[1]Rei"ued Aug. 18, 1936 Re. 20@070 UNITED STATES PATENT OFFICE 20,070 ELECTRIC TRANSLATING DEVICE FOR MUSICAL INSTRUMENTS Arnold Lesti, Los Angeles, CaUf. Original No. 2,026,841, dated January 7, 1936, Serial No. 25,100, June 5, 1935. AppHeation for reissue April 22, 1936, Serial No. 75,862 25 Claims. My invention relates to an electrical translating device for use with musical instruments which are not sufficiently loud when played in the normal manner. This device translates the musical vibrations Into corresponding electrical values and these are electrically amplifled and then translated into corresponding sounds by a loud speaker. The Invention is particularly adapted to steel stringed musiqal instruments such as the guitar. An Important object of my invention is to provide an adequate electrical translating device which is sufeciently small in size so that it may be easily attached to the most effective part of the musical instrument or easily detached from the same. Another important object of my invention is employing a solenoid means which may consist of one or moie electrical windings with or without a core but preferably with an iron core to' form the translating device to produce electrical currents caused by the vibration of the steel strings of the musical instrument. Another Important object of my- invention Is utilizing the @ame solenoid means with one or more electrical windings for magnetizing the steel strings which form the vibrating members of the musical Instrument, this being done by passing a direct electric current through the solenoid means, that is, the one or more electrical windings, for a short period of timeand then opening the direct current circuit prior to the playing of the instrument. In this connection I preferably provide a simplifled electrical switching means whereby the player of the instrument may close the direct current circuit for a short period of time, then open this circuit and close the amplifying circuit before playing the instrunient. A further object of my Invention is to provide an adequate translating device which will faithfully reproduce the musical tones of the instrument and not extraneous mechanical vibrations which may exist in the body of the Instrument when it Is played. I bave found that this feature is met by a translating device utilizing solenoid means to produce electrical currents caused by the vibrations of the steel strings of the musical Instrument, the said strings being p'ermanently magnetized beforehand adjacent to the solenoidal pick-up device. The solenoid nieans may be one or more electric windings arranged closely contiguous to all of the vibrating strlngs, preferably arranged with coil or coils extending transversely across the ngs of the instrument where such strings are (Cl. 84-1) arranged parallel or nearly parallel so that the assembly forming the solenoid means, that is, with one or more wire coils, reacts with the magnetized strings as the translating device and also functions for magnetizing all of the strings at 6 the same time when the direct current is passed through the coil or coils for a period of short duration. With my invention when the instrument strings are magnetized and then one or more of the strings are vibrated, the magnetic 10 field of the strings is itself placed In vibration. In this connection, a further detailed object of my invention is to provide means of changing the relative intensities of the bass and treble notes by m<)Ving the above mentioned solenoidal 15 device into proper relation with the magnetized portions of the steel strings. Where the solenoid device consists of one or more wire coils, such coil or coils may be adjusted to have different intensities of magnetizing effect on the bass and 20 treble strings of the instrument and also being susceptible to different reaction,s in the intensity of their electrical translating action when the bass and treble strings are vibrated in the playing of the Instrument. 25 Another Important object of my invention is to provide along with the above mentioned feat tures, a translating device which is free from pickup action engendered by extraneous electrical and magnetic influences. These last mentioned 30 influences are found to produce extremely objectionable noises. In the construction of my invention I have found that two or more solenoids may operate together so that each neutralizes the effects of the other insofar as extraneous un- 35 vianted magnetic influences are concerned, but that their positions with respect to the vibrating' magnetic portions of the musical lns.trument, causes an addition or summation of their respective translating currents. 40 A further detailed object of my invention is to provide means for properly magnetwng the steel vibrating members of the musical Instrument in a manner which will produce maximum effects. Wbile in some r-ases one magnetizing coil prop- 45 erly arranged in regard to the ' strings of the instrument would be satisfactory, nevertheless it is preferable to construct the solenoid means with a plurality of electric windings or coils arranged parallel to each other and extending 5o transversely across the strings of the musical Instrument where a plurality of such strings are closely contiguous one to the other. With the foregoing and other objects in view, which will be made manifest in the fouowing- de- 55
[2]tailed description, and more @@icularly In the annexed clainigl-..reference is had to the attached drawings for an illustmtive embodiment of the invention wherein, 5 Flgure I is a plan view of a guitar with my Invention applied thereto. Mgure 2 Is a side view thereof. Mgure 3 is a plan view of the translating device with top cover removed. 10 Mgure 4 is a sectional view throiigh the line 4-4 of Figure 3, and showing also how the device Is held to the instniment at the sound hole. Figure 5 is a sectional view through the line 5--5 of Mgure 3. 15 Mgure 6 is a plan view of the translating device showing an altemative method of fastening the same to instruments without sound holes. Mgure 7 is a diagrammetic view of the invention illustrating four coils and cores, the method 20 of magnetizing the steel strings, and the lines of magnetic f6ree during the process of magnetization. Flguie 8 Is a diagrammatic view of the invention somewhat similar to Mgure 7, but showing 25 the magnetic lines of force surrounding the steel string after magnetization, an Interfering stray field, an amplifier and loud speaier. Fligure 9 is a diagrammatic view showing the translating device with two coils and cores, the 3o lines of magnetic force surrounding the steel string after magnetization, an interfering stray field, a switch held in the playing position, an amplifier and loud speaker. Referring to the drawings wherein similar char.15 acters represent similar parts throug.bout, I is the body of a guitar and 2 the flngering board. Character 3 represents the sound hole at which is held the translating device designated generally by S. 7 represents generauy the steel strings @h h are vibrated during the. act of playing. 40 slat 'c ran Ing device 6 is held to the guitar by spring 24. The small spring 8 around the cable 9, where It enters the translating device 6, saf6guards 9 from excessive wear at that point. In Mgure 3 45 the coils IO and I 1, having Iron cores 12 and IS. are shown connected to insulated leads 14 and IS and their center connection 16 being connected to the case 17, made of nlagnette material. A shielding 18 around leads 14 and 15 constitutes a return lead, also r-onnected to the case 17. The 50 windings in cofls IO and' I I are in opposite directions, as can be seen from the direction of the ends, 19, 20, 21 and 22. The case 17, made of magnetic material, aids in the pick-up actlon by reducing the magnetic reluctance, giving greater 55 fleld strength from the relatively weak Inductive fields surrounding strings 7. Character 23, Is a non-magnetic top cover. While my invention ir, attachable to any steel stringedinstrument, best results are obtained 60 when the body of the instrument does not absorb the vibrations of the strings causing the tones to become rapidly damped. In Mgure I and Mgure 2 are shown a guitar with a smalier body I than 65 the conventional, and constructed with heavy wood 25 to prevent vibration. This perniits the tanes to be sustained much longer yielcung a more desirable effect. In Flgure 6 pins 26, 27, and 28 hold deto)chible members .29 and 30, fastened to the elastile belt 70 31 and 32 which may be continuous around the body of the instrument to hold the translating device when the Instrument has no sound hole such as the sound hole 3 in Flgure 1. In Figure 4 is shown a cross section of th6 75 steel strings represented generally by 7. It Will be observed that core 12 and also 13 are sufficiently long to provide nearly similar magnetic reluctance to the fields surrounding each string. The process of magnl-tization is represented in detail in Pligure 7 wherein 33 represents a battery, 34 a double pole throw switch connecting the coils to the battery and producing the magnetic fleld represented in dotted lines. Coils 35, 38, 37 and 38 are each reversed with respect to its neighbor asshown. Suitableironcoresareshownat39,40, I 41 and 42. 'Me small size of the translating device 6 Is due to the fact that there are no permanent magnets within it. The magnetic intensity of a permanent magnet, small enough to be placed in I the device 6, would not be effective, due to the distance of the strings 7, as shown In Mgure 4, to nugnetize the strings adequately. 'Me coils I 0 and II with cores 12 and 13 are converted into momentary electro-magnets to produce an intense 2 magnetic field to permanently magnetize the strings 7 which retain their magnetism for a long time. I have found that a steady magnetizing direct current cannot be maintained through the coils 10 and I I itt the same time that the 2 devlce translates the string vibrations, because of the high objectionable noise level thereby produced, due to the strong current and high magnetic intensity producing a hiss and noises of the Barkhaussen effect, with the high amplification 3 required. 7be position of the translating device 6, at the sound hole, produces the best quality of tone. At that point the steel strings are vibrating without an excessive amount of harmonies, such as near g the bridge 43. At or near the sound hole the device must be kept at a considerable distance from the steel strings so that It will not interfere with the act of playing. At this distance the important lnflu4 ence, for proper pick-up action, Is the permanent magnetism inherent in the steel strings themselves. After magnetization as in Mgure 7, the field of magnetic force is found by actual test, to be that represented by the dotted lines In Flgure 4 8. The steel string 7 divides magnetically into a series of magnetized zones 44, 45, 46 and 47 of reversed polarity In adjacent zones. The regions of maximum magnetic density 48, 49, 50 amd II. coincides with the positions of the cores 39, 41, 41 and 42 from which arose the original magnetizing 5 force represented by 52, 53, 54 and tl in Flgure 7. This condition is also that of ma)dmum pick-up action. It was generally held, in the prior art, for magnetic devices of s6mewhat similar purpose, 5 that the steel strings behaved as armatures to vary the reluctance of the magnetic path. I have found, In my invention, that the steel strings constitute a source of vibrating magnetic :fteld, when in vibration, and that the field of magnetic force, illustrated in Plgure 8, vibrates in space in consonance with the vibration of the steel string 7. The regions of maximum magnetic density, 49, 49, 50 and 51 shift rapidly allowing varying amounts of lines of force to be linked In the cores 39, 40, 41 and 42, and thereby inducing corresponding currents in the coils 35, 31, 37 and 38, referring to Mgure 8. After the strings are magnetized it is possible to reduce the intensity of the treble notes if thi y are deemed too loud with respect to the ba.-;s. The procedure is to shift, towards or away fro the bridge, the end 56, Flgure 4 while being car tW not to change the position of the other en
[3]with respect to the magnetizecl zones on the strings. The result may be represented in Mgure 8 for the treble strings dnly by the regions of maximum magnetic density not entirely coinciding with the cores 39, 40, 41 and 42, thereby producing less pick-up action at these places. In Flgure 8, 57 represents generally a vertical instantaneous component of a stray interfering magnetic field. It will be observed that this interfering stray field, due to some extraneous cause, Is of uniform direction and density over the region occupied by the translating device. Its inductive action on adjacent coils is equal, and since these are wound In opposite directions, .1 the Interfering stray currents are neutralized. On the other hand, the magnetic fields of the steel strings are of reversed polarity, such as 48, 49, and 50, 5 1. When vibrating, these will induce cumulative currents in the coils, 35, 36, 37 and 38, which are relatively. ihsensitive ' to other influences. Stray int@rfering fields are seldom heterogeneous over the small region occupied by this translating device. However, by using a larger number of smaller electromagnets, more satisfactory results may be obtained, to take care of extreme conditions. Mgure 9 is a diagrammatic view of the translating device, of which Figure 3, Figure 4 and Mgure 5 show constructional views. The pick-up device hac two reversed windings, 58 and 59 and cores 60 and 6 1. The windings are connected together @-t'62, and to a common return lead 63. The two outer leads 64 and 65 connect to the coils and Pre let together with 63 to the switch genern.Ily designated 66. Tn the instance s-hown the switch is in play,',-ig position vrith leads 63 and 64 and 65, coniiected directly to the amplifier 67, of which 8, 6r.@ --nd 70, i-S the tandem input. This is also 10 :eferrecl to in the art as a push-pull input. '@,j7hen 7 1, is turned the switch restores to norr,nal position by springing action. In this position t:,le input 60, 70, is shunted to 69, stabilizing the InDut which is connected directly to the grids t.5 of tt-i@des @-nd thereby prevent howling. Simulta,,ieously lead 63 i-s opened and the leads of direct current 71 ayid 72 are connected to leads 0-4 and ')5,,furni-Shing direct current to the coils 1',S and 09, to energize the same. This is the ,o magnetizing position of the switch. At the ampli'-@ler @DT is shown leads 73 and 74, which furco,,'@-,hode currevit -,vhile 71 and 12, connect "c , 6 @, source of plate potential for the triodes of @fl,ze amplifier. IZ;@,)e loud speaker 75, is shown with connecdS zlnd 77, leading to a source of potential -1-c p7.roduce field e7,citation. ti-ie playing position shown in Flgure 9, if t',-ie sieel st'ring 7 vibrates, the surrounding mag;o retic -,ileld 70 -,:vnd 79 will also vibrgte inducing -ci:u,- Lerits in the coils 58 and 59, while being iiiLL,,e@iasltive to the stray field 80, as above memt'@Oned. 'l,he etirrents are applied to the input, 68, @3S and 70 of the ainpli:fter 67, which aniplii ',Ies i-,hem, qri d from the output 81 and 812 of the o,mplifier they are connected to the loud speaker 'i6, which translates the amplifled currents into sol,nds. Various changes may be made In my invention, by those skilled in the art, without departing from the spirit thereof, as set forth in the drawings, specification and claims. 3:
