US1702438A - Reproducing device - Google Patents

Description

Patented Feb. 19,1929

. UNITED STATES PATENT OFFICE.

J'T J'RJEN S. HIGH, F. WILKINSIBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRICdc. MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

REPBODUGING DEVICE.

Application filed April 30, 1927. Serial No. 187,800.

My invention relates to reproducing devices and more particularly to pick-up devices designed and intended to translate the sinuosities of the usual phonograph record into electrical fluctuations that are subsequently amplified and utilized to actuate a loud-speaking telephone or its equivalent.

One object of my invention is to provide a pick-up device that is responsive to the highest harmonic frequencies accompanying instrumental or vocal music.

Another object of my invention is to provieda pick-up, device that will not over emphasize any particular frequency.

Another object of my invention is to provide a pick-up device that may be easily adjusted to preferentially respond to high or low frequencies.

Another object of my invention is to provide an improved pick-up device of the electrostatio type.

7 At the present time, there is a very decided Another, and more specific, object of my invention is to provide an electrostatic plckup device in whichis incorporated damping means that is equally effective over a wide range of sound frequencies. 1

tendency toward the electrification of phonograph reproducing devices. In other words,

instead of having the phonograph reproducer convert the 'sinuosities of the record directly into sound, they are first translated into electrical potential, orcurrent, fluctua tions which, in .turn, are utilizedto control a thermionic amplifying system similar to thosenow well known in connection with radio receiving apparatus. A system of the type referred to is shown in the patent to J ones, N0. 1,531,252, to which reference may advantageously be made.

The pick-updevices heretofore used havebeen of four general types, electrodynamic,

" electromagnetic, microphonic, and electrostatic. The electrodynamic type is exemplified in the Jones patent, the electromagnetic type is shown in a patent to Egerton, 1,284,

623, the microphonic type in a patent to Moore, 1,583,067, and the electrostatic type in a patent to Groenbaum, 1,544,001.

'My invention is concerned primarily with v the electrostatic pick-up, or reproducer, such as is shown in the Groenbaum patent, and is in the nature of an improvement thereon.- Specifically, I interpose sheets of textile damping material between the condenserelectrodes, and further provide resilient means whereby the initial pressure on the said electrodes may be fixed in order that the sensitivity of the device may be altered to suit the individual record it is desired to reproduce.

Among the novel features of my invention are those particularly set forth in the appended claims. The invention in its generic aspect, however, as well as further objects and advantages thereof, will best be understood by reference to the following description of certain specific embodiments taken in connection with the accompanying drawings, in which Figure 1 is a cross-sectional view of a preferred embodiment of my invention, taken along a line approximating the line II of Fig. 2;

Fig. 2 is a top plan view of the same embodiment of my invention, showing the appearance of the device with the cover plate removed;

Fig. 3 is a plan view of a single condenserplate element;

Fig. 4 is a diagrammatic elevational view of an assembly of condenser elements illustrating the textile dielectric interposed therebetween;

Fig. 5 is a view, partly in elevation and partly in cross-section, of an alternative form of my invention adapted for pushpull operamanner in which a condenser type pick-up device may be associated with an audio-frequency amplifier.

Referring specifically to Figures 1, 2, 3 and 4, a preferred embodiment of my invention comprises a circular block'l of insulating material provided with a cylindrical recess 2 with which are connected two rectangular recesses 3 and 4. The block 1 of insulatmg material is nested in a circular metallic casing 5 and held in position by a plurality of screws 6.

A plurality of metal-foil condenser plates 7 shaped as shown in Fig. 3, are positioned with their large ends resting in the cylindrical recess 2 and the elongated portions of each alternate plate lying in the rectangular recesses .before mentioned. Between adjacent conmaterial. A conical member 10,'preierably of bak'elite or other insulating material and having a cup shaped depression 11 at its apex,

rests upon the stack of condenser plates posi- I tioned in the cylindrical recess.

A self-adjusting bearing member 12 is affixed to the casing member and adjacent tothe cylindrical recess by means of a plurality of screws or analogous devices.

Aneedle-carrying member 13 is provided with a plurality of trunnion members 1a and 15 having reduced conical end portions, by means-otwhieli the member 13 is mounted for oscillatorymovement between the up standing portions or" the bearing member 12.

i The upstanding portions of the bearing memit from rattling during operation. The

needle-carrying member is provided with an'axi'al opening 16 into which may be inserted a phonograph needle 17 which is main tained in adjusted position by means of a set screw 18. i i

The end of the driving member 13 opposite the needle-receiving opening is provided with a depending portion 2Q which rests in the depression 11 formed in the-apex otthe conical member 10 and is retained there- :against by means of a resilient element 21 carried by a screw threaded device provided with a knurled adjusting llGZlCl'QQ. Tliescrewthreaded device is, in turn, carried by a mem 2 her 23 which'is affixed to the uppersurlace of'sthe block of iiisulatinginaterial, strad dlingthe cylindrical recess and being held in position by a plurality of bolts 24-. i

A cover plate'25 is provided which 2 either have. athreaded connection with the casing 5 or may merely be press-fitted thereon; The needle-holding set screw 18'pi'o3 ects "through an opening in the cover member and;

at thepoint whereit extends through the said member, it is surrounded by a flexible moisture-proof bushing 26,.preterably made of soft rubber or of an analogous material.

The end of the driving member 13which carries the phonograph needle pro eet's throughan opening in the side wall of the casing 5 and is also surrounded-by a flexible waterprooi bushing 27 at the point-where it extends through. the saidwall; Thecasing 5 is PlOVliClBClWlCll acylindr-icalextended portion 28 in which a block offinsulating material 30 is held by a bolt '31; This block of insulating material carriesia plu-v 38 and LO-through which extend rality of contact members 32 and 33 which are connected to the condenser-plate extensions 3 1 and 35, respectively, bymeans of conductors 36 and 37 which are firmly held in electrical contact withthe said'condenserplate extensions by means of clamping plates bolts 41 and 42.

It will be-notedthat the block 30 of insulating material is slightly less in diameter than the cylindrical extension 28 of the casing, the space tlierebetween being left to accommodate the small end of the usual phonograph tone arm. 'A screw 43, having a reduced end portion a l, extends through one side of the cylindrical extension 28 and is arranged to cooperate'with the bayonet slot which is part or the standard equipment of substantially all phonograph tone arms;

When the device is to be used in connection with an electrical phonograph, the phonograph tone arm (not shown) is preferably provided near the interior of the small end thereof with a plurality of resilient contact members which'cooperate with the members 32 and 33 carried by the insulating block to complete an electrical circuit. Y Fig. 5' is a view illustrating a modification of my invention inwhich a single relatively rigid plate is arranged to be movable with respect to two fixed plates in order that the device may be utilized in the push-pull manner. v This modification of my device comprises a casing 50 in which are fixedly mounted a plurality of plates 51 and 52 having any desired contour, and being provided with a plurality of passage-ways 53. The casing is provided with a resilient bearingdevice, comprising a plurality of upstanding ear members 59 between which-is trunnio-ned a needlecarrying arn 54 provided with needleretaining set scie\v,55. The end of the arm opposite theneedle-holdingportion is bent at right angles to the-long axis of the memher and terminates in a relat vely rigid plate. 56 having a contour approximating the same" as that of the .lixe'd plates. Dielectric mem bers, 57 and 58, preferably composed of silk, are interposed between the movable plate and the fixed plates. r The material composing the dielectric members 57 and58, and the number and sizeoii the openings '53 through thefixed'plates 51 and 52 are so chosen that the device will have an even response over a wide range of sound frequencies.

Previous to my invention, it was proposed by Moore anddis'closed in Patent-'No 1,583,- 067, to interpose elastic coupling and damping means between the driving and the driven members oiia pick-updevice of the micro-' phonic type. The coupling referredto pref-j erably, comprised a plurality of sheets of metal foil or'papei' loosely packed between the driving and the driven elements and serving to dissipate sufficient of the impressed energy to provide the desired amount of damping.

" Such an arrangement has not been found to be sure on the free end of the driving member."

efficient when the driven member is arranged to alter the capacity of a variable condenser in response to a phonograph record, for the reason that the higher harmonic frequencies are entirely lost, andobjectionable noises are introduced.

According to my invention, I secure the requisite amount of damping by utilizing, as a dielectric between the condenser plates, a material such as silk, or the like. The damping effect I accordingly obtain is quite different from that obtained when paper is used as a damping material. The air entrained between the several condenser plates, when forced to escape radially under pressure transmitted to the plates from the driving member, encounters, in its passage, not only the friction between-the various plates but also a definite amount of friction in the interior of the dampingmaterial itself. I am not prepared, at this time, to give the exact theory on which my device operates; I can state only that, as the result of numerous experiments and extensive observation, the interposition of textile damping material between the condenser plates gives rise to a much more even response at all necessary frequencies than any other type of damping means.

The resilient element 21 carried by the screw-threaded member serves to maintain the rounded end 20 of the driving member 13 in intimate contact with the cone-shaped driven member 10 and also has the additional function of providing an initial adjustment of the sensitivity of the device. The response to differing frequencies may be materially changed by the exertion of moreor less pres- This pressure alters the average or non-operating capacity of the condenser stack and also interposes a certain amount of resistance to the excursions of the driving member.

It is thus possible to adjust theresponse of the pick-up device to suit the requirements of the phonograph record being reproduced, if desirable. In the event that the device is to be so arranged that it may be adjusted at will by the user, it is preferable that the knurled headf23 shall be accessible from the outside excursions. I have found these gaskets to be tirely.

The manner in which my device is electrically connected to an amplifying system forms no part of the present invention. One possible mode of connection is exemplified in Fig. 6, which figure is substantially acopy of Fig. 2 of the patent to Fitch 1,307,862. A thermionic device 60 having a grid 61, a filament 62, and a plate 63 is provided with a source 64 of filament potential and a source 65 of plate potential, the plate or output circuit being connected in any well known manner to an audio-frequency amplifier 66. An electrostatic pick-up device comprising a plurality of electrodes 67 and 68 having textile or discontinuous dielectric material 70 therebetween, has one electrode thereof connected to the grid 61 of the thermionic device through a condenser 71 and the other electrode thereof connected to an intermediate point on the plate potential source 65 through a resistor 72. The pick-up device is illustrated as having but two electrodes, instead of the larger member actually used, this manner of illustration being chosen for convenience.

The grid of the thermionic device is maintained at the preferred operating potential by means of a C battery 73 and a gridleak resistor 7 4: connected between the said grid and the filament.

In the operation of the system shown in Fi ure 6, when the reproducing stylus or needle is caused to vibrate by following the groove on the record (not shown) this motion is transmitted to the condenser assembly and causes proportional changes in the capacity thereof. The variations in capacity of the condenser causes a corresponding variation in the charge on the blocking condenser 71 which, in turn, sets up potential variations on the grid. The potential variations are amplified in the plate circuit of the device and are further amplified in the audio-frequency amplifier and may be then utilized to actuate a loud speaker 75 of any conventional design.

By reason of the fact that the damping means I have provided is substantially as effective for high as for low frequencies, it .as been found that the sound output from an amplifier energized by my improved pickup device is practically free from distortion. In addition to the inherent characteristics of the condenser stack with its interposed textile dielectric, I have so arranged the driving member that it will have no natural period which corresponds to any frequency within the usual range of vocal or instrumental music.

I have accordingly provided an electrical reproducing device which will faithfully render all of the delicate overtones and hormonics accompanying the music recorded on phonograph records and one which is not subjected to appreciable deterioration during US8- only two specific embodiments of myvinvention, it is my understanding that many variations thereof are posslble. My invention, therefore, 1s not to be lmnted except in so far as is necessitated bythe prior art and by the condense-r having a discontinuous dielectric under-the control-of said driven member and resilient means for maintaining a portion of said driving member in contact with said driven member. a

2. 'A vibration responsive device comprising a driving member adapted to receive a phonograph needle or analogous element, a driven member, a variable condenser under the control ;of said driven member, resilient means for maintaining a portion of the drive ing member in contact with the driven member and resilient means for limiting the eX- cursions of the driving member.

, e 1927. .3. A phonograph pick-up device compris- I ing a driving memberadapted to receive a phonograph needle, a dr ven member adapted to be actuated thereby, a. variable condenser havin a textile dielectric and so dis osed o n 1 u l u With respect to said driven member that its capacity be altered in response to. movements thereof, and means for adjusting the average position'of said driven member with respect to said variable condenser; o

d. A phonograph pick-up device comprising a. variable condenser having a plurality of plates with discontinuous resilient dielectric resilient means for adjusting'the average capacity of said condenser. v

In testimony wthereoi', I have hereunto subscribed my name this 21st day of April,

. JURJEJNV s; men.v

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