US 2577051 A
Description (OCR text may contain errors)
Dec 4, 1951 E. N. voEGTLlN ETAL 2,577,051
TONE ARM AND TRIP ARM SYSTEM FOR AUTOMATIC PHONOGRAPHS Filed Aug. 25. 1949 F7C?. Z.
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` 27 27 J5 3. 1.x" 'u i -s IN1/amazes 0 r we /Pf ff/2 f J@ am@ D. x/GTL/D CL50/n 077ML Patented Dec. 4, 1951 UNITED STATES PATENT OFFICE TONE-ARM AND TRIP-ARM SYSTEM FOR AUTOMATIC PHONOGRAPHS Application August 25, 1949, Serial No. 112,268
The present invention relates to phonograph apparatus and, particularly, to improvements in combined tone-arm and trip-arm arrangements adapted for use in automatically operating phonographs.
Arrangements of the above mentioned variety usually comprise a tone-arm assembly and a triparm assembly. The tone-arm assembly includes an electrical pickup disposed for cooperation with a record to reproduce the recorded sound, and the trip-arm assembly includes a trip actuator adapted, when the end of the playing of a record is reached, to actuate a tripping mechanism which controls the automatic function of the phonograph. Usually the tone-arm and triparm are connected, at one of their end portions, to a mounting structure which provides for swinging movement of both arms in unison and in planes substantially paralleling the generally horizontal plane of the turntable. Also, the mounting structure provides for pivotal movement of said tone-arm with respect to the trip-arm and in planes at substantially right angles to the generally horizontal plane of the turntable. The tone-arm and the trip-arm connected as above stated, through the mounting structure, constitute a suspended vibratory two-arm leverage system. During normal operation of the phonograph, vibrational waves which are set up in this leverage system due to vibrational movement ofthe pickup needle, are reflected back to the pickup and, thus, are apt to create objectionable peaks in the frequency-response characteristic of the pickup. Moreover, vibrations which are set up in this leverage system are often the cause of mistracking and trip failure difdculties.
An important and hitherto unsolved diiiiculty stems from the fact that, in practice, some phonograph records, due to vibrations in the recording instrument, have a spurious tone recording thereon which tone is reproduced by light weight pickups. Most commonly this tone has a frequency of 30 cps. It is with elimination of this, and similar undesired frequencies, that the present invention is primarily concerned.
It is, therefore, the primary object of this invention to provide an improved combined tonearm and trip-arm arrangement which overcomes the above stated objections and diiiiculties.
It is also an object of the invention to control the resonance of the suspended tone-arm and trip arm leverage system in such a manner as to provide a desired high level of response over the useful bass register while, at the same time.
providing a very low level of response at a particular and undesired very-low frequency.
Another and more specific object of the invention has to do with the provision of a novel coupling between the ton-arm and the trip-arm assemblies, wherebyl it becomes possible to reduce the effective mass required to give good bass response and, further, to insure proper tracking and positive tripping.
Briefly stated, the above-recited general objects a-re attained, according to the invention, by providing a tone-arm and pickup, the effective mass of the tone-arm and the effective compliance of the pickup being such as to effect mechanical resonance at a particular, undesired low frequency, and by mechanically coupling to this rst system, a second mechanically-resonant system comprising the trip-arm assembly. said second system being also adjusted to resonate mechanically at said undesired low frequency. The degree of coupling between the two systems is sufficiently in excess of critical coupling to produce a pronounced double-peaked frequency-response characteristic. Thus, as a. result of the coupling of two systems tuned to the same frequency, two new resonant peaks and la valley are introduced in the electrical frequency-response curve of the pickup. The coecient of coupling is such that a deep valley occurs at the undesired very-low frequency, and one peak Vfalls above said frequency in the useful bass register, thereby giving the desired bass response, while the other peak falls below the lowest recorded frequency.
The above mentioned and other objects, and
- the manner in which they are obtained, will be more fully understood from the following detailed description based on the accompanying drawing which illustrates a practicable embodiment, and in which:
Figure 1 is a side elevational View illustrating theessential parts of a phonograph of the kind to which the invention is applied;
Figure 2 is an enlarged sectional-elevational view of the coupling arrangement provided between the pivot-ends of the tone-arm and triparm assemblies;
Figure 3 is a bottom view of the same;
Figure 4 is an enlarged fragmentary sectional view illustrating one of the members employed to effect the compliant connection between the tone-arm and the trip-arm assemblies; and
Figure 5 is a diagram illustrating the improvement in the frequency-response characteristic obtained by means of the present invention.
Referring more particularly to Figure 1 of the drawings, the phonograph, as shown, includes a mounting panel ID which serves to support the various parts. A turntable II is rotatably supported b y the panel and is adapted to hold the records during the playing thereof. A centering spindle I2 serves -to center the records and to retain them on the turntable. A tone-arm assembly I3, which includes a pickup I4 provided with a needle I5, is arranged on the mounting panel to swing horizontally and to pivot vertieally, with respect to the turntable, so that said needle may be brought into engagement with and may follow the modulated groove of a record placed in playing position on the turntable. i
A trip-arm assembly I6, which includes a trip actuator I'I, is arranged to swing horizontally and in unison with the tone-arm so as. to bring said actuator in cooperative engagement with a trip mechanism, generally indicated at I8, to actuate said mechanism when the pickup needle reaches the final groove of the Vrecord being played. The construction, operation and purpose of such Vtripping mechanism are Well known in the art, and need no explanation here.
The above mentioned swinging and lpivotal `moveinents are obtained by means of a mounting structure to which the tone-arm and the triparm are connected at one of their end portions I9 and y2i), respectively. As can be'seen in Figures 2 and 3, the mounting structure comprises a mounting bracket 2| and a supporting bracket 22, Which brackets are interconnected for relative pivotal movement by means of a cross-pin 23. A coil spring 24, having one end attached, as at V25, to the mounting bracket and the other end attached, as at 26, to the supporting bracket, acts on the tone-arm to maintain the desired pressure with which the pickup needle engages the irecord during reproduction. The mounting bracket 2I'is attached to the tone-arm end portion I9 `by means of suitable elements 2'I in screwthreaded engagement with bosses 28 provided in said portion of ythe tone-arm. A rigid shaft '23 'dependsfrom the supporting bracket 22 and, as
illustrated in Figure l, this shaft-projects vertically through 'a `lateral bearing 30 provided on 'panelfIL and'rests'on a `thrust bearing 3i `like- `wifse provided on saidpanel. As is also illustrated inTFgure V11, the trip-arm end portion 2 is rigidly aixed, by ,meansof 'a suitable clamping arrangement 32, to that'portion'of the shaft 29 which rextends between panel I and'thrust bearing 3I. Thus, 'shaft 29 provides for'horizontalswinging movement 'of the'tone-'arm and trip-arm, in uni-l son vand inplanes generally paralleling the playing surface of the record supported on the turntable, and thecross-pin 23 providesfor vertical pivotal movement of the tone-armwith respect to the trip-arm and in planes generally normal to lsaid record surface.
In accordance with'the invention, suitable ccmpliant means is included in the connection between the tone-arm assembly and the pickup assembly. In the embodiment shown, this coupling means takesthe form of soft rubber grommets 33, interposed between the attaching elements 2 and their points of engagement with the mounting 'bracket 2 I. As is more clearly shown in Figure 4,
each grommet is arranged on its associated attaching element 21 in such a manner as to eliminate the possibilityofV distorting the grommet and, thereby, affectits compliance when saidelernent is driven in screw-threaded engagement 'with its Cil associated boss 28. For that purpose, each grommet is retained between rigid spaced flanges SII-35, flange 34 being disposed to abut the corresponding boss and to act as a stop limiting the tightening of said element.
Also in accordance with the invention,y damping means in the form of a small block 36 of suitable material, for instance, cellulose nitrate plastic such as Pyralinv or Viscoloid, is disposed in snug engagement with adjacent portions of the tonearm and the mounting bracket. The above mentioned k.compliant rubber grommets and block of damping material constitute additional components in the mechanically resonant system, as will be-presently described.
As previously mentioned, the suspended vibratory two-arm leverage system which results from the interconnection, or coupling, of the tone-arm and the trip-arm through the above described mounting structure, is apt to resonate during the operation of `the phonograph, due to vibrational Waves transmitted through said system by 'vibration of the pickupneedle asit vfollows the `modulated groove of the record. As also previously stated, the vibrational waves set up in thementioned leverage system are, in turn, apt to produce Vdeleterious effects lin the frequency-response characteristic of the pickup, and to cause mistracking of thepickup needle.
Itis well understood in the art that the voltage output ofthe pickup depends upon deection. In other words, the voltage output of the pickup is `proportional to the deflection of the'generating element of `thepickup as it is deiected'by side-toside displacement of the needle tracking the modulated groove of the record.
The force `for -a given deflectionis groove. l'n practice, thekn'eedl'e pressure or'vertical Aforce must be atleast equal vto and preferably slightly, greater Vthan vthe lateral de'fl'ective force. However, the attainment of this relationship between the mentioned forces is no simple matter, particular-ly where a low needle vpressure of less than l0 grams is used, because lateral friction in the mounting bearings and other components of the system, as well as the resonance of said system, must be taken into consideration, since lsuch lateral lfriction and resonance are factors which affect the statedv relationship.
It has beenV found that when utilizing a tonearm and trip-arm system conventionally -de'- signed for 'satisfactory operation -of the automatic phonograph Yat, low `needle pressures, the resonant frequency ofthe system .falls at an undesirable frequency at the low endv of the band, thereby producing Y the hereinbefore mentioned problems and diiculties.
Tosolve these' problems and to overcome these diiculties, the present invention provides the novel arrangement, the operation of which will now be described. The tone-arm assembly, including the pickup, is so'devise'd that'the'mass of thetone-arml (without'the additionof the trip-arm mass) and the compliance of the pickup cause the resonance of the tone-arm assembly to fall approximately at the undesired low frequency. The rigidly interconnected trip-arm assembly and mounting structure are likewise so devised that their combined mass and compliance are also resonant at the same low frequency. Thus, the invention provides two resonant mechanical systems which are tuned to the same frequency. These mechanically-resonant systems are mechanically coupled by the compliant soft-rubber grommets 33 hereinbefore described. The degree of coupling provided thereby should be sufficiently in excess of vcritical coupling to produce a double-peaked frequency-response characteristic having a deep valley, between the peaks, occurring at the resonant frequencies of the tone-arm and trip-arm assemblies." The operation of these coupled systems, and the results obtained thereby, will be more clearly understood by considering the curves which are diagrammatically illustrated in Figure 5.
In Figure 5, curve 3l shows the output (at the lower end of the audio frequency band) which is obtained when the tone-arm and trip-arm systems are rigidly connected. It will be noted that, at frequencies below 100 C. P. S., the output or response increases rapidly with decreasing frequency. This condition is objectionable because it not only produces distortion, but is also apt to cause mistracking, when operating at the mentioned low needle pressure.
Curve 33, in Figure 5, shows the output or response which is obtained when the tone-arm and trip-arm systems are coupled in accordance with the invention. This coupling of the systems introduces, in the frequency-response characteristic, two peaks f and f and a valley fo. The spread of the peaks, in accordance with 'the invention, is governed principally by the compliance of compliant coupling means 33, while the amplitude of the peaks, and the depth of the valley, is controlled principally by the resistance (friction) of the damping means 36. By thus controlling the peaks and the valley, it is possible with the arrangement as herein described, to insure that valley fo will occur at the undesired very low frequency, thus producing attenuation at that frequency; that peak f" will fall above said frequency thereby giving the desired bass response; and that the other peak f falls below said frequency and outside the recorded range so as not to effect the frequency-response characteristic over the useful recorded range of frequencies.
The frequency at which f and f occurs is determined by the following formulas:
where f1 and f2 are the uncoupled resonant frequency of the individual system of the combined arrangement, and K is the coefficient of coupling between said systems.
From the foregoing, it will be appreciated that the invention provides a novel tone-arm and trip-arm arrangement in which the constituent elements are so constructed and arranged as to effect mechanical resonance near the lower limit of the frequency range, s` as to improve the frequency-response characteristic by positive control of the bass response While, at the' same time, providing a very low level of response at a particular, undesired very-low frequency. Also, the fact that the spread and amplitude of the peaks can be regulated, contributes to prevent mistracking and faulty tripping operations.
1. A phonograph combined tone-arm and triparm arrangement comprising a tone-arm system adapted mechanically to resonate at a predetermined frequency, a trip-arm system adapted mechanically to resonate at said predetermined frequency, and a mechanical coupling between the tone-arm and trip-arm systems, said coupling including compliant means having a compliance such as to produce a pronounced doublepeaked frequency-response characteristic with a deep valley between the two peaks and as to cause said valley to occur substantially at said predetermined resonant frequency of the tonearrn and trip-arm systems.
2. A phonograph combined tone-arm and triparm arrangement comprising a tone-arm system adapted mechanically to resonate at a predetermined frequency, a trip-arm system adapted mechanically to resonate at said frequency, a mechanical coupling between the tone-arm and trip-arm systems, said coupling including compliant means having a compliance such as to produce a pronounced double-peaked frequencyresponse characteristic with a deep valley between the two peaks and as to cause said valley to occur substantially at said predetermined resonant frequency of the tone-arm and trip-arm systems, and damping means arranged between the tone-arm and trip-arm systems to determine the amplitude of said peaks and valley.
3. A phonograph combined tone-arm and triparm arrangement comprising a tone-arm and pickup system having an effective mass and compliance to cause mechanical resonance of said tone-arm and pickup system at 30 C. P. S., a trip-arm system having an effective mass to cause mechanical resonance of said trip-arm system at 30 C. P. S., and a mechanical coupling between said systems, said coupling including compliant means having a compliance such as to produce a pronounced double-peaked frequency-response characteristic with a deep valley between the two peaks and as to cause said valley to occur at 30 C. P. S., one peak falling above 30 C. P. S. and the other peak falling below 30 C. P. S.
4. A phonograph combined tone-arm and triparm arrangement comprising a tone-arm and pickup system having an eective mass and cornpliance to cause mechanical resonance of said tone-arm and pickup system at 30 C. P. S., a trip-arm system having an effective mass to cause mechanical resonance of said trip-arm system at 30 C. P. S., a mechanical coupling between said systems, said coupling including compliant means having a compliance such as to produce a pronounced double-peaked frequency-response characteristic with a deep valley between the two peaks and as to cause said valley to occur at 30 C. P. S., one peak falling above 3G C. P. S. and the other peak falling below 30 C. P. S., and damping means arranged between said tone-arm and trip-arm systems to determine the amplitude of said peaks and valleys.
5. A phonograph combined tone-arm and triparm arrangement comprising a tone-arm system adapted mechanically to resonate at a predetermined frequency, a trip-arm system adapted 7 mechanically to kresonate at said predetermined frequency, `and a mechanical ,coupling between the tone-arm and trip-arm systems, said coupling including compliant means having :a l(z ompliance such as .to produce apronounced doublefpeakeld frequency-response characteristic with .a deep valley between the two peaks and -as to eause said valley to occur substantially at .said predetermined resonant yfrequency of the tone-ann and trip-arm systems, lthe .frequency at which said .two peaks occur being determined by V-the following formulas:
I8 @sie f4 @and I; are .th .uncoupled Tresurlfflnt ire' YQuality er the individual iQue-arm System and ti'ip-amn system, and K is the coefcient of coueline between seid Y.Sistemas- ELM@ N. VOEGTLIN.
CLEQN D. ONEAL. HENRY E. JOHNSTON.
REFERENCES CITED @.10 The vfollowing inferences are pf record in .the
fue -of this patent:
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