall stillness, although effective to some extent, have proved to be generally undesirable from the cost or weight standpoints and necessarily result in increased reflection of the sound waves into the source room. Attempts have also been made to increase the mechanical damping of the vibrating structure to thereby decrease the transmisstructural expedients intended to minimize transmission of sound through partitions may be found in the National Bureau of Standards Report BMS 1'7.entitled, Sound Insulation `of Waliand Floo Y Constructions, dated March 28, 1939 The present invention proceeds on the assumpnen that it 1s impossible. as a practical matter,

to prevent forced vibration of at least some element of a partition or door upon the surfaces` of which sound waves impinge. The structure of .the invention includes means for (1) minimizing the amplitude of the forced vibrations, (2) damping such vibrations, (3) preventing refiection of sound waves from the partition or f door, and (4) absorbing sdund within the source room to thereby minimize the sound level therein. A fifth component which is entirely unique with this invention comprises means for minimizing the coupling between the vibrating structure and the atmosphere adjacent the further surface of the partition: that is, means for preventing the generation of sound waves by the vibrating structure within the space adiacent the partition on the side thereof remote from the sound source. The structural expedients intended to perform these various functions are' illustrated in which Fig. 1 is a perspective view, partly in section,

'the accompanying drawings, in

of a portion of a partition and a door embodyingp section of the material having sulcient interconnected pores f to admit'of entrance of the sound waves without `substantial reflection thereof. In Figs. 1 and 2 apertured panelsl and 2 comprise the exposed surfaces of partition 3 and door 4. As is more fully pointed out in Norris Patent No. 1,728,500, a panel which would ordinarily reflect a large part of the sound waves striking it may be made to transmit substantially all of the sound by perforating the panel as shown in Fig. l. For example, panels l and 2 are made sound pervious and suitable for the purposes of the invention by Vproviding them with approximately fourteen if inch holes per square inch throughout their areas.

Each form of the invention also includes an air-impervious inner member which is referred to herein as a diaphragm because it may be set into vibration -by the action of sound waves. The diaphragm 5, for example, is spaced between apertured panels l and 2 and is so mounted within the structure that 'air particle movement on one side of the diaphragm may not be transmitted to the other side thereof except as a result of the vibration of thediaphragm itself. A stiifening grid 6 of intersecting strips may be cemented in place between diaphragm i and apertured panel i and another between diaphragm I and apertured panel 2, if desired, with definite beneficial .results in addition to improved structural strength. It has been found that the increased stiffness limits the amplitude of vibration of the partition or door and for this reason added stillness4 is elective in preventing trans'- mission of sound waves. The remaining spaces vbetween the diaphragm and the facing panels are each filled with lntersticed mass 1, materials such as me c, mineral, or cellulosic wool, ceramic nodules or a ceramic body having intercommunicating pores,exfoliated venniculite,

' vibratile or acoustically dead" material mty be above-described partition or door construction as a sound barrier, it is exceedingly' difficult to analyze the action and demonstrate the manner in which this desirable over-al1 result is accomplished. The various data available point to a plausible explanation of the action of the bar rier. In order that the invention may be clearly .l

understood, but without limitation to the particular action described, this explanation is given here. It is `believed that the intensity of sound waves approaching the side of the partition adjacent the space indicated at A, Fig. 2, is sub. stantially undiminished as the waves travel through the perforations of the .apertured panel l and the interstices of the filling material l. The alternating pressures applied to the olaphragm A5 -by these'sound waves cause the diaphragm to vibrate. The process thusA far involves the transformation of the acoustical energy of sound waves into mechanical energy of vibration of the diaphragm. If the structure on the further side of diaphragm 5, that is, on the side adjacent that indicated by the letter B, were omitted, the mechanical energy of the vibrating diaphragm would be reconverted into acoustical energy as sound waves emanating from the diaphragm. However, it has been found that this reconversion is minimized by the presence of the intersticed masses 1 at the further surface of diaphragm 5. Apparently the presence of this filling material prevents the formation of sound waves or at least minimizes their manifestation in the space B. Stated in a different way, the presence of the filling material l results in poor acoustical coupling of the vibrating diaphragm 5 with the atmosphere in the space B. It is likely that apertured panel 2 itself contributes in some measure to this decoupling effect.

It should be pointed out that the structure on the incident side A of diaphragm 5 apparently operates in this same manner to prevent return of acoustical energy in the form of sound Waves into the space A from the vibrating' diaphragm. Once the diaphragm is set into vibration, whether from pressure waves approaching from A or from B, it tends to generate sound waves which would, except for the decoupling structure of the invention, travel in both directions from the two the partition from the source space to the receiving space.

The eiliciency of the barrier structure' may be improved somewhat by providing means for internally damping the vibrations of diaphragm 5 and thus dissipating the energy to some extent.- Mismatching and interference between the non-rigid non-vibratile sheets 8 and the dia- Phragm to which they are loosely applied result in a decreased amplitude of vibration of the dialoosely fastened to diaphragm B on either one or u phragm. Also, the diaphragm may itself be made of a suitable non-elastic material having substantial internalndamping qualities, s uch as ordinary roofing felt. Such materials are referred to herein as non-rigid, non-vibratile materials. It should be recognized that the terms vibratile and non-vibratile as used herein are relative terms, it being understood that all materials will vibrate to some extent. The former term refers to such materials as sheet iron, plywood, etc.

I which tend to sustain vibration when struck and the latter term refers to relatively non-elastic materials which may be non-rigid and acoustically dead, such as asphalt impregnated felt, or which may be rigid, such as masonry panels. In order to further limit vibration of the structure, the stiiening grids 6 are provided. It `has been found that such grids increase thebarrier eiliciency of the partition, particularly in the lower frequency ranges. Staggering of the grids in the is hung like a curtainfrom a supporting rail II` to form the diaphragm element of the structure. This embodiment of the invention is primarily intended for use in a door or in the fabrication of units which may be arranged edge-to-edge in vertical position as shown in the drawing to form a partition. The mass and internal damping characteristics of this sheet should be as great as practicable. 'I'he diaphragm ID is preferably supported only at its .top edge, the side and bottom edges of the diaphragm being in contact with but not aixed to the sides or bottom of the door or unit frame. As in the structure of Figs. 1 and 2, the diaphragm'is spaced between exposed apertured panels I2 and I3, stiffening grids I4 and I5 being provided to strengthen the structure and give some support to the diaphragm III. The grids in this case are in register with each other and grip the diaphragm between them. A suitable intersticed iilling material I6 is loosely packed into the cavities between the diaphragm and the apertured panels.

In the embodiment illustratedin Fig. 4. a single grid I1 spans the space between the outer apertured panels I8 and I9. Each cavity so formed is .provided with a diaphragm 29 which may be either a vibratile or a non-vibratile sheet, and may, if desired, comprise two or. more coextensive sheets inl contact with each other. When a plurality of`sheets are used, it is advantageous to provide them in diilerent thicknesses, as this results in interference and damping of vibration. These diaphragms should t snugly ybetween the strips forming the grid il but are free to move laterally to some extent Aso that the coupling between these vibrating members and the grid maybe as poor as possible in view o f the frictional engagement with the grid. The laminated diaphragm structure resulting from the use of two or more sheets introduces an additional damping factor resulting from interference between the individual sheets and frictional losses resulting from the sliding of the edges of-the sheets against the grldwork and of one sheet against the adjacent sheet. 'As in the other forms of the invention, the spaces 2l and 22 between the diaphragm and the apertured outer panels I8 and I9 are loosely packed with a filling material as described above.

Although the several embodiments oi the invention herein described are' equally adaptable to partitions or doors, the structure of Fig. yiis Vimprovement in acoustical performance.

particularly intended for sound barrier partitions. In place of the usual two by four',I studding, studs 23 y be employed to support an airimpervious diaphragm 24 of plywood or other suitable sheathing. 'I'hese supporting members also serve as fui-ring strips to which the outer apertured panels 25 and 26 may be fastened'. A suitable illing material is loosely packed into the spaces 21 and 28. .t

In the structure of Fig. @self-supporting intersticed bodies 29 and 30 are provided on either side of diaphragm 3|. As indicated in the drawing, these bodies may be in the nature of layers of ceramic material having considerable stillness and interconnected crevices for the entrance thereinto of the sound waves. Since the material is self-supporting, separate apertured outer panels are not necessary.

Two spaced diaphragms 32 and 33 are provided in the embodiment illustrated in Fig. 7. In other respects the structure is similarto that of Fig. 5. Suitable spaced furring strips, not shown, may be used to support the diaphragms if they are not in themselves rigid and self-supporting. Also, a set of grids, not shown in this ligure, may be used in the spaces between each diaphragm and the contiguous apertured panel.

The structure illustrated in Fig. 8 is similarto that of Fig. 4 except that thevdiaphragms 3B are arranged diagonally within the cavities between the strips forming the grid 31 and apertured panels 38 and 39. These diaphragms-arev preferably, although not necessarily, rigid. They may be arranged in -parallel orientation, as shown, or alternate diaphragms may span opposite diagonals of the cavities. The employment of such members greatly increases the stiness' of the structure with corresponding substantial Furthermore, the diagonaldiaphragms tend to diffuse the sound waves andapparently contribute to improve the over-all efllciency of the barrier and provide a more uniform action throughout the audible frequency range.

The operation of the several modified forms of the invention is believed to be similar to that of the embodiment of Figs. 1 and 2 which is fully described above. It will lbe appreciated that various other modiilcations of the invention may also be made. Such structures, although not specifically described and illustrated, are intended to be included within the scope of the appended claims.

I claim:

1. A sound barrier wall construction comprising a pair of spaced substantially parallel apertured panels forming the exposed surfaces of said wall construction, an air-impervious diaphragm spaced between said apertured panels in substantial parallelism thereto, a sheet of non-rigid, nonvibratile material adjacent and engaging at least a portion of at least one surface of said diaphragm at a point other than a point of support of said diaphragm, and intersticed masses substantially illling the spaces internally adjacent said apertured panels. l t

2. The construction of claim 1 in which said diaphragm Ais composed of non-rigid, non-vibratile material.

3. A sound 'barrier wall construction compris. ing'a pairof spaced substantially parallel aperl tured panels formingthe exposed surfaces of said wall construction, a non-rigid' diaphragm spaced between said aperturedpanels in substantial parallelism thereto, a grid of intersecting kstrips on each side o! said diaphragm, each said .gridn engaaina the contiguous surfaces of said apertured panel and said diaphragm and delining cavities therebetween, vand an intersticed mass in each of said cavities.

4. The construction of claim 3 in which the grids are so arranged that at least a portion ci in substantial parallelism thereto, a sheet of non- A rigid, non-vibratile material adjacent and engaging atleast a portion of at least one surface of said diaphragm at a point other than a point of support of said diaphragm, and intersticed masses substantially iilling the spaces internally adjacent said apertured panels.

6. A sound barrier wall construction comprising' a pair of spaced substantially parallel apen tured panels forming the exposed surfaces oi' said wall construction, a diaphragm spaced between points on the surfacethereof, and intersticed masses substantially lling the spaces internally adjacent said apertured panels.

7. A sound barrier wall construction comprising a pair oi spaced substantially parallel apertured panels forming the exposed surfaces of said wall construction, a vibratile diaphragm spaced between said apertured panels in substantial parallelism thereto. a sheet ofnon-rigid, non-vibratile material adjacent and engaging at least a portion of at least one surface of said diaphragm at a point other than a point of support of said diaphragm, and intersticed masses substantially illling the spaces internally adjacent said apertured panels.

8. A sound barrier wall construction comprising a pair of spaced substantially parallel apertured panels forming the exposed surfaces of said wall construction, a diaphragm spaced between said apertured panels in substantial parallelism thereto, a grid of intersecting strips on each side of said diaphragm, each said grid engaging the contiguous surfaces oi said apertured panel and said diaphragm and deiining cavities therebesaid-'apertured panels in substantial parallelism thereto, a sheet of non-rigid, non-vibratile material adjacent and engaging at least a portion of at least one surface of said diaphragm at a point other than a pointof support of said diaphragm, said non-vibratile material being loosely attached to said diaphragm only at spaced tween, and an intersticed mass in each of said l cavities.

9. The construction of claim 8 in which the grids are so arranged that at least a portion of the strips forming the grid on one side oi said y diaphragm'engage said diaphragm at points be- ,f' tween the points of engagement oi' the strips forming the other grid and said diaphragm.

RALPH L. ampamnn.

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