US2145603A - Microphonic relay - Google Patents

Description

Jan. 31, 1939. s. F. LYBARGER MICROPHONIC RELAY 2 Sheets-Sheet l 94. 9 u1 S iva/lux m u s. 4.. 6 m n m z la m w m n F '/0 M .lf/M/ A 1 m 6 y .fw 23 Il ,0. 2 a 1 522W ll flu Y n F n if V.. ,h .m B B Jm.31,1939. Is. F. LYBARGl-:R 2,145,603

MIGROPHNIC RELAY x Filed April 26, 1955 2 Sheets-Sheet 2 I VENTOR.

W/NESSE.: l w

BYMMMVM fj; ATTORNEYS.

Patented Jan. 3l, 1939 UNITED STATES PATENT OFFICE MICROPHONIC RELAY Edwin JfMyel's 'Application April 2s, 1935, serial No. 18,385

4 Claims.

This invention relates to an improvement in microphonic relays, and more particularly to a relay of the amplifier type such as is employed to increase the amplification in telephonic type 5 hearing aid sets used by people with defective hearing.

To satisfy the demands of users of portable hearing aid sets of this nature it is necessary to make the parts thereof, including the amplifiers,

as small and as inconspicuousas possible, and

also in such a way that they w'ill require a minimum of attention. Because of this and the fact that they must be capable of standing up under continuous and rather strenuous use their construction becomes considerable of a problem. As heretofore made the amplifiers employed in these sets have embodied several objectionable features. Among the more pronounced of these is the tendency of their operating characteristics to change with changes in temperature. Another is their tendency to cut out and lose efliciency when oriented to certain positions of rest. Others are their lack of convenient and satisfactory means for adjusting the air gap between the pole piece and armature of the electromagnet employed in them and also their inability to respond to a very wide range of frequency impulses as well as their relatively low efficiency. v

With the foregoing in mind it is an object of 3() this invention to provide an improved amplier of the character referred to which while small and inconspicuous is exceedingly sturdy and simple of construction, dependable and highly sensitive, as well as efficient in operation and susceptible of being manufactured lat a low cost.

A more particular object is to provide an ampliiier of this type which will not cut out in service irrespective of its position of rest.

Another particular object is to provide a relay of this kind with a continuously adjustable air gap and one in which variations in spacing thereof, due to temperature changes in its armature, are substantially eliminated.

A further object is to improve frequency response and flexibility characteristics of sucha relay.

These and Various other objects, as well as the other various novel features and advantages of the invention, will be apparent when the following detailed description is read in conjunction with the accompanying drawings, of which Fig. 1 is a side elevation; Fig. 2 a plan view; Fig. 3 a front View; Fig. 4 a rear view; Fig. 5 a sectional View taken on the line V-V of Fig. 2 of a micro- .55 Phonic ampliiier designed in accordance with this invention for use in a hearing aid set; Fig. 6 a typical schematic wiring diagram of a hearing aid set showing the amplifier circuit; Fig. 'l an enlarged fragmentary sectional view of the microphone cell in the amplifier showing the dispo- 5 sition of its' carbon spheres when the amplifier is in a vertical position; Fig. 8 a View similar to Fig. 7 but showing the cell disposed in a horizontal position; Fig. 9 another view similar to Fig. 'l but showing the cell rotated from the posi- 10 tion shown in Fig. 8; Figs. 10, 11 and 12 views similar to Figs. 7, 8 and 9 of a modified form of microphone cell; Figs. 13, 14 and 15 views also similar to Figs. 7, 8 and 9 of another modified form of the microphone cell; and Figs. 16, 17 and 15 18 like views of a still further modification of the microphone cell.

Referring in detail to the embodiment of the invention illustrated in Figs. 1 to 5, the numeral I designates a base plate on which the other parts 20 of the amplifier are mounted and which is preferably made of some suitable insulating composition. On the upper surface of this base at one end thereof there is mounted a block 2 of cold rolled steel or similar material which is em- 25 ployed to function as a part of the magnetic circuit of the electromagnet in the amplifier and also as a support for various of the other amplilier parts. As shown, this block is secured to the base I from the under side thereof by a. screw 30 3 and a. threaded circuit connecting jack plug 4, and has secured to a projection 5 on one of its faces by screws 6 an .upwardly extending armature 'l and on its other face by screws 8 a similarly disposed high-grade bar-type permanent mag- 35 net 9.

At the top of the permanent magnet 9, which is preferably made of cobalt steel or like material having a high coercive force, there is mounted a pole piece II. The latter is made of soft iron o or other highly permeable material and is employed as a core for a magnetic coil I2. As shown it is formed in substantially the shape of, or similar to the shape of, a question mark, and is mounted with its curved end fitted over the up- 45 per end of the magnet and its stem portion on which. the coil I2 is mounted projected toward the armature 'l in parallel relation with the base plate I. To hold it in place it is secured by screws I3 to the magnet 9 at a point spaced from 50 the upper end of the magnet. A j

The projection 5 on the block 2 to which the armature 'l is mounted is made in the shape of the letter L, for a purpose which will presently appear, and is disposed with its stem portion F parallel with and slightly above the base I.

The armature 1 which is preferably made of soft iron, silicon steel, or like material having a high permeability combined with high magnetic saturation point, and in the shape of a flat bar, is secured to the base I0 of this L-shaped projection 5 and spaced sui'llciently from the pole piece II to provide an adequate air gap therebetween to permit its necessary vibratory operation. To readily and'eifectively, as weil as accurately, adjust this air gap an adjustment screw I4 is threadably extended through the pole piece II near the upper end of the permanent magnet 9 with its inner end bearing against such magnet'. Through the use of this arrangement when the screw I4 is turned in one direction it causes the curved portion of the pole piece II, which is weaker than the bar magnet 9, to be exed and in such a way that the outer end of the pole piece is drawn away from the armature 1to thereby increase the spacing of the air gap. When it is turned in the opposite direction it permits the pole piece, due to the latters resiliency, to move toward the armature and reduce the spacing of the air gap.

The advantage of this adjustment will be appreciated when it is considered thatl normally this air gap fin devices of this type is maintained at from .002 to .003 of an inch and is customarily obtained by machining the various elements and that their machining to such accuracy isy extremely diicult. An error of .0005 of an inch in the machining of any one piece causes an error in spacing of 25 per cent. Furthermore, there is always some variation in the strength of the permanent magnet 9, in the amount of bending in the armature 1, and in the spring portion of the armature supporting projection 5. Through the use of this adjustment the pole Apiece II may be readily adjusted with respect to the armature over a range of several thousandths of an inch, which makes accurate machining of the parts involved unnecessary, and at the same time accurate and sensitive adjustment of the air gap is provided.

At the side of the armature 1 opposite to the magnetic coil I2 a microphone cell 20 is provided. As shown this comprises a housing I5 formed of insulating material which is held in place by a bar I6 secured to the permanent magnet 9 by the same screws that hold the pole piece II in place, and a pair of rods I1 which are connected between the ends of the'bar and the adjacent face of the housing lI5. This bar and these rods are made of some non-magnetic material, such as brass, so as to. not impair the operation of the electromagnet. Through the center of. the housing I5 there is provided acircular chamber forming a hole I8. The outer end of this hole is enclosed by a removable electrode I9 which is made of carbon or other suitable. material and seated in an' enlargement 2I provided for such purpose at the outer edge of the hole. To hold such electrode in place a resilient current conducting terminal and clamping plate 22 is cmplo'yed being connected by screws 23 to the housing I5 with its free end bearing against the electrode. y

The inner end of the chamber forming hole I8 in the housing I5 is covered by a second electrode 24 which is also formed of carbon or similar material and soldered or otherwise secured to the adjacent face of the armature 1. Between thel latter electrode and the housing Il there isl allowed a sumcient space to permit the necessary vibration of the amature but at the same time insuicient to permit the escape of the current ow regulating material which is placed in the chamber I8. The material that is preferably used for this latter purpose is small carbon spheres having a diameter below 1 millimeter and to prevent their escape the electrode 24 is spaced from thehousing I5 a-distance which is not greater than one-half of the diameter of the spheres. If granular carbon is used in place of the spheres, as it may be, as well as other suitable material, a loose felt ring or the like, not shown, may be inserted between the housing and electrode to prevent its escape.

For connecting the amplier in a headphone and transmitter circuit 25 and 26, as well as in a current-supplying battery circuit 21 as shown in Fig. 6, four additional jack plugs, 28, 29, 3l and 32 are provided. Three of these, 28, 29 and 3|, are mounted in spaced relation on the upper surface of the base I adjacent the microphone housing I5 and the fourth, 32, is mounted on the bottom of the base adjacent the previouslymentioned jack plug 4. Of these, the jack plugs 28 and 29 into which the transmitter and headphone circuits 25 and 26 are adapted to be plugged, are preferably of the female type and are connected respectively to one end of the electromagnet coil I2 and to the stationary electrode I 9 by current-conducting metallic - strips 33 and 34. To secure such strips rigidly in place they are mounted with one end disposed between the lower end of the plug 28 or 29 and the base. I

and the other attached by a screw to the microphone housing I5.

The two lower jack plugs 4 and 32, which are of the male type and adapted to be plugged into a casing in which the battery circuit 21 is customarily housed, are connected respectively to the other end of the coil I2 and tothe intermediary jack plug 3| which is also of the male type and used to connect the batteries to the headphone and transmitter circuits 25 and 2B yby way of a current regulating rheostat 35.

As previously stated one of the faults of the prior amplifiersl of this character is that they cut out in service and lose their efficiency when they are oriented to different positions. This is due to the falling of the Acarbon granules or spheres in the microphone cell away from one of the electrodes when they are so oriented. To completely overcome this diculty irrespective of the position of the amplifier and to greatly reduce the loss of efllciency when the amplier is inclined at an angle to the vertical, the electrodes I9 and 24 at the two ends of the microphone, in accordance with this invention, are made in shapes such as illustrated in Figs. 7 to 9 and 10 to 12, or, in shapes of this character which give the desired result. As shown in Figs. '1 to 9 this result is obtained by providing the electrodes I 9 and 24 with similarly projecting centrallyy disposed cone-shaped indents' which insure continuous contact between the carbon spheres of the microphone cell and the electrodes at all times and also a very substantial area of contact in all positions of the 'amplier which makes for eiliciency in the operation of the cell. This is also true of the cell construction shown in Figs. l0 to-12 where instead of being provided with like disposed conical indents the electrodes are made in the shapes of ilanged hemispheres mounted with their convex portions projecting from the opposite ends of the cell housing.

The customary prior practice has been to make 4 guapos the microphone cell electrodes in the shapes oi' discs, which, as is obvious, allows the circuit therethrough to cut out gradually as the cell is canted at an angle to the vertical and completely when the cell is disposed in a horizontal position as in such position the upper plateis completely out of contact with the carbon spheres. As an improvement upon such practice only one of the electrodes may be made as shown in Figs. 13 to 15 and 16 to 18 in the shape of the electrodes illustrated in Figs. 7 to 9,- and 10 to 12, respectively. While with the latter constructions thecells will cut out gradually when canted in one direction and completely when disposed on one side they do so only under such conditions and accordingly represent a decided improvement over the older type of construction.

As also previously stated, another objectionable tendency of the prior amplifiers is that they change their operating characteristics with temperature changes. In this respect the armatures have been thechief source of evil and such is brought about by the heat generated by the current iowing through the carbon Vcell and the electromagnet coil both oi which are adjacent the armature and communicate such heat either directly or indirectly to the amature. In the prior amplifiers as the armature is heated up by this generated heat it usually moves towards the pole piece of the electromagnet and as a result the air gap is made continuously smaller the longer the current is on. This of course causes a variation in the sensitivity of the amplifier and under extreme conditions, which are not infrequent, the armature actually touches the pole piece. More frequently, however, it is moved to such an extent that while not in actual contact with the pole pieces it strikes the latter when ii i: vibrated by the voice current passed through the electromagnetic coil I2, and bad distortions are developed in the amplification produced. Such change in spacing of the air gap occurs in all devices Where the armatures are held at two or more positions, as they customarily have been in the past. In most of the devices the heating of the armature is usually greatest at the point closest to the carbon cell where the most heat is generated and as a result its length is'increased most at such point. If the armature is of the strip type clamped atboth ends there is considerable movement, due to heat, at the center thereof perpendicular to its plane, and as its central portion is normally displaced slightly from a common plane in which its ends lie by the permarient magnet as the motion increases the armature moves toward the pole piece. also true of a circular diaphragm having the armature attached to it.

In accordance with this invoention the aforementioned difiiculty is overcome by clamping the armature 1 at only one end. As a result there is no bending in the armature due to heating since all oi' its expansion takes place in the direction of its length and such expansion in no way affects the air gap. While there may be a slight change in thickness of the armature due to increases in its temperature this effect is infinitesimal in comparison to the deleterious effects referred to in the prior devices. The importance of this phase of the invention will be best appreciated when it is considered that it insures practically constant sensitivity in the armature regardless of the temperature of the armature, or the changes in temperature of the rest of the structure, as the latter Thisisbecause the horizontal expansion in the mounting block is very nearly the same as the horizontal expansion in the coil. Thus the air gap spacing due to these variables is kept constant.

Another outstanding feature of the invention resides in the construction of the armature mounting, the chief advantages of which are that it renders the amplier responsivel to a wider range of frequencies and adapts it to be readily varied to respond to different frequencies. Another advantage is that by making the armature support capable of allowing the armature to vibrate and making the armature long to function as a lever on its support the varmature can be made heavy enough to properly carry the magnetv ux of the magnetic circuit. Through the use of the projection 5 on the block 2 as -a support for the armature 1 and the armature being secured at only one end, as well as the base I of the projection having some considerable weight, the mounting oi' the armature is not unlike two weights being suspended in series by separate springs. By reason of this, a mounting is provided which has a plurality of natural frequencies which give a maximum of amplification. With a mechanical structure such as this it can be shown experimentally and theoretically that as the frequency of the alternating force on the amature, which is produced -by the action of the current in the electromagnet, is increased, the amplitude of vibration of the armature will remain reasonably constant then rise to a point of maximum vibration or resonance, then decrease until a certain point is reached and then increase again to another point of maximum response. Thusthe system has two frequencies at which maximum vibration occurs and between which there lies a point of less vibration.

The construction asis apparent is one in which the characteristics referred to can be readily changed by changing the values of the various elements comprising the mounting, such as changing the length, thickness and width of the armature, changing the weight of the screws 6, adding or subtracting weight from the base I 0 of the projection 5, or removing some of the material from the stem of the projection. A very easy and recommended method of changing these characteristics is to machine the stem of the projection 5. By doing this, spring action of the projection is'changed and the thinner it is the weaker its spring action becomes, which makes for a lower first resonant frequency which is desirable.

-In general it is desirable to keep the mass of the armature small to insure good high frequency response, and to so proportion the elements of the mounting that the rst resonance or point of maximum vibration only is used so that the frequency of minimum vibration is very much higher than the highest frequency which it is desired to transmit through the amplifier. 'I'he construction recommended is one in which the irst frequency of maximum response is between twothirds and three-fourths of the maximum frequency which it is desired to transmit through the amplier. 'I'he actual choice of this frequency, of course, will depend upon the apparatus with which this amplier is used. The invention contemplates that a number of different types of construction will be provided which have diilferent frequencies of maximum vibration bel tween 1500 and 4000 ,cycles so that the most suitable ampliioation characteristics can be chosen to satisfy the demands of dinerent iny divlduals and as will be obvious and as has been pointed out the construction provided is such that it lends itself readily to the provision' of such a range of devices. y

It will also be appreciated thatthe characteristics lof thisconstruction' atlord'othei advantages.' For example, in many cases in actual practice it is found thatv other parts of the apparatus with which it is used, such as the transmitter and headphones, have pronounced resonances or peaks ofy response. By utilizing the fact that a point of minimum response followed by another frequency of maximum response is objectionable with this invention, the invention can be used to advantage to smooth out the over-al1 amplification curve of the joint apparatus by making the' frequency `of minimum response of the ampliiier coincide with a resonance peak in the associated apparatus., The over-all response can in this way be made nearly uniform over a considerably wider range than is otherwise possible.

'According to the provisions of the patent statutes, I have explained the principle and construction of my invention and have illustrated and described what I now consider to represent its4 best embodiment. However, I desire to have it understood that, Within the scope of the appended claims, the invention may be practiced otherwise than as specically illustrated and described.

I claim:

1. In a microphonic amplier, a supporting base, a block of magnetic material secured to said base, a permanent magnet secured at one end to one side of said block, a pole piece adjustably secured to the free end of said magnet, an electromagnetic coil mounted on said pole piece, a flexible projection on the side of said magnetic block opposite to said permanent magnet extended in spaced parallel relation to said base, an elongate armature secured at one end to said projection with its free end disposed in spaced relation thereto opposite the free end of said pole piece.

2. In a microphonic amplifier, a support, an elongate pole piece disposed with. an end portion in overlapping engagement with one side of said support, means for rigidly connecting the end of the pole piece to the support, the projecting portion of the pole piece being provided with a reverse bend to provide a portion extending along the opposite side of the support and terminating f armature disposed, a.dj acent the free end of the pole piece withj an'air gap normallyy between', 5

and 'an adjusting screwimounted izr'saidl over# lappingportion of' the polepiece and bearing against Atli'ead'loining support for springing the pole piece away from the support to widenjsaid air gap. Y, 1

' 3. In a microphonic amplifier, a support, an elongate pole'pie'ce disposed with an endvportipn in overlapping engagement with one side of said support, means for rigidly connecting 'the end of the pole piece tothe support,'the projecting portion of the pole piece being provided with a reverse bend to provide a portion'extending along the opposite side of the support and terminating in a portion extending substantially perpendicular to the support, an actuating coil mounted on .1 said last portion of the pole piece, a block mounted at one side of said coil and provided with a fiexibie extension substantially parallel to the coil supporting portion of said pole piece, a

movable armature rigidly connected at one end 2.

to the free endr of said exible extension, the opposite end of the armature being disposed adjacent the free end of the pole piece with an air gap normally between, and means for springing the pole piece away from its support to vary f said air gap.

4. In an electromagnetic vibrating device for hearing aids, a substantially straight bar magnet, an elongate pole piece disposed near one end of the bar magnet with an end portion in overlap- 3- ping engagement with one side of said magnet, means for securingthe end of the pole piece to the magnet, the projecting portion of the pole piece extending substantially at right angles across said end of the Vmagnet in very close proximity thereto and substantially at right angles away from the opposite side of the magnet, an electromagnetic coil mounted on the free end of the pole piece, a movable armature disposed adjacent said freeend with an air gap between them, and an adjusting screw threadedly mounted in said overlapping portion of the pole piece in very close proximity to said end of the magnet against which it bears for springing the pole piece away from the magnet to, widen said Vair gap.

SAMUEL F. LYBARGER.

Images