US3040136A - Electro-mechanical transducer - Google Patents

Description

June 19, 1962 J. F. GRADO 3,040,136

ELECTRO-MECHANICAL TRANSDUCER Filed Jan. 14, 1959 2 Sheets-Sheet 1 FIG. 2. FIG.

INVENTOR. JOSEPH F GPA DO ATrORA/trs June 19, 1962 J. F. GRADO 3,040,136

ELECTRO-MECHANICAL TRANSDUCER 2 Sheets-Sheet 2 Filed Jan. 14, 1959 JNVENTOR.

JOSEPH F. GQADO Ar raR N6);

United States Patent 3,040,136 ELETRO-MECHAN1CAL TRANSBUCER Joseph F. Grade, 641 46th St, Brooklyn 20, N.Y. Filed Jan. 14, 1959, Ser. No. 786,819 18 Ciaims. 3'. 179103.41)

The present invention relates generally to electromechanical transducers, and in particular to a movingcoil type of transducer or cartridge for stereophonic and monophonic reproduction.

Various types of electro-mechanical transducers of the moving-coil type have been available on the market for monaural or monophonic reproduction from records of the type formed with a laterally cut groove. Such mov ing coil type of transducers or pickups difier from other magnetic types, such as variable reluctance or moving iron pickups, in that the coil motion in the magnetic field incident to tracking of the record groove by the stylus produces a voltage output proportional to the velocity of the coil motion and not its displacement. Such transducers are inherently linear, comparatively rugged, and capable of sound reproduction with a high order of fidelity.

Broadly, it is an object of the present invention to provide a moving-coil type of electro-mechanical transducer suitable for both stereophonic and monophonic playback of records.

Rather rigid requirements are imposed upon the design of a stereophonic transducer or cartridge in order to obtain high fidelity in reproduction. The two stereophonic channels or outputs must be exactly alike, for any deviation of one channel or output relative to the other results in unbalanced sound which manifests itself as distortion in stereophonic playback. Coupled with this is the further requirement that such transducer or cartridge must be suitable for monophonic playback. The geometry of the stereophonic cartridge is such that if you have essentially the same moving mass as in a high quality monophonic cartridge the distortion will be considerably higher for stereophonic playback. In order for a stereophonic cartridge to play back with low distortion, the moving mass must be less than that of the monophonic counter part.

It is a further object of the present invention to provide an electromechanical transducer of the moving coil type which has an exceptionally low moving mass and is particularly suitable for reproduction of stereophonic and monophonic recordings. Specifically, it is within the contemplation of the present invention to provide a moving-coil type of stereophonic pickup which has a high order of efficiency in translation of mechanical motion into electrical energy such that low distortion and high fidelity reproduction may be realized when employing such pickup or cartridge.

In accordance with an illustrative embodiment demonstrating aspects of the present invention there is provided an electro-mechanical transducer which comprises a base, means on the base for producing a magnetic field in a magnetic gap bounded by pole f ces, a moving-coil generating system including a common support having a stylus arm with first and second coils wound on said. support and having the turns thereof geometrically substantially congruent and in substantial symmetry with each other, a stylus on the stylus arm, and means mounting the generating system with the first and second coils in the magnetic gap and with the turns thereof extending substantially at right angles to the pole faces. Since this type of transducer includes essentially only one balanced moving mass, it is possible to achieve substantially identical outputs from identical stereophonic channels with identical resonant frequencies and a low order of distortion with comparable high fidelity monophonic reproduction.

With a monophonic transducer the mass should be low "ice enough such that the vertical and lateral resonance of the transducer for monophonic reproduction occurs outside of the audio range or spectrum. If the mass of the stylus of such transducer is equal in all directions of movement, then the resonant frequency in all directions will occur at the same frequency. Since the pinch efiect which is a vertically generated signal (disturbing to stylus action in the record groove) occurs at a frequency which is twice the modulated or lateral signal frequency, it becomes necessary to have separate masses for lateral and vertical signal generation. The vertical mass must be reduced over the lateral mass so that the pinch effect resonant frequency occurs at twice the lateral resonant frequency. This results in all resonant frequencies occurring at the same lateral frequency. Furthermore, to further reduce distortion I have found that it is desirable to introduce a mechanical low pass filter into the transducer to attenuate, at approximately 6 decibels per octave, all frequencies occuring above one octave below the lateral frequency at which the resonances occur. This attenuation results in a considerable reduction in the disturbance caused by the stylus contact with the groove at the resonant frequency, thereby providing reproduction which has a high order of fidelity. Further as generally understood, in stereophonic reproduction, the vertical signal becomes exaggerated at the higher frequencies of the audio range due to an increasing plastic resonance which becomes progressively worse from a pure lateral stylus movement to a pure vertical stylus movement. By appropriate design of the mechanical low pass filter, the attenuation may be established to equalize the increasing vertical plastic resonance such that an essentially fiat frequency characteristic may be realized over the audio range in all planes of stylus movement.

in accordance with further aspects of the present invention, the controlled vertical filtering action is realized by dimensioning the vertical cross section of the stylus arm from the point of attachment for the stylus to the common support or coil bobbin to provide a progressive decoupling action between the stylus and the common support such as to completely decouple or attenuate vertical signals at the higher frequencies above the resonant frequency of the system. Such progressive filtering or decoupling of vertical signals materially reduces the distortion since most of the distortion in stereophonic recordings may be traced to vertical signals cut into such recordings, which vertical signals should not be accentuated. Essentially, a stylus constructed in accordance With the invention is characterized as being stiff or non-compliant to torsional and lateral movement and progressively compliant vertical movement at increasing frequencies whereby progressively increasing decoupling is attained for increasing frequencies above said predetermined value. For monophonic reproduction, the progressive decoupling of the vertical signal which is due to the pinch eifect enables acceptable low distortion playback, particularly as compared to stereophonic cartridges which generate the full signal of vertical pinch eflect. The quality of such monophonic reproduction may be made optimum by coupling the coils of the stereophonic transducer in phase opposition such that the vertical signals produced incident to the pinch eifect will be cancelled out during such monophonic playback.

A further important factor in the design of transducers of this type is the realization of substantially equal linear compliance in all directions for the moving-coil system. In the reproduction of stereophonic sound, it is important that a light tracking force be applied since the true working compliance of the transducer or cartridge is dependent upon such tracking force. A light tracking force can only be used when the inertia of the moving mass is extremely low and the compliance very high, approximating a free air compliance which is substantially equal and linear in all directions. Still further, a lowering of the inertia of the moving mass assures better transient response and corresponding lower distortion. Coupled with the above, is the further requirement that the moving-coil system, after mounting and during use, maintain its orientation in the magnetic field of the cartridge and its 45/ 45 orientation to the plane of the record.

It is a further object of the present invention to provide a transducer for both stereophonic and monophonic reproduction which has substantially equal compliance in all directions, with a relatively high true working compliance enabling the use of a relatively low tracking force for sound reproduction. Advantageously, such low tracking force reduces stylus and record wear.

In accordance with this aspect of the present invention, a yieldable grommet in the form of an annulus surrounds the common support of the moving-coil generating system and mounts such moving-coil generating system within the magnetic gap. With such grommet it is possible to have substantially equal amounts of mounting material in all directions from the axis of the generating system, with the true working compliance approaching free air compliance.

The above brief description, as well as further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description, of a presently preferred but illustrative embodiment, when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevational view of an electro-mechanical transducing device suitable for stereophonic and monophonic reproduction demonstrating features of the present invention;

FIG. 2 is a bottom plan view of the device shown in FIG. I;

FIG. 3 is a fragmentary sectional view on an enlarged scale taken substantially along the line 33 of FIG. 2 and looking in the direction of the arrows;

FIG. 4 is a sectional view taken substantially along the line 4-4 of FIG. 3 and looking in the direction of the arrows;

FIG. 5 is an exploded perspective view showing the moving-coil generating system, the mounting grommet, and the mounting plate in unassembled condition;

FIG. 6 is a perspective view showing the components illustrated in FIG. 5 as assembled;

FIG. 7 is a fragmentary bottom plan view on an enlarged scale and with parts broken away, showing the details of the means for mounting the moving-coil generating system in the magnetic field; and

FIG. 8 is a series of fragmentary elevational view on an enlarged scale and with parts broken away, showing the successive steps of constructing and mounting a stylus on a stylus arm in accordance with features of the present invention.

Referring now specifically to the drawings, there is shown my improved electro-mechanical transducing device suitable for both monophonic and stereophonic reproduction, which has been generally designated by the reference numeral 16, and includes a molded base or housing 12 of substantially conventional construction. The base or housing 12 includes a substantially horizontally-extending top wall 14 having at the rear side thereof a depending rear wall 16 and at opposite sides thereof depending side walls 18, 2!} which define therebetween a longitudinally extending guideway 22 which is open at its bottom, forward and rearward ends. Accommodated within the guideway 22 is a permanent magnet 24 which produces the requisite magnetic field and includes a yokeshaped body of an appropriate magnetic material (i.e. Alnico) having opposed pole faces 24a, 24b which extend substantially transversely of the elongated base or hous ing 12 and define therebetween a magnetic gap 26 which extends substantially longitudinally of the housing or support 12.

Mounted within the magnetic gap 25 is a moving-coil generating system, generally designated by the reference numeral 28, which produces two substantially identical stereophonic output signals as will hereinafter be described. The moving-coil generating system includes a substantially cubical common support 39 having a forwardly projecting stylus arm 32 at the lower forward corner thereof. The common support 30 and stylus arm 32. are integrally molded out of an appropriate material, such as plastic, with the flats or faces 36a, 30c, Iifie and 3th extending in planes oriented at 45 to the horizontal and with the faces 3%, Siid extending in vertical planes and adapted to be mounted in planes parallel to the gap-defining faces 24a, 24b of the permanent magnet 24. The stylus arm 32 projects or cantilevers from the lowermost front corner of the common support 30 at the junction or corner of the faces 3nd, 300, 3%.

At each of its corners, except for the corner where the stylus arm 32 emerges, the common support 30 is formed with integral projections or cars, such as the ear designated by the reference numeral 33, whereby the flats or faces 35a, 36b, 30c and 30d and the respective projections 33 define a first winding bobbin adapted to receive a first moving coil 34; and the flats or faces E-tle, 30b, 30 and 38d and the respective projections 33 define a second winding bobbin adapted to receive a second moving coil 36. Since in the preferred form, the common support is cubical, the respective faces or flats which define the winding bobbins are mutually perpendicular or at right angles to each other, with the respective moving coils 34, 36 oriented for 45 45 movement. In a preferred form of the invention, each of the moving coils 34, 36 includes of the order of 800 turns of silver-copper alloy wire of the order of .0004 of an inch in diameter which is preferably triple gold-plated against corrosion and insulated. A typical size for the generating armature 30 is of the order of .070 inch from side to side of each fiat or face.

The requisite output connections to the respective moving coils 34, 36 is achieved by the provision of four terminal elements or contact pins (i.e. pin 38) which are mounted on the rear wall 16 of the housing or support 12 which serves as a terminal strip. The contact pins have respective electrical connections to the ends of the coils 34, 36 (i.e. connection 4% from contact pin 38). To facilitate making the proper electrical connections to the contact pins or terminal elements, the contact pins are colorcoded. For monophonic reproduction, the moving coils 34, 36 may be readily coupled to each other in phase opposition to completely cancel the vertical signals generation incident to the pinch effect.

Mounted on the forward or terminal end 32a of the stylus arm 32, which terminal end is seen to extend substantially horizontally, is the stylus assembly, generally designated by the reference numeral 42. The stylus assembly 4-2 is seen best in the lower right hand showing of FiG. 8 and includes an elongated support 44 fabricated of metallic material and a stylus element 46 of diamond, sapphire, or the like. The enlarged progressive showings of FIG. 8 illustrate the sequential steps by which the stylus assembly 42 is constructed in accordance with further aspects of the present invention, although other methods of manufacturing the stylus assembly 42 are within the contemplation of the present invention. Initially, the elongated metallic support 44 is in the form of a continuous cylinder from one end thereof to the other and is formed with a seat or depression 44a at its under surface within which there is mounted the stylus element 46 in its rough or unformed condition. The stylus element 46 may be bonded to the support 44 in position to project therefrom by any known method. Thereupon the subassembly of the elongated support 44 and the stylus element 46 are formed with a substantial conical shape 44]) at its forward end with the apex of the conical shape providing the required tip on the stylus element 46. The stylus assembly 42 is completed by forming the same with a reduced neck 46a in the remaining cylindrical portion thereof and by cutting away the unused portion of the elongated support at the end remote from the stylus element 46 to form the end face 44d. The terminal or leading end 32a of the stylus arm 32 is formed with a through bore 32b opening into or communication with the top and bottom faces of the arm, which bore is of a diameter slightly less than the diameter of the cylindrical portion of the support 44 such that the support 44 may be inserted into the bore 32b with a snap action or force fitting. Such snap action is facilitated by the yieldable characteristics of the stylus arm and by the undercutting of the cylindrical portion of the stylus support 44. The joinder of the stylus assembly 42 to the stylus arm 32 is completed by the application of bonding layers 48, 59 to the top and bottom surfaces of the stylus arm about the contiguous portions of the stylus assembly 42. Preferably the bonding layers 48, 50 are of a homogenized epoxy resin, preferably of the same composition as the resin employed in the molding of the stylus arm' 32, which homogenized epoxy resin layers 48, 50 are applied in accordance with techniques which are generally understood. After mounting, for all intents and purposes the stylus assembly 42 is unitary with the stylus arm 32 such that the armature 30, stylus arm 32 and stylus assembly 42 constitutes a single moving mass.

Means are provided for mounting the moving-coil generating system 28 on the support 12 with the signal generating or output coils 34, 36 disposed in the magnetic gap 26, and with the turns thereof extending substantially at right angles to the pole faces 24a, 24b and in the required 45/45 orientation for discrete stereophonic signal generation in accordance with the groove of the 45/ 45 recording. The mounting means includes a yieldable grommet 52 in the form of an annulus or toroid which grommet preferably is fabricated of an elastomeric material. The annular or toroidal grommet 52 may be made from a rubber which is compounded to minimize any cold flow or hardening tendencies. The characteristics of the grommet 52 are selected to assure the return of the stylus element 46 to the center of the record groove such that the record groove may carry the stylus element past the dead-center position with respect thereto. It will be appreciated that the use of yieldable mounting means which includes substantially the same amount of mounting material in all radial directions from the axis of the generating system 28 contributes to achieving equal compliance factors in all directions.

In order to achieve the assembly of the annular or toroidal grommet 52 about the common support 30, specifically in the mounting saddle defined by the flats or faces 30a, 130e, 30c and 36 and the adjacent projections 33, the cross section of these faces are built up to a diameter substantially equal to the inner diameter of the grommet 52. As seen in FIG. 4, this is achieved by the application of an insulating coating, such as varnish, which is generally designated by the reference numeral 53, over the coil turns traversing and overlying the faces 39a, 30c, 30c and 30 such that the cross-section of the cubical support 30 in the plane presented to the grommet is built up to be substantially complementary to the inner peripheral or annular surface 52a of the mounting grommet 52.

The mounting means further includes a mounting plate or bracket 54 having a circular grommet-seating aperture 54a intermediate its end and oppositely directed wing sections 54b, 540. The diameter of the grommetseating aperture 54a is smaller than the diameter of the outer peripheral surface 52b of the annular grommet 52 such that the grommet is placed in radial compression when assembled with the mounting bracket. The

outer peripheral surface 52b of the mounting grommet is provided with a slit-like circumferentially extending groove 520, with the base or bottom wall of the slit-like groove being of a diameter somewhat larger than the diameter of the grommet-seating aperture 54a. Accordingly, when the grommet 52 is received within the grommet-seating aperture 54a, with the portions of the mounting plate or bracket 54 bounding the aperture 54a being accommodated within the slit-like groove the grommet 52 is precisely oriented within the seating aperture 54a and respective compression seals are provided between the inner periphery 52a of the grommet 52 and the builtup diameter of the generating armature 30 and the inner periphery 52b and the mounting plate 54.

As seen best in FIGS. 1 to 3 inclusive, the opposite side walls 18, 20 of the housing 12 are formed with transversely-extending slots 18a, 20a which are disposed in a common plane substantially equally distant from the pole faces 24a, 24b of the magnet 24. The slots 18a, 201; are of a width substantially equal to the thickness of the mounting bracket 54 and are of a height such that when the edge 54d of the mounting bracket 54 bottoms on the slot 18a, 20a, the moving-coil generating system 28 is properly positioned vertically in the magnetic gap 26. The overall length of the mounting bracket 54 is substantially equal to the overall Width of the housing 12; and upon laterally or transversely adjusting the mounting bracket in relation to the housing, the proper lateral orientation may be imparted to the moving-coil generating system 28. When the movingcoil generating system is properly oriented, both vertically and laterally in relation to the magnetic gap and the respective pole faces 24a, 24b of the permanent magnet 24, the mounting bracket 54 is fixed in position by the use of an appropriate elastomen'c adhesive which will readily adhere to the base or housing 12 which in turn is fabricated of a highly damped material, such as a rubber impregnated styrene. A typical elastomeric adhesive for bonding the mounting bracket 54 to the base or housing 12 is Pliobond which is a commercially available product. Further, I have found that if the yieldable mounting grommet 52 is given a permanent deformation toward one pole face, substantial equalization will be brought about in variations in the compliance of the material from which the mounting grommet is fabricated, which variations occur incident to changes in ambient conditions. For example, in warm weather the grommet material may become more compliant. In accordance with this aspect of the invention, a permanent pressure is imparted to the mounting grommet 52 toward one pole face by the provision of a plug 56 of magnetically susceptible material which is mounted in an axially extending bore 32g formed in the common support 30. As seen best in FIG. 4, the plug 56 of the magnetically susceptible material is offset in the magnetic gap 26 toward the pole face 241) of the magnet 24 which tends to impart a permanent pressure on the mounting grommet 52 toward the pole face 24b which take up compliance variations and result in a more perfect standardization of the mount for the moving-coil generating system. Typical magnetically susceptible materials are iron and Permalloy. Although, the common support 30 is initially displaced closer to one pole face than the other, this does not change or aifect the stereophonic or monophonic signal output since the overall gap width is constant and motion components at right angles to the pole faces do not contribute to the signalgenerating function. Since the common suuport 30 is fabricated of plastic in this illustrative embodiment, the presence of the plug 56 axially of the common support 30 and at right angles to the pole faces 24a, 24b enables the development of a greater flux concentration through the portion of the generating system which physically carries the coils 34, 36.

In order to reduce distortion the stylus arm 32 is constructed to serve as a mechanical low-pass filter which attenuates, at approximately six decibels per octave all frequencies occuring above one octave below the lateral frequency at which the resonances occur. This is achieved by making the portion of the stylus arm 32 intermediate the stylus assembly 42 and the common support 30 of progressively increasing vertical extent from the stylus assembly to the armature such that a progressive mechanical decoupling action occurs between the stylus assembly 42 and the common support 30 in response to increases in frequency over the prescribed audio range. The progressive increase in vertical extent of the stylus arm 32 is determined experimentally and established to introduce the desired attenuation in response to increases of frequency. The stylus arm 32 is arranged to have a vertical compliance which is less than the suspension compliance at the low end of the operating range of frequency, a vertical compliance which is greater than the suspension compliance at the high end of the operating range of frequencies, lateral and torsional compliances which are always less than the suspension compliance over the operating range of frequencies, and may have greater compliance in all planes at a prescribed frequency to completely filter the actual main resonant action of the stylus in the groove. Further the stylus is of progressively increasing lateral cross section from the point of support of the stylus as sembly 42 toward the common support 30 to eifectively reduce the lateral mass of the stylus arm, consistent of course with the compliance requirements.

In order to facilitate a more thorough understanding of the present nivention, a typical, but nonetheless illustrative sequence of assembly steps will now be described:

The stylus assembly 42 is secured to the stylus arm 32 of the moving-coil generating system 28 either before or after the Winding of the coils 34, 36 over the respective mandrel or bobbins provided by the flats or faces of the common support 30. Only a few turns of the coils have been shown in the drawings, but it will be appreciated that there are a large number of turns of exceptionally fine wire, with the coil turns crossing over each other at opposite flats 3%, 30d of the common support 30. Since the coils are wound on a common support and are geometrically substantially congruent, and it is possible to precisely form the common support, substantially perfect coil symmetry may be realized, with the coils oriented at righ angles to each other and at 45 to the horizontal. Although reference is made throughout the specification to orientation of the coils at substantially 90 relative to each other for maximum signal generation and channel separation, it will be appreciated that if the coils were symmetrically wound at angles less than 90 relative to each other, they will still function to produce two separate outputs, but under less optimum conditions of signal reproduction. After the completion of the moving-coil generating system 28, the diameter of the cross section of the mounting saddle defined by the flats or faces 36a, 30 30c, 30d is built up to be substantially equal to the diameter of the inner periphery 52a of the mounting grommet 52, which mounting grommet is of sufiicient radial extent to provide respective compression seals between the inner periphery of the grommet and the built up section of the common support and the outer periphery of the grommet and the bounding portions of the aperture 54a in the mounting bracket 54. Upon completion of the subassembly illustrated in FIG. 6, the mounting bracket 54 is assembled within the housing 12 as seen best in FIGS. 1 to 3, care being taken to impart the requisite vertical and lateral orientation to the moving-coil generating system within gap 26 of the magnet 24. Finally, the requisite electrical connections are made to the four coil ends by lead wires 40 to respective pins 38, such electrical connections being preferably made by thermowelds and the use of silver contact pins.

Since both coils are rotationally and electrically balanced, and since there is only one moving mass within the single magnetic gap, there is maximum assurance that the reproduction from the respective stereophonic channels will be exactly alike. This in turn results in sound which is smooth and well defined and eliminates any falsecolorations in either of the stereophonic channels. The transducer, due to its relative simplicity in construction, may be made exceptionally rugged, completely reliable and capable of reproducing the recorded sound, virtually with the same quality as the master tape employed in the preparation of the stereophonic record. When used for mono-phonic reproduction, the present transducer re sults in fidelity which surpasses a comparable high quality monophonic transducer particularly when the output coils are connected in phase opposition such that the vertical signals produced incident to the pinch effect are cancelled out for such monophonic playback.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

What I claim is:

1. An electro-mechanical transducer comprising a base, a magnet mounted on said base and including opposed pole faces defining a magnetic gap, a first output coil, a second output coil, a common support mounting said coils substantially at right angles to each other with said common support and said coils providing a balanced moving mass with said coils having substantially identical mechanical and electrical properties, a stylus and Stylus arm operatively connected to said common support, and means mounting said common support with said first and second coils in said magnetic gap and extending at right angles to said pole faces.

2. An electro-mechanical transducer comprising a base, a magnet mounted on said base and including opposed pole faces defining a magnetic gap, at first output coil, a second output coil, a common support mounting said coils substantially at right angles to each other, a stylus and stylus arm operatively connected to said common support, and means including an elastomeric grommet mounting said common support with said first and second coils in said magneic gap and extending at right angles to said pole faces.

3. An electro-mechanical transducer comprising a base, a magnet mounted on said base and including opposed pole faces defining a magnetic gap, a first output coil, a second output coil, a common support about which said coils are wound with the turns thereof at right angles to each other, a stylus arm integral with and projecting from said common support, and means including an elastomeric grommet mounting said common support with said first and second coils disposed within said gap and extending at right angles to said pole faces.

4. A stereophonic pickup cartridge comprising a support, means or producing a magnetic field in a magnetic gap bounded by pole faces, a moving-coil generating system including a support having a stylus arm and first and second coils wound on said support with the turns thereof in substantial symmetry with each other, a stylus on said stylus arm, and means having substantially equal compliance in all directions mounting said generating system with said first and second coils in said magnetic gap and with said turns extending substantially at right angles to said pole faces.

5. A stereophonic pickup cartridge comprising a base, means on said base for producing a magnetic field in a magneic gap bounded by pole faces, a moving-coil generating system including a support having a stylus arm integral therewith, and first and second coils wound about the faces of said support with the turns thereof in substantial symmetry with each other, a stylus on said stylus arm, and yieldable means having substantially equal compliance in all directions surrounding said support and mounting said generating system with said first and second coils in said magnetic gap and with said turns eX- tending at right angles to said pole faces.

6. A stereophonic pickup cartridge comprising a base, means on said base for producing a magnetic field in a magnetic gap bounded by pole faces, a moving-coil generating system including a support having a stylus arm and first and second coils wound on said support with the turns thereof in substantial symmetry with each other, a stylus on said stylus arm, and suspension means having substantially equal suspension compliance in all directions mounting said generating system with said first and second coils in said magnetic gap and with said turns extending at right angles to said pole faces, said stylus having a beam compliance which is less than said suspension compliance and which is of progressively increasing compliance at higher frequencies, said beam compliance at said higher frequencies being greater than said suspension compliance such that there is a progressive mechanical decoupling at higher frequencies.

7. In a pickup for translating mechanical movement to electrical signals over a prescribed range of frequencies, a moving-coil system including a support, a stylus arm projecting from said support, and a stylus mounted on said stylus arm at a point spaced from said support, and means suspending said moving coil system with a substantially uniform suspension compliance for movement in response to actuation of said pickup, the portion of said stylus arm intermediate said stylus and support being of progressive increasing cross section from said stylus to said support to provide a progressive mechanical decoupling action between said stylus and support in response to increases in frequency over said prescribed range of frequencies, said stylus arm having a stylus arm compliance which is less than said suspension compliance at the low end of said prescribed range of frequencies and a stylus arm compliance which is greater than said suspension compliance at the high end of said prescribed range of frequencies.

8. In a pickup for translating mechanical movement to electrical signals over a prescribed range of frequencies, a moving-coil system including a support, a stylus arm integral with and projecting from said support, and a stylus mounted on said stylus arm at a point spaced from said support, and means suspending said moving coil system with a substantially uniform suspension compliance for movement in response to actuation of said pickup, the portion of said stylus arm intermediate said stylus and support being of progressive increasing cross section from said stylus to said support to provide a progressive mechanical decoupling action between said stylus and support in response to increases in frequency over said prescribed range of frequencies, said stylus arm having a stylus arm compliance which is less than said suspension compliance at the low end of said prescribed range of frequencies and a stylus arm compliance which is greater than said suspension compliance at the high end of said prescribed range of frequencies, said stylus arm having a lateral and torsional compliance which is less than said suspension compliance over said prescribed range of frequencies.

9. A stereophonic pickup comprising a base, a permanent magnet on said base including a yoke-shaped body terminating in opposed pole faces defining a magnetic gap, a cubical bobbin having a projecting stylus arm, a stylus secured to said stylus arm, a first output coil wound about four faces of said bobbin, a second output coil wound about four faces of said bobbin, the turns of said first output coil extending at right angles to the turns of said second output coil and crossing thereover at one pair of opposite faces of said bobbin, insulating means about the remaining faces of said bobbin building up said remaining faces such that the crosssection of said bobbin is substantially circular, an annular yieldable grommet encircling said bobbin with its inner periphery engaging the circular cross-section thereof, and mean engaging the outer periphery of said grammet and movably suspending said bobbin in said magnetic gap with said one pair of faces of said bobbin extending parallel to said pole faces.

10. A stereophonic pickup comprising a base, a permanent magnet on said base including a yoke-shaped body terminating in opposed pole faces defining a magnetic gap, a cubical bobbin having a projecting stylus arm, a stylus secured to said stylus arm, a first output coil wound about four faces of said bobbin, a second output coil wound about four faces of said bobbin, the turns of said first output coil extending at right angles to the turns of said second output coil and crossing thereover at one pair of opposite faces of said bobbin, a grommet of elastomeric material encircling said bobbin with its inner periphery engaging said bobbin, and means engaging the outer periphery of said grommet and movably suspending said bobbin in said magnetic gap with said one pair of faces of said bobbin extending parallel to said pole faces.

11. A stereophonic pickup comprising a base, a permanent magnet including a yoke-shaped body terminating in opposed pole faces defining a magnetic gap, a moving mass fabricated of plastic and including a substantially cubical bobbin having an integral projecting stylus arm, a stylus, means including an homogenized plastic securing said stylus to said stylus arm, a first output coil wound about said bobbin, a second output coil wound about said bobbin, the turns of said first output coil extending at right angles to the turns of said second output coil, a grommet of elastomeric material encircling and engaging said bobbin, and means engaging said grommet and movably suspending said bobbin in said magnetic gap.

12. An electro-mechanical transducer comprising a base, a magnet mounted on said base and including opposed pole faces defining a magnetic gap, a first output coil, a second output coil, a common support of nonmagnetic material mounting said coils substantially at right angles to each other, a stylus and stylus arm operatively connected to said common support, resilient mounting means movably mounting said common support on said base with said first and second coils in said magnetic gap and extending at right angles to said pole faces, and means for imparting a permanent pressure to said resilient mounting means urging the same toward one pole face.

13. An electro-mechanical transducer comprising a base, a magnet mounted on said base and including opposed pole faces defining a magnetic gap, a first output coil, a second output coil, a common support of nonmagnetic material mounting said coils substantially at right angles to each other, a stylus and stylus arm operatively connected to said common support, resilient mounting means movably mounting said common support on said base with said first and second coils in said magnetic gap and extending at right angles to said pole faces, and means for imparting a permanent pressure to said resilient mounting means urging the same toward one pole face, the pressure-imparting means including on armature of a magnetically susceptible material extending at right angles to said pole faces and mounted on said common support in closer proximity to said one pole face than the other pole face.

14. An electro-mechanical transducer comprising a base, a magnet mounted on said base and including opposed pole faces defining a magnetic gap, a first output coil, a second output coil, a common support mounting said coils substantially at right angles to each other, a stylus and stylus arm operatively connected to said common support, and resilient mounting means having a substantially equal compliance in all directions movably mounting said common support with said first and second 11 V coils in said magnetic gap and extending at right angles to said pole faces.

15. A stereophonic pickup cartridge comprising a base, means on said base for producing a magnetic field in a magnetic gap bounded by pole faces, a moving-coil generating system including a support having a stylus arm and first and second coils wound on said support in substantial symmetry with each other, a stylus on said stylus arm, and resilient mounting means having substantially equal compliance in all directions operatively connected to said support and mounting said generating system with said first and second coils in said magnetic gap and with said turns extending substantially at right .angles to said pole faces.

16. An electro-mechanical transducer comprising a magnet including pole faces forming a magnetic gap, a first coil and a substantially congruent second coil each having a winding axis, a common support mounting said coils with their axes intersecting substantially at right angles, a stylus arm operatively connected to said common support, and means mounting said common support in said magnetic gap With said intersecting axes in a plane parallel to said pole pieces.

17. An electro-mechanical transducer comprising a magnet including pole faces forming a magnetic gap, a first coil and a substantially congruent second coil each having a Winding axis, a common support mounting said coils With their axes intersecting substantially at right angles, a stylus arm operatively connected to said common support, and means mounting said common support in said magnetic gap with said intersecting axes in a plane parallel to said pole pieces, said mounting means including an elastomeric grommet grasping said common support and having an axis of rotational symmetry normal to said plane and passing through the intersection of said coil axes.

18. A stereophonic pickup comprising a base, a permanent magnet including a yoke-shaped body terminating in opposed pole faces defining a magnetic gap, a movingcoil generating system including a support having at least six faces, a stylus arm projecting from said support and secured thereto, a stylus mounted on said stylus arm at a point spaced from said support, a first output coil wound about four faces of said support, a second output coil wound about four faces of said support and substantially congruent with said first output coil, the turns of said first output coil extending substantially at right angles to the turns of said second output coil and crossing thereover at one pair of opposite faces of said support, and resilient means mounting said support on said base with said first and second output coils in said magnetic gap and extending substantially at right angles to said pole faces.

References Cited in the file of this patent UNITED STATES PATENTS 2,563,196 Spry Aug. 7, 1951 2,640,888 Combs June 2, 1953 2,749,131 Kelly June 5, 1956 FOREIGN PATENTS 697,239 Great Britain Sept. 16, 1953 OTHER REFERENCES Ruben E. Carlson: Manufacture of a High-Quality Cartridge, Audio, August 1958, pp. 30-32.

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