US3513938A - Acoustical covers for office machines - Google Patents

Acoustical covers for office machines Download PDF

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US3513938A
US3513938A US3513938DA US3513938A US 3513938 A US3513938 A US 3513938A US 3513938D A US3513938D A US 3513938DA US 3513938 A US3513938 A US 3513938A
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Prior art keywords
paper
acoustical
cover
typewriter
wall
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William L Buehner
Donald L Greer
Richard W Mccornack
Paul L O'brian
Henry W Simpson
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International Business Machines Corp
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International Business Machines Corp
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    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10KSOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41JTYPEWRITERS; SELECTIVE PRINTING MECHANISMS, e.g. INK-JET PRINTERS, THERMAL PRINTERS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J29/00Details of, or accessories for, typewriters or selective printing mechanisms not otherwise provided for
    • B41J29/08Sound-deadening, or shock-absorbing stands, supports, cases or pads separate from machines

Description

May 26, 1970 w. BUEHNER T A 3,

- ACOUSTICAL COVERS FOR OFFICE MACHINES Filed June 2, 1969 3 Sheets-Sheet 1 FIGJ INVENTORS. WILLIAM L. BUEHNER DONALD L. GREER RICHARD W. M CORNACK PAUL L. O'BRIAN HENRY W. SIMPSON QAM ATTORNEY.

May 26, 1970 w'. L. BUEHNER ETA!- 3,513,938

ACOUSTI CAL COVERS FOR OFFICE MACHINES Filed June 2, 1969 3 Sheets-Sheet 2 May 26, 1970 w. L. BUEHNER L 3,513,938

' ACOUSTICAL COVERS FOR OFFICE MACHINES Filed June 2, 1969 3 Sheets-Sheet 5 FIG. 9

OCTAVE PASS smos- CYCLES PER SECOND 70 45 9o 1ao 555 -no -1400- g 995s0o: 120o FREQUENCY-CYCLES PER SECOND United States Patent Office 3,513,938 Patented May 26, 1970 US. Cl. 18133 9 Claims ABSTRACT OF THE DISCLOSURE A low profile acoustical cover for an office machine adapted to fit over the opening in the machine housing which accommodates paper feeding and handling. The acoustical cover incorporates a plastic hood having angled walls enabling operator observation of the printing on the paper with a minimum of glare from the ambience of the machine and an acoustic device which is placed in proximity to paper entrance and exit slots in the plastic hood to prevent the emission of undesirable audible sounds therethrough. The plastic hood pivots to enable ready access to the machine mechanism and to the paper being operated on and the entire acoustical cover is readily removable from the machine.

CROSS REFERENCE TO RELATED APPLICATION The following application is assigned to the same assignee as the present application.

US. patent application Ser. No. 15,231, filed Dec. 30, 1968, entitled Typewriter or the Like, Eliot F. Noyes, inventor.

OTHER REFERENCES The following additional reference is of interest:

IBM Customer Engineering Instruction Manual for the IBM Selectric 1 Composer, Form Number 241-53404), dated October, 1966. 1

Brief background of the invention Field This invention relates to an acoustical cover for an office machine, and more particularly, to an improved acoustical cover for the platen area of a typewriter.

Description of the prior art Typewriter machines or the like which incorporate paper feeding platens which are strikable by type elements generally emit a substanital amount of noise into their environment. This noise can be excessive, especially when the machine is operated from a secondary media, such as magnetic or paper tape or from a transmission line at its maximum output rate for long periods of time in the environment of a business oflice. Much of the noise which is emitted from the machine, is emitted through the opening in the machine housing above the platen which facilitates paper handling and there have been many attempts made in the past to absorb this noise. The prior art attempts may be classified into two general categories: (1) large cabinets which completely surround the typewriter and (2) smaller enclosures adapted to fit over the opening in the typewriter housing above the platen. The large cabinet devices are usually constructed with a transparent window through which the operator can observe the printing operation. The paper is generally maintained completely within the eni (Trademark) closure, although several such prior art devices include slots through which the paper is fed. In order to prevent sound from escaping through the paper slots, rubber rollers or gasket type devices have been utilized to provide a relatively tight seal with the paper. While these cabinet devices have been successful in appreciably reducing the sound emanating from a typewriter or the like device, none of them have met with any degree of commercial success because of their bulkiness and because of the paper handling problems which they create. That is, when such a device encloses a typewriter, it is necessary for the operator to open doors to reach into the device in order to align paper, make corrections and in some instances to vieW the printed lines. Additionally, these devices are generally not designed for optimum viewing of the line being printed and those preceding it. In fact, in many instances, these devices incorporate lights to enable the operator to see the print line and also contain mirrors for reflecting the print line to a position where it can be viewed by the operator.

As described above, a second class of acoustic hoods exist in the art which cover only the platen opening in the machine housing. Some of these devices form only a partial covering for the housing opening to thereby facilitate the feeding of paper and are virtually ineffective to reduce emitted sound. Instead, they direct the emitted sound away from the operator without affecting the sound level within the ofiice or environment in which the machine is located. Other such devices form a complete covering for the platen opening thereby appreciably reducing the emitted sound, but they create paper handling problems. That is, it is necessary to either maintain the paper completely within the cover thereby creating operator visibility problems or to feed the paper through an opening having a seal adapted to coact with the paper to prevent the emission of sound. When such a seal is utilized, it forms an obstruction which makes it difiicult for the operator to properly align the paper with respect to the platen. Additionally, such prior art covers usually make it quite difficult for the operator to access the print line to make corrections thereon without necessitating the removal of the cover. Further, many such prior art devices incorporate mirrors or the like to provide the operator with a view of the line being printed thereby creating operator non-familarity problems with the equipment.

Summarizing, the prior art teaches two basic approaches to reduce the noise emitted through the platen opening of a typewriter or the like machines: enclosure of the entire operating mechanism within a large hood with the resultant loss of ease of paper handling ability and viewing ability and enclosure of the platen opening with a resulting lack of noise reduction or a resulting lack of visibility and ease of paper handling.

SUMMARY In order to overcome the above noted shortcomings of the prior art and to provide an acoustical cover for office machines which greatly reduces the noise emitted therefrom without appreciably disturbing the visibility of the printed lines and without appreciably disturbing the paper handling manipulations which the operator is accustomed to, the present invention provides an acoustical cover adapted to fit over the platen opening and having angled walls enabling ready operator observation of that portion of the paper which has been printed upon, and an acoustical device mounted in close proximity to the paper entrance and exit slots of the cover for eliminating the audible sound which would otherwise escape through the slots into the ambience of the machine. The walls of the acoustical cover are so angled to prevent glare or unwanted reflections at the normal operator viewing position as well as to allow pivotal motion of a portion of the acoustical cover to an open or inoperative position to enable the operator to rapidly access the platen area for corrections, and for type element and ribbon changing operations. The acoustic device forms an integral part of the acoustical cover and is mounted directly over the platen area and forms unobstructed slots with the angled walls of the acoustical cover to enable paper to be readily fed into and out of the platen area. Additionally, the proximity of the acoustic device to the paper slots and to the platen enables it to dissipate sounds that would otherwise emanate from the slots.

An additional unique feature of the present invention is its relatively small size which enables it to be readily removed from or placed on the machine with minimum difficulty. When it is not being used, it can be stored in a small volume.

The foregoing and other features and advantages of this invention will be apparent from the following more particular description of the preferred embodiments of the invention as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a perspective sketch of a typical typewriter having the acoustical cover of the present invention mounted thereon.

FIG. 2 is a perspective sketch of a partial end view of a typical typewriter having the acoustical cover of the present invention mounted thereon.

FIG. 3 is a perspective sketch of a partial front view of a typical typewriter which has been modified to re ceive the acoustical cover of the present invention.

FIG. 4 is a cross-section end elevational view of the acoustical cover of the present invention and a portion of a typewriter.

FIG. 5 is a schematic diagram of typical operator viewing positions with respect to a typewriter having the acoustical cover of the present invention mounted thereon.

FIG. 6 is a schematic diagram of light rays and re flected light rays along the typical operators line of sight to the acoustical cover of the present invention.

FIG. 7 is a partial front view of the foam strips of the acoustic device.

FIG. 8 is a diagram of a basic low pass acoustic slot filter.

FIG. 9 is a frequency plot showing the sound level emitted from a typical typewriter compared with that of various configurations of the acoustical cover of the present invention.

DESCRIPTION Referring now to the drawings, and more particularly to FIG. 1 thereof, a perspective sketch of a typical typewriter having the acoustical cover of the present invention mounted thereon is depicted. The typewriter 11 is a single element typewriter incorporating a typewriting mechanism similar to that described in US. Pats. 2,879,876 and 2,919,002 assigned to the same assignee as the present application. The outer cover design of the the typewriter 11 enclose the platen 13 and paper bail referenced copending application of Eliot F. Noyes and includes an opening above the platen 13 to facilitate operator access to the paper 15 and the print element 17. The acoustical cover 19 is adapted to fit over the platen opening and rests upon the outer covers of th typewriter 11 as will be described.

When in its fully operable position as depicted in FIG. 1, the acoustical cover 19 and the outer covers of the typewriter 11 enclose the platen 13 and paper bail 21 as well as the print element 17 and thus forms a container therefore. In order to facilitate the feeding of paper 15 around the platen 13 without necessitating the removal or opening of the acoustical cover 19, a paper bail release lever 23 is connected to the paper bail 21 to ettect the conventional movem nt of the paper bail toward and away from the platen 13. Additionally, operation of the feed roll release lever 25 effects the pivoting of a paper stacker (not shown) against the platen to facilitate the alignment of paper as it is inserted into the typewriter. The operation of this mechanism can be identical to that described in the afore-referenced IBM Selectric composer instruction manual at page 15-1.

An additional modification which may be made to the typewriter machine 11 to facilitate paper handling when the acoustical cover 19 is mounted thereon, is the inclusion of a paper guide 27 upon which the paper may rest when it is being inserted into the machine. The paper guide 27 can be mounted upon the fixedly secured acoustic cover support member 29.

When it is desirous to insert the paper 15 into the typewriter 11, the operator moves the feed roll release lever 25 to effect the disengagement of the feed rolls (not shown) from the platen 13, the engagement of the paper stackers (not shown) with the platen, and the movement of the paper bail 21 from the platen. Thereafter, the paper 15 is inserted into a slot (not shown) created between the acoustical cover 19 and the cover support member 29 until the paper rests upon the paper stackers. With the paper thus squarely aligned, the feed roll release lever 25 is returned to its initial position thereby effecting the engagement of the feed rolls with the platen and the subsequent disengagement of the paper stackers from the platen. Thereafter, the platen 13 is rotated in the conventional manner effecting the feeding of the paper around the platen past the type element 17. Manipulation of the paper bail release lever 23 returns the paper bail 21 to the platen after the paper is fed thereunder in order to insure contact of the paper 15 with the platen 13. Continued rotation of the platen will cause the paper to be fed through a second slot (not shown) in the acoustical cover 19 as will be described hereinafter.

With the paper 15 thus inserted in the machine, the operator can readily view the print line 31 through the transparent from wall 32 of the acoustical cover 19. Additionally, the operator can also view the lines immediately preceding the print line through the front wall 32.

Referring now to FIG. 2 of the drawings, a perspective sketch of a partial end view of the typewriter 11 having the acoustical cover 19 mounted thereon is depicted. When thus mounted on the typewriter, the acoustical cover 19 forms a paper passageway, slot 33 with the cover support member 29 through which paper may be inserted into the typewriter. A second paper passageway, slot 35 formed within the acoustical cover is provided for paper to emanate thereform. The acoustical cover, when viewed from its end, is in the general shape of the letter M. The left-hand portion of the cover as viewed pivots in the direction of arrow 37 about pivot studs 39 and 41 (FIG. 1) from a position wherein the front wall 32 engages the lip surface 43 of the typewriter cover to a position wherein the wall 45 of the acoustical cover rests against the wall 47 of the acoustical cover. In its thus open or inoperative position, the operator may readily access the :print element 17 or the paper 15 (FIG. 1) at the writing line in order to make corrections, print element changes, etc. A partially open cover is depicted in phantom.

A pair of mounting screws 49 and a similar pair (not shown) located at the opposite end of the acoustical cover 19 fixedly secure an acoustic device 50 to the end wall 51 and the opposite end wall (not shown) of the acoustical cover 19.

Referring now to FIG. 3 of the drawings, a perspective sketch of a partial front view of the typewriter 11 which has been modified to receive the acoustical cover of the present invention is depicted. The cover support member 29 is shaped to form a continuous surface with the surface 52 of the cover of the typewriter 11. The surface 52 corresponds to the paper table which supports the the paper as it is inserted into a standard machine. With the machine modified to receive the acoustical cover, the surface 52 along with the cover support member 29 and the paper guide 27 supports the paper 15 as it is inserted into the machine to be wound around the platen 13. The cover support member 29 has an end wall 53 and a second opposite end wall (not shown) located at each end thereof, each of the end walls containing a stud 55 on which the acoustical cover of the present invention rests. That is, the two opposite end walls (i.e. wall 51 of FIG. 2) of the acoustical cover each have a slot (not shown) formed therein which engages the studs 55, the uppermost portion of the slot resting against the stud when the cover is in place. A small projection (not shown) located at the end edges of the rear surface of the acoustical cover spaces the cover from the paper table and prevents it from rotating about the studs 55.

Referring now to FIG. 4 of the drawings, a partial cross-section end elevational view of the acoustical cover 19 and a portion of the typewriter 11 is depicted. The front wall 32, the wall 45, the wall 47, and the end walls (end wall 59 of FIG. 2 and the end wall (not shown) at the opposite end of the acoustical cover) :are formed of a transparent acrylic resin such as Lucite or Plexiglas. The front wall 32 as well as the end walls are transparent. The wall 45 is frosted on each of its surfaces to minimize glare and unwanted reflections of the printed page off of its surfaces. Additionally, the outside surface of the wall 47 is frosted to further prevent glare and unwanted reflections. Although the wall 47 is frosted, it is sufiiciantly translucent for images appearing on the paper 15 immediately thereunder to be clearly discernable. Each of the acrylic resin walls are approximately .100 inch thick in the preferred embodiment.

An acoustic device 50 is located directly above the platen 13 and extends for approximately the entire length of the platen. The rear surface 67 of the acoustic device forms the paper slot 33 with the paper table 52 of the typewriter and with a portion of the cover support member 29. The paper 15 is fed into the machine through this slot until it engages the set of paper stackers (not shown). Thereafter, the rear feed rolls (not shown) are caused to engage the paper so that it may be fed around the platen 13 to the paper bail 21 as has been described.

As the paper 15 leaves the paper bail 21, it is directed toward the inclined surface 69 of the acoustic device 50. Thereafter, it is fed under the radius 71 formed by the wall 47 of the acoustical cover 19 and through the slot 35 located between the wall 47 and the front surface 73 of the acoustic device. The paper is thus fed through slot 35 without necessitating operator intervention upon the rotation of the platen 13.

OPTICAL CHARACTERISTICS OF THE ACOUSTICAL COVER Referring now to FIG. 5 of the drawings, a schematic diagram of typical operator viewing positions with respect to the typewriter 11 having the acoustical cover 19 of the present invention mounted thereon is depicted. Viewing position 91 is representative of the eye location of a tall operator with respect to the typewriter 11 while viewing positions 92 and 93 are respectively representative of the average typist and the short typist with respect to the typewriter 11. Each of these viewing positions remain unaltered when the acoustical cover 19 is placed on the typewriter or removed therefrom. As can readily be seen from the diagram, each of the lines of sight from the respective viewing positions to the print point 95 pass through the transparent front wall 32 of the acoustic cover. It will further be noted that operator visibility of the paper 15 through the front wall 32 is at a maximum at the viewing position 93 and the minimum at the viewing position 91 since all printing will appear on the paper 15 at or above the print point 95. Since the wall 45 ditfuses light rays, viewing of paper 15 through the surface is precluded. Thus, at viewing positions 91 and 93, a portion of the previously printed text is not clearly discernable since the surface 45 interferes with the operators view through the wall 32 of this text. It should be noted, however, that the operator at viewing position 91 can see the print line as well as 3 or 4 lines there-above while the operator at viewing position 93 can see the print line as well as 9 or 10 lines there-above. Thereafter, a slight discontinuity in the view of the printed lines appears until the operator has a direct line of sight through the Wall 47 to the paper 15. The wall 45 is angled so as to correspond to the line of sight 97 between the average viewing position 92 and the upper-most portion of the front wall 32 thereby effecting a minimum blockage of the average operators view by the wall 45.

It has been found experimentally that the viewing position 91 of a typical tall female operator is 15 /2 inches above the axis of the platen 13 and 14 /2 inches horizontally away from the axis of the platen 13. The viewing position 93 represents the viewing position of a short female operator typically found to be 13 inches above the axis of the platen and 17% inches horizontally away from the platen.

Referring now to FIG. 6 of the drawings. A schematic diagram of light rays and reflected light rays along the typical operators line of sight to the acoustical cover of the present invention is depicted. The light ray 99 is representative of the typical operators line of sight to the transparent wall 32 of the acoustical cover 19 and thence to the print point 95. Light which is reflected 01f of the front wall 32 back along the line of sight to the operator thereby representing glare or unwanted reflections must emanate from the top surface 100 of the typewriter 11 as depicted by the light ray 101 since the angle of reflection along the light ray 99 is equal to the angle of incidence along the light ray 101 with respect to the front wall 32. By utilizing a dark top surface 100 (e.g. an outer cover painted black) unwanted reflection is virtually eliminated.

The angle that the front Wall 32 makes with horizontal plane 102 may be varied as shown by the broken lines 32' and 32". When the front wall 32 is caused to slope outward as depicted by the front wall 32, light rays 103 are caused to be reflected off of the surface of the front wall 32 and transmitted back along the operators line of vision as depicted by the light ray 99. The light ray 103 is depicted as a horizontal light ray. In most environments, such horizontal light rays emitting from light sources such as windows would be blocked by the operator prior to striking the wall 32. However, if the wall 32' were sloped outward to a greater degree than depicted, unblocked light rays emanating from windows and from overhead light sources would be reflected off of the surface of the front wall 32' back into the eyes of the operator creating undesirable glare.

Movement of the front wall 32 in the opposite direction as depicted by the front wall 32" causes light rays 105 which are incident on the surface of the wall 32" to be reflected back along the operators line of vision. Since such light rays would have to emanate from within the machine, the chances of such light rays producing glare to the operator are negligible. However, such inward movement of the front wall 32 reduces the operators viewing window through which the print point and the lines of print immediately above it are observed. This could in turn be somewhat alleviated by increasing the height of the front wall 32 with a resulting increase in size of the acoustical cover 19.

It has been found that for a preferred embodiment wherein the front wall 32 has a height of 2 inches above the top surface of the typewriter 11, the front wall may be angled as depicted by front wall 32' by approximately 20" with respect to an imaginary plane which is perpendicular to the horizontal surface 100 without incurring an appreciable amount of undesirable reflection or glare. The front wall as depicted by front wall 32 may also be angled approximately with respect to the perpendicular plane without incurring an appreciable reduction of the operators viewing window. This assumes an environment wherein the light source is either above the typewriter (e.g. ceiling lighting) or horizontal (e.g. windows in sidewalls as found in a typical business oflice. Thus, in a typical office environment, the front wall should be substantially vertical.

As has been described, the wall 45 is angled to approximate the typical operators line of vision to the top of the wall 32 as depicted by light ray 97. In a preferred embodiment, this angle has been found to be approximately with respect to the horizontal when the height of the front wall 32 above the surface 100 of typewriter is approximately 2 inches. This angle increases if the height of the front wall is increased. The wall 47 forms a 102 angle with respect to the wall and is approximately parallel to the paper 15 as it is emitted from the acoustical cover 19. In this manner, the paper is located directly under the Wall 47 for ready visibility through the translucent but yet diffused surface of the wall 47.

The wall 107 makes approximately a 35 angle with respect tohorizontal so as to direct any acoustical noise emitting from the paper slots formed therein upward and toward the rear of the machine. The junction of the walls 47 and 107 is approximately 1.4 inches above the uppermost surface 100 of the typewriter in the preferred embodiment.

SOUND CHARACTERISTICS OF THE ACOUSTICAL COVER Referring once again to- FIG. 4 of the drawings, it has been described how the acoustical cover 19 when placed on the typewriter 11 completes the enclosure of the area around the platen 13 of the typewriter. The only openings in the cover 19 through which sound may emit are the slots 33 and 35 through which the paper 15 passes. In order to greatly reduce the noise passing through the slots, an acoustical device is located in close spaced relationship to the platen and to the slots and absorbs the sounds that would otherwise emanate therethrough.

The acoustic device 50 can be a large open cavity or an acoustic filter. The preferred embodiment of the acoustic device 50* is an acoustic filter depicted in FIG. 4 of the drawings. In this embodiment, the acoustic device 50 is formed by two bent-sheet metal walls 111 and 113 which, together with two end pieces (not shown), form a large cavity 115. The end pieces (not shown) are of the same cross-sectional shape as the cavity 115 and are fixedly secured to the end wall 51 (FIG. 2) and the opposite end wall (not shown) of the acoustical cover 19 by mounting screws 49 (FIG. 2) and a set mounting screws (not shown). In the preferred embodiment, the acoustic device is 15.4 inches long, approximately the length of the platen 13 and the cross-sectional area of the cavity 115 is approximately 0.8 inch by 1.9 inches or approximately 1.5 square inches.

The cavity 115 is filled with four strips of inch thick open cell polyurethane foam material 117, 118, 119, and 120. Any form of sound absorbing material which has good high frequency absorption characteristics such as fiberous glass or open cell sponge rubber could also be utilized in lieu of the polyurethane foam in order to absorb and dissipate sound. The strips of polyurethane foam material 117 and 120 have a plurality of 0.44 inch diameter holes 122 located therein as depicted in FIG. 7. The holes are located on horizontal centers .625 inch apart and on vertical centers .56 inch apart. The percent of open area of the foam is approximately 48% of the total surface area of foam strip which extends almost the length of the acoustic device 50 or approximately 14.4 inches in the preferred embodiment. The polyurethane foam material members 118 and 119 are separated from one another by a strip 123 made of a polyethylene terephthalate such as Mylar which is coated with pressure sensitive adhesive on either side. The strip 123 runs the entire length of the acoustic device and thus creates two acoustic cavities 125 and 126 within the cavity 115, the acoustic cavity 125 being located adjacent the slot 35.

The two bent sheet metal members 111 and 113 each have a grill-like opening member 128 and 129 located therein, each of the grill-like opening members being contiguous to the slots 35 and 33 respectively, and each running for approximately the entire length of the slot or approximately 14.4 inches in the preferred embodiment. The openings are formed by eleven horizontal rows of staggered .077 inch diameter holes placed horizontally of an inch from one another and vertically of an inch from one another yielding an open area of approximately 45% of the total area of the grill-like opening members. Each of the grill-like opening members are approximately 1.02 inches wide.

In order to determine the effective frequency range of an acoustic slot filter, it is necessar to make various calculations which are based on the dimensions of the filter and associated mass. Thus, in the discussion which follows, reference will be made to an acoustical compliance and to an acoustical mass there being an acoustical compliance and an acoustical mass associted with each of the slots 33 and 35. With reference to the slot 35, the acoustical compliance consists of the cavity 126 and that portion of the slot 35 adjacent to the grill-like opening member 128. The acoustical mass is the air mass located in that portion of the slot located above the radius 71 of the wall 47 which is not adjacent to the grill-like opening member 128. Thus, the acoustical mass is located in a lower portion of the slot 35 located above the radius 71 and below the grill-like opening member 128 and in an upper portion of the slot 35 located above the grill-like opening member and below the outer edge of the slot 35.

The most basic form of a low pass acoustical slot filter is shown in FIG. 8. The acoustic masses (M represents the mass of air in the open slot which is accelerated by a net force that acts to displace the gas (air) without compressing it. The acoustic compliance (C is associated with a volume of air that is compressed with a net force without acceleration. The cut-off frequency of the slot filter is inversely proportional to the acoustic mass and acoustic compliance. The acoustic mass of a narrow slot is given by the equation A 5 wt where l=length of slot in which the sound wave is travelling,

w=width of the slot as viewed from the direction from which the sound wave is coming,

t=thickness of the slot p =density of air which is equal to 1.19 kg./m.

For the preferred embodiment of the acoustic device 50 of FIG. 4

l=0.25 in. t=0.078 in. w=14.4 in.

Hence, M =12.5 kg./m. The equivalent mass of the acoustic device is equal to 2M representing the mass on either side of the acoustic compliance which is equal to 25 kg./m. in the preferred embodiment.

The acoustic compliance of an enclosed volume of air V with an opening for entrance of pressure variations is given by the following equation:

V=volume of air =density of air 0 =speed of sound=344.8 m./sec.

For the acoustic device depicted in FIG. 4,

V=(l4.4 in.) 0.4 in.) 1.9 in.)

Hence,

V CA -(1.263)(1O 9) newton The cut-off frequency of the filter is given by the following equation:

The above computation shows that the acoustic device acts as a filter which effectively eliminates sounds emitting through the slots 33 and 35 of FIG. 4 which have a frequency greater than 1790 c.p.s.

Referring once again to FIG. 4 of the drawings, it has been described that an alternate acoustic device 50 in the form of a large open chamber could be utilized instead of the acoustic filter depicted. Such a device could be shaped in the identical shape of the acoustic filter depicted with the lower-most surface 131 of the sheet metal wall 113 removed therefrom thereby creating an inverted U-shaped cavity. Additionally, the grill-like opening members 128 and 129 would be replaced by solid walls and the inside surfaces of the thus formed inverted U-shaped member can be lined with 4 inch thick sound absorbent material thereby creating a large sound absorbing surface directly over the platen area and located immediately adjacent to the slots 35 and 33 through which the paper emanates. Such a device appreciably reduces emanated sounds of frequencies above 1,000 c.p.s.

Referring now to FIG. 9 of the drawings, a frequency plot showing the sound level emitted from a typical typewriter compared with a typewriter having the acoustical cover of the present invention incorporating the acoustic device 50 depicted in FIG. 4 and compared with a type writer having the acoustical cover of the present invention incorporating an inverted U-shaped acoustic device as heretofore described is depicted. The sound was measured by a microphone placed parallel to the paper path and one foot above the top of the acoustical device. The ordinate of the frequency plot represents the RMS sound pressure level as measured within each octave pass band denoted on the upper abscissa scale. The lower abscissa scale denotes the center frequencies of the octave pass bands.

The curve 138 is that of a typical typewriter operating without any acoustical cover over the platen area, the curve 139 is that of the same typewriter operating with the acoustical cover of the present invention having an inverted U-shaped acoustic device and the curve 140' is that of the same typewriter operating with the acoustical cover of the present invention having an acoustic filter type acoustic device. As can be seen, the acoustical cover incorporating either acoustic device effects a 3 db sound reduction in the 710 to 1400 cycle per second pass band and an 11 db reduction in the 1400 to 2800 cycle per second pass band as compared with the typical typewriter.

As has been described, the cut-off frequency of the acoustic filter in the preferred embodiment is 1790 cycles per second. Thus the curve 140 is appreciably below the curve 139 in the frequency bands above 1790 c.p.s. representing the sound diminuation effected by the filter. However, it should be noted that the acoustical cover of the present invention effects a substantial noise reduction in the frequency bands above 1790 c.p.s. when either acoustic device is incorporated therein.

While the above discussion has related to an acoustical cover for the platen area of a typewriter or the like machine, it is understood by those skilled in the art that noise which emits from other locations of typical typewriters should also be minimized in order for there to be a substantial reduction in the noise generated by such a machine. For example, the keyboard opening and slots such as the margin lever slots could be sealed by utilizing respectively, a flexible membrane fitted over the keystems and a closed cell foam material fitted within the slot areas. Additionally, the interior walls of the machine could be lined with sound absorbent material Where possible, and the machine could be shock mounted on its base in accord with conventional and well-known practices.

A further modification which could readily be made to the acoustical cover of the present invention would be to mount the end walls thereof on the typewriter housing. Thereafter, the remaining portion of the cover could be placed on the machine to form an integral container over the platen area as has been described.

While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it should be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the scope of the invention.

What is claimed is:

1. An acoustical cover for an office machine of the type having a housing for enclosing the machine operating elements and an opening for accommodating paper access, said cover being configured to enclose said opening and comprising:

a first substantially vertical transparent window wall;

a second wall connected to the upper portion of first wall and sloping downward therefrom;

a third wall connected to the lower portion of said second wall and sloping upward therefrom;

a pair of oppositely faced end walls connected to the side edges of said first, second, and third walls;

an acoustic device having one surface thereof substantially parallel to said third wall and forming an unobstructed paper feeding slot therewith through the enclosure formed by said cover, said acoustic device defining at least one acoustic cavity located in close proximity to the paper feeding slot for reducing the noise that would otherwise emanate from the paper feeding slot.

2. The acoustic cover set forth in claim 1, wherein said first and said second walls are pivotally connected with respect to said acoustic device.

3. The acoustical cover set forth in claim 1 wherein said second and third walls are constructed of a transluscent light diffusing material.

4. The acoustical cover set forth in claim 1 wherein said acoustic device comprises an acoustic slot filter hav ing an opening between said slot and said cavity whereby said cavity forms an acoustic compliance with the acoustic air mass within said slot, said acoustic slot filter acoustically filtering audible sounds that would otherwise emanate from the slot.

5. The acoustical cover set forth in claim 1 wherein said acoustic device comprises an inverted U-shaped member which forms said cavity, one wall of said member providing said substantially parallel surface, the open ing in said inverted U-shaped member being oriented directly above the machine operating elements and adjacent to the paper feeding slot created by said surface.

6. The acoustical cover set forth in claim 1 further compnsrng:

a fourth wall substantially perpendicular to the pair of end walls and forming a second unobstructed paper feeding slot with a second surface of said acoustic device.

7. The acoustical cover set forth in claim 6 wherein said acoustic device comprises two acoustic slot filters each having an acoustic cavity associated therewith and each being associated with one of said slots, each of said slot filters having an opening between its corresponding slot and cavity whereby each of said cavities forms an 11 12 acoustic compliance with the acoustic air mass in its cor- 9. The acoustical cover set forth in claim 8 wherein responding slot, each of said acoustic slot filters acoussaid hood forms an integral portion of said elongated tically filtering audible sounds that would otherwise empassageway. anate from its associated slot. References Cited 8. An acoustical cover for an office machine of the 5 UNITED STATES PATENTS type having a housing for enclosing the machines operating elements and opening for accommodating paper ac- 2511147 8/1950 cess, said acoustical cover comprising: FOREIGN PATENTS a hood configured to enclose said opening and having 492 502 9/1938 Great Britain at least one unobstructed paper slot located therein; 10 an acoustic slot filter having at least one elongated un- THER REFERENCES obstructed p p pa having openings at Acustica (periodical) vol. 12, No. 3, 1962, pp. 139- PQ ends to facllltate the feeding of Paper from 152, The Performance of Acoustic Hoods at Low Fre- Sald P p slot to the machlne Operating elements, quencies, by R. S. Jackson, copy in Patent Office sciensaid filter further comprising at least one acoustic 15 tifi 111 cavity forming an acoustic compliance with the acoustic air mass in said passageway for filtering ROBERT D, 111., Pnrnary Examiner audible sounds over a wide frequency range that US. Cl. X.R.

would otherwise emanate from the paper slot. 17842; 181-48

US3513938A 1969-06-02 1969-06-02 Acoustical covers for office machines Expired - Lifetime US3513938A (en)

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US82940669 true 1969-06-02 1969-06-02

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US3513938A Expired - Lifetime US3513938A (en) 1969-06-02 1969-06-02 Acoustical covers for office machines

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US (1) US3513938A (en)
JP (1) JPS497450B1 (en)
BE (1) BE749849A (en)
DE (1) DE2024227B2 (en)
ES (1) ES380252A1 (en)
FR (1) FR2052342A5 (en)
GB (1) GB1282693A (en)
NL (1) NL171245C (en)

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3688866A (en) * 1971-08-30 1972-09-05 Ibm Noise muffler for magnetic tape vacuum column
US3802536A (en) * 1972-10-27 1974-04-09 Storage Technology Corp Mufflers for magnetic tape drive system
US3901372A (en) * 1974-07-22 1975-08-26 Teletype Corp Protective cover with viewing window for printers
US3912069A (en) * 1974-08-12 1975-10-14 Robert Faulhaber Sound confining typewriter cover
USRE29301E (en) * 1971-08-30 1977-07-12 International Business Machines Corporation Noise muffler for magnetic tape vacuum column
US4252453A (en) * 1978-04-20 1981-02-24 Centronics Data Computer Corp. Acoustic attenuator system for quietizing printers and the like
US4355914A (en) * 1980-05-01 1982-10-26 International Business Machines Corporation Acoustic hood with glare shield
EP0092291A1 (en) * 1982-04-19 1983-10-26 Philips Electronics N.V. Printer comprising a noise-sealing paper-transport roller
US4422787A (en) * 1982-05-10 1983-12-27 Guthrie George L Tear bar for a printer
US4493573A (en) * 1982-03-19 1985-01-15 Ricoh Company, Ltd. Printing apparatus
US4502804A (en) * 1982-09-24 1985-03-05 Willcox Frederick P Paper feeding and guiding system
US4605145A (en) * 1984-01-10 1986-08-12 Mannesmann Ag Sheet separating structure
US4674899A (en) * 1982-12-07 1987-06-23 Canon Kabushiki Kaisha Recorder with improved paper feeding including multiple feed paths for selective feeding of webs and cut sheets
EP0270030A2 (en) * 1986-11-29 1988-06-08 Kabushiki Kaisha Toshiba Printer
US5970866A (en) * 1994-09-12 1999-10-26 Tohoku Ricoh Co., Ltd. Printing machine with sound reducing apparatus
US20170101280A1 (en) * 2015-10-08 2017-04-13 Ricoh Company, Ltd. Sheet conveying device, sheet feeder, and image forming apparatus

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS4996007U (en) * 1972-12-11 1974-08-19
JPS5047506U (en) * 1973-08-30 1975-05-12
JPS50147852U (en) * 1974-05-27 1975-12-08
JPS5812952U (en) * 1981-07-20 1983-01-27
JPH0237869B2 (en) * 1983-02-10 1990-08-28 Seikosha Kk
DE4022141C2 (en) * 1990-07-11 1993-08-26 Aeg Olympia Office Gmbh, 2940 Wilhelmshaven, De
JP6143200B2 (en) * 2014-12-09 2017-06-07 株式会社リコー Image forming apparatus

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB492502A (en) * 1937-02-27 1938-09-21 Siemens Ag Improved sound proof casing for printing telegraphs and like machines
US2517147A (en) * 1948-09-30 1950-08-01 Teletype Corp Silencer for printing telegraph apparatus

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB492502A (en) * 1937-02-27 1938-09-21 Siemens Ag Improved sound proof casing for printing telegraphs and like machines
US2517147A (en) * 1948-09-30 1950-08-01 Teletype Corp Silencer for printing telegraph apparatus

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3688866A (en) * 1971-08-30 1972-09-05 Ibm Noise muffler for magnetic tape vacuum column
USRE29301E (en) * 1971-08-30 1977-07-12 International Business Machines Corporation Noise muffler for magnetic tape vacuum column
US3802536A (en) * 1972-10-27 1974-04-09 Storage Technology Corp Mufflers for magnetic tape drive system
US3901372A (en) * 1974-07-22 1975-08-26 Teletype Corp Protective cover with viewing window for printers
US3912069A (en) * 1974-08-12 1975-10-14 Robert Faulhaber Sound confining typewriter cover
US4252453A (en) * 1978-04-20 1981-02-24 Centronics Data Computer Corp. Acoustic attenuator system for quietizing printers and the like
US4355914A (en) * 1980-05-01 1982-10-26 International Business Machines Corporation Acoustic hood with glare shield
US4493573A (en) * 1982-03-19 1985-01-15 Ricoh Company, Ltd. Printing apparatus
US4465390A (en) * 1982-04-19 1984-08-14 U.S. Philips Corporation Printer comprising a noise-sealing paper-transport roller
EP0092291A1 (en) * 1982-04-19 1983-10-26 Philips Electronics N.V. Printer comprising a noise-sealing paper-transport roller
US4422787A (en) * 1982-05-10 1983-12-27 Guthrie George L Tear bar for a printer
US4502804A (en) * 1982-09-24 1985-03-05 Willcox Frederick P Paper feeding and guiding system
US4674899A (en) * 1982-12-07 1987-06-23 Canon Kabushiki Kaisha Recorder with improved paper feeding including multiple feed paths for selective feeding of webs and cut sheets
US4826335A (en) * 1982-12-07 1989-05-02 Canon Kabushiki Kaisha Recording apparatus having a rotatable cover including a guide for guiding a non-continuous record sheet to a recording head and having another guide for guiding a continuous record sheet having holes therein to the recording head
US4605145A (en) * 1984-01-10 1986-08-12 Mannesmann Ag Sheet separating structure
EP0270030A2 (en) * 1986-11-29 1988-06-08 Kabushiki Kaisha Toshiba Printer
EP0270030A3 (en) * 1986-11-29 1990-05-30 Kabushiki Kaisha Toshiba Printer
US4943173A (en) * 1986-11-29 1990-07-24 Kabushiki Kaisha Toshiba Sound dampening impact printer
US5970866A (en) * 1994-09-12 1999-10-26 Tohoku Ricoh Co., Ltd. Printing machine with sound reducing apparatus
US20170101280A1 (en) * 2015-10-08 2017-04-13 Ricoh Company, Ltd. Sheet conveying device, sheet feeder, and image forming apparatus
US9938099B2 (en) * 2015-10-08 2018-04-10 Ricoh Company, Ltd. Sheet conveying device, sheet feeder, and image forming apparatus

Also Published As

Publication number Publication date Type
NL171245C (en) 1983-03-01 grant
ES380252A1 (en) 1972-09-01 application
DE2024227B2 (en) 1972-03-23 application
NL171245B (en) 1982-10-01 application
DE2024227A1 (en) 1971-11-18 application
NL7007565A (en) 1970-12-04 application
GB1282693A (en) 1972-07-19 application
FR2052342A5 (en) 1971-04-09 application
BE749849A (en) 1970-10-01 grant
BE749849A1 (en) grant
JPS497450B1 (en) 1974-02-20 grant

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