US3377439A

US3377439A - Binaural piezoelectric pickup

Info

Publication number: US3377439A
Application number: US726212A
Authority: US
Inventors: Rouy Auguste Louis Mar Antoine
Original assignee: Erie Technological Products Inc
Current assignee: Erie Technological Products Inc
Priority date: 1958-04-03
Filing date: 1958-04-03
Publication date: 1968-04-09
Anticipated expiration: 1985-04-09
Also published as: GB860767A; DE1150215B; FR1222093A

Description

April 9, 1968 A. 1.. M. A. ROUY BINAURAL PIEZOELECTRIC PICKUP Filed April 5, 1958 4 Sheets-Sheet 1 500 /000 5000 0,ooo'

INVENTOR.

AUGUSTE LOUIS MARIE ANTOINE ROUY v FIG. 6

April 9, 1968 A. M. A. ROUY 3,377,439

I BINAURAL PIEZOELECTRIC PICKUP Filed April 5, 1958 v 4 Sheets-Shet z INVENTOR. AUGUSTE LOUIS MARIE ANTOINE ROUY April 1968 r A. 1.. M. A. ROUY 3,377,439

BINAURAL PIEZOELECTRI C PICKUP Filed April 3, 1958 I 4 INVENTOR. AUGUSTE LOUIS MARIE ANTOINE ROUY BY v 4 Sheets-Sheet 3 April 9, 1968 A. L.. M. A. ROUY 3,377,439

' BINAURAL PIEZOELECTRIC PICKUP Filed April 3, 1958 4 SheetsSheet 4 I INVENTOR.

AUGUSTE LOUIS MARIE ANTOINE ROUY BY W I United States Patent 3,377,439 BINAURAL PIEZOELECTRIC PICKUP Auguste Louis Marie Antoine Rouy, Scarsdale, N.Y., assignor to Erie Technological Products, Inc., a corporation of Pennsylvania Filed Apr. 3, 1958, Ser. No. 726,212 17 Claims. (Cl. 179100.41)

This invention is a phonograph pickup havinga smooth response curve throughout the audible range with an absence of mechanical resonance peaks which introduce distortion. It may be made for use with the conventional or monaural records or for compatible use with monaural and single groove binaural records.

In the drawing, FIG. 1 is a longitudinal section through a compatible binaural pickup; FIG. 2 is a section on line 2-2 of FIG. 1; FIG. 3 is a section on line 33 of FIG. 1; FIG. 4 is a section on line 4-4 of FIG. 1; FIG. 5 is a frequency response curve for the pickup; FIG. 6 is a curve of cross talk between channels; FIGS. 7-9 are sections of other elements which may be substituted in the pickup, FIGS. 7 and 8 being elements for compatible monaural-binaural use and FIG. 9 being an element for monaural use only; FIG. 10 is a circuit diagram for the binaural pickup with a push-pullpreamplifier; FIG. 11 is a section through an element which does not need a push-pull preamplifier; FIG. 12 is a circuit diagram for a binaural system using a pickup equipped with the FIG. 11 element; FIG. 13 is a top view of a cartridge having two needles each for a different record speed; FIG. 14 is a side view of the cartridge; FIG. 15 is a section on line 15-15 of FIG. 14; FIG. 16 is a section on line 16-16 of FIG. 14; FIG. 17 is a section on line 17-17 of FIG. 16; FIG. 18 is a longitudinal section through the needle chuck; FIG. 19 is a circuit diagram using transformers to eliminate the push-pull amplifiers; and FIG. 20 is a circuit diagram using resistors to eliminate the push-pull amplifiers.

The compatible monaural--binaural pickup cartridge shown in FIG. 1 of the drawing has a casev 1 which may conveniently be molded of plastic and have an external shape which may be varied to fit the tone arm in which the cartridge is to be mounted. Extending longitudinally through the case is a cylindrical bore 2 having a reduced section 3 at its front end providing an inwardly extending shoulder 4.

The phonograph needle point 5 is suitably secured, for example, by cement 6 to a needle chuck 7 which is pref erably a cylindrical or tubular bar of magnesium. 'The needle point is secured as close as possible to the longitudinal axis of the chuck to minimize torsion or twisting stresses which introduce interchannel cross talk.

Twist of the element by either needle input from either channel causes a torsional stress which appears in both channels. While the outputs due to torsional stress would cancel for an element of perfect symmetry and of absolute linearity such perfection is not attainable in practice with the result that the torsional stress causes an output to appear in both channels and to increase the cross talk. A large part of the torsional stress is dissipated energy which does not produce a useful output and, therefore, reduces the efficiency. The reduction in cross talk is of great importance in binaural pickups.- Magnesium is preferred because of its high modulus of elasticity compared to its specific gravity and because of its high internal damping factor. The high modulus of elasticity of magnesium raises the mechanical resonance frequency. The low specific gravity of the magnesium reduces the damping requirement which varies as the square of the specific gravity. The high internal damping of the magnesium reduces the damping requirements of the supsulting in polarization in plementary damping. The only other metal having properties comparable with magnesium is beryllium which is perhaps slightly superior to magnesium although it is more expensive. The same properies can be obtained from glass reinforced plastics but cannot be obtained from plastics alone because of lack of rigidity.

The needle chuck is symmetrical about its longitudinal axis so that its mechanical properties are isotropic or the same in all directions about the longitudinal axis. In other words, the moment of inertia of a cross section with respect to an axis in any direction perpendicular to the longitudinal axis is constant. This is important in binaural pickups where the response must be the same for both channels to prevent distortion.

As shown more clearly in FIG. 3, the upper end of the chuck 7 has a socket 8 telescoped over the lower end of a piezoelectric element 9. The pickup element may be cemented directly to the inner surface of the socket 8 or there may be an intervening layer 10 of paper or other insulating material such as enamel interposed between the inner surface of the socket 8 and the adjoining surfaces of the pickup element. The pickup element 9 is preferably made in accordance with application Ser. No. 516,638, filed June 20, 1955, now Patent No. 2,944,- 117, in the form of a bar of cross shaped section of one of the polarized piezoelectric ceramics such as barium titanate. In the cross shaped element there are four radially projecting axially extending flanges or ribs 11 spaced degrees from each other and there are four electrodes arranged in two 'diametrally opposed

pairs

12 and 13 with each electrode being between two adjacent flanges 11 and with the pairs of

electrodes

12 and 13 centered on axes 90 degrees apart. The ceramic is polarized by a voltage applied from the electrodes 13 to the electrodes 12 rethe direction of

arrows

14, 15, 16 and 17. With respect to the axis 18 extending through the electrodes 13, it will be noted that the polarization of arrows 14 and 15 is in a direction opposite to that indicated by the

arrows

16 and 17. This means that for bending about the axis 18, a voltage will be produced across the electrodes 12 in proportion to the magni tude of the bending. It will also be noted that with respect to the axis 19 through the electrodes 12, the arrows 14 and 17 on one side of the axis 19 are in a direction opposite the

arrows

15 and 16 on the other side of the axis. Accordingly for bending about the axis 19 there will be produced between the electrodes 13 a voltage proportional to the magnitude of the bending. The cross shape is isotropic about its longitudinal axis so that the mechanical properties are the same in all directions about the longitudinal axis. This means that the deflection characteristics about the axes 1'8 and 19 are equal to each other and do not introduce distortion.

In addition to isotropic deflection characteristics, the needle chuck 7 and the piezoelectric element 9 are designed for equal velocity of elastic deformation waves. This prevents partial reflection at the junction between the needle chuck and the element which could result in interchannel cross talk. This condition for equal Wave velocity is satisfied by the equation:

E E =Youngs modulus of the materials of 7 and-9 S S =specific gravity of the materials of 7 and 9 I I =moments of inertia of the cross section of 7 and 9 with respect to any axis perpendicular to the longie dudinal axis A A =the cross section area of 7 and 9 The pickup element 9 is oriented with respect to the movement of the needle so that movement of the needle by one of the binaural channels causes bending of the element about axis 18 while movement of the needle by the other channel causes bending about axis 19. The bending of the element about the

axes

18 and 19 are independent of each other so that the response from one channel does not carry over to the other channel. Of course, nonuniformity in the element will interfere with the independence of response but the design is such that even with variation in the uniformity of the element 9, the cross talk between channels is inherently low. Preventing cross talk by design of the piezoelectric element for independent response to the channel produces better results than mechanically separating the needle movement into components and feeding each component of needle movement to a separate piezoelectric element. The mechanism for separation of the components of needle movement results in distortion and interchannel cross talk.

The end of the ceramic element 9 opposite the chuck 7 is telescoped into a rubber bushing 20 having essentially the same outside diameter as the bore 2 in the case 1. The rubber bushing 20 has a tapered extension 21 of lesser diameter than the bore 2 which prevents an abrupt concentration of stress in the ceramic element and also reduces reflection of elastic deformation waves. The bushing 20 has a center oepning 20a receiving the element which conforms to the outer configuration of the element and serves to hold opposite pairs of

leads

22, 23, 24, 25 in contact with the associated

electrodes

12 or 13 as the case may be.

Leads

22 and 23 are the output leads for one channel while leads 24 and 25 are the output leads for the other channel. Adequate contact between the leads and the electrodes is maintained by pressure so that soldering of the leads to the electrodes is not necessary. The bushing 20 has the same stiffness in all radial directions, thereby providing a support for the element which is isotropic about its longitudinal axis.

When the frequency of movement of the needle corresponds to a natural frequency of vibration of the element, there is a mechanical resonance which introduces an unwanted peak in the response. At resonance, the response is no longer proportional to the excursion of the needle but is greatly amplified. To reduce the response at resonance, damping is required. In the present pickup there are two resonant frequencies which occur within the audible range. The lowest of these resonant frequencies corresponds ,to a quarter wave length vibration where'the element 9 and chuck 7 vibrate as a beam supported at one end. This occurs between 6,000 and 8,000 cycles per second. The next higher frequency corresponds to half wave length vibration where the element 9 and chuck 7 vibrate as a beam supported at opposite ends. The frequency of the half wave length vibration for the present pickup is between 15,000 and 16,000 cycles per second. The higher modes of resonant vibration are above the audible range.

Two expedients are used for damping the resonant vibrations, (l) by the internal friction of a resilient element such as natural or synthetic rubber and (2) by the viscous friction of a damping fluid. The rubber damping element comprises a cup shaped rubber body having an outwardly projecting rim 26 cemented to the shoulder 4 and to the inner surface of the bore 2. The side walls 27 of the cup shaped member extend around the needle chuck 7 in spaced relation to both the chuck and to the reduced diameter section 3 of the housing. The bottom wall 28 of the rubber'member has an opening 29 through which the needle chuck 7 extends and to which the needle chuck is united by cement. Vibration of the element is transmitted through the bottom wall 28 of the clamping member and is absorbed by deflection of the side walls 27. The bottom wall 28 is located between the needle (which would have the maximum excursion for quarterwave length resonance vibration) and the node for half wave length resonance vibration. This locationprovides adequate damping for both modes of vibration. It will be noted that the side walls are of rib bon-like thinness so that little restraint is offered and the damping takes place primarily by internal friction in the rubber. The damping of the rubber element takes place primarily in 'the side walls 27 and not in the more massive rim 26 or bottom wall 28. Because there is an entire absence of sliding friction, the damping characteristics are very constant. The rubber damping member also acts as a flexible seal for the bore of the housing to prevent leakage of the damping fluid which is inserted through a hole 30 in the housing sealed by cement 31. The damping fluid fills the entire cavity around the element and provides viscous damping. The damping fluid preferably has a viscosity which is essentially constant throughout the normal range of temperatures so that the damping characteristics will be unaffected by temperature. Because the thermal'expansion characteristics of damping fluids are different from plastic, provisions for thermal expansion are necessary which are provided in this case by the flexible side walls 27 of the rubber damping element. It will be noted that the rubber damping element by reason of its circular section throughout is isotropic about the longitudinal axis of the element.

In the assembly of the cartridge, the needle 5 is cemented to the outer end of the needle chuck 7 which is then inserted into the opening 29 in the bottom wall 28 of the rubber damping member and cemented in place. The piezoelectric element 9 'is then inserted in the socket 8 at the upper end of the needle chuck and is cemented in the socket in proper orientation with respect to the needle so that needle movement by one of the two binaural channels will cause deflection about the axis 18 and movement of the needle by the other binaural channels will cause deflection of the element about the axis 19. In this respect it should be noted that the cross shape of the element 9 is ideal for securing precise orientation of the element. The opposite end of the piezoelectric element 9 is then inserted in the opening 20a in the rubber bushing 20', the leads 22-25 being laid in contact with the respective electrodes prior to insertion so that upon assembly into the bushing 20, electrical contact is made to the take-

off electrodes

12 and 13 of the element. The assembly operations so far described can be carried out entirely outside the housing. The assembly is then slid axially into the housing with the needle 5 in proper alignment to follow the binaural excursions in the record groove. The assembly is secured in place by cement between the rim 26 and the shoulder 4 and the inner bore of the housing and is also secured in place by cement 32 sealing the outer end of the bore 2 in the housing. After applying the sealing cement 32, the damping fluid is inserted through the opening 30 which is sealed by cement 31.

The response of the pickup plotted logarithmically against frequency is shown in FIG. 5 from which it will i be noted that there is a smooth response curve throughout the entire range from 30 cycles per second to 20,000 cycles per second (the frequency at the uppermost end of the curve). There is no peak at either the quarter or half wave mechanical resonance frequencies of the pickup. In this plot which was made from a test record having binaural frequencies cut in a single groove, the response of the pickup is measured in decibels above and below the theoretical input from the record groove. The drooping at the low frequency end is due to the impedance of the measuring circuit fed by the element. The effect of the impedance is greater at the lower frequencies and the drooping of the low frequency end is to be expecteduThe smooth curve such as FIG. 5 is very easy to match to amplifier characteristics.

In order to measure the cross talk, measurements were made in one of the channels while the needle was tracking a record groove cut exclusively by response for the other channel. Curve 33 shows the pickup in the left channo] when the needle is excited solely by excursions of the right channel of the needle groove while curve 34 shows the pickup in the right channel caused by tracking of the needle in a groove excited solely by the left channel. In the low frequency spectrum where cross talk between channels is most important, it will be noted that the cross talk is kept to a very low value. Although the pickup is designed to have equal response or to be isotropic in all directions, manufacturing variations can cause interchannel cross talk. In the first place, the record may not be perfectly cut. There also may be variation in the cross section of the needle chuck or of the piezoelectric element, or the element and needle may not be perfectly aligned with each other or with the record groove, or the electrodes may not be perfectly located or may differ in size. Attention to these details can reduce the cross talk, although the cross talk level shown in FIG. 6 is well below that required for commercial use.

Instead of the shape of element shown in FIG. 2, other isotropic shapes are available such as the circular or annular cross section shown in FIG. 7 where the polarized ceramic is in the form of a tube 35 having an inner electrode 36 which is intended to be connected to the ground and having four equally spaced axially extending

electrodes

37, 38, 39 and 40 with the

electrodes

37 and 38 on opposite sides of the axis 41 and with the

electrodes

39 and 40 equally spaced between the

electrodes

37 and 38 and on opposite sides of the axis 42. The ceramic element is polarized from the inner electrode 36 to the electrodes 37-40, inclusive, thereby producing polarization indicated by the arrows 37a, 38a, 39a and 40a. The element of FIG. 7 can be substituted in the cartridge of FIG. 1. When so inserted, it is oriented so that the axis 41 coincides with one of the binaural axes and the axis 42 coincides with the other binaural axis. Bending about the axis 41 causes a voltage to appear across

electrodes

37 and 38 while bending about the axis 42 causes a voltage to appear across the

electrodes

39 and 40. The element of FIG. 7 has the same kind of response as the element 9. It is more diflicult to orient and there is more likelihood of introducing cross talk due to misorientation of the element with respect to the needle.

The element shown in FIG. 8 is of modified cross shape where there are four radially projecting flanges 11a corresponding to the flanges 11 and there are opposed pairs of electrodes lZa and 13a corresponding to the

electrodes

12 and 13. In this form of element, the center section of the element has been enlarged and a grounded electrode coating 43 placed on the inner surface of an axially extending bore 44. The element of FIG. 8 retains the ease of orientation of element 9 shown in FIG. 2. It is somewhat more difiicult to make because of the need for providing the bore 44.

FIG. is a circuit diagram showing the use of the element of FIG. 1, it being understood that a similar circuit diagram could be used for other elements such as the elements of FIGS. 7 and 8. In this diagram, the output of one of the binaural channels appears across the electrodes 12 and the output of the other channel appears across the electrodes 13. Each of the channel outputs is fed to a separate push-pull preamplifier 45 or 45a and from there through an amplifier 46 or 46a to a speaker 47 or 47a. The speakers are spaced so as to reconstitute the binaural sound. Double ended or push-pull output is particularly important in binaural pickups because it prevents electrical feed back between the channels thereby reducing cross talk. Push-pull is not merely a matter of reducing the distortion in each channel. The push-pull preamplifier is one way of obtaining the push-pull output. Inorder to convert an existing monaural system to a binaural system, it will be necessary to purchase an additional speaker 47, an additional amplifier 46 and the two preamplifiers 45, 45a. The two preamplifiers 45, 45a and an amplifier 46 can be included in a separate chassis as indicated by the parts enclosed by dotted lines 48. With these additions to the reproducing system, the substitution of the binaural cartridge will enable the playing of binaural records.

While the push-pull input from the binaural element in the sound system is preferable because it has lower distortion, it is possible to modify the polarization of the pickup element so that the need for push-pull input can be eliminated. Such an element is being claimed in application Ser. No. 730,006, filed Apr. 21, 1958, now Patent No. 2,947,821, and is shown in FIG. 11. This element is of the same structure as the element 9 in FIGS. 1 and 2 and differs only in the polarization. The element of FIG. 11 has a cross shaped ceramic body 49 with four equally spaced radially projecting

flanges

50, 51, 52 and 53 with a longitudinally extending electrode 54 arranged between the

flanges

50 and 51, a longitudinally extending electrode 55 arranged between the

flanges

51 and 52, a longitudinally extending electrode 56 arranged between the

flanges

52 and 53, and a longitudinally extending electrode 57 arranged between the

flangs

50 and 53. The element is polarized by first connecting

electrodes

54 and 56 to one side of the polarizing voltage and

electrodes

55 and 57 to the other side of the polarizing voltage. This produces a polarization indicated by

arrows

58, 59 and 61 and a polarization opposite to that indicated by arrow 60.

Electrodes

54 and 55 are then connected together and to one side of the polarizing voltage and

electrodes

56 and 57 are connected together and to the other side of the polarizing voltage. The polarity of the polarizing voltage is such as to maintain the polarization in the direction of the arrow 58 and to reverse the direction of polarization in the flange 50 and bring it to the direction indicated by the arrow 60. This last polarization step must be carried out below the Curie point or transformation temperature of the ceramic. The first polarization step maybe carried out either by heating to and cooling from the Curie point or at temperatures below the Curie point.

In the use of the element shown in FIG. 11, any two opposite electrodes, e.g. 55 and 57, are connected to each other by ground conductor 62. The pickup element is mounted in the cartridge of FIG. 1 so that response in one of the two binaural channels causes bending about axis 63 and response in the other of the "binaural channels causes bending about axis 64. The output for the first binaural channel appears between ground and the elect-rode 56 and is fed to an amplifier 67 and speaker 68. The output for the other binaural channel appears between ground and the electrode 54 and is fed to amplifier 65 and speaker 66. The

speakers

66 and 68 are so spaced as to reconstitute the binaural sound.

While the pickups so far described are intended for use with binaural records, they are all capable of compatible use with monaural records. When used on a monaural record the same output appears in both chanmonaural record the same output apepars in both channels. FIG. 9 shows a construction which is designed solely for use with monaural records and which can be substituted in the FIG. 1 cartridge. The piezoelectric element is of H section with upper and lower pairs of

flanges

69, 70 and 71, 72 connected by a center section 73. The inner surfaces of the

flanges

69,71 and 70, 72 as well as the connecting surfaces of the center section 73 are coated with

electrodes

74 and 75 while the top and bottom surfaces of the flanges are coated with

electrodes

76 and 77. The ceramic is polarized by a voltage applied from the

electrodes

74 and 75 to the

electrodes

76 and 77 producing the polarization indicated by the arrows 78 and 79. It will be noted that the polarization is in opposite directions at the

electrodes

76 and 77 so that when the element is subjected to a bending stress about a horizontal axis midway between the electrodes, voltages are developed which are proportional to the deflection. When mounted in the cartridge of FIG. 1, the FIG. 9 element is orientd so that the

electrodes

76 and 77 are at right angles to the excursion of the needle 5. When so oriented, one end of the element is cemented in the socket 8 in the needle holder 7 and the other end of the element is inserted in the bushing 20 which both grips the element and holds suitable take-off leads (not shown) in contact with the

electrodes

76 and 77. The other assembly steps are the same as those given for the FIG. 1 cartridge. With the element of FIG. 9, the cartridge is not suited to binaural records because the characteristics of the element are not the same in all directions. The element does, however, have superior characteristics for playing monaural records due to the improved damping provided by the cup shaped walls 27 and the viscous fluid which surrounds the element.

In FIGS. 13 through 18 inclusive is shown a pickup cartridge for compatible monaural-binaural use and having two needles for playing records of different speed ranges. This cartridge accordingly is adapted to all of the records which have heretofore been made as well as to the newer single groove binaural records. The cartridge is of design similar to the previously described construction.

The needle chuck 80 is a magnesium rod of circular cross section having at its outer end diametrically opposed flats 81 and 82, each inclined at an angle of approximately 30 degrees to the longitudinal axis of the needle chuck. In each of the flats is a

needle socket

83, 84 for receiving a

needle

85, 86. The

needles

85, 86 are shown as of the same size but in practice one of the needles will be of larger point radius required for playing standard speed records while the other needle will be of smaller point radius required for playing slow speed or long play records. The

needles

85, 86 project at right angles to the flats 81, 82 and each makes the same angle with the longitudinal axis of the needle chuck 80. At the inner end, the needle chuck has a socket 87 in which is cemented the outer end of a cross shaped piezoelectric element 88 polarized, for example, as shown in FIG. 3. The piezoelectric element is aligned so that the

needles

85 and 86 make an angle of 45 degrees with both of the

axes

18 or 19. The other end of the piezoelectric element '88 is received in a cylindrical rubber bushing 89 which frictionally holds leads 90, 91, '92 and 93 in contact with the electrodes of the element. A cup shaped rubber damping member 94 has its bottom wall 95 telescoped over the needle chuck 80 and cemented thereto and has an outwardly projecting rim 96 and sidewalls 96a extending from the needle chuck along and in spaced relation to the piezoelectric element 88. The parts so far described may be assembled externally of the cartridge.

The cartridge housing consists of two symmetrical molded plastic parts 97 and 98 which are cemented to- .gether and provide a sealed enclosing and supporting housing for the piezoelectric element and needle chuck assembly. As shown in FIG. 14, the housing parts 97 and 98 are beveled at right angles to the

needles

85, 86 to allow the needle points to project outside the cartridge housing. When viewed perpendicular to the needle points, each of the housing parts has an internal clearance groove 99 which is spaced from the needle chuck 80 to allow for the vibratory movement of the needle chuck as the needle follows the record groove. At an intermediate portion of the housing, each of the housing parts 97 and 98 is provided with a semi-cylindrical recess 100 providing the cylindrical chamber surrounding the piezoelectric element 88. In this recess is formed an annular groove 101 for receiving the rim 96 of the cup shaped damping member 94 which is cemented in the groove to provide a liquid tight joint. The rubber bushing 89 iscemented in semicylindrical grooves 102, each of which is provided with a keyway 103 for receiving an integral tongue 104 on the bushing. The keyways 103 angularly locate the piezoelectric element-in proper alignment with the housing. At the rear end, the housing has an annular groove 105 for receiving a terminal board or disc 106 carrying four symmetrically located contact pins 107, 108, 109, 110 (FIG. 17). The pins 107-110 are electrically connected respectively to lead wires 93 prior to cementing the two housing parts 97, 98 together. In assembling the cartridge.

into its housing, the terminal board 106 with the leads 90-93 connected to the pins 107-110 together with the assembly of the piezoelectric element and its needle chuck is dropped into one of the housing parts, for example the housing part 97, and then the other housing part is cemented in place to complete the enclosure. Before cementing the housing, the rubber bushing 89 and the rim 96 of the damping element must be coated with cement in order to obtain a liquid tight joint. After the assembly, the cavity provided by the semi-cylindrical recesses is filled with damping fluid through an opening (not shown), after which the opening is sealed. The assembly thus far described constitutes a complete operative cartridge ready for mounting in the tone arm.

The mounting for the cartridge consists of a unitary supporting structure having brackets 110a for fastening to the outer end of the tone arm. At the back end of the supporting structure is secured a terminal board 111 having four symmetrically spaced contacts 112 secured thereto by rivets 113. Electrical connection to the contacts 112 may be made by permanently soldered connections to the rivets 113. Each of the contacts 112 has a flexible tangentially extending section 114 which makes contact with the associated pin 107-110 as shown in FIG. 17. The pins 107-110 may be rotated with respect to the contacts 114 and will make proper contact therewith each time the pins approach the relative position shown in FIG. 17. At the front of the cartridge support is a ring section 115 guiding the front end of the cartridge assembly and at the back of the cartridge support is a cylindrical section 116 which guides the back end of the cartridge assembly. Between the ring 115 and the cylindrical section 116 is secured a U-shaped clip 117 having arms 1'18 and 119 straddling flats 120 on a reduced section 121 on the cartridge assembly. When the cartridge assembly is inserted in its support, the

arms

119 and 118 must be spread apart sufficiently to allow the cartridge assembly to be inserted into its support. After reaching its intended position, the

arms

118 and 119 snap into place and hold the cartridge assembly in its support. The flats 120 are so arranged that when engaged by the

spring arms

118 and 119, the cartridge assembly is properly oriented so that one or the other of the

needles

85, 86 is in playing position. Rotation of the cartridge between the two playing positions is effected by an integral arm 122 on the cartridge housing 97, 98.

After assembly, the cartridge can be used for playing either standard speed or long play records by turning the cartridge degrees in its support in order to present either the needle 85 or the needle 86. In each of these positions, the cartridge can be used for playing either binaural or monaural records. The contact pins 107-110 are properly connected in each of these positions through engagement with the spring contacts 114.

The operation of the pickup is the same as that of the pickup shown in FIG. 1. The bushing 89 is not provided with the tapered section at its juncture with the piezoelectric element 88 such as shown at 21 in FIG. 1.

FIGS. 19 and 20 are circuits using the FIG. 1 pickup and eliminating the push-pull preamplifiers shown in FIG; 10. In both circuits, one channel output appears across electrodes 12 and is fed to amplifier 46 to speaker 47 and the other channel output appears across electrodes 13 and is fed to amplifier 46a to speaker 47a. This much is the same as FIG.'10.

In FIG. 19, the output is fed through center grounded push-pull transformers 123 and 123a connected across the

electrodes

12 and 13 and the amplifier'is connected between ground and one end of the .transformer output.

In FIG. 20, one of the

output electrodes

12 or 13 is connected directly to the associated amplifier 46 or 46a and the ground terminal of the amplifier is connected to the

other electrode

12 or 13 through a resistance 123 or 123a 9 matching the input resistance of the amplifier. This balances the outputs of

electrodes

12 and 13 and prevents electrical feed back in much the same manner as the pushpull preamplifiers. Eliminating the need for push-pull preamplifiers simplifies the conversion of existing monaural systems. I

What is claimed as new is:

l. A phonograph pickup comprising, a bender type element including means for coupling a needle to one end, a support, means anchoring the other end of the element to the support, a cup-shaped damping member of a flexible elastomer having side walls fixed to the support and surrounding and extending axially along the element and in spaced relation to the element and to the support, and means fixing the bottom wall of the cup shaped member to the element to transmit bending movement of the element to the cup shaped member.

2. A phonograph pickup comprising, a bender type element including means for coupling a needle to one end, a support, means anchoring the other end of the element to the support, a damping member of a flexible elastomer having annular walls fixed to the support and surrounding and extending axially along the element and in spaced relation to the element and to the support, and means coupling the element to said annular walls at a point spaced axially from the connection of the walls to the support to transmit bending movement of the element to said walls.

3. A phonograph pickup comprising, a bender type element including means for coupling a needle to one end,'a support having a bore surrounding the element, means anchoring the other end of the element to the support, a cup-shaped damping member and fluid seal of a flexible elastomer having side walls fixed in the bore of the support and surrounding and extending axially along the element and in spaced relation to the element and to the support, means fixing the bottom wall of the cup shaped member to the element to transmit bending movement of the element to the cup shaped member, and a damping fluid retained in the bore of the support by the cup shaped member.

4. A phonograph pickup comprising, a bender type element including means for coupling a needle to one end, a support having a bore surrounding the element, an annular bushing of a flexible elastomer fitting in the bore, said bushing having an extension extending into and spaced from the bore, and said bushing having a central opening receiving and holding said other end of the element.

5. A phonograph pickup comprising, element having longitudinally extending take-off electrodes including means for coupling a needle to one end, leads at the other end of the element contacting the electrodes, an annular bushing telescoped over the other end of the element, a cup shaped damping member of a flexible elastomer having its bottom wall fixed to the element intermediate its ends and having side walls surrounding and extending axially along and in spaced relation to the element, an outwardly projecting rim n the side walls of said member, a support having a bore into which the element with said member and bushing can be inserted, and a shoulder seating the rim of said member and supporting it with its side walls in spaced relation to the bore.

6. A phonograph pickup comprising, a bender type element including means for coupling a needle to one end, a support having a bore, a bushing of a flexible elastomer fitting into and sealing one end of the bore, said bushing having a center opening receiving and yieldably anchoring the other end of the element to the support, a diaphragm of a flexible elastomer sealing the other end of the bore, said diaphragm being sealed at its center to the element and having flexible walls extending axially along the element in spaced relation to the element and said bore.

a bender type 7. In a phonograph pickup, a bender type element including means for coupling a needle to one end, a support for the other end of the needle comn'sing a bushing of a flexible elastomer telescoped over the other end of the needle, said bushing having a tapered extension extending part way along the element to prevent abrupt transition in the stress in the element, and a damping member comprising a diaphragm of a flexible elastomer fixed at its center to the element and having flexible walls extending axially along and in spaced relation to the element.

8. A binaural phonograph pickup comprising, a bender type element having provisions at one end for coupling to a needle movable in two directions substantially at right angles to each other and to the longitudinal axis of the element, the needle excursion in said two directions corresponding respectively to one and the other of two bin-. aural channels, two pairs of diametrally opposed electrodes on said element with the electrodes respectively transverse to one and the other of said two directions, means anchoring the other end of the element as a cantilever, and a damping member of a flexible elastomer surrounding the element intermediate its ends, said clamping member and said element having equal resistance to deflection in all directions transverse to the longitudinal axis of the element.

9. A binaural phonograph pickup comprising, a bender type element having provisions at one end for coupling to a needle movable in two directions substantially at right angles to each other and to the longitudinal axis of the element, the needle excursion in said two directions corresponding respectively to one and the other of two binaural channels, two pairs of diametrally opposed electrodes on said element with the electrodes respectively transverse to one and the other of said two directions, an annular bushing of a flexible elastomer telescoped over the other end of the element and supporting the element as a cantilever, a damping member having a diaphragm of a flexible elastomer telescoped over the element between its ends, and a support for the bushing and damping member.

10. A phonograph pickup comprising, a bender type piezoelectric element having equal resistance to deflection in all directions transverse to its longitudinal axis, a needle coupler fixed to and projecting axially from one end of the element, said coupler having equal resistance to deflection in all directions transverse to its longitudinal axis, and the coupler and element having matching velocities of mechanical wave propagation.

11. A binaural phonograph pickup comprising, a bender type element having provisions at one end for coupling to a needle movable in two directions at right angles to each other and to the longitudinal axis of the element, the needle excursion in said two directions corresponding respectively to one and the other of two binaural channels, two pairs of diametrally opposed electrodes on said element with the electrodes respectively transverse to one and the other of said two directions, an annular bushing of a flexible elastomer telescoped over the other end of the element, a damping member having a diaphragm of a flexible elastomer telescoped over the element between its ends, a support having a cavity sealed at opposite ends respectively by said bushing and by said diaphragm, and a viscous damping liquid in said cavity.

12. A phonograph pickup comprising, a bender type element including means for coupling a needle to one end, a support having a bore, a bushing of a flexible elastomer fitting into and sealing one end of the bore, said bushing having a center opening receiving and yieldably anchoring the other end of the element to the support, a diaphragm of a flexible elastomer sealing the other end of the bore, said diaphragm being sealed at its center to the element and having flexible walls extending axially along the element in spaced relation to the element and said bore, and a viscous damping fluid surrounding the element in said cavity.

-13. A binaural phonograph pickup comprising a bender type piezoelectricv element having equal response to bending in two directions substantially at right angles to each other, and having provisions for coupling one end to a needle,.the needle excursions in said two directions corresponding respectively to one and the other of two binaural channels, .said element having equal moments of inertia about axes at right angles to its longitudinal axis, separate electrodes for the piezoelectric output from the respective channels, means anchoring the other end of the elementa's a cantilever, and a cushioning element engaging the element between its ends and offering equal restraint to movement of the element in said two directions. I i

14. A-binaural phonograph pickup member comprising a bender type piezoelectric element having response to bending in two directions substantiallyat right angles to each other, and having provisions for. coupling one end to a needle, the needle excursions in said two directionscorresponding respectively to one and the other of two binaural channels, and resilient means for mounting the other end of the element as a cautilever, said means offering substantially equal restraint in said two directions.

15. A phonograph cartridge for stereophonic records comprising a casing having a cavity therein, a signal 1 generating element disposed within the cavity having an elongated piezoelectric body and two pairs of spaced elec trodes disposed on opposite sides of the axis of the element, compliant means attached to one end of the element having approximately equal compliance 'in all directions relative to the axis of the element for mounting the element on the casing, an elo'ngatedmember mounted on the end of the element opposite the means for mounting the element to the casing and disposed on the axis of the element, a short rigid stylus mounted on the end of the member .oppo'sitefthe element, and electrically conducting means mounted to the casing in electrical contact-with an electrode of each pair.

16. A phonograph cartridge for stereophonic records comprising a casing having a cavitytherein, a si'gnal generating element disposed within the cavity having an elongated piezoelectric body and two pairs of spaced electrodes disposed on opposite sides of the axis of the element, compliant means attachedto one end of the element having approximately equal compliance in all directions relative to the axis of the element for mounting theelement on'the casing, an elongated membermounted on the end of the-element opposite the means for mounting the element to the casing and disposed on the axis of the element, said member being rigid in all directions relativeto the axis of the element, a short rigid stylus mounted on the member remote from the element, and electrically conducting means mountedon the casing abutting an electrode of each pair.

17. A binaural phonograph pickup member comprising a bender type piezoelectric element having response to bending-in two directions and substantially at right angles to each other, and having provisions for coupling one end to a needle, the needle excursions in saidtwo directions corresponding respectively to one and the other of two binaural channels, a support having a 'bore surrounding the element, an annular bushing of a flexible elastomer fitting in the bore, and said bushing having a central opening receiving and holding said other end of the element. I

References Cited UNITED STATES PATENTS Germano et al l79100.41

,480,907 9/1949 Dally 179 100.41 I ,594,948 .4/1952 Lynch 179--100.41 1 2,625,663 1 p 1/1953 Howatt 3108.5 1 2,841,722 I 7/1958 Gravley 3108.5 2,594,841 4/1952 Arndt 179100.4 2,858,373 1 10/1958 Hollmann 179100.4 2,492,446 12/1949 Schumann 179100.41 152,518,348 8/1950 Mason 179-100.41 2,594,948 4/1952 Lynch 179-100.41 fi -2,614,143 10/1952 Williams 179100.41 2,944,117 7/1960 Gray 179100.41 2,852,619 9/1958 5 WOOd 179-10041 5/1958 Peterman 179-l00.41 8/1959 Palo 179'100.41

Gray 179-40041 FOREIGN PATEN S v1/1957 Germany.

TERRELL W. FEARS, Primary Examiner.

M- ANDRUS, I.- .L. SRAGOW, R.H.' ROSE, NEW- ON N. LOVEWELL, Examiners,

J. 'R. HOPKINS, KIRK, P. c. FLATTERY, H. s.

; i-' -WILLIAMS, R. F. CARDILLO, Assistant Examiners.

Claims

14. A BINAURAL PHONOGRAPH PICKUP MEMBER COMPRISING A BENDER TYPE PIEZOELECTRIC ELEMENT HAVING RESPONSE TO BENDING IN TWO DIRECTIONS SUBSTANTIALLY AT RIGHT ANGLES TO EACH OTHER, AND HAVING PROVISIONS FOR COUPLING ONE END TO A NEEDLE, THE NEEDLE EXCURSIONS IN SAID TWO DIRECTIONS CORRESPONDING RESPECTIVELY TO ONE AND THE OTHER OF TWO BINAURAL CHANNELS, AND RESILIENT MEANS FOR MOUNTING THE OTHER END OF THE ELEMENT AS A CANTILEVER, SAID MEANS OFFERING SUBSTANTIALLY EQUAL RESTRAINT IN SAID TWO DIRECTIONS.