US2222057A - Stringed musical instrument - Google Patents

Description

Nov. 19, 1940. H. BENIOFF STRINGED MUSICAL INSTRUMENT Filed April 2, 1958 3 Sheets-Sheet 1 [I111 anion Hugo Benioff.

Nov. 19', 1940. H. BENIOFF 2,222,057

STRINGED MUSICAL INSTRUMENT Filed April 2, 1938 3 Sheets-Sheet 3 In 11871 for.

filler-my.

Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE 20 Claims.

This invention relates to electrical musical instruments of the stringed type wherein amplification of sound energy from the strings is accomplished electrically. The general object of the invention is to provide a system, arrangement and construction which provides for controlled transduction of the energy of string vibrations into electrical energy vibrations. It is also an object and a feature of the invention that the means employed are extremely simple and of such nature that no uncontrollable vibrations are introduced to the system.

Generally speaking, the invention is applicable to any type of stringed instrument but, without limitation thereto, is here particularly described as applied to instruments of the violin, piano and similar types. As applied to any such instrument, the invention contemplates a bridge made up of one or more transversely flexible members or elements arranged and designed to respond under close control to the transverse vibrations of the string or strings. These bridge members are preferably, though not necessarily, single (unitary) vibrating string engaging elements with the transducer, or one member of the transducer, directly affixed thereto or operating directly thereon. In eiiect, the bridge element becomes a part of the transducer; and because it is unitary, rather than made up of a plurality of interconnected or articulated parts, it vibrates as a single element and no uncontrollable or troublesome vibrations of multiple parts are introduced.

For the purpose of this case, the bridge element may be defined generally as a string engaging member that defines one end of the length of the vibrating string or equivalent member or forms a nodal point at its point of engagement with the string. The bridge will usually support the string, but that may or may not be so. It is only necessary that the bridge element engage the string to form a node for its transverse vibration. The

bridge may also, for the purpose of this case, be defined generally as an element fixed at one end, capable of vibrational movement with the string at the other, string engaging, end. In one embodiment of the invention the bridge members are shown more specifically as bending members in the form of short, thick reeds or cantilever beams, as shown in the accompanying drawings and explained hereinafter. The reeds are so designed that their free vibration frequency preferably lies above the ordinarily audible range, say in the neighborhood of twenty to thirty thousand cycles per second. Under these conditions the eifective bending of the reed is substantially proportional to the transverse angular displacement of the string at the bridge.

Utilizing such a bridge element which responds accurately to the string vibration Without the introduction of any foreign vibrations, the electro- -5 mechanical transducer may take a variety of forms, of which I prefer here to show the piezoelectric crystal. A simple and effective arrangement is to cement a crystal or crystals directly to a bending surface or surfaces of the reed in such a position that the crystal will be distorted with the bending reed. Bending of the reed then results in straining the crystal in extension and compression and those strains produce, on the crystal surfaces which are parallel to the direction of strain, electrical charges proportional to the bending of the reed.

Illustrative forms of the invention are hereinafter described, as shown in the accompanying drawings, in which, 20

Fig. 1 is a plan showing an instrument of the violin type equipped with my invention;

Fig. 2 is a side elevation;

Fig. 3 is a detail perspective showing a typical and preferred type of bridge arrangement;

Fig. 4 is an enlarged section taken on line 4-4 of Fig. 2, showing the bridge and crystal arrangement in end elevation; and diagrammatically illustrating a circuit;

Fig. 4a represents a modified circuit arrangement;

Fig. 5 is a diagram illustrating one preferred form of circuit;

Fig. 6 is a fragmentary elevation showing a modified bridge structure for an instrument of the violin type;

Figs. 7, 8 and 9 are fragmentary perspectives showing modified forms of bridge structure applicable to a piano or harp type of instrument;

Fig. 10 is a similar view showing the application of the last mentioned type of bridge structure to an instrument of the violin type; and

Fig. 11 is a similar fragmentary view showing another form of reed.

In the drawings a structure is illustrated which is physically somewhat similar to an instrument of the violin type, but without the usual sound box and its appurtenant parts. It will be understood that my invention may be applied to a standard violin. The sound amplifying functions of the box or sound board are unnecessary in my invention; but the box or a frame representing it may be desirable from the standpoint of appearance, or from the standpoint of the performer who is accustomed to the physical form and feel of the standard instrument. Functionally, however, the box is not necessary to the invention. Thus the illustrated structure includes the peg box ID with the usual pegs II, a neck l2 which may carry the usual finger board, and a string anchoring member I3 to which the ends of the strings are attached. The arrangement of these parts is shown as reversed to that of a usual violin though not necessarily so; that is, the peg box It] is at the end of the instrument adjacent the bridge, and the chin piece I5 may be conveniently mounted on the peg box. And the strings are permanently anchored to the member l3 which is at the outer end of the neck.

As a preferred construction, the parts l0 and I2 are made as separate pieces and are secured together at that part of the instrument which I may term generally the bridge mounting 20. That part of the instrument is made up of a flat faced lug or flange 2| which is formed as a part of the peg box ll]; of another fiat faced lug or flange 22 which is formed as a part of neck I2; and of a flat-faced bridge base or block 23 which is clamped between the flat faces of the two parts 2| and 22, the structure being held together by a screw or screws 24. The materials of these several parts may be chosen as desired; they may even be metallic.

The bridge proper is, in this case, composed of four relatively stiff reeds 25, one for each of the strings 26. Bridge block 23 is composed of a suitable material, and thereeds 25 are preferably formed integrally with and project above that bridge block. The material of which the block and the bridge members 25 are formed is selected primarily in view of the requisite characteristics of the several reeds; that is, that each reed shall be stiff enough with regard to transverse bending that its vibration frequency shall preferably be above ordinary audibility. As an illustration, the bridge block and reeds may be made of machine aluminum alloy; and the illustrative figures for the bridge reed dimensions are based on the use of such a material. In a suitable and illustrative design, the reed members may be of somewhat the proportionate dimensions shown in Figs. 1 and 2; and their suitable dimensions (for a violin) calculated on the formula may be typically as follows: Length (height) inch; width T"; inch; thickness 1}; inch.

The above described arrangement is preferred; but a reed design having a lower periodicity has certain advantages. For instance, if the reed be such that its frequency is substantially less than above stated, say well within audibility, the much lessened stiffness of the reed allows it to bend proportionately more with the string movement, resulting in a proportionately higher energy of output from the transduction element connected with the reed. In that case, the result is a pronounced resonating of the string vibration at the reed frequency; but that limited frequency predominance may be eliminated by use of a suitable network at some point in the output system. The application and use of such a network for such purpose is commonly understood and needs no illustration.

The reeds, as viewed in the aspect of Fig. 4, stand in a fan-like formation, the longitudinal axis of each reed being preferably in a direction normal to the circular are which passes through the several strings at the bridge. Each reed preferably has an outer end formation composed of two diagonal faces and a central small flat face 3| in which there is a notch 32 to take the string the string cleanly clearing the diagonal faces 30.

The string fitting the notch snugly, and the vibrant periodicities of the bridge reed being as aforesaid, the lateral displacement of the free or string supporting end of the reed is at all times substantially proportionate to angular lateral displacement of the string at its point of contact with the bridge. Consequently the bridge reed is set into synchronous flexing vibration or mode of vibration by its string, without any uncontrolled vibrations being introduced. It is to be noted that the reed, being relatively stiff and engaging the string, forms a nodal point in the string. This nodal point is common to all of the frequencies occurring in the string and results irrespective of whether the string is supported by the reed as shown in the violin structure above described, or whether the reed merely engages the string as in certain of the structures to be described below wherein the string is entirely supported by other elements.

As before stated, the energy of the flexing vibrations of the reed may be transduced to electrical energy in a variety of electro-mechanical manners, chiefly by electrostatic or electromagnetic means; but the piezo-crystal is now preferred in this form of the invention because of its simplicity and high sensitivity. Thus for instance, and as best shown in Figs. 3 and 4, I may utilize, on one or both of the opposite faces of each reed 25, a thin crystal slab 35, provided on opposite faces with an electrode foil or sheet 36, and the whole cemented or otherwise suitably intimately fixed to the face of reed 25. One face of each crystal is thus grounded on the metal frame of the instrument; the opposite electrode of each crystal may be connected into a circuit wire 4| which, together with a circuit wire 42, goes to an amplifier A. As illustrated here, the several crystals may thus be connected in parallel to a single input circuit; or, as will be readily understood, each crystal, or set of crystals on a reed, or any selected plurality or group of crystals, may be connected to the in-put circuit of a separate amplifier. The manner in which the reeds 25 bend will be readily understood. In Fig. 4 for instance their upper ends flex back and forth from right to left, the reeds bending like a cantilever. 0n bending in one direction, say to the left in Fig. 4, the left hand crystal, cemented as it is to the face of the reed, is consequently compressed in length; while the right hand crystal is elongated. The opposite takes place as the reed bends toward the right. With the crystals properly oriented, the strains accompanying these changes in length set up varying charges on their electrodes.

With the crystals arranged as illustrated in Fig. 4, one on each of the opposite sides of each reed, and circuited as shown, their relative orientations must be such that the elongation of one and compression of the other set up charges of the same sign in the common parallel circuit. That is, their orientations relative to each. other and. the reed may be described as opposite.

However it will be well understood that a single crystal on each reed will produce substantially the same results as a double set, and in my present work with the invention I have satisfactorily used such a single crystal arrangement.

The crystals of the several pairs may be connected in push-pull relation, as shown in Fig. 40;. Here the crystals 35 with their electrodes 36 are shown as if they had insulation 40 between them and reeds 25, as the cement may in some cases be an insulator. A connection 43 may electrically connect the inner electrodes 36 of each pair; and these electrodes grounded through the connection 42 as shown. The outer electrodes of each crystal set are connected, respectively, to the two leads 4!, 41a that go to a push-pull amplifier, indicated at Al. The relative crystal orientation in this case is such that an extension of one crystal of a pair produces a charge on its outer electrode of the same sign as that produced by an extension on the outer electrode of the other crystal.

In Fig. 5 several crystals (or sets) are represented diagrammatically at C2, C3, C4, connected at one side to ground (the equivalent of connection 42 in. Fig. 4). At their other sides the crystals are connected through resistances TI, 2, 3, 4, to the common wire 4| leading to amplifier A. A resistance r5 connects M to ground. Resistances 1'! etc. are so chosen that the capacity reactances of Cl, etc. are small compared to the resistances. For instance, capacity of Cl, etc. may be 0.0005 microfarad. The resistance of Ti, etc. may be 5 10 ohms. Resistance r5 is chosen so that its value is small compared to the resistance of the shunt capacity of the connecting cable M; for instance r5 may be around ohms.

Fig. 6 shows a modification in the reed structure, illustrating the fact that a plurality of strings may be engaged by, and vibrate, a single vibratory bridge member or reed. Here two reeds 25a are shown, each engaging two strings 26. Each reed has an upper end surface of sufficient extent to engage two adjacent strings; and as the reed thicknesses are not conveniently of sufficient dimension for that extent of upper surface, each reed is provided with a head 251), as illustrated.

Fig. 7 and following show other dispositions of the bridge member or reed; Figs. 8 and 9 showing applications particularly suitable to instruments of the piano or harp type and Fig. 10 showing application to the violin type. These figures illustrate various dispositions of the bridge with relation to the string or strings; but in each of them it will be noted the length (the bending axis) of the reed is at an angle (preferably a right angle) to the direction of vibratory movement of the string. In an instrument of the violin type the plane of support, and the length axis of the supporting reed in that plane, may be as heretofore described, approximately at right angles to the plane of string excitation and vibration; although not necessarily so as hereinafter pointed out. In a piano the hammer impact, and the plane of normal vibration, are in the plane of string support; and it becomes necessary to arrange the supporting reed so that its length is at an angle, preferably a right angle, to the plane of impact and vibration.

Fig. 7 shows such an arrangement. Here a string 250 is shown attached at one end to a pin iic which may represent either the anchor pin at one end of the piano string or the tuning peg at the other end. The pin is mounted on frame F, typical of the frame of a piano, harp, or any similar instrument. Of course no sound board is necessary; and because no large amount of string energy is necessary I show but a single string instead of the usual pair or triad.

The string rests in a notch 32a on a ledge 25d formed at the free end of a horizontal reed. 25c. It may be advantageous to have the string engage the reed at about the center of its cross section, and I have so shown it. The other, or base end, of the reed 250 is here shown joined to a supporting bracket 23c having a foot 23d supported on frame F.

In this arrangement the reed, unlike the reed in the violin type, will be under a normal bending stress, due to the fact that its length is at an angle to the plane of string support. If the crystals 35a are attached to the reed before it is stressed, they also will be under a normal stress; but that may be immaterial because it is not the normal or steady crystal charges that are used in my system, but only the charge vibraticns. However, normal stressing and charging of the crystals may be avoided, if desired, by simply cementing the crystals undistorted to the reed after it has been normally stressed.

Fig. 8 shows another arrangement adaptable specifically to a piano. Here the frame is shown at F and a group of three strings 26a is shown contacting and supported by each reed 25a. The plane of string excitation and vibration is vertical (in the figure) and so also is the plane of reed bending. The crystals 356 are therefore mounted on the upper or lower faces of the reed.

Fig. 9 shows a similar arrangement for an instrument of the harp type where the string eX- citation and vibration are more or less in the plane of the frame F (shown horizontal in the figure). Here the string 26 engages the reed 25 as in Fig. 8, but the reeds bend horizontally and the crystals 35 are shown mounted on the opposite vertical faces of the reed.

In both Figs. 8 and 9 the strings engage in notches 32f in raised ribs 5!] at the ends of the reeds. The reeds are shown as being formed integrally with the frames F, that being a convenient means of rigidly anchoring their nonvibratory bases.

In Fig. 10 a reed. formation like that of Fig. 9 is shown applied to an instrument of the violin type. Here the horizontally extending reeds 25g are shown attached integrally to the bridge block 239. Their formation and relation to the strings 26g, and the position of crystals 35; are the same as described for Fig. 9.

Fig. 11 shows another form of reed which is used in the relative positions of the reeds of Figs. 7-10. Here, instead of the string 36h engaging a notch at the upper surface of the reed, the string engages a notch 32h located within the reed, and it may be located at or near the longitudinal axis of the reed. In this form the reed 2571 has a bore Bil extending through it 1ongitudinally at a slight downward angle, and a small insert 8| is placed in the forward end of the bore to carry the notch 32h. The string 387i engages the notch and extends through the bore (53. In this form the string engagement may be at the reed axis, although that is not necessary; and the form has the practical advantage that the string cannot slip down over the side of the reed and engage the crystal if it should by any circumstance become disengaged from the notch.

I claim:

1. A musical instrument comprising a substantially rigid frame and an elongated Vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed.

2. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, said reed having a fundamental frequency above the audible range in said mode of vibration, and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed.

3. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and tranversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, said reed having a fundamental frequency above the audible range in said mode of vibration, and hav ing a much higher frequency in all other modes of vibration, and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed.

4. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, said reed forming the bridge element for said vibrating member, and means operatively associated with said reed for producing an electromotive force proportional to the flexure of the reed.

5. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, said reed being disposed at an angle with respect to said member whereby said end mayvibrate transversely with said member, and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed.

6. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member,

said reed being disposed substantially at right I angles with respect to said member whereby it may vibrate transversely therewith, and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed.

'7. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, said reed being positioned between said member and said frame and substantially perpendicular to the plane of vibration of said member, and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed.

8. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, said reed being disposed substantially parallel with said member and disposed to vibrate transversely of the length of said member, and means operatively associated with said reed for producing an electromotive force proportional to the flexure of the reed.

9. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed, said means including a piezo-electric element disposed on the side of said reed whereby the flexing motion of the reed produces said electromotive force.

10. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed, said means including piezo-electric devices on each side of said reed whereby the flexing motion of the reed produces said electromotive force.

11. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to 5 the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-Vibratorily fixed at one end to said rigid frame with its opposite end free to Vibrate in said plane and transversely with said member, said reed upstanding under the string and supporting the latter, the length of the reed being substantially in the line of the normal thrust of the supported string and being at an angle to the direction of string vibration, and means operatively associated with said reed for producing an electromotive force proportional to the flexure of the reed.

12. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, and means operatively associated with said reed for producing an electromotive force proportional to the flexure of the reed, said means including an electro-mechanical transducing element attached directly to a vibratorily bending surface of the reed.

13. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, said reed supporting said member, the

length of the reed being at an angle to the normal thrust of said supported member and being also at an angle to the transverse direction in which the member vibrates, and means operatively associated with said reed for producing an electromotive force proportional to the flexure of the reed.

14. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free tovibrate in said plane and transversely with said member, the length of the reed being at an angle to the length of the member and being also at substantially a right angle to the transverse direction in which the member vibrates, and means operatively associated with said reed for producing an electromotive force proportional to the flexure of the reed.

15. A musical instrument comprising a sub- 7 stantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming 75 reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, the reed being disposed with its length approximately parallel with the length of said member, 5 and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed.

16. A musical instrument comprising a substantially rigid frame and an elongated vibrating 10 member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed 15 being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in plane and transversely with said mem ber, the length of the reed being approximately parallel to the length of the member, the reed 20 having a longitudinal opening through it, the opening formation including a member engaging portion at the free end of the reed, the member engaging the reed at said portion and passing longitudinally through the opening, and means 25 operatively associated with said reed for producing an electromotive force proportional to the flexure of the reed.

17. A musical instrument comprising a substantially rigid frame and an elongated vibrating 30 member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, the length of the reed being at an angle to the length of the member and being also at an angle to the transverse direction in which the member vibrates, and means operatively associated with said reed for producing an electromotive force proportional to the flexure of the reed, said means including a piezo-crystal at- ,7 tached directly to a bending surface of the reed.

18. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substanti-ally in a single plane and transverse-1y to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in 55 said plane and transversely with said member, said reed being disposed at an angle with respect to said member whereby said end may vibrate transversely with said member, said reed having a fundamental frequency above the audible range m in said mode of vibration, and having a much higher frequency in all other modes of vibration, and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed. ,5

19. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, said reed being positioned between said member and said frame and substantially perpendicular to the plane of vibration of said member, said reed having a fundamental frequency above the audible range in said mode of vibration and having a much higher frequency in all other modes of vibration, and means operatively associated with said reed for producing an electromotive force proportional to the fiexure of the reed.

20. A musical instrument comprising a substantially rigid frame and an elongated vibrating member supported from said frame, said member being adapted to be positively vibrated substantially in a single plane and transversely to the length of the member, an elastic nodal forming reed in contact with said member, said reed being non-vibratorily fixed at one end to said rigid frame with its opposite end free to vibrate in said plane and transversely with said member, said reed having a fundamental frequency above the audible range in said mode of vibration and having a much higher frequency in all other modes of vibration, and means operatively associated with said reed for producing an electromotive force proportional to the flexure of the reed, said means including a piezo-electric element disposed on the side of said reed whereby the flexing motion of the reed produces said electromotive force.

HUGO BENIOFF.

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