GB2030344A - Phonograph Tone Arm - Google Patents

Abstract

A phonograph tone-arm assembly for use with a record turntable includes a coupling member 32 extending from a movable pick-up cartridge support arm 20. The member 32 rigidly couples the arm with a record 18 by way of the record grooves as the record rotates on the turntable. The coupling member imparts movement to the support arm which tracks radially over the record surface along a guide bar 24, and also isolates the cartridge stylus 26 from inertial effects of the arm when the coupling member contacts the record grooves, which is of advantage with warped records. The effective length of the rod 32 is adjustable and the rod is locked by a nut 40. A pad 34 of low- friction material is provided on the lower rod end. <IMAGE>

Description

SPECIFICATION Phonograph Tone Arm The present invention relates generally to phonograph tone arms, and more particularly to tone arm assemblies which provide minimal tracking error and distortion of recorded information.

As the overall performance of phonograph record reproduction equipment continues to attain greater heights in terms of linearity, low distortion levels and frequency response, a need has arisen for turntables and tone arms of special construction capable of minimizing extraneous noise and playback distortion which may become audibly perceptible to a listener using a high quality system.

In particular, with regard to conventional tone arms and phonograph record pick-up cartridges, tone arm mass and cartridge compliance together create low frequency resonance problems wellknown to those familiar with the audio high fidelity art. These resonances arise from unwanted vibratory movement of the tone arm, and cause the cartridge to produce a low frequency signal at its output which can overload sensitive high fidelity equipment connected to the cartridge. Such overload in turn creates distortion in the reproduction of the recorded sound, so that the full capabilities of most modern day equipment are often not realized when used in conjunction with many of the currently available tone arm assemblies.

Undesirable tone arm movement also arises from normal record warpage, wherein the arm is caused to move up and down by way of the cartridge stylus or needle riding within the grooves of a warped record. The stylus is usually mounted at one end of a rigid supporting member, the other end of the supporting member being connected to the cartridge body by means of a compliant or elastic piece to define a compliant stylus suspension within the cartridge.

The cartridge body is itself solidly joined to the tone arm. Therefore, the tone arm is moved upwardly in response to upward movement of the stylus in the record grooves which is communicated to the tone arm by way of the compliant suspension system in the cartridge.

When the stylus moves downwardly, the tone arm falls by gravity along with the stylus and, because of the arm inertia and the cartridge compliance, will tend to "bounce" or vibrate up and down when the stylus ends its downward movement along with the record. It will be readily appreciated that because of the compliant suspension provided between the stylus and the cartridge body, any unwanted tone arm movement such as that described above will result in relative movement between the cartridge body and the stylus since they are not solidly joined to each other, and initial movement of one of them will not produce an immediate responsive movement on the part of the other.Since any relative movement between the stylus and cartridge body provides a corresponding signal at the cartridge output, it then becomes easy to understand that susceptibility of conventional tone arm assemblies to create distortion while tracking grooves in a record which has even a relatively slight amount of warpage or undulations formed on its surface.

A conventional method of controlling this unwanted arm motion is to create a damping member at the rear of the arm to arrest the arm motion. Unfortunately, this damping occurs after the undesirable stress on the cartridge compliance has occurred and the tracking error has been increased beyond acceptable limits.

Another problem arises from the fact that conventional tone arms are moved over a record surface in response to corresponding movement of the cartridge stylus as it tracks the record grooves towards the center of a record.

Accordingly, the stylus must not only move in perfect alignment with the recording pattern cut within the grooves to enable the cartridge to provide an electrical output corresponding to the recorded information, but must also exert a moving force, via the cartridge compliance, to the tone arm. This force presents an added burden to the lateral or horizontal compliance of the stylus relative to the cartridge. This interaction of arm and cartridge is further aggravated due to record eccentricity and produces considerable misalignment between the tone arm and cartridge (i.e., tracking error).Also, conventional tone arms must impart a particular downward vertical force on the stylus in order that it remain within the record grooves to track the recorded patterns therein while it overcomes restraints on lateral movement of the tone arm over the record surface, such as friction in the tone arm bearings and drag resistance of cartridge lead wires running out from the arm. This downward force represents an additional burden on the vertical compliance of the stylus of a much higher degree than that borne by its horizontal compliance. In static form, the vertical compliance is lower while the lateral compliance is higher. The result is an asymetrical compliance, whereas a symetrical compliance is required for best results.

From the above, it will be understood that a cartridge which is mounted in present day tone arms more often than not has its stylus compliance strained in a non-linear fashion. In other words, the vertical compliance of the cartridge structure must convey a minimum tracking force to the stylus, while the lateral compliance undergoes a strain many times less.

Therefore, working through 900 from horizontal to vertical displacement of the stylus, there is a gradually increasing non linearity in compliance.

Since a recorded groove pattern is usually cut in both horizontal and vertical directions, this asymetrical compliance will affect the faithfulness with which the stylus will reproduce the recording.

Conventional pivoted tone arms introduce a further, lateral force on the cartridge compliance which becomes stronger as the tone arm is moved toward the center of the record by the stylus. "Anti-skating" devices have been designed to compensate for this inward pull but, since this pull is variable and not predictable, and the compensating force fixed, it is virtually impossible to entirely cancel these lateral forces. Also, pivoted tone arms introduce a tracking error when they deviate from absolute tangential alignment with the record groove configuration, as is wellknown to those skilled in the art. This latter problem has been met by turntables having a "radial" tone arm configuration such as disclosed in U.S. Patents Nos. 1,868,304 and 2,676,808, for example.Although radial tone arms are geometrically aligned to the record groove, the arm mass is still moved over the record by way of the cartridge compliance. Non-linearity of compliance and stylus deflection are therefore still present. Thus, although the radial arm is geometrically correct in its static form, it still has considerable tracking error in its application dynamically.

A known prior configuration wherein the tone arm and the cartridge are not fixedly joined to each other so as to overcome problems arising from tone arm resonances and added strains on cartridge compliance is disclosed in U.S. Patent No. 3,046,024. However, allowing the cartridge body to be partially free of the tone arm as in the '024 patent requires a relatively complex linkage to be coupled between the cartridge body and the tone arm pivot to maintain the cartridge in proper alignment with the record. This makes such an arrangement impractical and unsuitable for radial tone arm configurations and introduces severe resonances.

It is therefore an object of the present invention to overcome the above and other shortcomings in prior art phonograph tone arm assemblies.

It is another object of the present invention to provide a tone arm assembly in which a movable arm fixedly supporting a cartridge is rigidly coupled to the record by a coupling member, so that undesirable resonances and distortion are eliminated.

It is yet another object of the present invention to provide a tone arm assembly of basically simple and inexpensive construction, and which can be adapted for use with various existing turntables and cartridges.

It is still another object of the present invention to provide a tone arm assembly in which the arm is coupled to the record so as to present an effectively infinite mass to the cartridge compliance under dynamic operating conditions.

It is yet another object of the present invention to provide a tone arm assembly which allows a cartridge fixedly secured thereto to operate with the record and be independent of arm mass effects so as to enable the stylus to provide a faithful reproduction of a record groove pattern.

It is still a further object of the present invention to overcome undesirable inertial properties of cartridge support arms by providing a coupling member between the support arm and the record which allows the cartridge stylus to respond only to the recording patterns in the record grooves, independently of movement of the support arm.

In accordance with a specific embodiment of the present invention, a tone arm assembly comprises a cartridge support arm which is mountable for relative movement with respect to a record turntable. A coupling member extends from the support arm for substantially rigidly coupling the arm with the record so that the coupling member imparts the relative movement to the support arm. The coupling member also operates to remove all strains on the compliance of the cartridge stylus other than those created by recorded patterns already cut into the record grooves.

The present tone arm assembly preferably includes guide means on which the support arm is slidably pivotally mounted for movement over a predetermined path, the support arm movement being imparted by the coupling member.

The above brief description, as well as further objects, features and advantages of the present invention, will be more fully understood by reference to the following detailed description of the presently preferred, but nonetheless illustrative embodiment in accordance with the present invention, when taken in conjunction with the accompanying drawing, wherein:: Fig. 1 is a fragmentary plan view of a tone arm assembly according to the present invention, showing a support arm including a coupling member mounted on guide means in operative relationship with a record on a phonograph turntable; Fig. 2 is a schematic view representing the rigidity of coupling between the support arm and the record as shown in Fig. 1, and in accordance with the present invention; Fig. 3 is a side view of the support arm showing the coupling member mounted thereon in rigid coupling relationship with the record on the turntable, according to the present invention, as viewed substantially from line 3-3 in Fig. 1 and in the direction of the arrows; and Fig. 4 is an enlarged view; partly in section, of the coupling member mounted to the support arm, taken substantially along line 4-4 in Fig. 3 and in the direction of the arrows.

Referring now in detail to the drawing and initially to Fig. 1 thereof, in accordance with an illustrative embodiment demonstrating objects and features of the present invention, there is provided a tone arm assembly generally designated by the reference numeral 10. Tone arm assembly 10 is shown operatively mounted on a phonograph turntable 12 which includes a stationary base 14 and a record platter 16 which is driven by unshown motor means beneath the turntable base 14. Phonograph record 18 is placed atop platter 16 to be played by way of the tone arm assembly 10, as will be described later below.

Tone arm assembly 10 includes a cartridge support arm 20 of relatively light rigid material for fixedly supporting a phonograph cartridge 22 therein in operative relationship with the record 18. Support arm 20 is slidably pivotally mounted on a guide bar 24 which extends over the surface of platter 16 and the record 18 thereon, so that as support arm 20 slides on bar 24 over the record surface, cartridge stylus 26 maintains a substantially tangential relationship with grooves in the record 18 as the support arm 20 moves thereover when lowered to enable stylus 26 to engage the grooves, as shown in Fig. 3. Bar 24 extends from a mounting block 28 which is fixedly secured to the turntable base 14 at a predetermined location (Fig. 1).

By the above construction, it will be appreciated that the present tone arm assembly 10 may be independently fabricated and later mounted on base 14 of the turntable 12 by way of the mounting block 28. Unshown electrical leads connected between the phonograph cartridge 22 and unshown reproducing equipment may then be directed from cartridge 22 through an opening provided in the turntable base 14.

Referring now to Figs. 3 and 4, a coupling member 30 in the form of an elongated rod 32 extends downwardly from the support arm 20 to dynamically rigidly coupled the arm 20 with the rotating record 18. In the preferred embodiment, rod 32 is positioned slightly forward of the cartridge 22 as shown in Fig. 3, and is formed of a relatively stiff, dense material. A pad 34 of material having a low coefficient of friction is secured to the bottom of the rod 32. Pad 34 directly contacts the surface of record 18 to engage the rotating record grooves with a given vertical force slightly forward of the stylus 26.

Accordingly, the coupling member 30 will dynamicalry rigidly couple the support arm 20 with the rotating record 18, and urge the support arm 20 toward the center of the record 1 8 as record 18 turns on platter 16 while stylus 26 is maintained in proper alignment-within the record grooves. Fig. 2 illustrates the degree of rigidity of dynamic coupling provided between support arm 20 and the record 18 in accordance with the present invention.

In further detail, rod 32 has a threaded portion 36 which extends through a correspondingly threaded opening 38 provided in the body of the support arm 20. The distance over which the coupling member 30 extends from the support arm 20 can therefore be varied in response to rotation of the rod 32. A knurled locking nut 40 threadably engaging the upper portion of the rod 32 can be tightened against a collar 42 extending up from support arm 20 to enable the coupling member to be locked at a desired position relative to the support arm 20. A knurled cap 44 is provided atop the-rod 32 to facilitate rotation thereof within the support arm opening 38, when coupling member 30 is adjusted by hand.

Not only does coupling member 30 impart sliding movement to the support arm 20 while record 18 is being played due to its engagement with the record grooves, but all undesirable forces or strains which would otherwise be communicated between the support arm 20 and the stylus 24 are substantially eliminated because of the rigid coupling between the arm 20 and the record 18. For example, the coupling member 30 will directly respond to record warpage or undulations by causing an immediate corresponding movement of the support arm 20, and, hence, the cartridge 22 and stylus 24. The compliance of stylus 24 is therefore left unaffected by such forces or strains, and the stylus is allowed to provide a faithful reproduction of the recorded information which can be made audible by the associated electronic equipment.

Moreover, the rigidity of coupling depicted in Fig.

2 causes the mechanical resonant frequency of the present tone arm assembly 10 to become potentially D.C., so that no vibratory movement of the support arm 20 can be induced by warpage or other undulations on the record surface.

Undesirable inertial effects on the stylus by the support arm are thus avoided or significantly reduced.

Operation of the tone arm assembly 10 in accordance with the present invention will now be explained.

Once the turntable motor is energized and the platter 16 begins to rotate, the support arm 20 is moved to a desired position over the surface of the record 18 and lowered thereon, the coupling member 30 being initially adjusted to extend far enough so that the cartridge stylus 26 does not engage the record grooves. Locking nut 40 is then loosened and rod 32 of the coupling member 30 is rotated by way of its cap 44 until the"cartridge stylus 26 begins to engage the record grooves.

Audible sound will then begin to emanate from the reproducing system. This indicates that stylus 26 is assuming a desirable vertical tracking force within the grooves to be in proper operative relationship with the recorded patterns therein.

Depending upon the thread pitch provided on rod 32, continued rotation thereof will lower the stylus 26 to the proper level within the record grooves. At this point the locking nut 40 is tightened and the cartridge 22 will reproduce the recorded material with lowest distortion, and the compliance of stylus 26 will be free to respond only to the vertical and horizontal recorded patterns cut within the record grooves. It is also noteworthy that the desired vertical tracking force on stylus 24 will be considerably lower than that required for the same cartridge-stylus combination when supported by a conventional tone arm which has the same mass as the support arm 20.

The present invention thus provides a tone arm design wherein the arm is effectively rigidly coupled to the record in both the vertical and horizontal directions under dynamic operating conditions. Undesirable inertial effects on the cartridge stylus by the arm mass are thereby overcome. This rigid coupling presents a substantially infinite tone arm mass to the cartridge compliance to thereby create a potential D.C. resonance. This D.C. resonance, along with the totally linear compliance of the cartridge at all frequencies and amplitudes result in superior record reproduction.

Cartridges of varying compliance can therefore operate optimally in the tone arm assembly 10.

Further, the coupling member 30 creates a dynamic mass which is equal in all planes, regardless of variations in lateral and vertical static mass. By controlling the support arm motion, the coupling member 30 allows the cartridge 22 to maintain a virtually zero degree tracking error. Adjustment of the height of the coupling member allows the stylus tracking force to differ from the force exerted through the coupling member by the support arm. Each operates at its own optimal, albeit different, tracking force. Finally, the stylus responds only to the patterns cut within the record grooves, independently of all support arm motion.

As will be readily apparent to those skilled in the art, the present invention may be realized in other specific forms without departing from its spirit or essential characteristics. The present embodiment is, therefore, to be considered as illustrative and not restrictive, the scope of the invention being indicated by the claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalents of the claims are therefore intended to be embraced therein.

Claims (5)

Claims

1. A phonograph tone arm assembly including a transducer for use in the reproduction of recorded information from record grooves, the prescribed motion of said tone arm assembly being powered by the action of the record grooves, said tone arm assembly comprising a tone arm and a record groove coupling member substantially rigidly coupled to said tone arm and depicted to be substantially rigidily coupled to the record grooves during the playback mode, said record grooves guiding the movement of said tone arm assembly during the playback mode.

2. The tone arm assembly according to claim 1, wherein said transducer is substantially rigidly mounted to said tone arm in all planes, said coupling device is adapted to contact and be guided by the record grooves relative to said record in accordance with the sequence of information recorded in said record grooves to present and maintain said transducer to said record grooves in a predetermined attitude regardless of record eccentricities, the sole function of said transducer being to reproduce the recorded signal without affecting the guidance of the tone arm assembly relative to the record.

3. The tone arm assembly according to claim 1 or 2, wherein said coupling member includes adjustable means.

4. The tone arm assembly according to claim 3, wherein support means is provided for the record which is rotated at a predetermined speed, said adjustable means provides vertical adjustment of said coupling member, and said coupling member includes a locking element to determine the height of said coupling member to make contact with said record.

5. A phonograph tone arm assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.