Piezoelectric vibrator device

June 23, 1936.

E. C. NICHOLIDES

PIEZOELECTRIC -VIBRATOR DEVICE

Filed May 24, 1933

2,045,404

Sheets-Sheet 1

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June 23, 1936.

2,045,404

E. C. NICHOLIDES

PIEZOELECTRIC VIBRATOR DEVICE

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ATTORNEY

Patented June 23, 1936

2,045,404

UNITED STATES PATENT OFFICE

2,045,404 piezoelectric vibrator device

Emmanuel Christ Nicholides, New York, N. Y-> assignor, by mesne assignments, to Sonotone Corporation, New York, N. Y., a corporation of

New York

Application May 24, 1933, Serial No. 672,561

Claims. (CL 179—107)

This invention relates to piezo-electric vibrator devices and it has among its objects improvement of the energy transmission and increase of the low frequency vibration output of the same.

Special objects of the present invention are piezo-electric sound apparatus, and particularly hearing-aid bone vibrator devices with improved vibratory power transmission and increased low frequency output.

The foregoing and other objects of my invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings, where-

Fig. 1 is a vertical cross sectional view through a bone vibrator unit;

Fig. 2 is a horizontal sectional view along line 2—2 of Fig. 1; ., _ .

Fig. 3 is a vertical sectional view of a modified 20 form of bone vibrator;

Fig. 4 is a vertical sectional view of Fig. 3 along line 4—4; ,___

Fig. 5 is a horizontal sectional view of the bone vibrator of Figs. 3 and 4 along line 5—5 of Fig. 3;

Fig. 6 is a view of the bone vibrator device as carried on the head of a person;

Fig. 7 is a circuit diagram of a bone-conduction hearing-aid device utilizing the bone vibrator;

Fig. 8 is a vertical sectional view of a telephone 30 receiver embodying the invention;

Fig/9 is a horizontal sectional view through the coupling connection between the vibrator and the diaphraghm of the telephone receiver of Fig· » along line 9—9;

Fig. 10 is an elevational view partially m section illustrating a spectacle frame with a bone vibrator unit in accordance with the invention, the front cover of the vibrator chamber being removed’

Figs 11 12 and 13 are elevational views partially in section of loud speakers embodying modifications of the invention; and

Fig. 14 is a detailed view of the vibrator unit of Fig. 13 as seen from the left side of Fig. 13.

In my copending application on piezo-electric devices, Serial No. 672,560, filed concurrently with the present application, I have described improvements in sound producing devices driven by piezo-electric vibrator units, and particularly Rochelle crystal vibrator unite. Vibrator i^te made by uniting crystal plates or strips of highly piezo-electric crystal substances, such as Rochelle salt crystals, have been chiefly used in this field.

One type of vibrator unit, known as twister consists of two flat X-cut plates of Rochelle salt crystal, or similar piezo-electric substance, mechanically united to each other along a common junction face, with electrode sheets attached to the faces for applying thereto electric fields tending to impart to the two adjacent plates oppositely directed deformations, restraining one plate by the other, and producing a ^¹⁴^ bending motion of the unit larger than the motion that would be imparted to said crystal plates in unrestrained condition. __

The other type of vibrator unit known as “bender” consists of two flat crystal 45 -X-cut bars (cut from a Rochelle salt crystal plate perpendicular to the electrical X-axis under an angle of 45° against the optical axis Z) mechanically united to each other along a common junction face, with electrode sheets applied to the faces for impressing upon the crystal bars electric fields tending to impart longitudinal expansion to one bar while imparting longitudinal contraction to the adjacent other bar and thus mutually restraining their longitudinal movements and causing the united bars to bend in a direction perpendicular to the faces with a greater motton «ban could be obtained by the imre- ₂₅strained independent longitudinal motions of the two bars. ,.

Such twisters and benders reverse their deformations on reversal of the electric field to the individual crystal layers. By applying 30 sound-frequency electrical oscillations to tne electrode sheets on the faces of said crystals, alternating electric fields are impressed on the two crystal bars, imparting to the two-layer crystal unit a vibratory bending movement of a ₃₅frequency corresponding to the impressed oscil^Suchi twisters and benders may be constructed either as two-layer units described above, or as four- six- or multiple-layer units in which case, ₄₀the adjacent faces of individual two-layer unite are united to each other to act as a single unit with a multiple of the power of a two-layer wait. As used broadly herein, the terms twister and “bender” apply to two-layer units as well as to larger multiple-layer units.

Heretofore, loud speaker diaphragms, record cutters and similar acoustic instruments have been driven with such vibrator crystal units by clamping one tod portion of such unit to a heavy mass to definitely locate one end of the unit in space, and coupling the load to which the vibrations are to be imparted to a vibrating end portion of the crystal unit having the largest amplitude, and thus utilizing the vibratory motion ol δ,045,404 the unit for imparting vibratory energy to the coupled load.

While it is relatively easy to impart to a vibratory load high frequency vibrations of several thousand cycles by means of a piezo-electric vibrating unit, the amount of low frequency vibratory energy that can be imparted with such vibrating unit greatly decreases with the decrease of the frequency and very little of such, energy can be transmitted at frequencies of several hundred cycles per second important for speech and music reproduction, and in hearing-aid devices. Since Rochelle salt crystals have a much greater piezo-electric effect than other available piezoelectric substances, Rochelle salt vibrator units are able to deliver more vibratory power at low frequencies than vibrator units made of the other crystal materials. But even with Rochelle salt crystal vibrators as heretofore known, the amount of low frequency vibration energy that can be imparted to an acoustic load is relatively small, thus making difficult practical sound producing devices of good quality.

This difficulty is particularly great in case of bone vibrators for bone-conducton hearing-aids which must be made very small in order to permit their inconspicuous wear on the head of the user, thus restricting the size of the crystal to small dimensions making impossible transfer of large vibratory power.

I have found that the difficulties of producing sufficient low frequency vibrations and transferring the same with a small crystal vibrating unit to an acoustic load car be overcome by a special construction and mounting of the crystal vibrating unit and utilization of the reactive forces produced by the vibrator unit during its vibration.

In accordance with the invention, I mount the । crystal unit on a relatively light support of little weight and small inertia and utilize the reactive forces produced in the support by intensive vibration of the crystal vibrator unit for imparting ____________VU1U „ _lo corresponding vibrations to the acoustic load that sound-frequency oscillations is driven by the crystal unit. ^Jlduuns

A simple small-size bone vibrator for a boneconduction hearing-aid device made in accordance with my invention is shown in Fig. 1 of the drawings.. The vibrator unit is in the form of a bender bar 20, made by uniting to each other two 45°-X-cut Rochelle salt crystal bars 21, 22 as explained in my copending application identified above. To the outer faces of the bar 20 are secured electrode sheets 23, 24 and an intermediate electrode sheet 25 is provided at the junction of the two crystal surfaces, these electrode sheets being of thin metal and being intimately united with the faces of the crystal strips to consume only little of the potential drop available for producing an electric field through the crystal bars. Because of the requirement that the vibrator be inconspicuous, very small crystals are used in the vibrator unit, the size of the individual crystals being about 1½ x % x A of an inch.

At its lower end the flat portion of the crystal unit bar 20 is clamped against a clamping member 26 comprising two metallic clamping blocks 27 and 28 secured to a mass of rigid insulating material such as Bakelite. A clamping cavity 29 is formed between the two metallic clamping members 27, 28 into which the lower flat end of the vibrator bar 20 is fitted, a clamping bar 30

But even with Rochelle salt screws 31 holding the vibrator bar in place. To prevent nonuniform pressure at the clamping surfaces,, layers 32 of yieldable material are interposed between the clamping members and the clamped portions of the crystal faces. Electrode sheets 33 on the outer surfaces of the crystal bars and the intermediate electrode sheet 34 are connected to the blocks 27 and 28, respectively, through the contact strips 35 and the contact strip 36, respectively. Electrical oscillations are supplied to the electrode sheets 33, 34 by means of plug pins 37 inserted into perforations 38 extending from the bottom side of the contact blocks 27 and 28, the plug pins being connected to a conductor cord 39 leading to a source of 1 electric sound-frequency oscillations, such as the output of an audio amplifier of a hearing-aid or radio broadcasting receiver.

To the upper free end of the vibrating crystal bar 20 is attached a weight 40, of lead, for instance having an interior cavity providing a portion fitting tightly and attached to the end of the crystal bar and an additional projecting skirtiike portion for accommodating additional weight without clamping additional crystal surface a ree space 4 ί being provided above the upper end surface of the crystal bar.

The clamping member 26 has an upwardly extending projecting wall 45 having a slightly ^{Portion 46 which ma}y be apferrinl Χ,Γ ^{structure of the} head for transsfde ? ^{7 power thereto}· To the front screws Jh! ,^Clampmg Woek 30 is secured, as by 47 connPrXd°r^r₊H^nd °^{f Ά &amp;at gPipping memb}er nwfno pf ¹ h^d t°^^{he end of a head} band 48 by ³¹ing may bl hew ^{its mount}’

F °? ^{the head of a} Ρθ^Γ3θη having Snst thehnL °^rganS’ ^and Pressed bone structure, such as the mastoid . ^vibrator held against the bone struc ture and the electrode sheets of the crystal unit ^a the vibratory energy produced by the vibratnr unit to the bone structure of the head without the necessity of coupling buttons or other special couplmg connections to the vibratory portion of the bar and without in any way restraining the free vibration thereof. The mounting of the crystal unit is thus simplified and more efficient transfer of energy secured.

With the reactive coupling it is easy to provide a coupling connection between the clamping member and the bone structure of the head at which a good impedance match is secured between the vibrator unit and the head structure thus enabling an increase of the amount of low frequency vibrations transmitted to the bone structure without the difficulties of getting direct held pressed to the blocis^ «“bTrne^ . “yftaTS^ ^°°¹¹ °^f

4C

3,045,404 to produce current oscillations from battery 73 in accordance with the sound vibrations impinging on the diaphragm of the transmitting microphone 70. The produced oscillations are amplified in the amplifier 72 and are suPP¹¹®* from the output thereof through a rheostat 74 and a transformer 75 to the two leads 37 which are connected with the electrode sheets 23 and 24 of the vibrator unit 20. Such small crystal vibrator will satisfactorily reproduce sound when operated with an oscillation source applying about 10 volts to the individual crystal plates.

The weight of the crystal parts without the additional weight is about 2½ grams, and the total vibrator units with the casing weighs only about 16 grams. The completely assembled bone vibrator as shown in Figs. 3 to 5 is about 1A about %” wide, and about %” thick, being small and inconspicuous when worn on the head of a person, for instance, against the mastoid bone. Many persons of impaired hearing do not mind carrying the hearing-aid on a lorgnette handle as long as the weight of the hearing-aid is small. The vibrator made according to the invention, as shown in Figs. 3 to 5, is particularly light and suitable for use with a lorgnette handle by inserting a fiat strip mounted on its upper end into the channel 64 provided for carrying it with the head band. ₃₀

In Figs. 8 and 9 my invention is shown ap- ° plied to a telephone receiver. It comprises a diaphragm 81 in the form of a circular thin metal sheet held at its edges between two washers 82 which are clamped between the shoulder 83 of an enclosing casing and the annular projecting portion 84 of the cover 85. The center of diaphragm 8i is connected to a coupling clamp 88 which embraces and clamps firmly the center portion of a crystal unit 89 like bender 20 shown in Figs. 1 to 5, but smaller in size. The crystal unit. 89 is preferably made of Rochelle salt crystal strips and provided with electrode sheets and electrical connections therefrom to a lead 90 in a way similar to the bender shown in Figs. 1 to 5. Instead of clamping the crystal unit at one end, it is clamped in the center so that the two oppositely projecting bar portions extending from the clamp vibrate in synchronism between positions at which they approach the diaphragm 81 and positions at which they move away therefrom. The clamp 88, shown in detail in Fig. 9, comprises a pair of clamping members 91 embracing the flat crystal faces and clamped thereto by screws 92, resilient layers 93 on the clamped portions of the crystals serving to equalize the clamping pressure. One of the clamping members is connected by a coupling rod 94 to the center of the diaphragm 81 and is connected thereto by clamping members 95 so that the two θθ vibrator bars of the crystal unit 89 project on the opposite sides of the clamp 88 and are carried by the center of the diaphragm 8 f, being free to vibrate like two individual bendersj. Weights 96 are attached to the ends of the two vibrating _C5bars like to the bender 20 of Fig. 1.

Upon energization of the crystal umt by connecting its leads 90 to a source of vibratory electric sound-frequency oscillations, a vibratory bending movement will be imparted to the iwo ₇₀projecting bender members extending from the damn 88 the vibrating units swinging in syneXsm back and forward and transferring their vibratory energy to the diaphragm 8 through the reactive coupling connection between 75

The increased, amount of low frequency vibratory energy secured by the additional weight 40 attached to the vibratory portion of the crys- ] tai is thus increased by the reactive coupling the crystal bar to the bone structure and the re- suiting vibrations of the free bar

While the vibrator unit shown in Figs. 1 and 2 is very convenient for observing and studying the reaction-type bender unit, I prefer to enclose it completely in a casing for practical use as a hearing-aid bone vibrator. This is greatly facilitated by the fact that no coupling connections are required between the vibratory portion of the vibrator unit and the bone structure. Such bone vibrator is shown in Figs. 3 to 5 in which the vibrating bender crystal bar 20 is clamped in the interior of a small casing 51 to the_ metafile clamping blocks 27 and 28, imbedded in and rigidly held by the interior of the casing wail 52 which has on its rear side an elevated P°^rt^ . 53 constituting the contact surface engaging the bone structure of the head of the user.

The vibrating portion of the crystal vibrator unit 20 is weighted at the top, and its lower end . is clamped in the same way as in the arrangement shown in Fig. 1, and the connection to its electrode sheets is made by plug pms and cord likewise in the same way. The rear side of the casing has an opening 61 through which the • crystal unit is inserted into the casing and properly clamped therein. The casing opening is closed by a sheet cover 62 which has attached thereto a second sheet member 63 of the same size having formed in its lower portion a chan35 nel 64 for engaging the flat end 65 of a gripping member 66 connected to a head band.67 by ' means of which the unit is supported on the head and held pressed with its contact surface 53 against tire bone structure, such as the mastoid 40 bone, as shown in Fig. 6. The two cover sheets 62 and 63 are suitably secured to the casing, ior instance, by screws 68 and completely enclose the vibrator unit so that the vibrator is protected against contact with the body of the per45 son and against disturbances from the exterior.

By making the junction between the cover and the casing sufficiently tight, entrance of moisture into the interior casing may be positively prevented and its operativeness under all oper50 ating conditions maintained. Sufficient space is provided in the chamber for permitting free vibration of the vibrating unit under the forces induced therein by the applied electric fields.

Through the reactive coupling of the vibrating unit with the head structure, which^is exactly like that explained m connection with Fig. 1 it will transfer a large amount of vibratory energy to the bone structure of the user without requiring any coupling between the vibratory portion of the crystal unit and the head.

low frequency will be produced, and transferred from the vibrator to the head because of the additional load attached to the vibrating crystal bar section and due to the good impedance match between the crystal vibrator and the bone structurc

To actuate the vibrator unit, it may be.suppled with electric sound-frequency oscillations either from the output circuit of an amplifier of a radio or phonograph instrument, or fronva special sound transmitting apparatus as shown special soun^ _{apparatus comprises a} transmit« Γmirronhone 70 connected through a cord input circuit of an amplifying device ** 2,045,404 the clamp 88 with the diaphragm 81 like the coupling connection between the bender clamp and the bone structure in the bone vibrator of Fig. 1.

An efficient and simple telephone receiver is thus obtained which gives a sound output having enough low as well as high frequency sound oscillations to permit good reproduction of speech and music.

In Fig. 10 is shown a piezo-electric crystal unit like that used in the telephone of Fig. 8 for imparting bone vibrations to the head bone structure through the nasal bone. To this end, a spectacle frame 100 is provided with a bridge member iOi forming a chamber 102 in which is mounted a bender crystal unit 103 similar to the bender 89 of Fig. 8, the chamber being normally closed by a cover which fits the chamber opening. The bender is weighted with weights 104 at its ends and is held clamped at the center by a clamp 105 which is attached to the lower bridge wall 106 extending between the frame portions 107 which rest on the nasal bone of the wearer of the spectacle, the clamp 105 being con25 structed like the receiver clamp 88. Bending vibrations are imparted to the two projecting weighted bender portions by supplying to their electrode sheets sound-frequency · oscillations through a cord 108 mounted in the spectacle ”>0 frame. These vibrations are reactively transmitted through the coupling member 105 and the lower bridge wall 106 to the contact portions 107 engaging the nasal bone. The vibratory energy of the pair of benders within the bridge 15 chamber is thus transferred through the reaction forces acting on the coupling member to the bone structure of the spectacle wearer in a way similar to the action of the double bender in the telephone of Fig. 8.

Fig. 11 shows a cone speaker driven by reactive coupling with a double bender in accordance with my invention. The speaker cone f 10 has its front end supported on a bracket ί 11 which is attached to a casing ί ί 2 having a relatively heavy support 113. Attached to the center of the cone ί 10 on the side facing the interior df casing 112 is a clamp member '114 similar to the clamp 88 of the telephone vibrator, but of suitable larger size, clamping the center portion of ) a relatively long bender unit 115 having weights

116 attached to its opposite vibrating ends. Additional flexible support is supplied to the junction of the cone center and to the bender coupled thereto by a flexible sheet 118.

i Electrical sound-frequency oscillations supplied to the electrode sheets of the bender unit 115 through cord 117 impart a synchronous vibration of the two bender halves and the reactive forces exercised thereby on the clamp 114 cause transfer of vibratory energy to the cone 110 imparting thereto a vibratory movement producing a large volume of sound rich in low frequencies.

In Fig. 12 there is shown another modification of the invention in which a somewhat smaller cone 129 has attached to its center portion a clamp 121 holding a double bender vibrator unit 122 like that of the structure of Fig. 11 and a light casing 123 enclosing the vibrator unit and its additional weight members 124, the weight of the vibrator unit being sufficiently small not to place an excessive strain on the cone. By impressing sound-frequency oscillations on the electrode sheets of the bender unit 122 through a suitably connected cord 125, the two weighted bender portions 'of the crystal unit 122 are set into a synchronous vibration and the reactive forces exercised by the vibratory motion reacts through the coupling clamp 121 on the cone, imparting to it vibratory energy rich in low frequencies.

In the modification of the invention shown in Figs. 13 and 14, a cone loud speaker constructed similar to the speaker shown in Fig. 12 is actuated by the reactive forces of a pair of twister units 130, referred to hereinbefore, and made in io the way disclosed in my copending application on Piezo-electric devices, Ser. No. 672,560, filed concurrently herewith. Each twister unit 130 comprises two rectangular crystal plates 131 and 132 cut from a Rochelle salt crystal perpendicu- 15 lar to the electric axis and united to each other, ^{lnterlor and} exterior electrode sheets 133, 134 connected to produce bending of the diametrically opposite corners in opposite directions when in unclamped condition. Two ad- 20 jacent edges 135, 136 of each crystal unit are h ^am,^{ped to a cross_sha}Ped rigid supporting member 138 by means of clamping plates 139, insulating yieldable layers 140 of fibre being inter^P^^d..^a.^fc !^{he clampln}8 surfaces. The center 25 ? Λ ⁴ °! ^suPP°^rting member 138 is attached to the center of a cone 142 to transmit reactive vibratory forces impressed by the vibrating action of the twister units 130 upon the supporting member 138 on the cone 142 and Impart corre- 30 spending vibrations thereto. The unclamped corner of each twister unit has attached thereto a weight 143, and the entire vibrator unit is enclosed in a casing 144. The small weight of the ^mak!^S further support of the vibration 35 imparting structure unnecessary. By impressing through le-ads from a source of electric soundfJl^Q?®^ncy ,°®?^iUations going through cord 145 to the insulated electrode sheets 133 and 134 re spectively, oscillations on the two twister units to 130 vibratory motion is imparted t“to £nd the reactive forces developed by the crystal unit act through the central member 141 on the cone 142 impressing thereon vibrations producing sound rich in low frequencies. producing h^^er^Pri^nCiples underlying the invention may be utilized m many other ways that will suggest thl'taTOM “ ^c°^nsttuct,°” »»me»₅urate with so