US2126566A

US2126566A - Acoustic device

Info

Publication number: US2126566A
Application number: US759679A
Authority: US
Inventors: Robert N Marshall
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1934-12-29
Filing date: 1934-12-29
Publication date: 1938-08-09
Anticipated expiration: 1955-08-09
Also published as: BE412830A; FR799518A; NL45821C; NL43957C; GB464996A

Description

ug. 9, 1938. R, N MARSHALL y 2,126,566

ACOUSTIC DEVICE Filed D60. 29) 1934 5 Sheets-Sheet 2 /N VENT @MMA/95124 'BV @am 6,. 1M

' A TTORNEY Aug. 9, 1938. R. N. MARSHALL' u I 2,126,566

ACOUSTIC DEVICE Filed Deo. 29. 1934 5 Sheets-Sheet 4 /NVENTOR By. RNMARSHALL @am 5. 141% ,i

A TTORNEY R. N. MARSHALL 2,126,566

ACOUSTIC DEVICE Filed Dec. 29. 1934 5 Sheets-Sheet 5 maan, 6, Map2.

ATTORNEY Patent-ed Aug. 9,1938

UNITED STATES PATENT I oFFicE y Application netsnoer ze, 1934, serai No. '15am 17 Claims.

I'his invention relates to acoustic devices; and, more particularly, to microphones or transmitters of the moving coil or electrodynamic type.

An object of this invention is to improve the structure and operating characteristics of acousl means for enhancing the low frequency response of the device.

Still another feature comprises an enclosure or case for an acoustic device in which the case interior is divided into at least two chambers conv nected by a passage that may be open or closed at the will of the user to control the effective volume of the case.

' Other and further features will be evident from the detailed description which follows hereinafter.

In accordance with this invention, an acoustic device comprises a case open at its ends of different sizes, and enclosing a devicecomprislng a diaphragm, moving coil, and magnet structure,

3c the diaphragm being in alignment with and closing the ysmaller end of the case. The larger end of the case is closed by a plate or wall member, supporting the magnet structure and. diaphragm in position, andv containing a passage. A cover member forming part of the case is secured tothe remaining lportion of the case by a plurality of plug pins, each projecting at one end from the 'l cover and threadably engaging the wall member at the other end. 4The cover and wall members denne another air chamber in which is positioned an elongated, open-ended tubular member, one open end of which is secured to the cover and in alignment. with an. apertured portion, thereof. -lf desired, the tubular member may replaced by an elongated groove in the case, either on the inner or outer surface thereof, a closure member overlying vthe groove, the closure member and case containing passages connecting the interior of the case and' the atmosphere through the :30V groove.' The closure member may be adjustable in position to vary the effective length of the i groove. The passage connecting the chambers in the case may be covered with anacoustic resistance material, means being provided to vary the 'I 55 effective area thereof,

A more complete understanding of this invention will be derived from the detailed description which follows, taken in conjunction with the appended drawings, wherein: l

Fig. 1 is an enlarged cross-sectional view of anx 5 acoustic device constructed in accordance with this invention;

. Fig. 2 is a cross-sectional view of the device of Fig. 1, taken along the line 2-2 thereof;

Fig. 3 is-an end view of the device of Fig. 1, 10 taken along the line 6-3 thereof;

Fig. 4 is a view of the cover orclosure member of the device of Fig. 1, taken along the line 4--6 thereof:

Fig. 5 is a sideelevation, substantially actual 15 size, of the device of Figs. 1-4, a jack or connector being shown associated with it; Y Fig. 6 is an enlarged cross-sectional view of another acoustic device constructed in accordance with this invention; 20

Fig. 'l is an end view of the device of Fig. 6, taken along the line 1-1 thereof with the cover or closure member removed, and partially broken away to show the cord; Y

Fig. 8 is a cross-sectional view, apprczdmately 25 actual size, of the device of Fig. 6, taken along the line 6-6 thereof;

Fig. 9 is an enlarged, cross-sectional view of still another acoustic device constructed in accordance with this invention;

Fig. 10 is a cross-sectional view, approximately actual size, of the device of Fig. 9,y taken along the line IO-ll thereof; f A

Fig. 11 is a front viewsubstantially actual size, of another acoustic device in accordance with 35 this invention; i A

Fig. 12 is a side elevational view of the device of Fig. 11;

Fig. 13 is an enlarged, cross-sectional view of me device of ng. 11,1:axen along me une n n 40 thereof, and with the front screen and associated frame removed; y

Fig. 14 is'a cross-sectional view of the device of Figs. 11 l3, taken 'along the line II-Il of Fig. 13; and

Fig. v15 is a plan view of afragment of the device of Fig. 11. A

The acoustic device of l'lgs.' 1-5 comprises an electrodynamic microphone or transmitter, designated generally, Il. -It comprises a hollow housing, container, enclosure or case Il, of insulating material, for instance, phenol linen, inwardly curved'to present a substantially hemispherieal outer surface at its front end 22, which contains acircularopening inwhichanaperturcdplate 5';

or protective grid 2|, for instance, of brass, is positioned. The interior of the case is divided into two air chambers or compartments 2l, 2B by a disc, plate or partition member 21, held against the internally projecting shoulder or flange 2l by a lock or clamping ring 2l, externally threaded for engagement with the internally threaded annulus Il oi' the case.

An electrodynamic unit 2| ls mounted in one chamber 2i, and comprises a Ushaped permanent magnet 32, preferably of cobalt steel or cobait-molybdenum steel; an outer pole member 3l, preferably of magnetic iron; an inner or central and substantially cylindrical pole member 24. preferably of cobalt steel or cobalt-molybdenum steel; and a dome-shaped or cap member l5, preferably of magnetic iron. The outer pole has an annular, central portion 28, and a pair of radially outwardly, downwardly projecting extensions 21, Il, one extension 31 containing a circular passage II, and the other a slot Il ex tending inwardly from its periphery, the passage Y and slot receiving pin members 4|, for instance,

of steel, projecting from the ends 42 of the magnet. Pole member 24 has a central passage '4I for a clamping member or bolt Il, the central pole and the cap member being fastened to the central and straight portion 45 of the permanent magnet by this bolt, the threaded end I6 of which is engaged by a pair of nuts l1.

'111e diaphragm 4I is of any suitable material, for instance, a light-weight, high-strength material, such as duralumin. It comprises a centrally stiiiened, dome-shaped portion 49; an outer, annular peripheral portion Si; and an-in termediate, flexible, tangentially'corrugated portion Il. The annular portion is secured to the annular ridge or flange $2 of the outer pole, preferably by cement, and such that the coil 53, which may be of edge-wound, insulated, aluminum ribbon or tape and secured to the diaphragm at the junction Il of the portions 49 and 5| thereof, is centered in the annular air-gap defined by the

members

22, 35. The coil leads (not shown) are connected to terminal members (not shown) carried by arcuate-shaped terminal strips Il of insulating material, that are fastened to the inner surface 5l of the pole member 23.

Acoustic damping means is positioned under the air-gap and comprises an annulus 58 of damping cloth, preferably silk. It is supported by a plate or ring member l! of non-magnetic material, for instance, brass, containing a pluralityof elongated passages 8|. The ring 59 is maintained in position by a resilient sleeve or ring Il, preferably of soft rubber, that encircles the central pole and is carried by the ring member Il supported on the shoulder or ledge I2, and ls spaced from the under surface il of the outer pole by a resilient washer or ring Il, preferably of soft rubber.

The diaphragm end of the unit llcloses the case opening 23, a resilient washer il, for instance, rubber, being interposed between the outer portion of the diaphragm and the radially extending nange portion to provide an air proof seal. It is apparent that the electrodynamic unit 2| is compact and may be .mounted in a confined and substantially hemispherical space in such a manner as to utilize the available space to the greatest extent possible.

The partition member 21 is of insulating material and contains a frusta-conical shaped opening or passage 01 connecting the chambers 2l, 2i,

the smaller end opening into chamber 2B. It has embedded in it a pair of internally threaded bushings 8l, and a cup-shaped member 69, each of which may be of brass. The cup member contains a helical spring 10, for instance, of phosphor bronze. The clamping nuts 41 bear against the spring 10, which with the partition member in place, is under compression, whereby the unit 3| is forced forward to cause the diaphragm outer portion to bear against the washer E5. The bushings 62 are electrically connected by suitable conductors (not shown) with the coil lead terminals on the members 5B.

The second chamber 26 is defined by the partition member and a removable portion or cover 1| of the case. This cover supports on its inner surface, an elongated, coiled tubular member 72, open at each end, and one end 'i3 of which is secured to the cover by a clamping plate 14, screws 92 and gasket l5, in line with the multiaperture portion l! thereof. This tubular member is provided in accordance with the teachings of A. L. Thuras Patent 1,869,178, issued July 26, 1932, and in a device constructed in Vaccordance with Figs, 1-5 was approximately six inches long and one-eighth inch in inner diameter.

The cover contains an elongated slot or recess l1 adapted to receives jack 'i8 for engagement with three pins or contacts 19 which are supported by the case and project into the slot. The pins have threaded extremities all, which thread into the bushings and cup member to secure the cover to the remaining portion of the case. Where the pins extend from the cover into the slot, they are surrounded by a suitable sealing compound Il, for instance, sealing wax. A tight seal between the cover and the rest of the case is ensured by providing the cover with sharp-edged annular ridge l2, and inserting between it and the shoulder portion 83 of the case, a resilient ring I4 adapted to be compressed when the cover is united to the rest of the case.

The

chambers

25, 26 and the passage El permit wave propagation from the rear of the diaphragm when the microphone is being used. The tubular member, of course, causes the response of the microphone to be enhanced in the region of the low sound wave frequencies.

Supported on the case and in front of the grid 2Q, is a screen comprising a double layer 85 of cloth, preferably, silk. It is mounted between a pair of protective brass screens I6, within a channeled ring l1, together with a ring member Il having three equally spaced projecting portional! having rivets Sl at their extremities for engagement with three equally spaced recesses S2 in the case. I'his screen is provided in accordance with the teachings of the pending application of F. F. Romanow, Serial No. 729,759, filed June 9, 1934, Patent No. 2,106,813, issued Feb. 1, 1938, to render the open field response characteristic of the microphone substantially uniform regardless of the microphones position with reference to the sound wave source.

The acoustic device of Figs. 6, 7 and 8 comprises an electrodynamic microphone or transmitter, designated generally, |00. It comprises .a hollow housing, container, inclosure or case Illl, the interior of which is divided into two air compartments or chambers |02, lll by a disc, plate or partition member IM containing a frusto-conically shaped passage or opening |05 Join ing the two chambers. With such a shaped passage, the acoustic mass effect of the air in the passage is substantially negligible. 'Ihe chamtion or cover member |05 of the case. The casev is curved at one end |01 so as to present a substantially vhemispherical outer surface, and contains a circular opening 20 in which the grid 24 is positioned. The electrodynamic u'nit |03 is substantially the same as the unit like parts bearing like identifying numerals. The magnet 45, pole member 34 and dome-shaped or 'cap pole-piece |00 are secured together by a screw ||0, the head of which nts into the central aperture ||2 in the partition member. A sealing washer ||0 is interposed between the magnet and partition member. The unit is maintained in position by the partition member, which, in turn, is held in place by a lock or clamping rin'g ||4, externally threaded for engagement with the threaded annulus |I of the case. Y

The case contains a circumferentially arranged groove, channel or receas ||5 in its outer surface, a closure member or ring ||1 being disposed thereover, having a sliding t with the annular surface portion ||0 of the case, and resting against the shoulder or ledge portion H9. The

member ||1 contains an opening or aperture |20 (see Fig. 8) connecting the atmosphere outside of the case with the groove; the groove at one end connects with the interior of the case, speeically, chamber |02, through a passage or opening |2|. These apertures |20,' |2| are circular and of approximately the same area as the crosssectional area of the channel or groove ||5. The

member ||1 is rotatable such that the position of the aperture |20 with reference to the aperture |2| is variable to varylthe effective length of the tubular passage. If the member ||1 is adjusted so that the aperture |20 is positioned over the portion |22 of the case, the interior of the case is closed, of course, from the atmosphere outside the case. This groove or channel functions,

like the tubular member 12, to enhance the low frequency response of the acousticdevice and, since its effective length is variable, the low fre vquencyresponse may be varied at will.

It may be desired to modify the wave propagation in the chambers |02, |00. Closure means |20 is provided for closing the passage |05, and by isolating chamber |03, to reduce lthe eil'ective volume of air on the rear side of the diaphragm. It comprises a pad |24 of'resilient material, such as rubber, between a pair of washers |25, and fastened by a bolt |25 and nut |21 to one end of a wire frame member |23, the other end of which is supported Vin vslideways |20 of a U- shaped frame member |00 securedto the partltion member by any suitable means, for instance, rivets |0|. A helicalspring |02 is connected at one end to the pad end of the member |20, and at its other end to the lug portion |00 of the member |00. The angularly projecting end portion |04 of the member |20 is engaged by one end of a link |05 whose other end |05 projects through an opening |01 in the case wall and terminates in a button member' |03 adapted tol indicated by the broken lines.- A' slight pressure onanebutton lss returns the closure means u; its original position under the'. restoring "action frame member |00. The latter is engaged by thehead of the bolt H0. The terminals |4| 'are electrically connected by suitable conductors (not shown) with the terminal members on the insulators 55.

The devices of Figs. 6, '1 and 8 and Figs. 9 and are substantially alike, like parts bearing likereference numerals, that of Figs. 9 and 10, however, embodying a different arrangement of the low sound wave frequencies enhancing means. The inner surface |50 of the case |5| contains a groove, channel or recess |52 over which is positioned a ring-shaped closure member |50, preferablysecured to the surface |50 by a screw |54. 'I'he case contains an aperture or passage|55 at one end of the groove connecting it with the atmosphere outside the case, and the closure member contains an aperture or passage |56 at the other end of the groove connecting 'the' latter withv the interior of the casing, specifically, chamber |02. 'The passages |55, |55 are preferably circular and of approximately the same area as lthe cross-sectional area of the groove.

- threaded for engagement. with the threaded por- A removable portion or.

tion |51 of the case.'l cover |55 defines, in part, the chamber |53'. The case outer surface contains a groove |59, similar to the groove ||5 ofthe device of Figs. .6-8, a ring-shaped closure member |10 being slidably positioned thereover and bearing against the shoulder or ledge |1| of the case. A retaining member orl screw |12 prevents the closure n-iem-v ff ber from shifting toward the front of the transmitter. The closure member contains an aperture 20| similar to the aperture |20 of the closure member H1; the aperture or passage |13 connectsthe groove |59 and the interior of the case, specifically, chamber |52. To ensure that the closure member .will remain in its adjusted position, one edge is provided with spaced notches |14 adapted tovbe engaged by the stepped-end |15 of a finger-operable rod |15., This rod extends -through a passage |11 in the upperpart of the case. and is encircled for a portion of its length by a helical spring |18-, normally under compression. Normally, therefore, the ,rod cooperates with the closure member. When it is desired to adjust the position of the aperture in the closure ,member with reference to the aperture leading from the'groove to the case interior and, thereby, to vary the effective length of the path between the exterior -and interior of the case, the nger engageable member |19 on'the rod |15 is pushed rearwardly to move the end of th'e rod out of the notch against the restoring action of the spring. Theclosure member is then turned to the desired degree, the pressure on'the member |10 isreleased, andthe rod engages again with a notch-in the closure member.

'7'5 of thespring. A three conductor cord |00 ex- The partition member contains a plurality of 75 spaced passages |88, preferably of less diameter than the thickness of the partition member and connecting the air chambers |52, |83. A strip |8| of damping material, for instance, silk, is secured to one surface |82 of the partition member and across these passages. on the other surface of member |88`and is adapted to be adjusted in position manually from outside the case by means of a rod |84, so that some or all of the passages |88 are obstructed. Not only is the effective volume of air on the rear or inner side of the diaphragm thus controllable, but the case resonance is eliminated by the provision of the right number of passages or holes |88 and/or damping material ill. In small microphone design, in which large cases in comparison with the size of the electrodynamic unit are required, uncontrolled case resonance has been found undesirable.

The opening 28 is closed by a multi-apertured plate or grid I 85 which fills the cavity in front of the diaphragmand increases the normal range of the electrodynamic unit at high frequencies by preventing resonance by the air in the opening 28 until, for example, about 12,00015,000 cycles per second, or by leaving unaffected the normal reso nant effect of the air of the opening, but adding another resonance at a higher frequency. 'I'he passages or holes |88 in the grid are shown of greater length than diameter although they may be of greater diameter than length, and, since the effect of a particular grid is critical with its distance from the diaphragm, the high end response of the transmitter may be made variable by providing the grid with an externally threaded portion |81 for engagement with the internally threaded portion |88 of the case.

Supported on the case |8| and in front of the grid |88, is a framemember |88. It comprises an apertured plate member |88 behind which a strip of damping cloth, silk (not shown), is positioned in accordance with the disclosure ofthe pplication of F. F. Romanow, Serial No. 729, 59, filed June 9, 1934, Patent No. 2,106,813, issued Feb. 1, 1938. lIhe member |80 is integral with a plurality of spaced supporting arms |8I, integral at' their other ends with a ring member |82 which contains an elongated slot |88. A guide member Vor screw |88 projects from the case, specifically, from the closure member |18. When it is desired to adjust the position of the cloth screen with reference to the case, the screw is loosened, the frame member turned with the screw acting as a guide in the slot, and the screw tightened to fasten it in its new position.

While the featuresrQt-jthis invention have been disclosed with reference to several specic embodiments, it is to be understood, of course, that various modifications may be made therein without departing from the scope of this invention as defined in the appended claims.

What is claimed is: f

1. An acoustic device comprising a case having anopen end, a sound wave translating unit in said case and including a diaphragm and a magnet, said diaphragm closing said open end, means in said case between said magnet and the other end of said case dividing it into two chambers and bearing against said magnet to hold it in position so that the diaphragm closes said case open end, said means containing a restricted. small area passage connecting said chambers, and means constituting a restricted sound wave passage for enhancing the low frequency response of the de# A slide |83 is supported vice, connecting one of said chambers with the atmosphere outside of the case.

2. An acoustic device comprising a case having an open end, a diaphragm in said case and closing said open end, and means supported by said case and defining with the case a variable length,

restricted sound wave passage connecting the in-` terior of the case and the atmosphere, for enhancing the low frequency response of said diaphragm.

whereby the distance between said passages may be varied.

4. A n acoustic device comprising a case having Van open end, a diaphragm in said case and closing said open end, said case having an elongated groove in one surface, and a closure member over said groove, said member and said case containing passages for connecting the interior of the oase and the atmosphere through said groove.

5. An acoustic device comprising a hollow enclosure having an open end, a diaphragm closing said open end, said enclosure having a groove in one surface, and a closure member over said groove, said member and enclosure containing passages of substantially the same area as the cross-sectional area of the groove for connecting the interior of the enclosure and the atmosphere through said groove.

6. An acoustic device comprising a hollow enclosure having an open end, and a diaphragm closing said open end, said enclosure comprising a wall containing an elongated, restricted sound wave passage and having an aperture connecting the passage with the atmosphere outside the enclosure and another aperture connecting the passage with the interior of the enclosure on the inner side of the diaphragm.

7. An acoustic device as claimed in the preceding claim in which the effective length of said passage is variable.

8. An acoustic device comprising a hollow enclosure having an open end, a diaphragm closing said open end, said enclosure comprising a wall containing an elongated, restricted sound wave passage and having an aperture connecting the passage with the atmosphere outside of the enclosure and another aperture connecting the passage with the interior of the enclosure on the inner side of the diaphragm, a partition member in said` enclosure dividing it into two chambers with one of which said passage connects, said partition `member containing a passage connecting said chambers, and means for closing said last-mentioned passage.

9. An acoustic device comprising a hollow case having an open end, an electrodynamic unit in said case and including a diaphragm closing said open end but exposed to sound waves therethrough, means for varying the effective volume of the case on the rear side of the diaphragm, means for varying at will the response of the device at the lower end of the audio frequency range, and means to vary at will the response of the device at the upper end of the audio frequency range.

10. An acoustic device comprising a hollow case having an open end, a sound translating unit in said case and including a diaphragm closing said open end and being exposed therethrough to sound waves on one side, said case having a groove in its outer surface connected through an aperture in the case with the interior of the case on the other side of the diaphragm, and a closure member on said case and disposed over said groove, said member having an aperture therein connecting the groove with the atmosphere outside the case and being slidable relative to the case to vary the distance between the two apertures.

11. An acoustic device comprising a hollow case having an open end, a sound translating unit in said case and including a diaphragm closing said open end and being exposed therethrough to sound waves on one side, said case having a groove in its outer surface connected through an aperture in the case with the interior of the case on the other side of the diaphragm, and a closure member on said case and disposed over said groove, said member having an aperture therein connecting the groove with the atmosphere outside the case and being slidable relative tothe case to vary the distance between the two apertures, and means to hold said closure member against movement after adjustment of the closure member for the desired spacing of the aperture.

12. An acoustic device comprising a hollow case having open ends, a diaphragm within the case in alignment with and closing one of said open ends, a coil attached to said diaphragm, magnet structure for said coil, said case including a cover member for its other end and supporting an elongated open ended tubular member in the case, one open end of the tubular member being in alignment with an apertured portion of the cover, and a single wall member in said case dividing it into two chambers and supporting the magnet structure, diaphragm and coil in one chamber, said wall member having a restricted aperture dening a passage connecting said chambers.

13. An acoustic device comprising a hollow case having an open end, a sound wave translating unit in said case and including a diaphragm, a disc partition member slidably insertable in said case and dividing it intotwo chambers and having its central portion only bearing against said unit to hold the latter in position so that the diaphragm closes the case open end, means engaging the interior surface of said case and bearing against the peripheral portion of said partition member to maintain the latter in position, said partition member containing a small area, off-center passage connecting said chambers, and means independent of said partition member constituting a restricted sound wave passage for enhancing the low frequency response of the device, connecting one of said chambers with the atmosphere outside of the case.

14. An acoustic device comprising a case having open ends, a diaphragm within the case closing one open end, a coil attached to said diaphragm, a magnet structure for said coil, said case including a cover member for its other end and supporting an elongated open ended tubular member in the case, one open end of the tubular member being in alignment with an apertured portion of the cover, and a wall member in said case dividing it into two chambers connected by a passage in the wall member, one of said chambers containing the diaphragm, coil and magnet structure and the other chamber containing said tubular member.

15. Anacoustic device comprising a hollow case having a substantially hemispherical section having an apertured Wall portion extending across its region of greatest diameter, and containing a sound wave passing opening in its curved surface portion, a diaphragm closing said opening, a cover member dening an air chamber with said wall portion, said member containing a passage ,connecting the chamber with the air outside the case, and a tubular member between said wall portion and cover member constituting a continuation oi the passage.

16. An acoustic device comprising a casing having openings at its front and back ends, a transmitter including a diaphragm and a magnet disposed within said casing, said diaphragm being positioned adjacent the front end of said casing, an apertured partition within said casing between said magnet and the back end of the casing, and a tubular member entirely within` the chamber nearest the back end of the casing and cooperating with an opening in the rear of the casing to acoustically connect they open air with the back side of the diaphragm solely via the apertured partition.

17. An acoustic device comprising a casing having an opening at its front and back ends, an apertured partition within said casing, dividing the interior into two chambers, a transmitter unit disposed in the chamber adjacent the front end of the casing, a tubular sound passageway member disposed in the chamber adjacent the back end of the casing and supported thereon, and means on said partition for holding said unit in place.

ROBERT N. MARSHALL.