US1648120A - Vibration-responsive device - Google Patents

Description

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H. C. HARRISQN VIBRATION RESPONSIVE DEVICE Original Filed Aprlil 27, 1925 2 Sheets-Sheet 2 Patented Nov. 8, 1927.

UNITED srATEs' PATENT orrics.

HENRY C. HARRISON, OF PORT WASHINGTON, NEW YORK, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

Application tiled April 27, 1923, Serial No. 634,983. Renewed May 3, 1927.

This invention relates to vibration responsive devices.

An object of this inyention is to provide a mechanical corrective or attenuating network which may be employed for improving the frequency transmission characteristlc of a mechanical vibrating system, for example an acoustic device, such as a telephone transmitter or an electric phonograph reproducer.

A second object is to provide an improved lever arm support for a phonograph reproducer or recorder.

A third object is to reduce or modify refiection effects in a carbon button Which tend to impair the constant frequency translation characteristic desired.

It has previously been shown in my patent application Serial No. 603,005, filed November 24, 1922of which this is a continuation in part, that it is possible to build up a mechanical net Work which may be employed in mechanical vibrating systems for the same purpose for which filters and other correct-ive networks are employed in electric systems. A mechanical filter may, for example. be made` each section of which comprises a series mass and a shunt. elasticity corresponding respectively to the inductancc and the reciprocal of thc capacity of the standard low pass electric filter ofthe Camphell type. as disclosed in his U. S. Patent No. 1,227,113 of May 22, 1917.

Such a mechanical filter would have a mid-series characteristic impedance of and a mid shunt characteristic impedance of both of which for all frequencies below the cut-off are substantially equal to l 3 Z.=vM s which in this specification is called the nomb inal characteristic impedance and a cut-0E frequency of 3,/s (4) fa* r M Where Zo is the characteristic impedance, M is the mass and S the elasticity per section of the mechanical filter, fc being the cut-off frequency.

Such a mechanical network is therefore of particular utility in the transfer of mechanical vibratory energy between component parts`of a vibration responsive device, such for example, as a telephone receiver or phonograph recorder due to its impedance, for frequencies below the cut-off frequency, being substantially constant over the transmitted frequency band. This is for the reason that the mass and elasticityiof a mechanical filter are `independent of t-he frequency and, therefore, the expression .for Z0 given above is also independent of the frequency.

The mass and elasticity of the vibrating parts to be coupled by this mechanical filter may also be coordinated with the filter, whereby they may be made substantially equivalent to additional sections of the filter and result in a mechanical transmission line having an impedance constant with frequency over a wide transmission band. This arrangement would therefore take care of the elasticity of the vibrating parts, which unless adjusted to cooperate with the mechanical filter in this special way, would tend to give rise to resonance effects Within the frequency range to be transmitted.

One arrangement for terminating the network on the side opposite the point of application of the driving force is to.connect the multi-section filter to animpedance equal to the nominal characteristic impedance of a filter of an infinite number of sections, the value of which is obtained by 'Equation 3 above. Such an impedance in an electric phonograph reproducer might be the mechanical impedance of the carbon granules of the carbon button or in an acoustic phonograph it mi ght be the horn. If such a termination is employed, the carbon chamer should preferably be made of sufficient depth to prevent vibratory energy impressed on the front of the carbon chamber from bcing reflected in appreciable amounts from the rear wall back to the mechanical filter, since such a reflection in appreciable quantities would, in general, seriously impalr the uniform transmission desired.

The series mass and the shunt elasticity of the coupling network may possess widely different forms and may comprise, for example, a packing between the driving and driven members comprising a plurality of weights separated by resilient means for conveying the motion of one weight to the succeeding weights. The form hereinafter ldescribed in detail in connection with t-he movable parts of the electric phonograph reproducer comprises a vplurality of discs enclosed in a suitable casing and separated fromeach other by a. plurality of thin metal foil sheets of a light material, such as aluminum. The mass per section of such mechanical transmission line is, therefore, due principally to the mass of-eachrdisc, while the lshunt elasticityv is-due effect of the thin film cent foil sheets and the sheets themselves as the sheets are compressed and separated by the vibratory mot-ion to be transm1tted.

Referring tothe drawings, Fig. 1 1s a representation of an electric low pass filter or lumped loaded transmission line. Fi'g. 2 is a rearrangement of the element-s of F1g.' 1 to illustrate satisfactory initial and termlnating conditions therefor. Fig. 3 is an electric low passfilter or lumped loaded transnission'l'in'e, each. section ofwhich comprises resistances for attenuating the transmitted frequency band. Fig. 4 is a. diagrammatic showing of the relation of the various component parts of an electric phonograph reproducer. Fig. 5 shows how this invention may be embodied to provide a coupling means between driving and driven elements. Fig. 6 is a sectional view of Fig. 5. Figs. 7 and 8 illustrate this invention embodied in a telephone transmitter. Figs; 9 and 10 illustrate this invention as applied to an electric push-pull phonograph reproducer; Figs. 11 and 12 show modifications of this invent-ionv applied to'a telephone transmitter and Fig. 13 illustrates the frequency transmission characteristic of the device of Fig. 9. As is well known in the art, a low .pass electric filter usually comprises a plurality of sections, each consisting ofa `series inductance and a sliuntcapacity, as illustrated A"inductances 15,

ythe -ronnectionswof-thewseris 16, 17 and 18 and shunt capacities 19, 20 and 21. Such aV filter as disclosed in the Campbell U. S. Patent No. 1,227,113 of May 22, 1917, may be arranged b v equations therein given to provide for the practicall)7 free transmission of a given range of frequencies, while almost entirely Lacasse suppressing frequencies above that range. In case it would be desired to attenuate appreciably the band mitted, each section may prise, as shown in Fig. 3, a 22, a series resistance 23, a shunt capacity 24 and a shunt inductance 25. Fig. 3, of course, may also be regarded as illustrative of a telephone line, for example, in accordance with the Pupin system in which the induct-ances 22 represent theinductance per section, re-

sistance 23 the resistance of the line er section, capacities 24 the capacity of the line per section and of the shunt resistances 25 the leak across the line or the conductance per section.

The mechanical wave filter which would be analogous to the electric filter of Fig. 1 would, therefore, comprise a plurality of sections, each section com rising a. series mass (inductance) and a s unt elasticity (capacity). These masses and elasticities may be assigned such values according to Equations 3 and 4 that the mechanical transmisa definite cut-off frebe made to com- Series inductance transmiii pharaeteristig below the cut-oli frequencies." finsadditimi Ato the masses and elasticities,

dissipative losses are introduced both effectively in series and in shunt to the line a mechanical system analogous to the electric system of Fig. 3 may be produced which may be employed, for example, as a pure resistance vor an artificial line in a. vibrating system. When the number of sections per wave length i. e., the number of sections required to give a phase shift of 21.- is large such a line is substantially `equi-valent to a line of distributed constants in which the condition that the impedance is substantially a pure resistance is where S is the elasticity per section, M the mass per section, r the series dissipative mechanical resistance and of the shunt dissipation in a unit section and corresponds to the shunt conductance in the "electrical case;

Fig. 5 illustrates the mechanical equivalent of the electrical transmission line shown diagrammatically in Fig. 3. The mechanical V'transmission of Fig. 5 comprises a cylindrical casing 30 enclosing a plunger 31 conneCfeFU-Qe Suitable similar plunger 34 which is to be driven by vibratory motion from the driving member 32. tween the plungers 31 and-33 of lumped masses comprising discs 35 which are spaced apart by a large number of thin sheets of material light in weight, such as paper or aluminum foil. The plungers 3l.

- (5) r-gM a re a plurality of frequencies to be transfrictional or drivingmember 32 andra 33 connected to a member Located hef for frequencies IOL' g is the measure and 33 serve to close each end of the casing 30 and the result of the movement of the plunger 31, for example, will be a motion transmitted through the air cushioned foil sheets 36 and the spaced weights 35 to the plunger 33 at the opposite end. The spaced weights 35 constitute the masses of a rnechanical transmission line and the air included between the thin air cushioned sheets of foil presents an elastic reactanc-e to give the shunt elasticity .desired so that Fig. is a mechanical equivalent of the electrical systemv of Fig. 1 or Fig. 3 depending on the presence or absence of dissipation; vThe system of Fig. 5 may be employed in a mechanical system with any desired frequency transmisslon characteristic and may be so constructed with respect to the distributed masses and elasticities as to have a substantially constant impedance for a vwide range of frequencies. The chief function of the foil sheets 36 is to provide thin layers of air to give the required elasticities to the line, that is, the elasticity is due to the air confined between the sheets and not due solely to the sheets themselves. If the sheets tit into the casing tightly so as to substantially prevent the escape of the air between the sheets, there is very little dissipation or energy loss and the mechanical line is the -substantial equivalent of the electrical line of Fig\.l.\f-the sheets fit loosely in the casing. the mechanical line will be equivalent to Fig. 3 since both elasticity and dissipation would be present.

In order that a smooth mechanical transmission line may result from the use of such an arrangement as that shown in Fig; 5 it will generally be preferable to design the vibratory elements of which plungers 31 and 33 are component parts to have` such series masses and shunt elasticities as to give equivalent additional sections to the mechanical filter. If a mid-shunt termination of a filter is desired. for example. each of the plungers 31 and 33 may be made to have a mass equal to the mass assigned to a section of the filter while the driving and driven members 32 and 34 are assigned elasticities. twice the elasticity of each filter section. Other terminating arrangements,^of course, may be employed as are well known in the art of electric filters. suchas midserics termination and the like.

Fig. 6 is a cross-sectional view of Fig;l 5A

and further explanation is believed unnecessarv.

""Fgg--Tand 8 illustrate ,a Specific applica' tion of the mechanical device of Fig. 5 and illustrate the device employed in a telephone transmitter. The telephone diaphragm 40 is coupled by a pin 41 to a carbon button 42, whereby in the manner well known in the art the vibrations of the diaphragm 40 produced by impressed sound waves will vary the pressure exerted upon the granular material in the chamber 42, thereby varying its resistance to t-he current tflowing therethrouglrfrom battery- 43., The diaphragm 40, however, usually has a rather pronounced resonance whereby kcertain frequencies tend to be unduly emphasized by the transmitter. In order to give the transmitter an approximately constant frequency transmission characteristic overa wide range of frequencies, thereby avoiding the resonance of the diaphragm, a plurality of spaced masses 44 are provided between the diaphragm and the side wall 47 of the Casing and spaced from each other and 'from the diaphragm by sheets 45 of thin material, such as'aluminum foil.k This causesA the diaphragm 40 which is the first section of the mechanical line to work into an impedance which is substantially independent of frequency over any desired range. The weights v'de for the coupling pin 41. With such a1 packing arrangement, the response of the diaphragm will depend upon the masses of the discs 44 and the elasticity of the-thin films of vair confined between the thin sheets 45. By suitably adjusting the elasticity and the dissipation in the masses accordin to equations above given, the resonance e ects of the diaphragm may be substantially overcome so that the transmitter may be employed for faithfully translating into electric waves, sound waves which are impressed thereon.A It is obvious, of course, that the mechanicalline comprising the weights and the foil sheets 45 may be in as many sections as is desired; The casing 48 enclosing the .mechanical lines should have such an internal diameter that the weighted discs and the metal foil sheets will slide readily along` the inner walls of the casing in response to the plunger action of thediaphragm 40 and will also allow for the escape of the air between the sheets. The discs 44 in general should have a diameter slightly less than the internal diameter of the casing 48. A suitable Supporting member 49 is shown for supporting the carbon button 42. The diaphragm 40 may be of any suitable material and either tight-ly stretched or under very little tension in its position of rest. 1

"'Figs.- 9 and 10 illustrate this invention embodied in an electri'c'push-pull phonograph reproducer. A hollow casing 50 is disclosed which suitably supports at a plurality of 'points by means of screws 51 a cylindrical carbon chamber.

insulating material tightly against the face of a metallic member 56 insulatingly supported from the conical-shaped member 53 by a screw 57 This member 56 has a hemispherical depression in its face to provide a The carbon chamber is closed by a sheet 58 of flexible insulating material, such as mica'for example, which -is held away vfrom the flange of the sleeve 54-f'by'- a :pluralityof thin angular rings 59 of materiallight in weight such as aluminum foil for example.

located between the apertured cap 60 fortheslvc54 and the mica sheet 58 is a mechanicaltransmission line constructedv in accordance with this invention. The transmission line `comprisesal plurality of spaced hatshaped weights 61 which are separated from 4each other as well as from the cap 60 aiigth'e micasheetl by a. lplurality of thin annular-rings 62 lof material such as .alumimirri'l foil; Located betweenthe two outside weights of the two parts of the reproducer is the upperend of the pivoted lever arm 65, inv the .other end of which is fastened a needle 66. -which may be employed to trav- Aerse a suitable sound record whereby the mechanical vibrationsof the lever arm 65 lresultingtherefrom will .vary the pressure '-.exertedupon the carbon granulesthrough -tlie'.fin'termediaryv of the vibrations of the vmasses 6 1.' Y

he novel manner 1n which the lever arm 65 is mounted should be noted. Projecting from a flattened portion or continuation of the g 52 `are two knife edges 96 a-nd 97 locate "on opposite sides of the opening in `the casing through which the arm 65 projects. Suitably fastened to the lever arm 65 1s a. fiat cross piece 98 which in one face has `two depressions in which the knife edges 96 and 97` rest while the opposite face is in 'contact-with two knife edges 99 and 100 which lare suitably supported from the casing 52. The metallic cross piece 98 should be flexible and elastic so that it may be sprung into place between the knife edges to provide a delicate pivot for the needle arm. All four knife edges should preferably be .in line.

The carbon button disclosed is of the barrier type as described and claimed in the yU. S. Patent to C. R. Moore, No. 1,583,416,

withinthe casing 52 and` held in place by the four knife edges 96, 9X;|` 99 and 100. Each carbon button is then S'rewed into one end of the casing 52 unti/l the outer dome 61 and dome 102 contact with the desired pressure against the upper end of the lever arm 65. This pressure ma-y be checked by measuring the deflection of the needle arm per unit force. It has been found unnecessary transmission line which may be employed between the lever 65 and the carbon cha-mber, the following illustrative values are given:

In one specific embodiment the weights 61 were .6 inches in diameter and each weighed .07l grams. The annular rings or elastic material between adjacent weights were made of aluminum foil having an external diameter of .8 inches and a thickness of .001 inches. Three sheets were employed between cap 60 and adjacent weights while between the mica sheet 58 and the adjacent weight five sheets were employed. The 4internal diameter of the cylindrical ring 54 was .85 inches. This was found to give a mass per section of .07 grams and an elasticity per section of .5 x 108 dynes per cm. which resulted in a mechanical transmission line having a substantially consta-nt frequency characteristic over the bands of frequencies from 100 cycles to 5,000 cycles per section as shown in the curve 70 of- Fig. 13 which is obtained by plotting frequency values as abscissae with the corresponding power output as ordinates. This curve 70 is shown plotted on a. logarithmic scale for` the reason that when so plotted octaves along thehorizontal axis are represented by equal distances. For example, the distance between 200 cycles and 400 cycles is the same as between 2500 cycles and 5000 cycles, and that is the manner in which the ear hears, by octaves.

The carbon chamber with a radius of .30 inches was found to be suflicient to provide an impedance substantially equal to the impedance of an infinite number of sections of the mechanical line, and also of sufficient length between mica sheet 58 and the back wall to avoid any substantial reflection effects which would tend to impair the uniform -fre uency transmission characteristic desired. (This depth of the carbon chamber .is considerably greater than is necessary for merely a carbon transmitter operation since only the carbon particles close to the elec- Leashes trede 54 and the barrier 55 are actually employed in carrying the electric current. The remainder of the carbon is added to give a mechanical impedance equal to the nominal characteristic impedance of the mechanical' transmission line in front of the carbon chamber. 'The impedance presented by the carbon chamberis substantially proportional to the cross sectional area of the carbon chamber and also increases somewhat with increase in depth.

rlhe termination of the carbon button in an'impedance of the above character does not vrequire that the impedance be dueto additional carbon granules since any other suitable material may be 'employed to provide the desired impedanceI termination. The feature of importance is to have the active carbon granules workin into some absorbent material capable of a sorbing the vibratory motion to an extent sufficient to prevent reflection losses while presenting the desired impedance. y

This mechanical termination of a carbon button in an impedance equal to the mechanical impedance as seen from the front of the button is of importance in other types of acoustic devices besides the phonograph reproducer, just described. For example, it may be employed in a telephone transmitter as shown in Fig. 11. A carbon button transmitter is disclosed having a carbon chamber comprising a front electrode 105 and a back electrode 106.l This back electrode'should be of iiexible material such as a wire mesh or gold plated cloth for example to allow the vibrations to be transmitted to that part of the carbon chamber behind electrode 106.

It has'been found that the best quality of reproduction of the mechanical vibrations of the :front electrode 105 takes place when only a thin layer of carbon is located between the electrodes. Preferably the distance between electrodes 105 and 106 should be not greater than 40 mils. A distance between electrodes considerably in excess of 4:0 mils will frequently impair the quality due to imperfect modulation in the' layers of the vcarbon remote from the front electrode.

The deep carbon chamber disclosed may be employed for providing mechanical means on the side of the active carbon granules opposite the diaphragm for preventing the reflection effects caused in shallow carbon chambers by the elastic reaction of the chamber causing a reflection eflect from the back wall of the chamber which varies with the frequency. The cross sectional area and the depth of the carbon chamber may also be adjusted to have a mechanical impedance equal to the mechanical impedance of the moving parts of the transmitter as seen from -the front of the carbon chamber.

Fig. 12 is a modification of Fig. 11 in which the inactive part of the granular material of the carbon chamber has been re placed by other means for providing the desired impedance. Members 115 and 116 constitute the electrodes. rlhe particular means disclosed comprises a plurality of sections of the mechanical transmission line illustrated in Fig. 9, each section comprising a plurality of thin sheets ot aluminum foil and a lumped A I cal transmission line employed behind the carbon chamber should be sufficient to prevent any appreciable amount of vibratory energy from traversing the length of the mechanical transmission line and being reflected back to the carbon chamber so as to produce the undesired reflection effects mentioned above. i

The equivalent circuit diagram for onehalt" of the phonograph reproducer of F ig. 9 is shown in Fig. 4, in which the capacity or elasticity 71 represents the elasticity ot' the needle point 66, inductance or mass 72 represents the mass of the lever 65, capacity or elasticity 73 represents the elasticity of the lever arm 65 which in most designs can be disregarded, capacity or elasticity 74 represents the elasticity of the flexible top end of the lever 65, inductances or masses 75 each represent the mass of one of the members 61 while the dissipation due to the motion ot the weight relative to the side walls (friction) is designated by the series mechanical resistances 76. The shunt capacit 77 represents the capacity or elasticity ue to the enclosed films of air between the sheets 62, and between the masses 61, while the resistance 78 represents the amount of dissipation produced as the air flows from the pockets between the sheets 62 and masses 61. This elasticity 77 may be due principally to the lilms of air between the sheets 62 or may be due principally to the air pockets between the central portions of themasses 61 as may be desired in any particular case. The capacity or elasticity 79 represents the elasticity of the sheets caused by the sheets being in contact with each other at certain points. The resistance 80 represents the mechanical impedance of the carbon and as mentioned above, impedance 80 should be substantially equal to the impedance of an infinite number ofthe sections of the mechanical line, that is,

These foil sheets 110 and masses 111 dance equal to the surge impedries with` t instead of all in shunt, as shownl in Fig. 3.

Since Equation 5 above holds only when all of the elasticity is in shunt to the conductance, the ratio of the elasticity 77 to the elasticity 7 9 should be made as large as possible and therefore insure that the network more nearly approximates the condition co ered by Equation 5.

Electrical networks such as that shown in Fig. 1, for example, may be terminated at each end in a. variety of ways, the impedance of the arrangement depending upon the manner of its termination. Two common terminations are the mid-series ype and the mid-shunt type. In the mid-series type, the end series inductances have values equal to one-half of the value of the inductance for a full section and in the mid-shunt .termination, the capacity has a value one half the capacity of that of a full section. The 111e-v chanical arrangement of Fig. 9 may be made to have a mid-shunt termination, for example,`at the needle end by having theelasticity 71 twice the elasticity of the full section, that is, elasticity 71 would have avalue twice the elasticity of element 74 or 77, 1n those cases in which theelasticity 73 may be disregarded. In other cases the elasticity 71 should have a value only approximately one half of that of the elements 77 So as to give the terminating section the same impedance as the other sections. The termination at the carbon chamber end need not be made special, since the impedance of the carbon chamber represents the impedance of a-n infinite number of sections. A ready explanation of the manner in which the network should be terminated is shown in Fig. 2, where both the series and the shunt elements are split into two parts. The inductance of a full section comprises the sum of elements 81 and 82, while the total capacity for a single sect-ion comprises the sum of the capacities 83 and 84. If the network is terminated at the points 86, the inductance 81 is mated with the capacity 85 which is the same value as either capacity 83 or 84. Inductance 82 is mated with capacity 83. Inductance 87 is mated with capacit 84 and inductance 88 is mated with capacity 89, all of the inductances shown being of equal value and all of' the capacities shown being of equal value.

Such a filter can also be-terminated at the points 90 and 91,-ind`uctance 81 and capacity 85 being omitted, or the network can be terminated at the points 92 and 93, inductances 81 and 82 and capacities 85 and y83 being omitted. l

It is to be understood that this inventon is not limited to the particular forms that have' coi-dance with speech frequency vibrations occurring on a sound record, a mechanical transmission line between said lever and said closure comprising a plurality of spaced weights separated 'by a loose packing of aircushioned material, said carbon chamber being of sufficient depth to avoid a preciable reflection losses from the Wall o said chamber opposite said closure back to said closure.

' 2. An electric device comprising electrodes, conductive granular material packed between said electrodes, means comprising a flexible member contacting with said material for subjecting said material to mechanical vibrations, and means cooperatin with said granular material for causing sai granular material to Work into a mechanical impedance on that side of said material opposite said flexible member having an impedance of the same order of magnitude as the impedance of said means which subjects said material to mechanical vibrations.

3. An electric device comprising electrodes, a chamber substantially filled with carbon granular material, means for causin an electric current to flow through said' granular material, and a flexible member included as one side of said chamber, said chamber being of' suflicient depth that the carbon material adjacent the back Wall of said chamber is substantially unaffected by the mechanical vibrations of said flexible member.

4. An electric device comprising a chamber substantially filled with carbon granular material, a flexible member acting as one side of said chamber, means for im ressing mechanical vibrations of signaling re uencies upon. said member, means for supp ying an electric current to a portion of said granular material, the mass of said carbon in said chamber being of sufficientdepth and cross sectionas to cause the active carbon material to work into an impedance of the same orderI of magnitude as the impedance of the said means f or impressing mechanical vibrations .upon sa1d granular material.

5. An electric device comprising elecgranular material, such that the impedance trodes, conductive granular material packed looking in either direction from the active between said electrodes, means comprising a granular material is of the same order of l0 l iexible member contacting with said mamagnitude. I

5 teral for subjecting said material to meln witness whereof, I hereunto subscribe chanical vibrations, and means for absorbmy name this 26th day of April, A D., 1923. ing the mechanical vibrations of the active HENRY C. HARRISON.

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