US2371960A - Sound producing device - Google Patents

Description

March 2Q, 1945. w. c. EAVES 2,371,960

SOUND PRODUCING DEVIC Filed Jan. 1, 1942 3 Sheets-Sheet 1 BYWMOM ATTORNEY March-2o, 1945. w C. EAVS 2,371,960

SOUND PRODQCING DEVICE Filed Jan. 1, 1942 s sheets-sheet 2v ATTORNEY Mau'chy 20, 1945. w. c. EAvEs 2,371,960

SOUND PRODUCING DEVICE' ATroRN'EY vilatentedMar. 20, 1945 i unirse .STATES PATENT? FFICE SoUNn rnoDUcING DEVICE william c. naves, Elyria, om, signor to raves Sound Projectors, Inc., New York, N. Y., a corporation o! Delaware' Y Application January 1, 1942, Serial No. 425,368A

I Claims. (Ci. 179-108) This invention relates to sound lproducing devices and more particularly to devices of this character which employ a modulated uid stream as the sound generating medium.

vOne of the objects of the present invention is to -provide novel means for modulating the stream of fluid passing through a fluid i'low type sound producing unit whereby sound reproduction of greater iidelity and greater volume can be obtained by-said unit Vthan has` heretofore been possible in devices of this type Operating at like input pressures.

Another object of the invention is to provide novel pressure responsive means for balancing the' control valve of a pneumatic sound projecting device.

A furtherA object is to providenovel means for operatively connecting the actuating mechanism of a iiuid ow sound producing unit with the vibrating fluid modulating element thereof.

Still another object is to provide a novel sound head for a reproducing mit wherein substantially all resonant frequencies, foreign to the frequency band being reproduced, are eliminated.

A still further object is to provide a novel grid valve for modulating the fluid ow in a sound vproducing device and novel means for pivotally mounting the movable element of said valve.

` acters refer to like parts throughout the several views,

Fig-11s of one type of soundhead embodying the present invention; v j Fig. 2 isy an enlarged sectional view taken substantially along line 2-2 of Fig. r1 and having parts thereof shown in elevation:

- Fig. 3 is a fragmentary sectional view of a portion ofthe apparatus shown in Fig. 2, the cover of the housing for the actuating mechavnisrn of said apparatus being removed,i

Fig. 4 is a fragmentary view in side elevation of the portion of the apparatus shown in Fig. 3; Fig. 5 is a sectional'view, with parts broken away, taken substantially along line 5-5 of Fig. 3;

of the sound head and therefor; l

Fig. 7 is an enlarged view in side elevation of said mounting spring; i l

Fig. 8 is a sectional view, rwith parts broken the mounting Spring away, of a form of heating unit utilized in the A further object is to provide novel adjuststream to -produce the sound wherein diil'erences .in the input pressure of the fluid stream have substantially no effect upon the fidelity of sound reproduction.

The above and further objects and .novel features of the invention will more fully appear from the following detailed description when the same is .read in connection with thev accompanying' drawings. 'It is to be expressly understood, however. that the drawings are for the purpose of illustration only and are not intended as a dennition of the limits of the invention. reference for the' sound head, the section being taken substantially'along line 8-8 of Fig. 1;

Fig. 9 is a fragmentary sectional view similar to Fig. 3 of an alternate embodiment of the present invention, with parts thereof grammatically; and

Fig. 10 is a view similar other embodiment. i

According to the present invention, fluid under I pressure is caused tolflow through a sound head, and this stream of uid is modulated by novel control means. The modulated fluid stream constitutes the medium for reproducing and amplifying sounds which have been converted by suitable apparatus into mechanical vibrations 28 mounted thereon, said casing together with this latter purpose being hadprimarily to the l appended claims.

In the drawings, wherein like reference charand as such' have beenimparted to the control means.

Referring to the embodiment of the invention illustrated in Figs. 1 to 8, the sound head com-: prises a housing 26 (Figs. 1 and 2) having a iiuid.

passage 21 extending therethrough 'and a casing the wall of .said housing forming a chamber 29 for containing control apparatus to be more fully described hereafter. Housing 26 is preferably formed in two sections 26o, 2Gb (Fig. 2l joined by suitable means, Such 'as screws 26o. A'source of iiuid pressure,v as. for example, an air coinpresser unit (not shown) comprising a pump and:-

a reducing valve Aor other means for maintaining. theuid outputA of the -pump ata substana view in elevation on a reduced scaleI Fig. 6 is a perspective View of the movable grid to Fig. 9 of still an- `or fa like aluminum alloy. i

tially constant pressure, is connected to passage A21. preferably by mans of a coupling member 30 threaded into the'upper end of said passage, the

1 bore of the latter being internally threaded at A suitable air'iilter 32 is held between the inner end ofsaid coupling member and an internal shoulder 33 formed in the wall of passage 21, said iilter, as 'shown, comprising av pair of screen members 34. having disposed therebetween a layer 35 of fibrous material, such as porous felt.

To modulate the stream of air flowing through passage' 21, novel valve means of the grid type are interposed in the path of said stream, said means comprising a stationary grid plate 33 (Figs. 2, 3 and 5) and a movable grid plate 31 shown mounted on the low pressure side of said stationary plate for cooperation with the latter. Grid 36 is xed between sections 26a and 28h of housing 2B to extend transversely across passage 21, and is provided with a plurality of parallel slots or ports v3i! (Fig. 5), each of said slots having side Walls vwhich are substantially perpendicular to the parallel faces of the plate. Slots 38 are prefcrably equally spaced across the plate and the solid portions or bars 33a between said' slots are of a greater width than the width of said slots, for example, twice the width ofthe latter.

Grid 31 (Figs. 5and 6) is also provided with a plurality of parallel slots or ports 39 having bars 39a therebetween, and said slots Yare of substantially the same, length and width as slots 33 and are spaced across said grid in a manner similar to the'spacing of slots 38 across grid 38. Grid 31 is mounted so that slots 39 and slots 33 (Fig. 5) are parallel and in staggered relation to each other, each slot ot one grid being opposite a bar of the other grid and-being pref` V erably located midway between the two adjacent v equally spaced laterally and tapering longitudinally toward the free end of-grid 31. Y

It is desirable that the faces of grid plates 3B and 31 be. smooth and that,"when valve 38, 31 is in closed or inoperative position, as shown in' Fig. the adjoining faces of said valve plates have good surface contact with each other.

ably honed and lapped .to obtain smooth, plane surfaces.. Moreover, in order to avoid 'electrolytic action between the plates and prevent corrosion,

the plates are preferably formed from dissimilar'Y metals having a high resistance to corrosion. For

example, plate 33 may be formed from brass or German silverwhile plate 31 is made of Dural .'rhetmcrer portion of plate- :1 extends through a recess 40 (Figs. 2 and 3) in theinnerendof.,

` l section 24h` and is mounted in a novel manner "".ln ychamber 23 by being formedas onaarm of an, L-shaped valve member 42, the other arm of said ymember being numbered 43. Arm 43 is prei'- 1 erably perpendicular to plate 31 and comprises a base portion. 43a' (Flea. 4. and 6)v adjoiningslid Accord-' ingly, during fabrication, said plates are preferof base 43a, saidy central portion being connected plate 'and an elongated lever portion 43h extending outwardly and centrally from said base portion.

Moisture condensed from the air stream in passage 21 if permitted to pass into the chamber 23 tends to corrode or otherwise'impair the operation of the .control and driving means in said chamber, and to prevent such an'occurrence recess 4i) has inserted in the wall thereof a member 40a (Figs. 3 and 4) of relatively soit, nonacter of the material of pad 40a, the latter also acts to dampen any resonance eiects set up in `I -shaped member d2, thereby preventing a foreign frequency from being imposed on the voice or other frequencies being produced by the air stream.

To mount valve member 42 for substantially frictionless pivotal movement, a thin, fiat member 44 is provided toserve as a torsion spring support therefor. Member 44, which may be formed from spring steel, is 'secured at theends thereof by suitable means, such as screws 45, to the wall of housing 26, and intermediate the ends thereof to base 43a, preferably by a pair of rivets 46. As shown, member 44 spans a groove 41 (Fig. 4) provided in the wall of housing 28, said grooveextending lengthwise beyond both sides of' base 43a. Spring 44 has enlarged end portions 44a for receiving screws 45 and a relatively wide central portion 44h (Fig. 6) for engaging the face to said end Aportions by relatively narrow strips 44o. It is preferable that the plane of portion 44h have a slight inclination relative to the plane of portions 48a when spring 44 is subjected to no external forces (Fig. 7) so that when vsaid portions are mounted to become coplanar, as shown in Fig. 3, grid 31 is biased in the direction 'of grid 36o l To control the pivotal movement of valve member 42 and prevent undue distortion of spring 44, novel bearing means are associated with said member and spring to provide a ilxed axis for said pivotal movement. As lillustrated, the bearing means comprise a pair' of pivot pins 48 (Figs. 3 and 4) embedded in or otherwise riga idly secured to the Wall of housingv 28 with the outer, pointedends 48a' (Fig. 3) thereof engaging the bottoms ot a pair of recesses 49 provided in the ends of rivets 46 (Fig. 6). It is to be understood that recesses 49 are not limited to location :in the ends of the rivets .but may be disposed at any -two points in the face of said spring along the selected pivotal axis and that, if desired, more than two sets of pins and recesses disposed along said axis may be provided to serve as the fulcrum for said Spring. Moreover, pins 43 may be mounted for direct engagement with the flat face of spring 44 or rivets d'may'have the heads thereof rounded for direct'engagement with the wall of houslng-26 so as to dispense with pins 43.

barrel.

member 63 between the end of portion 64 and a screw member 68, threaded into the outer end a. flat, metal diaphragm 53, mounted across an opening 54 in the wall of housing 26 to com,- municate with chamber I, the latter being con.-

stituted by the portion of passage 21 between block 52 is thus effective to transmit to lever 43h pressures applied by diaphragm 53 in a direction t'o oppose movement of said lever to the left-as viewed in Fig. 3l The provision o f a non-resonant link between diaphragm 53 and lever 43h prevents thetransmission of resonance vibrations from said diaphragm to valve member 42, and also acts as an additional pressure compensating element.

'I'he eiective area of diaphragm 53 relative to the eflectivearea of grid plate 31, when the latter is in closed'\position, is such that the torque .opposing the lpivotal movement in a counterbarrel 63 -to securely hold said barrel 'in axial adjustment.

When the relationship between the eective areas of diaphragm 53and grid plate 31 is such that 'the desired balance of valve member 42 is not attained, the'axial position of barrel 63 is ad.- ju'sted by a suitabletool so that pin 6I will apply tlie'desired pressure to the diaphragm to effect the proper balance. Pin 6|', or at least the headv thereof, is preferably formed from a relatively rigid, non-resonant material, such as hardrubber, vto minimize the possibility of setting up resonant vibrations which are foreign -to the sound frequency being reproduced.

AIn order to modulate the air stream flowing through passage 21 and valve 36, 31 and impart 'desired sound producing characteristics thereto,

controlled vibrations within the audible frequency range are transmitted to member 42 and-are, in turn, imposed on said air stream by grid plate 31 of said member. For this purpose, suitable actuating means 10 are mounted in chamber 23, for example, by a bracket 10a shown in broken lines (Fig: 2) andfasillustrated, said means comprise an electrical unit of the magnetic type having a U-shaped, permanent magnet 1i carrying a voice coil unit-12, the latter being adapted clockwise direction,.as viewed in Figs. 2 and-3, o f member 42 and applied by said diaphragm, is-V slightly less than the torque applied by the air under pressure in chamber 5 I to plate 31. This.

pivotal movement of member 42 is opposed not only by the air pressure on the inner face of diaphragm 53 but also bythe deformation of spring member 44 and the diaphragm. The reincreases with an increase in the pivotal movement of member 42, While the forces acting on grid 31 due to .air flow and air pressure tend to decrease in magnitude as the distance between grid plates 36 and 31 increases. Accordingly,

at a point in the angular displacement of member 42, the resisting torque becomes equal to the torque inducing the pivotal displacement and the member is placed in equilibrium or is balanced,

whereupon the slightest vibration applied to diaphragm 53 in order to increase the resistancev to counter-clockwise pivotal movement o f va'lve member 42 when'such increase-isinecessaruto` properly balance said member.- As shown. said means comprise a pin 6l slidably mounted in the inner portion 62 of the bore of an externally threaded barrel 63 which extends through a threaded opening in the wall of housing 26. Pinvv 6i, which projects b'eyond the inner end of the Y barrel, has a headportion 64 of enlarged diamef-fAv ter which engages an internal shoulder 65' insaid A spring 61 is positioned inthe bore of of barrel 63. Spring 61 urges the shoulder on A pin 6| into engagement; with-shou1der65and the.

pin intovengagement with the inner face of diaphragm 53, lthe pressure-applied by said spring being subject to control by the axial adjustment Y.

The barrel and pin are.

to respond to current modulations to produce vibrations in an armature 13 corresponding to said modulations.' Armature 13 is mounted to have the longitudinal axis thereof substantially parallel to grid 31 and is vibrated by said actuating means in a direction perpendicular to its longitudinal axis. `It is to be understood that other types of actuating means capable of imparting controlled vibrations to a movable arm.

such as armature 13, may be utilized instead of l' the magnetic voice coil unit 1l, 12;

sistance provided by spring 44 and diaphragm 53 40' To faithfully transmit the vibrations from actuating means 10 to grid 31 and thereby attain s ound reproduction of high fidelity, a novel connecting linkage is provided between member 42 and said means. As shown, the linkage comprises armature 13 and an element 14 rigidly vsecured at one endthereof to said armature to extend therefrom at an angle of approximately in the direction of member 42, said element being secured at the other end thereof to an arm 15 formed with or otherwise rigidly fixed to arm 43 of the valve member, for example, .bg

being threaded therein. A pair of nuts 16 are in -Y threaded engagement with the externallg threaded portion 15a. of arm 15, and link 14 il preferably secured to said arm by having the end thereof clamped between said nuts. Arm Il is mounted so that the extension of the longitudinal axis thereof passes through the center of mass of member 42 and intersects the pivotal axis of. said member as determined bybearings 48, 49.:

It is preferable to mount arm 15 perpendicular" to lever 43 and, accordingly, the 'pivotal axis of` Ymember 4-2 is located in a plane which is parallel f to movable grid 31and'which contains the center o f` mass of. said member. As a Vresult` ofthis member and theprobability of setting upint'erfeing resonant vibrations in the parts of said mountingLof 'arm 15 and member 42, a balancedcondition may be more readily imparted to `said member during operation is greatly minimized@ lThe modulated air iiowing from valve 36, 31v

passes through th'oatportionlof passage 21. to a suitable sound propagating device,` such asa horn (not shown), which lmay be mounted on theexternally threaded lower -end of section 2Gb (Fig. 2). However, as the entire volume of air der the sound head' inoperative.

:lowing through stationary grid 38 cannot be connection to said member from the actuating subjected to the modulatingeiiects of movable grid 31, some air iiowing past the edges .of the latter as straight jets, a throat 11 is formed to offer a maximum amount o! influence on these unmodulated straight Jets and, in the illustrated embodiment, said throat is constricted in somewhat the same manner as the throat portion of a Venturi tube, lbeing proportioned to dissipate the energy of the currents of unmodulated air and thereby preventing said currents fromilow ing to the horn as straight jets with ensuing hissing noises.

The formation of ice on the surfaces of grids 38 and 31 or on the walls of the portions oi' passage` 21 adjacent said grids seriously aiects the quality oi' the sound reproduction and may ren- Accordingly, suitable means for preventing theformation of ice on the wallsof passage 21 and on the surfaces ci plates 38 and 31 are provided, and in one form comprise a substantially cylindrical container 19 (Figs. 1 and 8) lformed with housing 28 in the lower end of section 28a of said housing, said container having an open end and a flange 80 formed at said end. An electrical heating 'assembly 8| is positioned in container 19 through the open end of the latter, and is connected by suitable means, such as a cable 82, to a source of electrical energy (not shown), said cable having an annular, transversely disposed disc 83 secured thereon and adapted to be xed to ange 88 by means of screws 8l. Heat generated in heating assembly 8l is conducted to valve 88, 31 and the adjacent walls of passage 21 to maintain the parts at a temperature exceeding the freezing temperature of water. arrangements may also be utilizedfor the purpose of preventing ice formation; for example, a heating assembly may be located on the interior o! housing 28 in chamber 5i, or a heating element may be mounted in contact 'with stationary grid 38 adjacent the walls of passage 21.

During the operation of the above-described air head, it is desirable that the pressure ofthe fluid admitted to passage 21 be maintained at a constant value. The pressures available for operation oi the unit range from pressures suiiicient onlyto produce an air stream through the air head, e. g., pressures less than 3 lbs. per sq. in. gauge, to pressures limited only by the structural resistance of the parts of the unit directing and controlling the air stream. I'he fidelity of sound reproduction obtained by the sound head is sub-` stantially unailected for cooperating pressure selected' from the range of pressures between 3 lbs. per sqin.- gauge and 45 lbs. per sq. in. gauge,

the higher operating pressure having the eiiect.,l

means, is shown in Fig. 9. The iiow o! iluid through passage 21 is'modulated'by a valve comprising statonary'grid -38 and a movable grid 85 cooperating with the stationary grid to pei'-l form the same function as plate. of Figs. 1 to 8. However, grid 88 is disposed on the high pressure side of grid 38 rather than on the low pressure side, as inthe first embodiment. and extends through a recess 88 in the lower end of housing section 26a, said recess being suitably lined with a layer 81 of relatively soft, non-resonant material, such as sponge rubber. If desired, grid 85 may be pivoted at the left hand end thereof to housing section 28a, or said grid may be floated inoperative position merely by its connection to armature 93 to be described hereafter, but preferably said grid85 forms one arm of a valve member 88, which is pivotally mountedon the exterior of passage 21 by a torsion spring 89 similar to spring Il, spring 89being initially deformed, however, to apply a counter-clockwise torqueV (as viewed in Fig. 9) to member 88.

Other heating Pressure responsive unit 58 is connected by formed with member 88 so as to apply a clockwise torque to the latter when actuated by pressures in chamber 5l. The eiective pressure are! of the diaphragm of said unit relative to the aren of grid 88 is such that the admission of air, or other uid, under pressure to chamber 5i causes said unit to apply a sufiiciently greater torque to member 88 than is applied thereto by the pressure of the air on grid to pivotA said member clockwise and move grid 85 away from stationary grid 36. The differential torque producing Ythis pivotal movement decreases as the magniat, a suitable point in the displacement of said of producing a greatervolurne of sound. Chamber 5| on the high pressure side of valve 86, 31

is of sufllcient'cross-sectional. area and volume to exceed the flow capacity of said valve at any given pressure of entering' iiuid. Accordingly,

member.

It is to be understood that suitable means, such as compensating means 80 (Fig. 3), for applying an additional force tendingl to balance'memberl88 may be provided in the unit.of Fig. 9 if proper balance cannot be otherwise attained, as for example at a low operating pressure.

To impart vibrations to member 88 and thereby modulate the air stream in passage 21, electromagnetic actuating means 9i are provided, and. are shown diagrammatically in Fig. 9 as comprising a magnet 82 and a voice coll 92a. To transmit vibrations to valve member 88 in accordance with modulations in the current passing through coil 92, anelement 93 is integrally formed with or rigidly secured to said valve member 88 and is mounted to be substantially parali'lel to'grid 85 and to extend inl the direction of said chamber acts as a reservoir for the uid stream and maintains the air pressure' adjacent the high-.pressure side of valve 38, 31 substantial'ly constant while a continuous stream of air flows through said valve. Grid 3,1 Ais balanced. in theair stream by pressure responsive means 58, compensating;meansv 88 and spring 44, and.

is vibrated by actuating means 10 to impart sound producing modulations to said stream.

Another embodiment of the invention, includv ing an alternate mounting arrangement for the movable grid 'of the control valve anda novel actuating. means 9i. The free Vend oi said element is located in the magnetic eld of sad actuating means to serve as the armature thereof and, accordingly.. provides for the directl transmission of vibrations from said-actuatingimeans to the movable valve member.

Still anotherl embodiment of the present invention is shown in Fig. 10 and comprises a heusing having-a iluid passage formedtherein. Valve means corresponding instructure to valve means 88, l2 of the embodiment of'Figs. f to 8 are provided for modulating-a duid streamflowingfthrough said passage, and comprise a stotionary grid 01 and a movable member 08 havi118 grid 99 formed therewith. Valve member 08 is pivoted on a torsion spring mounted and In order to actuate movable grid 99 and im' part-controlled vibrations to the latter, a lever or arm |02 is formed with or otherwise rigidly secured to said plate at the end thereof remote from the pivotal axis, said lever extending through a recess |03 in housing 9-4. A layer |04 of non-resonant material, 4such as sponge rub-` ber, may be provided in a groove inthe walls of said recess to engage and form a substantially fluid-tight seal with the side and bottom faces of said lever. The free end of lever |02 is'actuated by suitable electromagnetic means comprising a magnet |06 and a voice coil |01, said lever constituting the armature of said means. This novel arrangement provides a direct connection between the actuating means andthe vibrating valve member so that the vibrations are transmitted to the latter through a minimum mass of material whereby sound reproduction of a great.- er fidelity and superior tonal qualities may be -obtained by the unit embodying" this structure.

There is thus provided a novel sound reproduc-l ing unit of the fluid flow type, i'. e., of the-type utilizing a modulated fluid stream, preferably` anv air. stream, as the sound generating medium. The

novel sound head comprises valve means for modulating a uid current, and novel means responsive to the pressure of the fluid current for applying a balancing torque to the movable member of saidvalve means. A novel vibration transmitting linkage operatively connects the movable member of the valve with the actuating means, and novel means are provided for preventing the formation of ice in or 'on said unit where such formation would cause improper operation of said unit and for preventing moisture, which condenses from the fluid stream, from ilowing to the control and actuating apparatus mounted exteriorly of the fluid flow passage. Other novel Y means embodied in the present invention are operative to prevent the creation of" resonant vibrations in the parts of the unit connected to the control member and to thus maintain a high fidelity of sound reproduction. The movable member of the grid type, fluid modulating valve is mounted in a novel manner so' as to be readily pivoted by the fluid stream to an equilibrium position, in which position said member is extremelyisensitive to vibrations imparted thereto by the actuating means.

Although several embodiments of the inven- Y tion have been illustrated and described, it is to be expressly understoodtiat' the samefis not limited thereto. The ,.fflatdlhphragm, which constitutes the pressureresponsive element of the balancing means, may be replaced by other ele-y 'ments ormeans responsive to pressure differentials existingV between opposite sides or faces thereof. Various other changes .may be made in the design and arrangement of parts with- -outldepa'rting from the spirit and scope of thev invention. For a. definition of the invention, reference will be had primarily to the appended claims. a A

What is claimed is: y l. In a sound reproducing unit utilizing an air stream as the sound generating medium, the' combination with control means for modulating the air stream including valve means of the grid type having a movable member in the path of said air stream, of means actuated bythe pressure of s said air stream for applying a balancing force to said movable member opposed to the lforce exerted thereon by the uid stream, and springpressed means for augmenting the balancing force applied by said pressure actuated means, l0 said spring-pressed means and said pressure actuated means being so arranged and proportioned relative to said member as to lbalance the latter in open position in said stream.

2. In a sound head of the fluid flow type havn ing valve means for imparting modulations to a duid stream, the combination therewith 'of means `for balancing said valve means in open position in said fluid stream, vsaid balancing means comprising a mechanism `actuated by the .w pressure of the fluid vstream for en'gagingand applying a balancing force to said valve means, and a spring-pressed, non-resonant member adapted to engage said mechanism during the movement of said valve means to open position to augment the balancing force applied by said mechanism. y i

3, In a sound head adapted Ito reproduce sounds by means of a modulated iiuid stream, valve means in the path of said fluid stream for n modulating the latter, means for balancing said d valve means in open position in said fluid stream to render said valve means accurately responsive to actuating vibrations, and means connecting valvemeans in the path of said stream, for modulating the latter, and means for balancing sas-l valve means in open position in said nuid stream to render saidvalve means accurately responsive to actuating vibrations, said balancing means comprising a mechanism disposed substantially parallel to the fluid stream and actuated by the .pressure of the uid stream for engaging and applying a balancing force to said valve means 60 and a spring-pressed non-resonant member adapted to engage said mechaf mqduring the movement of said valve means "op'en position Ito augment the balancing force appliedby said K mechanism.

comprising a fluid passage, valve means for conl trolling a fluid stream produced 'by the admission into said passage of a fluid under pressure, said valve means comprising a. stationary-grid and a movable grid mounted on the low pressure side U ofv said stationary grid, a member rigidly secured to said movable grid, means for-fpivotally mounting said member on the exterior'of said passage,

said: last-namedmeans comprising a torsion 35 spring secured to said member, said spring urgv ing said movable grid toward closedposition, balancing means including an element responsive to the difference between the pressures on` y the interior and exterior of. said passage, and a applying torques to' said member balancing said grid in the fluid stream.l

76 6. In soundreproducingfapparatus of the type said balancing means to saidvalve means, said l 5. In apparatus of the class described, meanslinlr of non-resonant material' operatively connecting said .pressure responsiveelementto said member, said balancing means and said spring `having a movable grid member for modulating a uid stream in response to the movement of a vibratingv armature, a resilient element attached i to said member and having acentral portion inf.

. clined relative to the plane of the end portions having a movable valve member tor modulating a uid stream in accordance with the movement *of a vibrating armature, means for 'pivotally mounting said member-for angular movement v l about a xed axis. and means for operatively connecting saidarmature to said member to actuate the latter, said connecting means comprising a link rigidly lsecured to said member. and means for transmitting the vibration of said armature to said link in a direction perpendicularA to the longitudinal-'axis of said link, the latter `being mounted to have the longitudinal axis thereof pass through the center ot mass of said member-at an angle of 90 tothe pivotalv axis of 15 the latter.

WILLIAM c. naves

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