US1935185A - Sound producing device - Google Patents

Description

Nov. 14, 1933.- J. s. HIGH 1,935,185

' SOUND PRODUCING DEVICE Filed June lO. 1931 2 Sheets-Sheet l Nl/ENTOR. Jurgen 5.1'Ilgh, BY Qi ATTORNEY Nov. 14, 1933. J. s. HIGH 1,935,185

SOUND PRODUCING DEVICE Filed June 10', 1931 2 sheets-sheet 2 .I NV EN TOR.

d uT' en 5. Hgh,

ATTORNEY. C

Patented Nov. 14, 1933- l UNITED sTATl-:s PATENroFl-ICE I SOUND PRODUCING DEVICE Jurjen S. High, Oaklyn Manor, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 10, 1931. Serial No. 543,341

a a 25 claims. (c1. 214-6) t :My inventionjrelates .to sound-producing derated fromweach other by linear valve seat elevices `and,more particularly, to loudspeakers of ments which cooperate with the valve-head to the air-*flow type. a i throttle'V the elementary air currents in yparallel There have been many attempts to devise a relation during their passagel from sources to loudspeaker whereby, through the control or sinks. vThe latter communicate by a'hornfwith 60,

modulation of an air-current, tremendous sound.-I the atmosphere. y l output could be obtainedfrom a phonograph.. Thus `the valve seat is the locus ofa source, from a radio-receiver or from any appropriate a sink, and a throttle area, of which the ele-v source. For the purpose of controlling the airments are enmeshed according to a sequence current, slidingvalves, poppet valves and valves indicated by the following notation: Sink,

of many other types have been tried. v throttle, source, throttle, sink, throttle, source,L

Substantially al1 Valves of the poppet type. throttle, sink so that eachsource slit is lohave the drawback of high initial leakage, causcated between two throttle surfaces as well as ing hiss; they have a relatively high air conbetween two sink slits. Y

sumption and they are limited as to their fre- The advantage .of such a valve seatarrangequency-range and load-carrying capacity. Slidment is that the ratio 70 ing` valves vare prone to overshoot at low frequencies in the event that .they are adjusted 1mm-Mm' for optimum high-frequency response, even total smk area' though cushioning devices are provided, although can be so chosen thatfthe resultant of the aerothey are fairly satisfactory insofar as their static and aerodynamic forces which, after adrather limited frequency-range is concerned. mission 0f air-fiOW, are actingl 0n both SidesOf They also are prone to stick during operation the plate-Shape Valve head, Will be Substantially and precaution must be taken to prevent foreign Zero fel a Certain Constant input ail Pressure at substances from getting between the valve and which the valve is normally operated. The mass seat. of the valve head being extremely small, a` rela- It is, accordingly, an object of my invention tively Small amount 0f stiffness is ,necessary t0 to provide valve mechanism for air-flow loudobtain a resonant frequency sufiiciently high to speakers that shall have the advantages of both cover the required frequency range. Therefore,

poppet` and slide valves and the disadvantages the efnciency of the valve is comparatively high.

of neither. The novel features that I consider character- Another object of my invention is to provide istic of my invention are set forth with partienan improved air-flow loudspeaker that shall have lalily in the appended Claims. The inventionv frequency and fidelity characteristics comparable itself, however, both as t0 its vOrganization and with those of the best electrical loudspeakers. its method of operation, tOgethel' With additional A further, and more specific object of my inobjects and advantages thereof, will best be vention, is to provide a device of the type deunderstod from the following description of a scribed that shall be stable in operation and specific embodiment when read in connection free from non-linear distortion. with the accompanying drawings, in which:

My invention is characterized, broadly, by the Fig. 1 is a side elevational view of my improvision of) a valve-chamber which, at one side proved valve-mechanism for air-now loudof a movable valve-head, communicates with the speakers illustrating the connection thereto of atmosphere through a channel, the air-iiow reactuating means, s istance of which may be controlled to bias the Fig. 2 is a sectional view of the valve-mechavalve-head. nismA `taken along a line corresponding to the It is, furthermore, characterized by the fact line II-II in Fig. 1, looking in the directionof the that said valve-chamber accommodates a valve arrows, and seat wherein a system of linear, that is, slit- Fig.3 is an exploded view, in perspective, showshaped air-flow sources and a system of linear ing the laminated construction of the valve-seat.

air-flow sinks are located. The air currents l Referring to Figs. 1 and 2 of the drawings, an 105 yielded by the sources are operating in parallel air-flow loudspeaker constructed according to my `relation, as also are the air currents absorbed invention comprisesa valve-chestlwhich merges by the sinks. The sink system cooperates in into the small end of an exponential horn 3 in series relation with the source lsystem, the which chest are included an improved valve-seat sources being enmeshed with the sinks and sepa.` 5 and. a Valve-head '7. The valve-head is conno nected to the vibratory element of a driving device 9 by means of a light, rigid rod 11 which extends through a stuffing-box 13 or packing gland provided with means, such as a washer 15 of soft rubber, or the like, for preventing air leakage.

The driving device, the valve-chest and the horn may be suitably supported from a rigid metal base-plate 17 and means are provided to permit moving the driving device, relative to the valve-chest, to provide for adjusting the armature clearance in the driving device.

As shown in Fig. 1 of the drawings, the driving device may be carried by a plate 19 having a flexible portion 21, the end of the plate nearest the flexible portion being permanently affixed to the base-board and the other en'd thereof being movable with respect thereto. A resilient washer 23 or the like may be disposed between the movable end of the plate and the metal base-plate and an adjusting screw 25 may be provided for urging the plate against the said washer.

The angularity of the plate 19 with respect to the base-plate, therefore, is under the control of the adjusting screw and, since the relatively flexible armature is connected by the rod 11 to the relatively stii valve-head mounted upon the plate 17, the armature clearance may be adjusted by tightening or loosening the said screws.

It is not to be inferred, however, that I am limited to the armature clearance adjusting means illustrated. It is perfectly `feasible, for example, to adjustably'connect the driving rod to the vibratory element of the driving device, to bodily move either the valve-chest and horn or the driving device parallel to the base-plate 17 or to provide the necessary relative movement of the various elements in any other convenient manner.

The driving devices, also, may be of any desired type capable of translating fluctuating electric currents into physical movements of the rod 1l extending to the valve-head, or the rod may be immediately or mediately connected to the styluscarrying arm of a phonograph (not shown). I have, accordingly, illustrated the driving device merely as a rectangle devoid of specific details. The adjustment of the driver with reference to the valve, once established for a given input air pressure may be kept constant by a bracket or lock 26 whereby also microphonic effect and external audio feed-back is suppressed.

It is important, however, to so proportion the moving element of the driving device and the valve-head that the system is naturally resonant yto a frequency toward the upper limit of the acoustic frequencies to be reproduced. When this is done, the system is stiffness controlled and the valve amplitude, at all frequencies below the natural period of the system, is substantially constant. Specifically, stiffness control is obtained by using a light valve-head in the valve and large restoring force in the vibratory system. The initial valve-head lift at a given input air pressure is controlled for optimum operation by a mechanical and a pneumatic adjustment which will be indicated later.

Although my invention is not'to be limited by any present theory of operation or principle, it would seem that the remarkable results obtained thereby in sound reproduction may, in part at least, be attributed to the fact that it provides pneumatic means for biasing an air current in somewhat analogous manner as the space-current in a thermionic tube is biased by a C-potential applied to the grid thereof. In other words, I cause the main air current to be divided into a plurality of thin sheets which, by reason of the construction of the valve-chest, are caused to reverse their direction of flow in a common throttling chamber to build up a bias pressure therein, and then to expand, exponentially, into a common conduit which, in turn, expands exponentially to free air. The bias pressure is controlled by an adjustable pneumatic leak connected to atmosphere. The air passages, between the throttling area and free air, are devoid of abrupt changes in continuity which would tend to cause reflections and distortion.

It lies within the scope of my invention to provide any suitable means for dividing an air current into thin filaments or sheets and for recombining the filaments or sheets into a common exponential conduit subsequent to the throttling operation. I have, however, found it very convenient to construct the valve-seat from a plurality of peculiarly shaped predominately flat lamin 27, 29, 31, and 33 which, when sweated together or otherwise held in correct relative position, define a plurality of air channels that reverse their direction in a common throttling chamber 35 one side of which is constituted by the valve-head 7.

The preferred shapes of the lamin, and the directions of flow of the air currents in the passages dened thereby, from an inlet port 37 to the common outlet conduit, will be self-evident upon an-inspectionof Fig. 3 of the drawings. The lamin 33, it will be noted, are stream lined toward the common outlet conduit, or horn, for the purpose of reducing hiss and to permit each air-sheet to expand, exponentially, before it merges with the remaining sheets.

By making the laminae` flat the assembly of the device is facilitated. They may, however, be cylindrical or otherwise curved, without departing from the spirit of my invention.

In order that the valve-head 7 shall be satisfactorily balanced in operation, T have found it expedient to provide means for that purpose somewhat analogous tothe grid-leak resistor and biasing battery lutilized in connection with the use of a thermiomc tube as a detector. Such means, preferably, takes the form of an outlet conduit 39 extending to free air from the valvechest, through which, under control of an adjustable valve 4l, air is permitted to leak to an extent suliicient to maintain the average pressure behind the valve-head slightly less than the average pressure on the face thereof. It is, of course, feasible to derive the biasing pressure directly from the main air supply, through a separate reducing valve, if necessary. Such modification being more or less obvious, it has not been illustrated.

A conduit 43, communicating with the inlet port 37, permits the inlet air pressure to be observed and a reducing valve (not shown) may be interposed between the inlet port and the source of air supply for assuring the correct operating pressure.

To prevent the valve-head from self-oscillation, it is advisable to provide adjustable damping means therefor. The damping means may take the form of a layer 45 of sponge rubber or other material having the desired properties, which is pressed against the rear face of the valve-plate by an adjustable retaining plate 47. The retaining plate is pressed against the rubber layer by the inner end of a cylindrical element 49 which threadedly engages an opening in the end 51 of the valve-chest and which is provided with a knurled knob 53 through which extends the valve-actuated rod 11. y

The valve-head clearance, with respect to the valve-seat, is primarily adjusted by the screw 53 and by the bleeder-valve screw 41. In general, the valve clearance is a function of (l) the magnitude of the input air pressure, controlled by a reduction valve (not shown), (2) the bias-pressure which builds up in the valvechamber, controlled by the bleeder-valve, (3) the pressure exerted by the damping means, controlled by the screw 53, and (4) the armature adjustment, controlled by the screw 25.

The combination of the adjusting means enumerated provides for optimum operation over a wide range of air pressures. In fact, my improved air flow speaker is so extremely flexible that substantially perfect results have been obtained with pressures varying from zero to sixty pounds per square inch and h'igher.

The function of the adjustment means is easily understood by considering the operation of each separately, keeping in mind that the stiffness of the vibratory system is largely due to the compressed damping layer of spon'ge rubber which covers the valve-head.

` When the input air pressure is off, the valvehead rests on the seat and the armature of the. driving mechanism is out of center, By admitting the input air pressure to the valve chest the valve-head is lifted automatically from its seat, establishing an initial valve clearance of the order of 1.5 mils at approximately 40 pounds per square inch input pressure and the armature of the driving mechanism must be then in the central position.

The voice-current causes deflection of the valve-head which at maximum volume are of a magnitude of less than 1.5 mils in my present samples.

In the operation of my improved air-flow speaker, air at a pressureof from zero to sixty pounds per square inch is supplied to an inlet port 37. This input pressure should be maintained reasonably constant, preferably by suitable means adjacent to said inlet port.

As indicated by the arrows in Figs. 2 and 3, the incoming air current divides into a plurality of thin sheets which flow into the valve cham- Y ber, reverse their direction in the said chamber and now outwardly to the horn. The face of the valve-head is, broadly speaking, the locus of reversal of flow of all the currents. The average clearance between the valve-head and the valveseat, being slightly more than one mil, is considerably less than the thickness of one of the air-sheets and the air, consequently, has greater velocity in the valve chamber than it does in the passage-ways defined by the lamin of the Self-oscillation, however, is primarily suppressed by the damping layer 45 which is pressed against the entire back surface of the valve-head by the adjusting screw 53 and retaining disk 47. It is also feasible to suppress self-oscillations by feeding into the valve chamber, rearwardly of the valve-head, air pulsations derived from any sultable source such as the input conduit, Incidentally, those self-oscillations are of such a forceful, almost destructive character that they suggest the use of the device as a powerful and efficient fog-horn.

When the valve-head is caused to vibrate the air-flow in the valve-chamber is throttled in proportion to the movement of the plate but it is never completely stopped.l The throttling action requires onlyva small expenditure of power since the valve is partially balanced by the back-pressure thereon determined by the bleeder valve 41 and since the air current through the valve chamber has very high velocity. As a consequence, my improved loudspeaker is capable of giving enormous volume without distortion, the amount of acoustic watts radiated being many times the amount of electric watts required to operate the driving mechanism.

Among the principal advantages of my irnproved valve mechanism may be enumerated the following:

a. It requires no transverse adjustment. The well-known Parsons valve requires a very careful transverse adjustment in order that the rectangular bars of its grill-shape valve-head and the slits of the valve-seat shall be aligned. The slits in such a valve are over--lapped by the bars for a distance of only a few mils, thus making the effective throttling area of the valve small, when it is properly adjusted, as compared with the utilization of possibly two-thirds or more of the valve-seat area in my improved device.

b. By virtue of its relatively long throttle paths, the throttling action of my improved valve is mainly due to viscous air-flow resistance in contradistinction to the predominantly turbulent air-ow resistance which is set up in the Parsons valve. The modulation of air-flow by the variation of a viscous resistance produces a better tone quality than that obtained by variation of a turbulent resistance because, in the latter case, the tendency toward non-linear distortion and toward a reduction of the percent modulation at larger initial valve clearances is greater.

c. For similar reasons the load carrying capacity of my improved valve is larger.

d. By properly adjusting the clearance in my improved valve, the initial leakage and hiss may be made considerably smaller than in valves having predominant turbulent resistance modulation. And, moreover, the air consumption will be comparatively small.

e. The valve-head is rigid in construction. Valves of the type having a vibratory grill, as heretofore constructed, are rather delicate and easily damaged. My improved valve-head, however, being in the form of a rectangular or circular plate of aluminum or other light material, is substantially immune to damage during use.

f. The valve-head surface and the valve-seat may be modified as to contour to give any desired type of response. In other words. the valve-head may be provided with a plurality of rectilinear or circular channels of any desired contour and the ends of the lamina; between the inlet and outlet openings in the valve-head may be shaped to correspond to the channels. Furthermore, if desirable, the valve-head face adiacent valve seat 5 may be of any suitable material to obviate the chatter introduced by occasional over-loading, a feature which is substantially impossible of introduction into valves of customary type.

g. The valve mechanism is relatively inexpensive. It may be built up from sheet metal punchings soldered or brazed together and the size of the air channels is limited only by the thickness of the punchings. This feature is considered by me to be a radical improvement over valves of the customary type, since it enables more effective throttling without weakening the valve-seat structure.

h. The provision of balancing or biasing means of the valve. If the valve of my improved airow loudspeaker were operated in the open, i. e. with atmospheric pressure acting only on the rear face of the valve-head, the pressure of the air supply would cause the valve-head to be driven away from the seat. By introducing an adjustable pressure drop between the high pressure side of the valve-head and the rear face thereof, the resultant force tending to drive the valve-head away from the seat may be so adjusted that the valve-head is held in the position where the speaker operation is the best.

i. The provision of the valve bias chamber permits establishing acoustic counter-feed-back means to neutralize self-oscillation.

j. Prevention of reed-effect. The provision of controllable damping means covering the valvehead prevents the said valve-head from self-oscillation. This provision is impossible in the customary valves. The phenomenon of self-oscillation is often noticed in air-flow loudspeakers and is the cause of undesirable distortion and howling.

k. Maximum acoustic radiation efficiency may be obtained because it is easy to provide or construct a conduit of exponentially increasing crosssection from the throttling area to the mouth of the horn. This is substantially impossible to obtain with valves of other types with which I am familiar.

Z. The valve can be operated at higher air pressures than customary and is, accordingly, self-cleaning.

Although I have illustrated and described a specific embodiment of my invention, numerous modifications thereof will be apparent to those skilled in the art to which it pertains. My invention, therefore, is not to be limited except insofar as is necessitated by the prior art and by the spirit of the aprendedeclaims.

I claim as my invention:

1. The method of sound production which includes providing a plurality of separate air currents, causing said separate currents to flow in substantially the same direction in parallel paths, then causing the currents to combine and change their direction of flow, and throttling the combined currents at the locus of direction-change without completely stopping the flow thereof.

2. The method of sound production which includes providing a plurality of air currents, causing said currents to flow in substantially the same direction, then causing the currents to reverse their direction of flow, throttling the currents at the loci of their reversal and thereafter combining the currents.

3. The method as set forth in claim 1 characterized in that the change in direction of the air current is substantially 180 degrees.

4. The method of sound production which includes providing a plurality of air currents, causing the currents to reverse their direction of flow, constraining said air .currents to flow in thin sheets immediately before and subsequent to their reversal, throttling the currents at the loci of their reversal, and thereafter combining the currents.

5. The method of sound production which includes providing a plurality of air currents, causing the currents to reverse their direction of flow, throttling the currents at the loci of their reversal, thereafter combining the currents, and then permitting the combined air currents to expand exponentially into free air.

6. A sound-producing device comprising means providing a passageway for an air current and means for causing the current to substantially reverse its direction of flow between entering and leaving'said passageway, said last named means serving also to throttle the current in accordance with the sound it is desired to produce.

7. The invention as set forth in claim 6 further characterized in that means are provided for adjusting the operative position of the throttling means.

8. The invention as set forth in claim 6 further characterized in that means are provided for pneumatically adjusting the operative position of the throttling means.

9. The invention as set forth in claim 6 further characterized in that damping means are provided for the throttling means.

10. A sound producing device including a movable valve, a valve seat having a plurality of openings therethrough, inlet means communicating with certain of said openings and outlet means communicating with the remainder of said openings.

l1. The invention as set forth in claim 10 characterized in that the valve and valve-seat are substantially planar.

12. The invention as set forth in claim 10 further characterized in that the inlet openings through the valve-seat are adjacent to the outlet openings therethrough.

13. A sound producing device comprising means providing a plurality of inlet passageways for air currents, a valve-chamber communicating with said passageways, means providing a plurality of outlet passageways from the valve-chamber, and a movable valve-head disposed in said chamber and adapted to throttle air-currents in their passage through the said chamber.

14. The invention as set forth in claim 13 further characterized in that the outlet passageways increase in area smoothly.

15. 'Ihe invention as set forth in claim 13 wherein the outlet passageways increase in area smoothly, and further characterized in that a common outlet leading to free air is provided into which said passageways merge.

16. The invention as setforth in claim 13 further characterized in that the outlet passageways merge smoothly into a common outlet leading to free air.

17. An air-flow loudspeaker including a valveseat, a valve-head cooperating therewith, said valve head being of relatively light weight, and a vibratory system associated with said valve for providing a relatively large restoring force thereto whereby the valve head is stiffness controlled".

18. An air-flow loudspeaker including a valveseat, and a stiffness controlled valve head cooperating therewith, the natural period of the moving elements of said loudspeaker including the valve head being of the order of from 2500 to 5000 cycles per second.

19. In combination, a valve-seat in which terminate a plurality of parallel inlet and outlet channels and a valve-head movably supported in proximity to said seat to define, with the valveseat, a common throttling chamber communicating with said channels.

20. The method of sound production which includes providing a plurality of separate air currents, causing said currents to combine and change their direction of flow, throttling the combined currents at the locus of direction-change without completely ,stopping the iiow thereof and then causing said currents to again change direction and to ow in separate paths.

21. A sound producing device including in combination, means providing a valve seat and a plurality of passageways terminating in said valve seat, a movable valve arranged in cooperative relation to said Valve seat to provide a passage- Way common to said iirst named passagewaysl and means for imparting a stiffness control thereto, including a compressed layer of damping material associated with the valve.

22. A sound producing device including in combination, an inlet port, conduit means for dividing an air current therefrom into thin lamentary air currents, a valve seat and a valve cooperating therewith to provide a passageway for simultaneously receiving, combining and reversing the direction of flow of said filamentary air currents, conduit means communicating with said passageway for again dividing said air current into thin lamentary air currents, and a common conduit into which said last named conduit means are arranged to discharge.

23. A sound producing device including a movable valve, a valve seat having a surface and a plurality of substantially parallel passages terminating in openings in said surface, inlet means communicating with certain of said passages and outlet means communicating with the remainder of said passages.

24. A sound producing device including a movable valve, a valve seat having a plurality of openings therethrough, inlet means communicating with certain of said openings and outlet means communicating with the remainder of said openings, the moving elements of said device including the valve having a natural resonance period toward the upper limit of the acoustic frequency range of sounds to be reproduced.

25. A sound producing device including in combination, means providing a valve seat and a plurality of passageways terminating in said valve seat, a movable valve arranged in cooperative relation to said valve seat to provide a passageway common to said first named passageways and means for imparting a stiffness control thereto, including a compressed layer of damping material associated with the valve, the moving elements of said device including the valve having a natural resonance period toward the upper limit of the acoustic frequency range of sounds to be reproduced.

JURJEN S. HIGH.

Images