US2137188A

US2137188A - Piezoelectric crystal mirror system for sound recording

Info

Publication number: US2137188A
Application number: US175735A
Authority: US
Inventors: Stewart C Whitman
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-11-20
Filing date: 1937-11-20
Publication date: 1938-11-15
Anticipated expiration: 1955-11-15

Description

PIEZOELECTRIC" CRYSTAL MIRROR SYSTEM FOR SOUND RECORDING Filed Nov. 20, 1937 7 Sheets-Sheet l INVENTOR.

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NOV. 15, 1938. 5, w|-||TMAN 2,137,188

PIEZOELECTRIC CRYSTAL MIRROR SYSTEM FOR SOUND RECORDING Filed Nov. 20, 1937 7 Sheets-Sheet 2 cslwawt (9 MW Nov. 15, 1938. s. c. WHITMAN PIEZOELECTRIC CRYSTAL MIRROR SYSTEM FOR SOUND RECORDING 7 Sheets-Sheet 3 Filed NOV. 20, 1957 ////////////////Ill/1111111111M INVENTOR. cs t'e/wa z/l' 6 I? BY IICr-l E ATTORNEYS.

Nov. 15, 1938. s. c. WHITMAN 2,137,188

PIEZOELECTRIC CRYSTAL MIRROR SYSTEM FOR SOUND RECORDING Filed Nov. 20, 1937 7 Sheets-Sheet 4 l- I I.i. E.L

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Nov. 15, 1938. s. c. WHITMAN 2,137,188

PIEZOELECTRIC CRYSTAL MIRROR SYSTEM FOR SOUND RECORDING Filed NOV. 20, 1937 7 Sheets-Sheet 5 INVEN TOR. 6 w,

ZTORNEYS.

Nov. 15, 1938. s. c. WHITMAN PIEZOELECTRIC CRYSTAL MIRROR SYSTEM FOR SOUND RECORDING 7 Sheets-Sheet 6 Filed Nov. 20, 193? TEE E A ORNEYS.

Nov. 15, 1938. s, C w|-||TMAN 2,137,188

PIEZOELECTRIC CRYSTAL MIRROR SYSTEM FOR SOUND RECORDING Filed Nov. 20, 1937 7 Sheets-Sheet '7 3.12335 f. Ila-5 5 Ina-5 7 Patented Nov. 15, 1938 UNITED STATES PATENT QFFECE PIEZOELECTRIC CRYSTAL IWIRROR SYSTEM FOR SOUND RECORDING Stewart Whitman, New York, N. Y.

Application November 20, 1937, Serial No. 175,735

12 Claims. (Cl. 179-1003) My invention relates to the recording of sound p y a single crystal element of the bender type, on film and more especially to a system employand in a further modification I employ a pair of ing a piezoelectric crystal for impressing sound bender type crystal elements with one or with frequencies on light beam two separate mirrors. In the forms wherein a A purpose of my invention is to provide a syspair of crystal elements displace a single mirror, tem which will vary a light beam at sound fre- I provide a thin metallic ribbon which carries the quencies and which has minimum inertia of the mirror and which is attached to the crystal elemoving parts. ments.

Another object of my invention is to provide a My crystal elements may consist of a single slab sound recording system using piezoelectric crysor plate of piezoelectric crystal. Various crystal- 10 tal elements arranged to act as the bender line substances are known in the art to possess type as well as the twister type of crystal elepie oelectric properties, but I prefer to employ ments, Rochelle salt crystals in plates cut from the crys- A further object is tq provide a sound recordtal as it grows in nature in orientation to the crysing system employing a pair of piezoelectric crysallographic axes as is known in the art to pro- 15 tals arranged to cooperate to produce a maximum duce the desired type of mechanical reaction to mirror deflection applied voltage, or vice versa. In the twister Still another object is to provide a system for type of crystal, a trapezoidal shape of crystal gives Varying a light beam at sound frequencies while particularly good performance especially as to avoiding the employment of the electromagnetic range of frequency response. 20 efiect of a current actuating an armature ele- While I may employ a single slab or plate of ment in amagnetic field. crystal for each crystal element, better results Yet another object is to provide a sound remay usually be obtained by superposing in mutucording system employing two separate modually restrained relation two crystal plates so cut {33 lated light beams giving a sound track moduand oriented when mounted that under the action lated on both sides with double the sound value of an applied voltage one crystal plate tends to and making a duplicate sound unit and record elongate in a given direction when the other crysavailable in case one unit fails. tal plate is tending to shorten in that direction, Another object is to provide a piezoelectric which produces an intensified twisting or bendcrystal sound recording system wherein the crysing movement of the crystal assembly, depending 30 tal element is mounted in a casing filled with on the way the crystal plates are cut, and the mineral oil for damping the crystal vibrations. way they are mounted and restrained. What are A sti l ur er o j c s to provide a sound known in the art as 45 X cut plates are suitable recording system wherein the piezoelectric crysfor the purpose, and should be assembled in tal element is mounted behinda Window inclined pairs and mounted as is known in the art to 35 obliquely transverse to the reflected beam path. produce the twisters and benders. The volt- Other purposes will be in part obvious and in age may be applied to such a pair of superposed D pointed Out hereinafter- The usual electromutually restrained crystal plates by electrodes magnetic Oscillogmph heretofore employed in the positioned on the outer free facesiof the assemart possesses relatively large inertia and produces bled crystal unit or in addition to such outer o distortion which is avoided by my arrangementelectrodes there may also be provided an intert I i ig iif f cryszal 9 9 mediate electrode of thin metallic foil positioned romeo amca W m 1 e e amen carrying a between the abutting faces of the crystals.

ror attached to a point of the crystal element A crystal element fixedly mounted at one end where such element vibrates with considerable and when electrically actuated rotatably or l' h 0 ion f an lie lta amp ltude under t e a t o app d v0 ge sionally displacing its free end is known as a of audio frequency. One or more beams from a source of light are incident upon such mirror twister and is usually relatively long and narand the beam or beams are thereby reflected A crystal element which is so cut and through a suitable optical system upon the sound mounted that when electrically actuated it tends track of a sensitive film. to bend in a direction perpendicular to the faces, In one form of my invention I employ a single s Called a d is ua ly restrained crystal element of the twister or torsion type, along a number of s dges or at a number of and in another form I employ a pair of twisters. p While leaving at st e point and adja- In another modification of my invention I emcent edge portions freely movable. A convenient 55 form of bender is square. Other shapes of crystals may be used for either type.

My invention will be better understood by reference to the following specification and accompanying drawings wherein like reference characters designate like parts and wherein Figure 1 shows a schematic view of the general assembly of the elements of my invention employing a twister type of crystal element;

Figure 2 is a front elevation of the casing of the piezoelectric crystal mirror unit;

Figure 3 is a central vertical longitudinal sectional view thereof;

Figure 4 is a transverse vertical section taken on the line 4-4 of Figure 3;

Figure 5 is a horizontal sectional view taken on the line 5-5 of Figure 4;

Figure 6 is a similar view taken on the line 6-6 of Figure 3;

Figure 7 is a horizontal sectional view taken on the line 1-1 of Figure 3;

Figure 8 is a top plan view of a form of my invention employing a pair of bender type crystal elements which cooperate to displace a mirror;

Figure 9 is a front elevation with parts broken away'and in section of the arrangement of Figure 8;

Figure 10 is a horizontal sectional view of the arrangement of Figure 8 showing the details of the ribbon carrying the mirror;

Figure 11 is a horizontal section taken on the line lili of Figure 9;

Figure 12 is a central vertical longitudinal sectional view taken on the line l2-I2 of Figure 8 and showing the pair of "bender crystal elements and the ribbon carrying the mirror;

Figure 13 is a transverse vertical section taken on the line |3|3 of Figure 11, showing a detail of the mounting of the bender type of crystal element;

Figure 14 is a transverse vertical section taken on the line -14 of Figure 10;

Figure 15 is a transverse vertical section taken on the line l5l5 of Figure 10;

Figure 16 is a transverse vertical section taken on the line Iii-l6 of Figure 8;

Figure 17 is an exploded view of the bender crystal element of Figure 14 showing the crystal element and adjacent parts separated and in juxtaposition;

Figures 18 and 19 are schematic views illustrating the principle of the action of a pair of bender crystal elements in displacing the mirror carried on the ribbon;

Figure 20 is a vertical sectional view of a single crystal element unit of the bender type;

Figure 21 is a front elevation of the casing of a modification of my'invention employing a pair of twister" type crystal elements which cooperate to displace a ribbon carrying the mirror;

Figure 22 is a central vertical longitudinal sectional view taken on the line 22-'-22 of Figure 21- showing the twister crystal elements and the ribbon;

Figure 23 is a horizontal sectional view taken on the line 23-23 of Figure 22, showing the trapezoidal twister crystal elements;

Figure 24 is a transverse vertical section taken on the line 24-24 of Figure 23;

Figure 25 is a transverse section taken on the line 25-25 of Figure 23 Figure 26 is a. schematic view of the assembly of a modification of my invention employing two single bender crystal elements each with its own mirror which produce two separate modulated beams of light;

Figure 27 is a schematic detail view of a highfrequency exciter lamp for the arrangement of Figure 26;

Figure 28 is a detail of the exciter lamp with its mirror in the arrangement of Figure 26;

Figure 29 is a detailed view of the structure for swingably mounting the bender" crystal units in the arrangement of Figure 26;

Figure 30 is a diagrammatic representation of the principle of operation of the double-bender type of system of Figures 26-29, showing how the crystal elements tend to shorten and lengthen and thereby to bend under an applied voltage;

Figure 31 is an exploded view of a two-crystal element with intermediate as well as external electrodes, of either bender" or "twister type;

Figure 32 shows diagrammatically the light ray paths of a crystal and optical system including diaphragms, applicable to the systems of either Figure 1 or Figure 33;

Figure 33 shows for a modified form of my invention the arrangement of the crystal and optical elements with a semi-lunar diaphragm in the beam incident on the crystal mirror, and a slit diaphragm in the path of the reflected ray, to produce a triangular beam;

Figure 34 shows in detail a slit diaphragm with the apex of the projected triangular light beam in zero position in register with the slit;

Figure 35 shows the slit diaphragm of Figure 34 with the projected triangular light beam posi- 1 tioned with the slit entirely transverse thereof;

Figure 36 shows the slit diaphragm with a plurality of difierent successive positions of the triangular light beam corresponding to dilferent displacements of the crystal and its mirror; and

Figure 37 shows a background noise-reducing amplifier circuit for the input of the crystal unit, with an automatic crystal bias control.

As above stated, I find that a desirable form of crystal is Rochelle salt suitably cut, because of its relatively large piezoelectric efiect. Other crystals known to possess piezoelectric properties may also be used. Rochelle salt is deliquescent, and should be protected from moisture by some suitable protective coating such as a suitable varnish or collodion.

The Rochelle salt crystals which I employ are of substantially uniform thickness throughout their length, and for the purposes here in view, of the order of one-sixteenth inch thick.

- I provide preferably electrodes on Rochelle salt crystals which are formed of thin laminae of leaves of gold, silver, or other noble metal, to avoid corrosion, because of the sulphate ion present, and I preferably attach these electrodes to the crystals with nitrocellulose, balsam, varnish. rosin, similar gummy compound, or like substance.

The piezoelectric sound recording system which I provide is essentially a voltage operated system, and hence has minimum distortion.

Referring to the figures in detail, in Figure 1, an exciting light source is shown at l, which is advantageously a high-frequency actinic light source excited by a voltage of frequency above 20,000 cycles. The beam of light from source I passes through condensing lens 2 and thence to a diaphragm 3 having a pair of apertures 4 and 5 which provide two separated beams leaving diaphragm 3. 6 is a mirror element upon which the separate light beams delivered from diaphragm 3 impinge. I is a piezoelectric crystal element of the twister type hereinabove mentioned having

electrodes

8 and 9 provided with respective leads II and I2. mounted at its lower end, and at its free end is provided with a projecting arm III which carries mirror 6. Crystal element I may advantageously consist of two or more superposed crystal plates separated by intermediate electrodes, as shown for instance in Figure 3 and in more detail in Figure 31, andan additional lead may be connected to the intermediate electrode. The light beams reflected from mirror 6, as shown at 39 and 39, pass through condensing lens I; and slit diaphragm |4 having slit l5, cylindrical lens l6, condensing lens l1, and are jointly focussed by focussing lens l8 on the sound track 24 of film l9. The film 9 is carried around a film drum 28 past feed rollers 2| and 22. Film l9 has picture frames 23 as well as sound track 24.

The piezoelectric crystal element 1 is shown in Figure l as being of trapezoidal shape, which as has been stated has particular advantages, especially providing a wide frequency response. When voltage is applied to

electrodes

8 and 9, the crystal 1 twists about its longitudinal axis and rotates mirror 6 through a relatively small angle and thereby applies to light beams 39 and 39' as reflected, the voice modulation carried by the voltage applied to

electrodes

8 and 9. The reflected beams after passing through the optical system and being focussed on the sound track, produce on the sound track a photographic record of the applied sound modulation, modulated on both sides. A trapezoid about 1% inches long and inch wide at the base is suitable.

Such use of two separate modulated light beams and modulation on both sides of the photographically recorded wave, has the advantage that there is produced twice as much sound volume, and if a film being reproduced has a scratch on one side of the wave as recorded on the sound track which would mutilate the reproduced sound if the modulation were carried only on one side of the wave, a perfectly reproduced sound can still be obtained by the modulation carriedon the other side of the wave.

The showing of Figure l is schematic. In practice, the crystal element 1 with its electrodes, and the mirror element 6, is mounted in a suitable casing, as shown in Figures 2-7. The casing is shown at 25, and has a bottom portion 26 and a top portion 27 joined by a collar 28. The crystal element 33 is suitably mounted in an insulating plug member which closes the bottom end of casing 25, and crystal element 33 may as stated consist of two or more superposed crystal plates separated by intermediate electrodes. The external electrodes of crystal element 33 are shown at 34 and 35. The free end of crystal element 33 may carry a terminal cap 36 which may be of Bakelite or other suitable insulating material. Mirror element 3| is carried on a projecting arm 32 attached to cap 36. It is also possible to attach arm 32 to crystal 33 by cementing or other suitable manner.

Casing is provided in its upper portion 21 with a recess 39 inwardly sloped to carry a window element 29 in register with mirror element 3|. As shown particularly in Figure 6, window element 29 has one of its faces inclined, forming a substantially wedge shape, avoiding undesired reflections. The incident beam from a diaphragmv 3 in Figure l is reflected from mirror element 3| after passing through window 29, and after reflection again passes through window 29 The crystal element 1 is sultably in the opposite direction. The

electrodes

34 and 35 are provided with leads as 31, and if an intermediate electrode is used with a multi-layer crystal element, an additional lead may be provided connected to the intermediate electrode.

In order to provide means for avoiding undesirablygreat sensitivity of the mirror element and its. actuating means, I preferably provide damping liquid means as shown at 38 within casing 25, which may desirably be a suitable mineral oil.

Figures 8-17 show a double bender type of crystal element arrangement, wherein two fbenders actuate a single mirror element. In Figure 8, the top plan view shows the top of the casing of the crystal elements and mirror, including the top 40 of the casing, the window 4| in register with the mirror element, the

end portions

43 and 44 of the casing connected by the neck part 42 of the casing. Within the outer casing 40, the

crystal units

45 and 46 are suitably mounted. These crystal units have a suitable protecting structure which encloses the crystal elements proper shown at 51 and 64. The crystal unit 45 is carried on casing 40 by a suitable supporting means or lug shown at 41. A liquid damping medium such as mineral oil extends throughout the casing in contact with the crystal element and mirror and is shown at 48. The structure of the crystal unit surrounding the crystal proper may have top and

bottom metal plates

59 and 58. and insulating pieces shown at 6| which engage and support the crystal element proper.

The assembly of the crystal element is shown at 54, and has a terminal cap member 55 which is displaced when the crystal is actuated. A ribbon element or other similar element 49 is connected to the cap members 55 of the two

crystal units

45 and 46, and passes through a chamber in the intermediate neck portion 42 of outer casing 40. Mirror element 59 is centrally carried on ribbon 49 within this central chamber. Insulating collars as of Bakelite are shown at 52 at the ends of intermediate neck portion 42, and are provided with apertures 53 through which ribbon 49 passes.

The bender type of crystal element 51 may as shown be advantageously substantially square but may also have other quadrilateral shape or other shape. For the square form, the crystal may be fixedly supported at three of its corners by suitable engaging caps, and at its free corner provided with the terminal cap 55. Crystal 51 has

electrodes

62 and 63 which are provided with leads 5|. Crystal element 51 may consist of two or more crystal plates with intermediate electrode, as heretofore described. Terminal cap member 55 may be of Bakelite or other suitable material. As has been explained, when voltage is applied to

electrodes

62 and 63, the crystal plates constituting crystal member 51, supported and restrained in the manner described, tend to fold over or bend about an axis and to displace the free corner of the crystal element up and down from the plane of the paper in Figure 11. This bending movement of the crystal and its free corner carrying cap 55, will displace therewith the ribbon 49 attached to the cap. The simultaneous bending action of the two crystal elements 5'! and 64 at successive moments tilts ribbon element 49 and therewith mirror 50 in the manner shown in Figures 18 and 19, so that the reflected beam from a stationary light source is displaced as shown by arrow 65 in Figure 18.

The central portion 42 of casing 49 is provided with sloped recess 58 carrying window M in register with mirror element 58. The ribbon 49 may be so-called "shim ribbon, approximately onesixty-fourth inch thick and one-eighth inch wide. For damping the bender type of crystal there may be used padding instead of oil. Expense is lessened by using the relatively cheap oil. For the twister arrangement, however, the amount of padding which would be necessary for damping would be relatively, much more expensive, and it is not considered practical to use the padding for the twister type of crystal.

The exploded view of Figure 1'7 shows the relative arrangements of the crystal proper and the structural portions of the crystal unit. Figure 31 shows the detail of a crystal element composed of two superposed crystal plates 51 and 5'! having

external electrodes

82 and 63 and

internal electrodes

88 and 68'. the latter being joined to a common lead. The multi-crystal plate structure shown in Figure 31 may be applied in both the twister and the bender type of crystal element. By attaching a separate lead to the intermediate electrodes, it is possible to apply thereto voltages which will apply phaseopposed potentials to the crystals.

Figure 20 shows a complete casing with. a single crystal unit which employs only one crystal element, to actuate one mirror. The general arrangement of the elements corresponds to that of a double-crystal unit employing benders as shown in Figure 12, and the same reference characters are applied. The single crystal unit arrangement of Figure 20 will also bend the crystal element 51 and raise and lower the free end of the crystal, displacing therewith mirror ele-- ment 58 in a manner to give satisfactory sound reproduction, although not giving the same volume and flexibility of control which may be obtained with the double bender crystal arrangement of Figure 12.

In Figures 21-25 there is shown a double-crystal unit arrangement in a single casing, employing two crystal elements of the twister type 1| and I2, with a single mirror element. The outer casing 86 comprises

end portions

61 and 68 joined together by central portion 69. The central portion .69 is provided with a sloped recess and window as above described for the bender type of Figure 12. Cap members 13 are provided at the free ends of crystal elements 'II and 12, to which is attached the ribbon 49 carrying mire ror element 58, the latter being in register with the window I8 of the casing. The twister crystal elements 1| and I2 are in general similar to the twister crystal element 33 of Figures 3 and 4, and may be likewise of trapezoidal shape. These crystal elements when actuated will twist the free end and thereby twist ribbon 49 and mirror 58 to produce a displacement of the reflected beam. Besides other advantages, this provision of a pair of independent crystal units means that if there is failure of one of the electrical input circuits of a crystal unit, there still will be an active crystal unit.

Figures 26-30 show an arrangement of a pair of crystal elements of the bender type for independently modulating two separate light beams, and employs two displaceable mirror elements; one for each beam. The source of exciting light 18 produces direct beam 83 and also reflected beam 82 reflected from mirror 88, which pass through condensing lens 8| and slit 84 to impinge on

displaceable mirror elements

86 and 88. These mirror elements are respectively displaceable by crystal elements and 81 of the bender type, shown as substantially square and fixedly mounted at three corners, the mirror element being attached to the free corner. Thereflected beams 89 and 98 respectively reflected from

mirror elements

88 and 86, pass through condenser lenses 9| and slit lens unit 92 by which they are converged and focussed on sound track 91 of film 93. Film 93 is carried over drum 94

past feed rollers

95 and 98. The arrangement with two separately excited crystal elements makes possible duplicate units throughout, so that if there is any failure of a crystal unit or of a crystal input circuit, there is still a complete functioning system. The duplicate unit arrangement of Figure 26 also has the advantage of providing double the sound volume of a single unit system, and will also modulate both sides of the wave recorded on the sound track, so that if there is a scratch on one side of the recorded wave there will still be satisfactory sound reproduction from the other side of the recorded wave. i

Crystal elements

85 and 81 are preferably so selected that they have substantial response to frequency ranges which are different but overlapping, the separating point being, say, 4000 cycles. There may be two separate sound tracks for the two mirrors, which may be separately reproduced by reproducing equipment particularly responsive to the different frequency ranges.

Figure 29 shows a universal mounting for

crystal elements

85 and 81 each with three fixed corners, and one free corner which displaces

mirror elements

86 and 88. The universal mounting comprises the erect members 16 which carry panel members 11 on which the crystal element and mirror are mounted. Figure 30 shows the displacement of

bender crystal elements

85 and 81 when a voltage is applied thereto, the crystal element buckling or bending, foreshortening or lengthening and displacing the free end.

Figure 2'7 shows a detail of the exciter lamp 19, which may have

external electrodes

98 and 99 to which is applied a high-frequency voltage from high-frequency source I5.

Figures 32-37 show a modified form of my invention wherein a triangular beam of light is projected on a slit diaphragm, the quantity of light flux passing through the slit depending on the position of the reflecting crystal mirror and hence on the sound energy applied to the crystal electrodes.

In Figure 32, I88 is a filament of an exciter lamp, here as shown as a straight-line filament. The exciter lamp is mounted in a suitable housing IN, and delivers a beam through a condensing lens indicated schematically at I82. This lens delivers a cone-shaped beam I83 which passes through another lens barrel I84. At its outlet, lens barrel I84 has a semi-lunar mask or diaphragm shown at I88 in Figure 33, which passes only a segment of the circuit conical beam incident thereupon. The barrel I84 may contain no other elements than mask or diaphragm I88. The segment of light which gets past diaphragm I88 is shown at I89, and is incident on mirror I I8 carried on piezoelectric crystal element III, which, crystal is provided with suitable electrodes and input connections therefor.

Because of the semi-lunar shape of diaphragm I88 and its position in the ray path, only one part of the area of mirror I I8, here shown as the lower half, is illuminated by the incident beam. If mirror H8 is substantially square and positioned with one corner up as shown, the beam I I2 reflected from mirror I II) will be substantially triangular with one edge substantially horizontal,

as shown. Other arrangements may be employed which will produce a reflected beam having sides intersecting at a substantial angle.

A lens barrel containing condensing lenses may be positioned at H3 in the path of the reflected beam, and on its first lens element there will be formed a triangular image of the incident beam as shown at H3 in Figure 33.

The lens barrel H3 delivers a triangular beam as shown at H4. It is often possible to entirely omit lens barrel H3.

A final lens barrel I I8 has at its end on which 1 triangular beam H4 is incident, a slit diaphragm H5 having a slit H6. The triangular image of beam II4 as formed on diaphragm H5 is shown at III. Slit H6 is positioned preferably so as to be approximately parallel to one side of this triangle. Lens barrel H8 also contains other suitable condensing and focussing lenses, and the focussed beam H9 delivered from the final lens of barrel H8 is incident upon sound track I2I of film I20.

Preferably the straight-line filament I is parallel to the straight edge of diaphragm I08.

Piezoelectric crystal I I I is so adjusted mechanically and electrically that when no signal voltage is impressed on its electrodes, the apex of triangle III just touches slit H6 of diaphragm H5, as shown i Figure 34. This may be done, for instance, by applying a suitably adjusted directcurrent biasing voltage to the crystal electrodes. An arrangement for securing an automatic bias control for this purpose is shown in Figure 3'7.

Figure 35 shows the relative position of the triangular image II! of incident beam H4 with reference to the slit I I6, when the reflected beam is displaced by a voltage applied to the crystal electrodes, as by a signal.

Figure 36 shows four successive positions of the triangular image on diaphragm I I with reference to slit H6, corresponding to different values of voltage applied to the crystal electrodes. la is the image position corresponding to zero crystal voltage, I I1!) is the image position corresponding to a small crystal voltage, II'Ic the position corresponding to a stronger applied voltage, and I IId the position corresponding to a still stronger applied crystal voltage.

With the zero position of the crystal and its mirror properly adjusted with reference to slit H6, as the intensity of the applied signal voltage varies with the signal, the image III is displaced rapidly up and down over diaphragm I I 5 and slit H6, and different quantities of light flux are transmitted through slit H6 and are incident upon sound track I 2|.

In Figure 37 is shown a noise reduction amplifier circuit suitable for the crystal input, providing for automatic adjustment of the voltage biasing of the crystal to correct zero position, and providing for background noise reduction, when there is no signal.

The microphone is shown at I23, and its output is delivered to input amplifier I24. An input transformer I25 receives the output of amplifier I24, and delivers signal energy to the grid input of the push-pull amplifier comprising tubes I26 and I21. The output from the plates of this push-pull amplifier is delivered through by-pass condensers I32 and I34 and leads I33 and I35 to the electrodes of piezoelectric crystal element I36.

By connecting the crystal to the plates of tubes I26 and I27, a high impedance is provided for the crystal circuit. While if the plates of these tubes were connected to the crystal through a transformer, the crystal circuit would have relatively low impedance.

A direct-current biasing voltage for adjusting the position of crystal element I36 corresponding to zero applied signal voltage is shown at I53. A potentiometer or voltage divider I5I is connected through switch I 52 across battery I53, and the potentiometer terminals are connected through wires I49 and I50 to connecting points I41 and I48 on the leads of the crystal I36. By adjusting potentiometer I5I, the biasing voltage applied to the crystal, and the position of the crystal and its mirror, can be adjusted as desired.

When there is no input signal voltage applied to the crystal, it is desirable that the position of the reflected beam be returned promptly to zero position. Figure 37 shows a way'of accomplishing this. A portion of the output energy delivered from the plates of the push-pull amplifier is derived and applied to primary I29 of transformer I 28 and delivered from its secondary I30 through coupling circuit I39 to the primary I38 of transformer I3'I. whose secondary I40 is connected to gain potentiometer I4I. Amplifier tube I42 has its input connected to the gain potentiometer MI, and has its output connected to a potentiometer I43. Leads I45 and I46 are connected to potentiometer I43. A suitable rectifier I44 is connected in one of these leads, as in I46. The leads I45 and I46 are respectively connected to connecting points I41 and I48, and hence to the terminals of biasing battery potentiometer I5I. The battery I53 and the rectifier I44 are so poled and connected that they oppose each other. By suitably adjusting gain potentiometer MI, and battery potentiometer I5I, the circuit of Figure 3'7 will maintain the apex of triangle I I! just touching slit H6 with no applied signal voltage as shown in Figure 34, the full voltage of battery potentiometer I5I being applied to the crystal electrodes, but when input signal energy is received from the microphone, a portion of the energy is derived and rectified and applied to oppose the voltage from battery I53, so that the biasing voltage on crystal I36 is reduced and the crystal gives proper response to the applied signal voltage.

The arrangements which I have described possess marked advantages over those heretoforeknown, since there is provided a recording unit having extremely small inertia and immediately and accurately responsive to variations of im pressed voltage. The double forms of crystal unit greatly diminish the possibility of complete failure of the recording system, and hence have great practical importance in recording historically important events, or events which can be repeated only at great expense. The metallic reflection from the mirror element makes possible the use of my invention to provide a polarized light beam as for television.

In operation, the output voltage, amplified if necessary, of the microphone or other sound source, is applied to the leads of the electrodes of the crystal elements. The exciter light, preferably with high-frequency excitation, delivers beams incident upon the mirror elements, which after reflection from the mirror elements and through the optical system, impinge upon the sound track of the film, which is moved over a recording drum in the manner usual in the art. An extremely accurate sound record dependable in every respect, is produced by my arrange ments, and extremely satisfactory results have been obtained in practice. My system has important desirable operating characteristics not possessed by types of similar devices heretofore known in the art, and very sharp and accurately delineated sound records may be obtained by my arrangement.

The high-frequency actinic exciter light source, high in ultraviolet radiation, avoids glare that would smudge peaks.

From the foregoing description of the construction of my improved recording system, the operation thereof and the method of applying the same to use will be readily understood. It will be seen that I have provided a simple, inexpensive and efllcient means for carrying out the objects of the invention and while I have particularly described the elements best adapted to perform the functions set forth, it is obvious that various changes in form, proportion and in the minor details of construction may be resorted to, without departing from the spirit or sacrificing any of the principles of thte invention.

Having thus described the invention, what is claimed is:

1. In a system for recording sound on film, a source of light, a piezoelectric crystal element, electrodes for said crystal element, a mirror element carried by said crystal element in spaced relation thereto, said crystal element being adapted to rotatably displace said mirror element under the application of electrical voltage to said electrodes, optical means interposed between said light source and said mirror element for delivering two substantially parallel beams of light incident on said mirror element, a lightsensitive film having a sound track, optical means for delivering on to said sound track said beams reflected from said mirror element, and a source of electrical energy of sound frequency connected to said electrodes.

2. In a system for recording sound on film, a source of light, a pair of spaced piezoelectric crystal elements mounted approximately coplanarly, electrodes for saidcrystal elements, a mirror element, supporting means carried by each of said crystal elements and extending substantially coplanar therewith and carrying said mirror element, said crystal elements being adapted to rotatably displace said supporting means and said mirror element therewith substantially about an axis in the plane of said crystal elements under the application of electrical voltage to said electrodes, 2. light-sensitive film having a sound track and positioned so that light from said source incident on said mirror element is reflected on said sound track, and a source of electrical energy of sound frequency connected to said electrodes.

3. In a system for recording sound on film, a source of light, a piezoelectric crystal element of substantially quadrilateral shape, means for fixedly supporting said crystal element at all corners thereof except one, electrodes for said crystal element, said crystal element being adapted under the application of voltage to said electrodes to flex about a transverse axis of said crystal element and to laterally displace the free corner thereof, a mirror element carried by said crystal element on said free corner thereof in spaced relation thereto, a light-sensitive film having a sound track and positioned so that light from said source incident on said mirror element is reflected on said sound track, and a source of electrical energy of sound frequency connected to said electrodes.

4. In a system for recording sound on film, a source of light, a pair of spaced piezoelectric crystal elements mounted substantially coplanarly, electrodes for said crystal elements, said crystal elements being adapted under the application of electrical voltage to said electrodes to flex about respective transverse axes of said crystal elements and respectively bend two of their opposite portions closer together, said crystal elements being" so mounted and arranged that they displace in opposite directions under a given applied voltage, a mirror element, supporting means carrying said mirror element and carried by said crystal elements in spaced and substantially coplanar relation thereto and respectively on said bendably displaceable portions thereof, a lightsensitive film having a sound track and positioned so that light from said source incident on said mirror element is reflected on said sound track, and a source of electrical energy of sound frequency connected to said electrodes.

5. In a system for recording sound on film, a source of light, a pair of spaced piezoelectric crystal elements, electrodes for said crystal elements, said crystal elements being adapted under the application of electrical voltage to said elec trodes to flex about respective transverse axes of said crystal elements and respectively bend two of their opposite portions closer together, a pair of mirror elements carriedrespectively on said crystal elements in spaced relation thereto and respectively on said bendably displaceable portions thereof, a light-sensitive film having a sound track, optical means connected between said light source and said mirror elements for delivering two substantially parallel beams of light incident upon said mirror elements, optical means interposed between said mirror elements and said film for delivering on to the sound track on said film the beams of light from said source respectively reflected from said mirror elements, and a source of electrical energy of sound frequencyconnected to said electrodes.

6. In a system for recording sound on film, a source of light, a piezoelectric crystal element, electrodes for said crystal element, a mirror element carried by said crystal element in spaced relation thereto, said crystal adapted to rotatably displace said mirror element under the application of electrical voltage to said electrodes, a light-sensitive film having a' sound track and positioned so that light from said source incident on said mirror element is reflected on said sound track, a source of electrical energy of sound frequency connected to said electrodes, and a casing surrounding and supporting said crystal element and said mirror element, said casing being filled with a liquid damping medium wherein said crystal element moves and being provided with a window in register with said mirror element.

'7. In a system for recording sound on film, a source of light, a piezoelectric crystal element, electrodes for said crystal element, a mirror element carried by said crystal element in spaced relation thereto, said crystal element being adapted to rotatably displace said mirror element under the application of electrical voltage to said electrodes, a light-sensitive film having a sound track and positioned so that light from said source incident on said mirror element is reflected on said sound track, a source of electrical energy of sound frequency connected to element being said electrodes, a casing surrounding and supporting said crystal element and said mirror element and being provided with a window element in register with said mirror element, said window element having its exterior face inclined at an angle to the plane of said mirror element.

8. In a system for recording sound on film, a source of light, a piezoelectric crystal element, electrodes for said crystal element, a mirror element carried by said crystal element in spaced relation thereto, said crystal element being adapted to displace said mirror elmenet under the application of electrical voltage to said electrodes, a straight-edge diaphragm positioned with its straight edge in the path of the beam of light from said source incident on said mirror element, said mirror element being so shaped and positioned with reference to said source and said straight-edge diaphragm that the area of said mirror element illuminated by the diaphragmed beam incident thereon reflects from said mirror element a beam of substantially triangular shape, a light-sensitive film having a sound track and positioned so that the beam of light reflected from said mirror element is incident on said sound track, a diaphragm having a linear slit positioned in the path of said triangular reflected beam of light incident on said sound track with its slit substantially parallel to a side of the triangle of said beam, and a source of electrical energy of sound frequency connected to said electrodes, whereby a light flux of va ying area is transmitted through said slit as the voltage applied to said electrodes varies.

9. In a system for recording sound on film, a source of light, a piezoelectric crystal element, electrodes for said crystal element, a mirror element carried by said crystal element in spaced relation thereto, said crystal element being adapted to displace said mirror element under the application of electrical voltage to said electrodes, a straight-edge diaphragm positioned with its straight edge in the path of the beam of light from said source incident on said mirror element, said mirror element being so shaped and Positioned with reference to said source and said straight edge diaphragm that the area of said mirror element illuminated by the diaphragmed beam incident thereon reflects from said mirror element a beam of substantially triangular shape, a light-sensitive film having positioned so that thebeam of light reflected from said mirror element is incident on said sound track, a diaphragm having a linear slit positioned in the path of said triangular reflected beam of light incident on said sound track with its slit substantially parallel to a side of the triangle of said beam, a source of electrical voltage of sound frequency connected to said electrodes, an adjustable source of direct-current biasing potential connected to said electrodes, and means for deriving and rectifying a portion of said sound-frequency voltage and applying the rectia sound track and fled voltage to said electrodes in opposition to said biasing potential, whereby the position of said mirror element varies with the voltage of said sound-frequency source.

10. In a system for recording sound on film, a source of light, a piezoelectric crystal element, electrodes for said crystal element, a mirror element carried by said crystal element in spaced relation thereto, said crystal element being adapted to displace said mirror element under the application of electrical voltage to said electrodes, a straight-edge diaphragm positioned with its straight edge in the path of the beam of light from said source incident on said mirror element, said mirror element being so shaped and positioned with reference to said source and said straight-edge diaphragm that the area of said mirror element illuminated by the diaphragmed beam incident thereon reflects from said mirror element a beam of substantially triangular shape, a light-sensitive film having a sound track and positioned so that the beam of light reflected from said mirror element is incident on said sound track, a diaphragm having a linear slit positioned in the path of said triangular reflected beam of light incident on said sound track with its slit substantially parallel to a side of the triangle of said beam, a source of electrical voltage of sound frequency, an electron tube amplifier having its input connected to said soundfrequency voltage source and having an output space-current path connected to said electrodes, an adjustable source of direct-current biasing potential connected to said electrodes, and means for deriving and rectifying a portion of said sound-frequency voltage and applying the rectified voltage to said electrodes in opposition to said biasing potential, whereby the position of said mirror element varies with the voltage of said sound-frequency source.

11. In a system for recording sound on film, a source of light, a pair of spaced piezoelectric crystal elements, electrodes for said crystal elements, a mirror element, supporting means carrying said mirror element and carried by said crystal elements in spaced relation thereto, said crystal elements beingadapted to flex torsionally and to displace said mirror element rotatably substantially about an axis in the plane of said crystal elements under the application of electrical voltage to said electrodes, a light-sensitive film having a sound track and positioned so that light from said source incident on said mirror element is reflected on said sound track, and a source of electrical energy of sound frequency connected to said electrodes.

12. The subject matter of claim 11, said crystal elements being of substantially trapezoidal shape, and said supporting means being carried by the minor bases of said trapezoidal crystal elements respectively.

STEWART C. WHITMAN.