US2239985A

US2239985A - Electrical musical instrument

Info

Publication number: US2239985A
Application number: US224518A
Authority: US
Inventors: Benioff Hugo
Original assignee: Individual
Current assignee: Individual
Priority date: 1938-08-12
Filing date: 1938-08-12
Publication date: 1941-04-29
Anticipated expiration: 1958-04-29

Description

April 29, 1941. H BENfOFF 2,239,985

ELECTRICAL MUSICAL INSTRUMENT Filed Aug. l2, 1938 3 SheCS-Sheet l Apri 29, 1941. H. BENIOFF 2,239,985

ELECTRICAL MUSICAL INSTRUMENT Filed Aug. 12, 1938 3 Sheets-Sheet 2 4a-7- L40 .53a f f 60 97 J .64 l d es" j] /f f/V j /nvelzlon April 29, 1941. H BENIQFF 2,239,985

ELECTRICAL MUSICAL INSTRUMENT Filed Aug. 12, 1938 3 Sheets-Sheet 5 Patented Apr. 29, 1941 UNITED STATES PATENT OFFICE ELECTRICAL MUSICAL INSTRUMENT Hugo Benioif, La Canada, Calif.

Application August l2, 1938, Serial No. 224,518

19 Claims.

, is for illustrative purposes only and implies no vibrations into electrical energy vibrations. Two

variational methods of electromagnetic transduction of string energy into electrical energy are known: iirst, taking an electrical current from the winding of an electromagnet in the iield of which a paramagnetic string is vibrated, and second, taking the electrical current from an electrically conductive string vibrated in the field of a magnet. The string may of course be eitherv predominantly magnetic, as in the instance of a steel wire, or may be chosen or constructed for electrically conductive properties, e. g. a conductive wire, or a gut string wound with an electrically conductive wire, or may have both magnetic and conductive properties. While the present invention is broadly applicable to either of these methods of .electromagnetic transduction, I prefer to illustrate the invention in a preferred form in which the electrical current is taken from the string rather than from the windings of a ileld magnet, without, however, any implied limitation thereto except vwhere expressly indicated.

Objectsv of the invention are:

To provide an improved system of electromagnetic transduction of string vibrations into electrical vibrations;

To provide an electromagnetic system assuring effective transduction of all overtones within the desired range of the instrument;

To provide an electromagnetic system of trans- A duction wherein the fundamental and overtone frequencies vof a given tone are reproduced at a predetermined ratio;

To provide a practical and effective arrangel ment and construction of a magnet and string supporting means;

To provide a practical and simple stringed musical instrument having electromagnetic transduction and electrical output means; and

' To equip a string musical instrument oi the violin type with simple and practically arranged electromagnetic transduction and string supporting' means.

In accordance with the preferred form of the present invention herein chosen for illustrative purposes, a portion of each vibrating string adjacent one of its points of support, or adjacent a deiined end of the vibrating length of the string,

vibrates in a transverse magnetic field, the length of such portion of the string being no greater than one half, and preferably no greater than one quarter the Wave length (in the string). oi the highest overtone of interest. As a result of the cutting of magnetic lines `of force by the vibrating string an electromotive force is generated i'n the string which is proportional to the product of field strength string vibration velocity, and the length of the string in the iield. This electromotive force actuates an amplifier whose output is reproduced by a suitable speaker. Transduction in this manner from a limited length of string (one half wave length or less of the highest frequency of interest) adjacent one end of its vibrating length avoids the possibility of an occurrence of a node of any overtone frequency of interest within the string length in the magnetic iield, such as would result in partial or total suppression of any such frequency. However, as a result of transduction from a comparatively short length of string adjacent one end oi its vibrating length, the higher overtones are proportionately made predominant due to the string velocities being disproportionately higher in the higher harmonics for that section of the string. A feature of the invention is the use of a corrective network designed to compensate such predominance. Oi course, for special effects, it may be desirable that the overtones be reproduced at high amplitude, in which event the corrective net work would be omitted. Or, by suitable adjustment, the network may be employed to emphasize or suppress either the high or low `range of the instrument.

Figl. 2 is a cross section taken on line 2--2 of Fig' Fig. 3 is a view taken as indicated by line 3-3 o! Fig. 1;

Fig. 4 is a view taken as indicated by line 4--4 of Hg. 3;

Fig. 5 is a view taken on line 5--5 of Fig. 4;

Fig. is a section taken on broken line -5--5 of Fig. 4;

Fig. 6a is an enlarged detail of a portion oi Fis. 6;

Pig. 7 is a diagram showing a method of electrical connection of the strings or the instrument;

Fig. 'la is a diagram showing a variational method oi electrical connection of the strings of the instrument;

Fig. 7b is a diagram showing another variaharmonics;

, Fig. 11 is a view similar to Fig. 6 but showing a modincation;

Fig. 12 is a section on line I2-I2 of Fig,11;

Fig. 13 is a view similar to a portion of Fig. 6, but showing the addition of a magnetic shield, this view being taken on lines I3-I3 of Fig. 14; and

Fig. 14 Is a view similar to Fig. 4, --but showing the addition of the magnetic shield of Fig. 13.

In the drawings a structure is illustrated which resembles in physical outline an instrument of the violin type. comprising a skeletonized box or frame I5, exteriorly shaped like the box of a usual violin, but without the usual sound board, the front and back of the instrument being entirely cut away, for instance as outlined at I6. 'Ihe open frame I5 representing the box of the usual violin is desirable simply from the standpoint of appearance, or from the standpoint of the performer who is accustomed to the physical form and feel oi' the standard instrument; functionally, however, the framework I5 in the exterior shape of a violin box is not necessary, and any suitable means for support of the functional members of the instrument may be substituted if desired.

The illustrated structure includes a usual iinger board I1, positioned with relation to frame I5 in the usual manner, and supported by a neck Il of conventional form. At the outer end of fingerboard I1 and neck I8 is a peg box I9 with the usual pegs 2li.

Frame I5 supports a longitudinally extending rib 22, braced by transversely extending cross pieces 23. The inner end of linger-board I 1 is supported by a bracing member 24 extending upwardly from rib 22 (see Fig. 3).

Mounted on rib 22 and extending rearwardly 1 from member 24 is a base member 25 for the transducer generally indicated at T-. Base mem'- ber 25, which is preferably formed of non-magnetic material, is shown as secured to rib 22 by means of screws 2B. Secured to rib 22 immediately to the rear of base member 25 is an anchor piece 28, the underside of which is recessed, as indicated at 30, and bayonet slots 3| adapted io take the knotted ends 32 of strings 33 are formed in member 28 above said recess.

A quarter-round string engaging element 36 is formed on member 28 just forwardly of slots 3|, the strings anchored in slots 3| passing upward- 1y and forwardly over the curved string-engaging face 35a of this element, and being frictionally engaged by the latter, so as to reduce the pull of the tensed strings against knots 32. From element 35 the strings pass through transducer T, which includes a later-described bridge element for the strings, and then extend along fingerboard I1 to peg box I9.

The outer end of flnger-board I'l, adjacent peg box I9, is provided with a raised bridge portion Ila, and in the present illustrative form of the invention, this bridge portion has embedded therein two electrically conductive inserts 40 provided with string engaging notches 4I, each insert 40 engaging and electrically interconnecting two of the strings, as indicated in Figs. 1 and 2. The linger-board is of course formed of suitable insulation material.

The strings themselves, in the illustrative form of the invention, in which the electrical energy is taken from the strings, are of course electrically conductive.

Transducer T comprises, in its present illustrative form, a. permanent magnet block 50, a front lower pole piece 5I mounted against the forward side of block 5I) and extending upwardly therefrom to present an upwardly facing pole tip 55, anda rear and upper pole piece made up of a member 52 mounted against the rearward surface of block together with a forwardly extending member 53 mounted on the upper end of member 52 and provided with a downwardly facing pole tip 5I positioned immediately over the aforementioned pole tip 55. Pole piece members 5I and 52 are secured to magnet block 50 as by screws 56, pole piece member 53 being understood to be secured to member 52 as by means of suitable screws, not shown. The assembly is secured to base member 25 by means of screws 55 passing through base member 25 and engaging members 5I and 52.

Pole tip 55 serves as or supports a bridge for strings 33, being curved in substantial conformy ity to the shape of the usual violin bridge (see Fig. 4). Pole tip 55 is thus defined at the top by a surface curved in a direction transversely oi' the strings, and sloped downwardly in a forward direction, in parallelism with the strings, together with a similarly curved rearwardly beveled surface 6I. Mounted in recesses 53 in beveled surfaces 6I are vinsulation bridge-inserts 64, typically made of ivory, which project upwardly just above surface 50 and are provided at their upper edges with string engaging notches 56. One of said bridge inserts is provided for each of strings. 33, as illustrated in Fig. 5, and between said inserts, pole tip 55 is preferably formed with dividing notches $8, which serve a Purpose aD- pearlng later. The backs oi.' bridge inserts 5I are provided with electricallyconductive contact elements 10 which are engaged by the strings Just back of notches 68. Electrical connections are made to these contact elements, in a manner later to be described. It will of course be understood that any other suitable expedient may be employed for contacting the strings back oi' the bridge; that here shown however is simple and preferred at present. Strings 33 pass forwardly from quarter rounded element 36 through insulation tubes 12, typically formed of ivory, which extend through suitable bores in pole piece member 52. The strings next engage conductive elements Ill, and then bridge-notches 6B, which support them a short distance above pole tip sur face 60 (suiiicient clearance being provided to assure that the strings will not touch surface 60 when set into vibration), thence going forwardly and passing over conductive bridge elements 40 to the peg box, as previously described.

Upper pole tip I has a lower defining surface 15 which is curved, transversely of the strings, in conformity to lower pole tip surface 60, being spaced a shortvdistance above strings 3.3, with `iust suiiicient clearance to avoid interference with the vibrating strings. Upper and lower pole piece surfaces are symmetrical and parallel to one another and to the strings, so that the field between said surfaces will be perpendicular to the strings. Surface 15 is formed, between strings 33, with notches 16 similar to and positioned over the previously described notches 68 in the lower pole tip.

Magnet block 50 is so polarized that

pole tips

54 and 55 are of opposite magnetic polarity, and produce concentra-ted magnetic fields in the narrow air gaps g between surfaces 80 and 15. The notches in the pole tip faces serve to concen-trate the magnetic field in gaps g.

The pole tip surfaces 60 and 15, shaped as described (see Fig. 6a) provide a substantially uniform field concentration from the point of support, or point of vibrating end, of the strings defined -by bridge elements 54, to a point located somewhat forwardly of the co-planar front faces 5|a and 53a of the pole pieces. The length of this substantially uniform field, measured forwardly from the point of support of the strings by bridge elements 64, is designated as f in Fig. 6a. There is of course no precise end point at which the field terminates; the concentration of t e field falls off fairly abruptly, however, and dimension f is the distance from the ends of the vibrating lengths of the strings defined by bridge elements 64, to the effective boundary of the uniform field. This dimension should be no greater than the quotient of the vibrating length of the string (measured forwardly from bridge element 64) and one-half, or preferably one quarter, the wave length on the string of the highest overtone which it is desired to effectively reproduce. This consideration will be dealt with more fully at a later point in the specifica-tion.

The two electrically conductive bridge inserts I 40 `at the outer end of the finger-board electrically connect each outside string to Ithe inside 'string next to it, and the two inside strings arev electrically interconnected by an electrical connection 80 between the two conductive elements engaged by said strings just back of the rearward points of support of the strings .by bridge elements 64. External electrical connections 8| and 82 are made to conductive elements 10 engaged by the outer strings. The four strings are thus here shown as electrically connected in series, as indicated in the diagram of Fig. '7; a parallel connection is possible, but introduces cornplications, and the series connection is accordingly preferred.

Fig. 'la indicates diagrammatically a variatonal manner of connection of the strings. In this instance, the bridge or transducer ends of one outside string and the adjacent inside string are provided with external connections 8| and 82, and the same ends of 'the `two remaining strings are connected lby a conductor 80a. At the other ends of the strings, conductors |00 and |0| interconnect alternate strings, as indicated. It will be evident that the four strings form two loops Wound in opposite directions, so that electromotive forces generated in the two loops by -pick up of stray fields will buck and substantially cancel. Fig. 'lb shows a further modification, which avoids overlapping of the two loops, as its done in the form of Fig. '1a. In Fig. 7b, the outer end of the two outside strings are connected to the'adjacent inside strings -by conductors lila and Illa, external connection 8| is made to vthe bridge end of one outside string, the adjacent inside string is connected to the other outside string by conductor h, and the other external connection 82 is made to the remaining inside string. It will be evident that the two loops are again in opposition, so that electromotive forces generated by pick up of stray fields will be in opposition.

It will be understood `that external connections 0| and 82 may lead to any suitable amplifying system and loud speaker or other translating apparatus. Typical and :preferred forms of the output system will be described later.

Strings 33 are set into vibration by bowing, plucking, etc. in the usual manner. It may here be noted that while in a violin or cello type in-` strument the transducer is located at the bridge end of the string, i. e., near the point of string excitation, this is necessary only in an instrument of this type, where the strings are fingered, and the vibrating length of string is between the depressed finger and the bridge. vIn a harp or piano, on the other hand, the transducer may, if desired, be located at .the ends of the strings remote from the point of excitation, and in fact such location is of some advantage.

The' vibrating strings cut the magnetic lines of force between pole '

tips

54 and 55, and have electromotive forces set up in them proportional to the velocity components of the strings which are at right angles to the eld. The strings need not of course vibrate exactly at righ-t angles to the field, since an electromotive `force will be generated if the strings cut any of the lines of force i. e., vibrate in any plane except the plane parallel to the field. y

It has ypreviously been stated `that the length of the magnetic field in which the string operates (dimension f) should be no greater than one half the wave length along the string of the highest overtone which it is desired to reproduce. It being understood that the fundamental is Ithe first partial, the first overtone is the second partial. and so on, to assure transduction of thehigher partials, dimension f should therefore not exceed L/n, where L is the vibrating length of the string, and n is the number of the highest partial of interest.

As typical of the invention, it may be desired to reproduce up to the 60th` partial or thereabouts, in which case dimension .f is made no greater than L/GO, which is one-half the wave length in the string of the 60th partial. No node of any partial up to the 60th will .then occur between the lbridge element and the outer effective boundary of the magnetic field. There is of course a node of each partial at the bridge element, and a node of the`60th partial at the outer boundary of the field, but no node of any :partial up to the 60th loccurs between these limits. There is therefore avoided partial or total suppression or "cancellation of any overtone frequency withinthat range such as results from relative movement in opposite directions in the field of portions of the string on opposite sides of such a node.

For greater precision in the system as a whole, the field may be restricted to a dimension no greater than L/Zn, though experiment indicates length of a. violin, a length of no greater than L/n in `the magnetic field is a sufficient restriction for good results. For an instrument having greater string length, as in a cello, it is advisable to restrict the effective magnetic field to L/Zn. The transducer as Ithus described results Iin the delivery of an electrical current which is accurately related to the absolute velocity of the vibrating string of the instrument for a restricted length adjacent its defining point at one end. Because the effective magnetic field of the transducer is restricted to a given length adjacent end points of the vibrating lengths of the strings, the energy of .the fundamental of each string as well as that of all overtones designed .to be present is fully and faithfully transduced.

As previously mentioned, however, the higher harmonics tend to be proportionately made predominant, as compared to a conventional tone, in transduction inthe manner described. Accordingly, a corrective net-work may be employed where it is desired to compensate such predominance as far as desired. It will be evident that the corrective network may be employed at any point in the system, either between the transducer and the amplifier, within the amplifier, between the amplifier and speaker, or in the speaker; and that its corrective influence may be more or less, as desired.

Fig. 8 shows one illustrative circuit embodying a suitable corrective network. In the diagram of Fig. 8, the generator indicated at S is representative of the generator constituted by the series connected strings vibrating in the magnetic field. Resistance ro represents the resistance of the strings themselves. The strings are indicated as being connected by

leads

94 and 95 to the input side of a suitable amplifier 96, the latter having an output circuit 91 leading to a loudspeaker 9B. A variable resistor r1 and variable capacitor C, connected in series -with each other, are connected in shunt across

circuit

94, 95. Proper adjustment of the resistance and capacitance of n and C enables the required or desired correction or compensation to be made.

Fig. 9 shows a variational circuit, which is in general like that of Fig. 8, except that a corrective network is employed between the amplifier and speaker instead of ahead of the amplifier.

As typically indicated in Fig. 9, one of amplifier output leads 91 has connected in series therein a network comprising parallel connected variable inductor La, -variable capacitor C: and variable resistor rz. amplitude of different regions of the frequency spectrum may be emphasized or suppressed as desired.

Fig. 10 shows a further modified electrical circuit, in which a compensating network is employed within the amplifier. In this instance, circuit 34-95 connected to the instrument is coupled by means of transformer to the grid circuit I of the first vacuum tube ||2 of a suitable amplifier H3. Amplifier H3 is shown to have, in addition to vacuum tube H2, a vacuum tube H resistance-coupled to tube H2. As shown, the plate of tube ||2 is connected via coupling resistor |23 to positive B voltage, and an intermediate tap on resistor |23 is connected by conductor |2| to the grid of tube H5, a grid condenser |22 being included in conductor |2I. 'I'he fundamental circuiting for tubes H2 and H5 is conventional and will be understood without detailed description, though the following charac- By adjustment of these members the that, at least for an instrument having the string teristics of the illustrated circuit may be noted. Tube I I2 is preferably a pentode, with screen grid connected via conductor H20. and a series resistance v|2`| to positive B voltage, and with suppressor grid connected as usual to the cathode. The cathode elements of tubes H2 and H5 are connected to ground via grid biasing resistors |24, in a conventional manner, and tube H5 is provided with a grid leak |25. 'Ihe grid bias resistor |24 of tube H5 is shunted by condenser |26.

A compensating network |30 is connected between tubes I2 and I I5, and as here shown, comprises series arranged variable resistor r3, variable capacitor C3 and variable inductor L3, connected between circuit |2| and ground. The output of tube I5 is connected into a further amplifier section |34, which may comprise one or more additional tubes, and the output of' section |34 is connected as before to speaker 9B.

These examples are typical of corrective means which may be employed to approximate the normal or any desired relative sound energy levels of all frequencies within the range desired to be reproduced. By suitable adjustment, corrective systems of this type may be employed to give predominance to or to suppress the high or low frequency ranges of the instrument, as may be desired. For example, to relatively increase the predominance of the low frequencies, r1 in Fig. 8 may `be decreased relatively to C.

Figs. 11 and l2 show a modification, in which the strings are electrically connected just forwardly of the transducer instead of at the outer end of the finger board. It is to be understood that the conductive inserts at the outer end of the finger board may in this instance be omitted. As here illustratively shown, the forward side of pole piece 5| is formed with a projecting ledge |50, which serves as a support for a set of connections to strings 33. This ledge |50, which is arcuate shaped, and of the same curvature as pole faces 60 and l5, is illustratively shown as provided with insulation bushings |52 into which are threaded studs |53, one for each string. Conductive wires |55 are coiled at their upper ends around strings 33, as at |56, and at their lower ends are anchored to studs |53, for example, in the manner clearly illustrated in the drawings. As illustrated, the lower ends of the Wires are passed through passages |58 extending downwardly into the upper ends of the studs and then out through the sides thereof, being finally anchored by coiling around the outsides of studs |53. Studs |53 are so positioned in ledge |50 that wires |55 are disposed in a fan-like arrangement, so as to be 4substantially radial to curved pole piece faces 60 and l5 (seeFig. l2). Suitable connections are then made between proper conductors |55; for example, connections |60 and |6| are made just above studs |53, as illustrated.

By this means, the total length and therefore the electrical resistance of the electric circuit through the strings is reduced to a minimum. Stray pick-up by the strings from extraneous sources is also minimized. By making the connection points of wires |55 with the strings close to the plane defined by surfaces 5|a and 53a, as for example at the forward limit of the uniform neld, defined by f in Fig. 6a, the effects of fringng flux are greatly reduced. A further advantage is that connection wires |55 when properly tautened damp the tendency of the strings to vibrate in any direction except at right angles to the magnetic field. It will be understood that i, consists preferably of a number of paramagnetic laminations IBI, preferably of a high permeability alloy, mounted adjacent the fiat front surfaces Ila and 53a of pole pieces 5I and 53. These laminations, which may typically be approximately .015" in thickness, and of such shape as indicated in Figs. 13 and 14, are magnetically separated from one another; oxide coatings onv the surfaces of the laminations will serve this purpose. They are also separated from pole pieces il and 53 by a non-magnetic lamination |82, which may be of approximately .015" in thickness, and which may be of a material such as aluminum. The laminations are secured to pole piece I as by means of non-magnetic screws |83. Holes |84 are provided to pass the strings.

'This shield very greatly reduces the frlnging flux, v

and -limits the action to the space between the poles. It is also advantageous to grade the laminaticns I8I, using for the laminations in the stronger part of the eld, near the pole pieces,

alloys having high permeability for large magnetlzing forces, and for the more distant laminations, in the weaker portions of the field, alloys having high permeability for low magnetizing forces. i

It will be understood that the drawings and description are for illustrative purposes only, and that various changes in design, structure and ar x rangement may be made without departing from the spirit and scope of the invention or of the appended claims. It will be further understood that while I have shown the invention as applied to an instrument of the violin type, no limitation structure of opposite polarity reaching from said last mentioned magnet portion across the path of the strings and forwardly along the strings, said pole piece structure having apertures passing said strings with clearance, and being formed with a pole face located on the opposite side of the strings from and presented in opposition to said iirst mentioned pole face.

2. In a musical instrument having a longitudinally stretched lvibrating member adapted to be vibrated transversely; the combination of transducing means including a magnet structure with a pair of pole pieces having opposed pole tip faces positioned spacedly in substantial parallelism at opposite sides of the vibrating member, a bridge element mounted on one of the pole pieces and engaging the vibrating member to denne one end of its vibrating length, the pole tip faces of both pole pieces extendingfrom the bridge element longitudinally along said vibrating length a limited distance equal to a small part of the vibrating length and terminating at co-,planar end faces of the pole pieces which are transverse ofthe vibrating length, and a magnetic shield mounted on the pole pieces adjacent their end faces and having a passageway for the vibrating member: all so that a transverse magnetic neld is established which extends with substantial uniformity from the defined vibrating end a limited distance along the vibrating member.

3. A musical instrument comprising an extended vibrating member having a fundamental vibration and at least one overtone, and transducing means, said transducing means being positioned along the length of said vibrating member throughout a zone including a common thereto is to be inferred, as the invention is also applicable to other types of instruments of the stringed type, such as the piano or harp, and is even applicable, mits broader aspects, to instruments having vibrating elements of types other than stretched strings. Further, the use of the phrase electrical eld in the claims is intended to be generic to the magnetic field disclosed or any equivalent of such an energized field that is capable of being conned to the particular zone described and which will cooperate with the string or Aother vibrating member in said zone to cause a current to ilow proportional to the movement of the member.

I claim: 1. In a stringed electrical musical instrument having a frame and a plurality ci laterally spaced vibratable strings stretched thereon, a magnet Amounted on'said frame having one pole piece extending a limited distance beginning at saiddefined string ends along the vibrating strings,`

said magnet having a portion extending rearwardly from said pole piece structure in a direcnodal point of all of the frequencies of vibration occurring in said member, said zone extending along said member on one side only of said nodal point a distance no longer than one-half the wave length/of the highest frequency to be transduced, whereby all of the desired frequencies occurring' in the vibrating member may be picked up.

4. A musical' instrument in accordance with claim 3 wherein said zone extends on one side only of said nodal point a distance less than onequarter of the Wave length of the highest frequency to be transduced.

5. A musical instrument comprising an extended vibrating member having a fundamental said translated energy whereby lt may be made audible.

6. A musical instrument comprising an extended vibrating member having a fundamental vibration and at least one overtone, means for producing an electrical field. said means extending along the length of said vibrating member and adjacent` thereto throughout a zone including a common nodal point of all the frequencies of vibration occurring in said member, said zone extending along said member on one side only ofv said nodal point a distance nolonger than onehalf the wave length of the highest frequency tion along the strings. and having a pole piece t0 be picked 11D. Said eld being coniined substantially to said zone, the movement of said member through said field causing a current to fiow proportional to its movement, a circuit including an amplifier in which said current flows, said amplifier thus serving to make audible the vibrant energy in said zone.

7. A musical instrument comprising an extended vibrating member having a fundamental vibration and at least one overtone, means for producing an electrical field, said means extending along the length oi' said vibrating member and adjacent thereto throughout a zone including a common nodal point of all the frequencies of vibration occurring in said member, said means including a magnet, said zone extending along said member on one side only of said nodal point a distance no longer than one-half the wave length of the highest frequency to be picked up, said field being confined substantially to said zone, the movement of said member through said field causing a current to flow proportional to its movement, a circuit including an amplifier in which said current flows, said amplifier thus serving to make audible the vibrant energy in said zone.

8. A musical instrument comprising an extended vibrating member having a fundamental vibration and at least one overtone, means for producing an electrical field, said means extending along the length of said vibrating member and adjacent thereto throughout a zone including a common nodal point of all the frequencies of vibration occurring in said member, said means including a magnet having its pole pieces of different polarity on opposite sides of said member, said zone extending along said member on one side only of said nodal point a distance no longer than one-half the wave length of the highest frequency to be picked up, said field being confined substantially to said zone, the movement of said member through said field causing a current to flow proportional to its movement, a circuit including an amplifier in which said current flows, said amplifier thus serving to make audible the vibrant energy in said zone. Y

9. A musical instrument comprising an extended vibrating member having a fundamental vibration and at least one overtone, said member being electrically conductive, and means for producing a uniform electrical field extending along the length of said vibrating member throughout a zone including a common nodal point of all thefrequencies of vibration occurring in said member, said zone extending along said member on one side only of said nodal point a distance no longer than one-half the wave length of the highest frequency to be picked up, said vibrating member having a current induced therein proportional toits movement through said eld, and means to receive said current and convert it into sound energy whereby the vibrant energy in said zone may be made audible.

10. A musical instrument comprising an extended vibrating member having a fundamental vibration and at least one overtone, said member being electrically conductive, and means for producing an electrical field extending along the length of said vibrating member throughout a zone including a common nodal point of all the frequencies of vibration occurring in said member, said means including pole pieces of different polarity on opposite sides of said member, said zone extending along said member on one side only of said nodal point a distance no longer than one-half the wave length of the highest frequency to be picked up, said vibrating member having a current induced therein proportional to its movement through said field. and means to receive said current and convert it into sound energy whereby the vibrant energy in said zone may be made audible.

11.A stringed musical instrument having a frame and a stretched string thereon, said string having a fundamental vibration and at least one overtone, means for producing an electrical field, said means extending along the length of said string and adiacent thereto throughout a zone including a common nodal point of all the frequencies of vibration occurring in said string, a bridge on said frame for defining said nodal point, said zone extending along said string on one side only of said nodal point a distance no longer than one-half the wave length of' the highest frequency to be picked up, said field being confined substantially to said zone, the movement of said member through said field causing a current to flow proportional to its movement, a circuit including an amplifier in which said current flows, said amplifier thus serving to make audible the vibrant energy in said zone.

l2. A stringed musical instrument having a frame and a stretched string thereon, 'said string having a fundamental vibration and at least one overtone, means for producing'an electrical field, said means extending along the length of said string and adjacent thereto throughout a zone including a common nodal point of all the frequencies of vibration occurring in said string, said means including a magnet having its pole pieces of different polarity on opposite sides of the string, a bridge on said magnet for defining said nodal point, said zone extending along said string on one side only of said nodal point a distance no longer than one-half the wave length of the highest frequency to be picked up, said field being confined substantially Ito said zone, the movement of said member through said field causing a current to fiow proportional to its movement, a circuit including an amplifier in which said current fiows, said ampifler thus serving to make audible the vibrant energy in said zone.

13. A stringed musical instrument having a frame and a stretched string thereon, said string having a fundamental vibration and at least one overtone, means for producing an electrical field, said means extending along the length of said string and adjacent thereto throughout a zone including a common nodal point of all the frequencies of vibration occurring in said string, said means including a magnet having a pole piece engaging the string to define said nodal point, said pole having a face adjacent said string to determine said zone, said zone extending along said string on one side only of said nodal point a distance no longer than one-half the wave length of the highest frequency to be picked up, said field being conned substantially to said zone, the movement of said member through said field causing a current to fiow proportional to its movement, a circuit including an amplifier in which said current flows, said amplifier thus serving to make audible the vibrant energy in said zone.

14. A stringed musical instrument having a frame and a stretched string thereon, said string -`having a fundamental vibration and at least one overtone, said string being electrically conductive, and means for producing an electrical field extending along the length of said string throughout a zone including a common nodal point of all the frequencies of vibration occurring in said string said means including a magnet having pole pieces of different polarity on opposite sides of said string, one of said pole pieces engaging said string to define said nodal point, said pole pieces having faces adjacent said string to determine said zone, said zone extending along said string on one side only of said nodal point a distance no longer than one-half the wave length of the highest frequency to be picked up, said string having a current induced therein proportional to its movement through said field, and means to receive said current and convert it into sound energy whereby the vibrant energy in said zone may be made audible.

15. A stringed musical instrument having a frame and a plurality of stretched strings thereon, said strings each having a fundamental vibration and at, least one overtone, means for producing an electrical field, said means extending along the length of each of said strings and adjacent thereto throughout a zone including a common nodal point of all the frequencies of vibration occurring in each of said strings, said means including a magnet having pole pieces of different polarity on opposite sides of each of said strings, said oppositely disposed pole pieces being notched between said strings to provide portions extending into close proximity to each of said strings to concentrate said field, a bridge on said frame for defining said nodal points in each of said strings, said zone extending along each of said strings on one side only of its respective nodal points a distance no longer than one-half the wave length of the highest frequency to be picked up, said field being confined substantially to said zone, the movement of said member through said field causing a current to flow proportional to its movement, a circuit including an amplier in which said current flows, said amplifier thus serving to make audible the vibrant energy in said zone.

16. A stringed musical instrument having a frame and a stretched string thereon, said string having a fundamental vibration and at least one overtone, means for producing an electrical field, said means extending along the length of said string and adjacent thereto throughout a zone including a common nodal point of all the frequencies of vibration occurring in said string, said field being perpendicular to the plane in which said string vibrates, a bridge on said frame for defining said nodal point, said zone extending along said string on one side only of said nodal point a distance no longer than one-half the Wave length of the highest frequency to be picked up, said field being confined substantially to said zone, the movement of said member through said field causing a current to flow proportional to its movement, a circuit including an amplifier in which said current flows, said amplifier thus serving to make audible the vibrant energy in said zone. l

17. A stringed musical instrument having a frame and a stretched string thereon, said string having a fundamental vibration and at least one overtone, .means for producing an electrical field, said means extending along the length of said string and adjacent thereto throughout a zone including a common nodal point of all the frequencies of vibration occurring in said string, said field being perpendicular to the plane of string vibration, said means including a magnet having its pole pieces ofdifierent polarity disposed on opposite sides of said string to create said field, a bridge on said frame for defining said nodal point, said zone extending along said string on one side only of said nodal point a distance no longer than one-half the wave length of the highest frequency to be picked up, said field being confined substantially to said zone, the movement of said member through said field causing a current to flow proportional to its movement, a circuit including an amplifier in which said current flows, said amplifier thus serving to make audible the vibrant energy in said zone.

18. A stringed musical instrument having a frame and a plurality of stretched strings thereon, said strings each having a fundamental vibration and at least one overtone, said strings being electrically conductive, and means fon producing an electrical field extending along the length of each of said strings throughout a zone including a common nodal point of all the frequencies of vibration occurring in each of said strings, said means including a magnet having pole pieces of different lpolarity on opposite sides of each of said strings, said oppositely disposed pole pieces being notched between said strings to provide portions extending into close proximity to each of said'strings to concentrate said field, a bridge on said frame for defining said nodal points in each of said strings, said zone extending along each. of said strings on one side only of its respective nodal points a distance no longer than one-half the wave length of the highest frequency to be picked up, each of said strings having a current induced therein proportional to its movement through said field, said strings being electrically connected in series, and means to receive said current and con- .vert it into sound energy whereby the vibrant energy in said zone may be made audible.

19. A stringed musical instrument having a frame and a stretched string thereon, said string having a fundamental vibration and at least one overtone, means forproduclng an electrical field, said means extending along the length of said string and adjacent thereto throughout a zone including a common nodal point of all the frequencies o1' vibration occurring in said string. a bridge on said frame for defining said nodal point, an electrical shield spaced from said bridgeto determine'said zone, said zone extending along said string on one side only of said nodal point a distance no longer than one-half the wave length of the highest frequency to be picked up, said field being confined substantially to said zone, the movement of said member through said field causing a current to flow proportional to its movement, a circuit including an amplifier in which said current ows, said amplifier thus serving to make audible the vibrant energy in said zone.

HUGO BENIGFF.