US2200718A - Electronic piano - Google Patents

Description

May 14, 1940. B. F. MIESSNER ELECTRONIC PIANO Filed Jan 29, 1958 5 Sheets-Sheet l 6 lNVENTOR:-

May 14, 1940. B. F. MIESSNER ELECTRONIC PIANO Filed Jan. '29, 1938 3 Sheets-Sheet 2 I. l I

May 14, 1940. a. F. MIESSNER ELECTRONIC PIANO Filgd Jan. 29, 1958 3 Sheets-Sheet 5 Patented May 14, 1940 UNITED STATES PATENT OFFICE ELECTRONIC PIANO Benjamin F. Miessner, Millburn Township, Essex County, N. J., assignor to Miessner Inventions, Inc., Millburn Township, Essex County, N. 1., a corporation of New Jersey Application January 29, 1938, Serial No. 187,646

. 2'1 Claims. (01. 84-114) fier and then in turn translated (electro-acousti-- cally) into output tones.

It is anobject of the invention to enhance the l pianistic quality of, or approximation of conventional piano performance by, the output tones of an electronic piano.

It is an object to provide improved mechanicaelectric translating apparatus, and arrangements 15 thereof relative to other components, whereby It is another object to provide improved simple and readily adjustable translating electrodes and relationships thereof to the strings.

It is another object to provide improved and 35 simplified means for minimizing non-musical components attendant upon tone initiation, particularly in the high treble notes and without sacrifice'of electrode adjustability.

It is another object to provide novel electrical 40 means for minimizingsuch undesirable components as abovementioned.

It is another object to provide improved and.

simplified means for increasing the rate of damping of the output tones of the electric piano.

45 It is another object to provide improved and simplified means for decreasing the direct acoustic sound output of the electronic piano. It is another object to reduce feed-back from the loudspeaker to the strings.

It is another object effectively to control the apparent damping of the outputtones.

It is another object to control this apparent damping while maintaining substantially "constant the volume level of the output tones. 55 It is another object to provide effective, simplified and durable volume control means for the electronic piano.

It is another object to provide a coupling circuit, between the translating electrodes and the amplifier input, substantially free of the deficiencies of electrical leakage and mechanicalvibration.

It is another object to provide particularly effective and simple electrostatic shielding of sensitive portions of the piano. I

-It is another object to provide improved and particularly, eifective arrangements of electroacoustic translating devices in the electronic piano. v

'It is another object eflectively to minimizeor suppress regenerative or oscillation-sustaining effects of a feed-back from the. electro-acoustic translating device to the strings of the electronic piano.

Other and allied objects will more fully'appear from the following description and the appended claims.

In the description of my invention, hereinafter set forth, reference is bad to the accompanying drawings, of which- Figure 1 is a front elevational view' of an electronic piano according to my invention, with'the' front cover member and most of the action removed;

Figure 2 is a rear elevational view of the instrument of Figure 1, with the back cover removed;

Figure3 is a substantially vertical cross-sectional view of most of the instrument, taken approximately along the line H of Figure 1, Figure 3 further including a schematic showing of electrical portions 'of the instrument;

Figure 4 is a fractional substantially vertical cross-sectional view illustrating a modification in respect of the bridge means of the instrument;

Figure 5 is a fractional substantially vertical cross-sectional view illustrating a further modification in respect of the bridge means;

Figure 6 is an enlarged vertical cross-sectional view of the principal components of the hammer action, together with a schematic illustration of certain electrical control means interrelated with the action-control means;

' Figure 7 is a partial, inclined cross-sectional view of the bridge and electrode means for the upper treble strings, taken approximately along the line of Figure 1, together with a schematic illustration of certain electrical circuits which may beneficially be associated with those electrode means;

Figure 8 is a vertical cross-sectional view of one of the pedals, taken along the line 8-8 of Figure 1, together with a schematic illustration of electrical components associated with that pedal;

and.

Figure 9 is a rear elevational view of the vertical front cover member H when removed from the instrument.

Reference may be had to Figures 1, 2 and 3 for an understanding of the general mechanical construction of the electronic piano with which I have illustrated my invention. Herein will be seen a vertical, rectangular metallic plate or frame I serving as the basis to which all other components are directly or indirectly assembled; this plate is conveniently provided around its periphery with the forwardly extending flange 2. The central portions of the plate 'are apertured; but the plate is reinforced by cross-webs such as 3, some of these being in turn reinforced with forwardly extending flanges such as 4. To the back of the plate may be secured a peripheral framework, comprising for example the wrestplank 5 across the top, the. wooden cross-member 6 across the bottom, and the vertical wooden end member 1. To the plate I, through the medium of this framework, may be supported a vibratile system comprising certain bridges (hereinafter described) and a plurality of vibratile ribs 8the tops of the ribs being secured in the wrest-plank 5, the bottoms of the ribs being secured in the bottom cross-member 6, and the ribs being preferably slightly bowed forwardly in their central portions. Forwardly and backwardly extending vertical standards 9 may be secured to the two ends of the plate 9 to form a support therefor and, if desired, to form the exposed ends of the instrument. A bottom front cross-member may extend between the end standards 9, as may likewise a floor-member Illa, between the cross-member l0 and the plate I. There may also be provided between the end standards 9, extending upwardly from the front cross-member III, a removable front cover member H (see Figure 3). The illustration of ribs 8 has been omitted from Figure 1 in the interest of clarity of showing.

The top portion of the plate I is suitably apertured to permit a plurality of tuning pins l2 to extend forwardly therethrough from wrestplank 5, wherein they are secured. From these pins to respective hitch pins I3 in lower portions of the plate I extend the several tuned strings of the instrument, of which the upper treble strings are indicated as IS, the lower treble strings as 15, and the bass strings as I4-it-being understood that each of these groups of strings has been only fractionally shown in the interest of simplification of the drawings. strings have been shown as passing from the tuning pins I! under a pressure bar I! and over a ledge l8 defining the upper extremities of their active portions; the bass strings M, which may be overstrung (i. e., disposed slightly in front of and somewhat transversely to the treble strings), may pass around respective'localizing pins IS in the defining ledge l8. The bridges over which the strings pass, and which define the lower extremities of the active string portions, are hereinafter described.

For impulse excitation of the strings there may be employed a hammer action, for example of the dropped" type; this, while appearing fractionally in Figure 1 as A, has been indicated in enlarged detail in Figure 6. Briefly, it may comprise keys 20; upper levers 2| adapted to be raised All the treble.

by the rear ends of the respective keys upon key depression; lower levers 22 coupled to the respective upper levers; pivoted hammers 23 responsive, through the respective levers and action mechanism not necessary to detail, to the respective keys to strike the respective strings; and normally string-contacting pivoted dampers 26 responsive to the respective keys to move away from the respective strings. .A transverse rod 21 may be provided in front of the heels 26a of all the dampers, and may be moved rearwardly at will (as by depression of the conventional sustaining pedal 28, Figure 1) to move all the dampers 26 simultaneously away from the strings. A transverse rail 24 may be provided in front of all the hammer shanks 23a, being supported by rods such as 240 pivoted at fixed points such as 24b, and may be moved rearwardly and upwardly at will (as by depression of the pedal 25, Figure 1, acting through lever 25a and rod 251)) to reduce the normal separation of the hammers from the stringsand hence to reduce the length of the hammer stroke, and in turn the strength of the excitation of the strings by key depression.

For translating the string vibrations into sound there is employed a mechanico-electric-acoustic translating system, wherein the mechanico-elec- 'tric translation is effected electrostatically. Thus suitable electrode means, hereinafter more particularly described, are provided adjacent the strings to form therewith minute capacities which will'be oscillatorily varied by the string vibrations; these capacities are polarized or charged with a relatively high voltage through a high resistance, preferably connected to the electrode means. In Figure 3 a charging voltage source is schematically indicated as 30, having one terminal connected to the electrode means through the high resistance 3|; the other terminal of the source 30 may be connected with plate I and therethrough with all the strings, their joint potential being conveniently considered as ground potential. The electrode means are connected to electronic amplifying means, as through an input or blocking condenser 32 and an input grid leak resistance 33, for the impression on the amplifier 'of the minute oscillatory voltage changes abovementioned. The amplifier has been schematically indicated for convenience as comprising the tandemed portions 34, 36 and 38, with control means 35w-35b and 37 interposed between the portions. The output of the amplifier may be connected to electro-acoustic translating means; these I have schematically indicated in Figure 3 as the speaker 39 having for example a response at all audio frequencies but being particularly efficient in the lower frequency range, and the speaker 40 having for example an efficient response at the high frequencies only.

The general construction thus far outlined will be understood to be now known, and not in itself to comprise the instant invention.

According to the preferred embodiment of the instant invention I arrange the electrode or pick-up means for a group of strings in a bridge assembly which is integral with the stringsupporting bridge for those strings. In Figures 1, 2 and 3 the bridge which supports the treble strings is shown as ll, the strings passing over it with a bearing thereon and being secured to it as to vibrational movement by engagement with the conventional bridge pins therein. The bridge 4| is secured to the several ribs 8 in an appropriate curve transverse to the ribs; this securing, as by gluing, may desirably be not merely to the front surface of the ribs, but to the rib sides as well-by virtue of the illustrated thickening of the bridge between the ribs.- The bridge. 4| is provided with a portion 42 of reduced thickness extending underneath the active string portions (i. e., upwardly) and by this portion the electrode means for the treble strings are carried.

Q and to the charging resistance 3| and input condenser already mentioned.

I have found the presently described bridge construction to yield a. particularly pianistic output tone-apparently because of especially efficiency in the translation of the longitudinal vibrational eil'ect of the strings This effect is a vibratory pull by the string on the bridge, bicyclic and otherwise of second-power with respect to each of the various partial components of the normal string vibration; this pull in turn rocks the bridge vibratorily, roughly about a line transversely through the ribs opposite (i. e., behind) the region of the securing of the strings to the bridge. This second-power rocking movement of the bridge, occurring at the bridge pins in the longitudinal direction of the strings, causes the extending bridgeportions 42 and u to execute respectively corresponding rocking motions toward and away from the strings- -and hence produces a corresponding second-power varicadence and in increasing the initial steepness of that decadence. While in U. S. Patent No. 1,912,293 to me I disclosed electrode means secured to the side of a string-supporting bridge, and in another embodiment to the bridge-supporting ribs near the bridge, sothat this secondpower action occurred to an appreciable extent,

. I have nevertheless found the present integral bridge construction, with the electrodemeans- I intimately secured in the bridge,

to been appreciably improved one.

It is essential that the insulation resistance between the electrode means and the strings be of a very high order; hard-wood bridge materials as customarily employed have V in themselves proven deficient in providing this insulation reslstance in structures such as I have described above. 'I have found, however, that if the bridge be thoroughly treated with oil (castor oil, for,

example) so that at least a surface layer portion thereof contains a substantial percentage of oil, a satisfactory value of insulation resistance may usually be attained. As an expedient alternative or additional to the-oiltreatment, however, each of the electrode screws 45 maybe surrounded within the bridge by bushings 41 of high-grade insulating material, such as the phenol-resin com- The several positions available under the trade-name of Bakelitethe, bushings preferably extending slightly from both front and back surfaces of the bridge. Still another expedient, alternative or additional to the above, for increasing the insulation resistance is the longitudinal slotting of the bridge between the bridge pins and the electrode means; this has been illustrated in connection with the treble bridge 4| in Figure 3, the two longitudinal slots 48 appearing in the mentioned location. .While each of these expedients is a distinct benefit, I have not ordinarilyiound it necessary to resort to all coincidentally; for

service under unusually trying atmospheric conditions, however, they may all be included.

The oil-treatment and/or slotting are useful with other arrangements of electrode means on the bridge. Thus in Figure 4 I show a bridge 43' intended for optional substitution for one of the bridges of earlier figures-for example, for the bass bridge 43, in connection with which the importance of adjustability of the electrode means is at a minimum. This bridge 43' is provided with the extending portion 44 corresponding to the portion .44 above described; the electrode means carried by the bridge, however, are in the form of a fixed strip 48 held in spaced relationship to the bass strings l4 byan intimate securing to the surface of an insulating strip 50, which in turn is intimately secured to the surface of the extending bridge portion 44'. The bridge of Figure 4 may be either oil-treated or provided with one or more slots 48' as shown, with benefits as above described.

While I prefer the integral formation of the bridge for both strings and electrode means, the

advantage of that arrangement may be retained to an appreciable extent with separate bridges if at least thestring bridge and preferably both bridges are formed to fit around, and are secured to, the sides as well as the front surface of each rib 8 (i. e., to three faces of each rib, as described above as preferred even for the integral bridge) this'preserves a high degree of coupling,

between the bridges as to the rocking movement.

The alternative arrangement of such separate invention at least the treble strings are arranged in pairs, the two strings of each pair being substantially parallel and similarly tuned to a respective note, and being simultaneously excited and damped; and a singleelectrode screw is associated with each pair, the'axis of the screw being substantially centered between, and normal to the plane of, the two strings. For the bass strings I4 and the lower treble strings IS the electrode screws 45 may be flat-headed; but for the upper treble strings I6 I prefer to employ screws with conical heads and, further, to make the apex angles of those heads progressively more pointed for progressively higher notes. This I have illustrated in the cross-sectional Figure '7, wherein appear the strings ii for several mutually spaced higher treble notes; a flat-headed electrode screw 45 for the lowest-shown stringpair (connected by conductor 46 to the electrodes for the lower treble and base strings) a slightly, conical-headed screw 45a for a somewhat higher-- note string-pair; and so on to a sharply conicalheaded screw 45c for the highest-note string pair. By this arrangement there is provided in a particularly convenient manner, and with preservation of ready electrode adjustability, an angling of the electrode surfaces with respect to initial string vibration plane which is known as desirable for the reduction of undue initial nonmusical raphtransients accompanying the excitation of the higher frequency notes.

Figure 7, because of its appropriately large scale, has been selected also to show a purely electrical means for reducing these -rap effects. This comprises filter means at least partially interposed in the connections between the highnote electrodes 45c-- l5b45a and the lower-note electrodes 45, and effective-preferably in degree increasing with frequencyto eliminate from the outputs of the high-note electrodes a band of lower frequency components of which the rap is largely composed. Filter means so disposed may take a variety of forms, but the one I have chosen for illustrative purposes may comprise a shunt circuit, from the highest-note electrode 450 to ground, of inductance 55, capacity 56 resonant with the inductance to the mean rap component frequency, and resistance 5'! adjustable to control the circuit; and series elements comprising resistances 58 connecting the successive highnote electrodes together and to the lower-note.

electrodes 45. It will be clear that as to electrode 450 there is provided the maximum shunting to ground of the rap components, and a maximum of series impedance to the conductor 46 and amplifier input; and that both these characteristics are progressively decreased for electrodes associated with progressively lower notes.

The vibratile system which supports and couples the strings may be referred to as the resonator portion of the instrument, in that it is chiefly responsible for the direct acoustic sound output of the instrument. In the particularly illustrated instrument this portion has been made relatively restricted and skeleton-like, by the omission therefrom of a continuous soundboard; accordingly the rate of damping or general decadence of the tones of the instrument is normally appreciably less than that of the conventional piano, and in many instances it may be desirable to increase this damping rate. In the instrument according to the invention the damping rate may be increased by a damping means associated with the strings, preferably uniformly along their active portions so that their vibrations are not otherwise interfered with. Such a damping means may comprise a thin coating, about at least those active string portions, of elastic material characterized by at least some internal friction; a lacquer or rubber compound may for example be employed. Some-still further damping increase, due probably more to an increase of air-resistance than of internal friction, may be secured by blowing onto the lacquer or other compound, while wet, felt dust or other finely divided and relatively soft and sound-absorbent particles; upon drying of the coating the outer portions of these particles will remain exposed to the air. Such a coating on the strings has been fractionally indicated as 60 in Figure 3, but in greatly exaggerated thickness for the sake of clear illustration.

A similar coating with the felt or like dust, or other covering of felt or other sound absorptive material, may be applied directly to the resonator portion, whether that is or is not' restricted as in the particularly illustrated instrument. Thus there has been fractionally illusu-ated as ii in Figure 3 such a coating on both the front and back surfaces of the ribs 8, and as 62 such a coating on the backs of the bridges 4| and 43. Such a covering of the resonator portion not only increases the air-damping of that portion and hence the tone-damping rate, but also decreases the direct sound output of that system and hence of the instrument, and furthermore very beneflcially reduces acoustic feed-back of sound from the loudspeaker to the strings. This direct application of sound-absorbent material to the resonator portion of an instrument I have found to be a much simpler procedure than the absorption of sound which that portion has once been permitted to create.

The apparent damping of the tones of the instrument is always greater for high string-excitation strengths than for low ones, since the rate of damping appears to vary with string vibration amplitude; ordinarily, however, the distinction in damping rate so produced tends to be obscured by the accompanying large change in output volume. According to my invention I may effect an improved control over apparent damping rate by simultaneously controlling both the excitation strength and the efficiency of the mechanico electro-acoustic translation (e. g., the gain of the amplifier 3436-38)and I may do this while maintaining substantia ly constant volume level, by controlling that strength and that efliciency in appropriately predetermined inverse relationship. This I have illustrated in Figure 6 by employing, for example as the control means 31 above mentioned, a potentiometer 64 connected across the output of amplifier portion 36, and having a variable contact 65 mechanicaly connected with the rod 25b abovementioned as controlling the hammer-stroke in response to pedal 25--the input of the amplifier portion 38 being connected to one extremity of the potentiometer and to the variable contact 65. Ordinarily operation of the pedal 25 will not only decrease the hammerstroke but will also increase the translation efficiency by raising the contact 65, the potentiometer 64 being suitably tapered so that the effects of these two operations on output ,volume substantially annul each other; the apparent damping rate will be decreased, however, during the pedal depression. If desired, this action may be eliminated at will to leave the pedal 25 as a simple hammer-stroke control, by employing a switch 56 to break the connection of amplifier portion 38 to the movable contact 65 and instead to connect it to a fixed tap 61 appropriately positioned on the potentiometer 64.

For simple volume control purposes I incorporate, in the preferred instrument according to my invention, a pair of volume control meansone being a full-range control manipulable by hand to establish the general volume level; and the other being connected to an upwardly biased pedal, such as 10 in Figure 1 and the cross-sectional Figure 8, to temporarily reduce the volume within finite limits during periods of pedal depression. The former may be connected in the control means 351), and the latter may'be connected as the control means 351: abovemen tioned. Thus in 35!) (see Figure 8) there may be included, as the hand-manipulable control, a potentiometer ll connected across the output of amplifier portion 34, and having variable contact 12 and one extremity connected to the input of amplifier portion 36; while the pedalresponsive volume control may comprise a plurality of resistances 13 progressively shuntable I sealing 'means across the potentiometer Il asthe pedal 10 is depressed. This pedal, which may be both eflectively terminally pivoted and upwardly biased by spring 69', may be disposed above a plurality of normally spacedcontacts 14, 14a, 14b and 140; contact 14 may be'conn'ected to one extremity of thepotentiometer II, and the other contacts to the other extremity of the potentiometer through respective resistances 13. As the pedal 10 is depressed it will first close contact- I4 against contact 14a, shunting one of the resistances 13 across the potentiometer and slightly reducing the volume; and as the pedal is further depressed, more and more of the contacts will be closed, to shuntmore and more of the resistances across the potentiometer and to more and more reduce the volume. The limit of volume reduction, however, is deliberately made a-finite one for correspondence with normal piano soft pedal action.

If desired, the pedal-l8 may be made to function as a normal soft, or hammer-stroke-reducing, pedal coincidentally with its function as an electrical volume control pedal. This has been illustrated in. Figures 1 and 8 by the extension of the lever 25a to above the pedal 18, the free passage through the lever extremity of a rod 10a extending upwardly from the pedal, and the threading of a removable nut 10b onto the top of the rod 10a to a position just above the lever 2511. With the nut in place, depression of pedal 10 will rock lever 250. (about its pivoting spring 250, Figure 1) to reduce the hammerstroke simultaneously with the operation of the contacts 14, etc; but a like rocking of the lever 25a by the pedal 25 will neither move the pedal 10 nor operate those contacts, in view of the free passage of rod 18a through lever 25a. The simultaneous electrical and mechanical control of tone volume, with attendant influences of the mechanical control on other tone characteristics, has proven highly pleasing musically. t

The control means 35b may typically include,

ture or tone control means operating on an absolute frequency basis. These have been illustrated as a condenser 15 and variable resistance IS, in series with each other and together shunted across the output of potentiometer H, serving as a high-frequency control; and a condenser 11 and variable resistance I8, 11 being in series and 18 in shunt with the input of amplifier portion 36, serving as a low-frequency control. It will be understood, however, that the form and location 01' these controls have been chosen only by way of example and in no sense as limitative. The entire control means 35b may be physically arranged in a small panel assembly at the right of the instrument just above the keys 28, as has been indicated in Figure 1; this panel assembly may also include an on-off switch 19 for the amplifier 34--3838.

The charging resistance 3|, input condenser 32 and input resistance 33 are desirably encased within a grounded electrostatic shielding enclosure 38 as indicated schematically in Figure 3. To prevent vibration within, and consequent variation bf their capacity to, the enclosure 80, and simultaneously to .protect them against moisture and consequent leakage, I have found it advantageous to surround them within the enclosure by (fractionally shown as 80a) poured hot into the enclosure and imbedding ,thes elements therein when 0001. The shield-' ing provided by the enclosure 88 may advanin addition to potentiometer II, harmonic struc tageously be extended about the input and output leads therefor, as indicated by 8| in Figure 3.

Electrostatic shielding of further sensitive instrument portions, especially the electrodes, is basically provided on the front by the strings; to complete it on the rear there may be provided a removable back cover for the instrument, fractionally shown in withdrawn position as 82 in Figure 8. This may comprise a rectangular frame work 83 having horizontal cross-pieces such as 84 and vertical cross-pieces such as 8!, and grounded metallic screening 86 secured across the frame-work and cross-pieces and trimmed by moulding ,8] if desired. Preferably each individual element of the framework and cross-pieces will be provided with a coating of colloidal graphite solution which dries in a conductive state, as has been fractionally illustrated by the heavy lines 88 in Figure 3, and the coatings of the several elements individually electrically grounded.

With the back cover secured against the rear of the instrument the grounded screening 86 is disposed relatively near the electrodes 45; and

it is to minimize shaking of this screening, which would electrostatically influence the electrodes, that the cross-pieces 84 and 85 are employed.

To supplement this basic shielding the inside surfaces of the instrument, comprising for example those surfaces of the end standards 3, floor member Illa, and removable front cover member II, may be provided with similar grounded coatings. This has been illustrated in detail for the front cover member II in a back. view thereof appearing as Figure 9. This has been shown as formed of the several mutually secured boards Ha, Hb, .Ilo, lid, the whole exposed surfaces of all the boards being provided with respective coatings fractionally shown as 89. A convenient means of individually ground ing the coatings of individual elements has been illustrated for the several boards of which member II is formed; this may comprise a metallic conductor 90 successively connected as by screws 9| to one or more places on each element, the conductor being fully or substantially grounded, at one place for example, in any convenient manner. This expedient obviates excessive resistance in the shielding, both as resulting from large area covered by the coatings and as resulting from possibly poor continuity of the coatings between successive elements.

The low-frequency and high-frequency loudspeakers, 39 and respectively, are mounted within the instrument in a preferred embodiment of the invention, and they have been so illustrated. The low-frequency speaker may be supported to the plate I as by securing to a cross member 93 extending between one of the web-flanges 4 and the edge flange 2 above mentioned. It may be forwardly directed, and baiiled, if desired, by the removable front cover member ii when in its installed positionthis member having been illustrated as provided with the appropriate sound-emitting aperture H. The relatively smaller high-frequency loudspeaker 48 may be secured to the plate I in any convenient manner, likewise preferably fcrwardly directed, and the front cover member ay be provided with the second soundin any convenient manner,

emitting perture ll" appropriate to it. A pre-,'

the high-frequency speaker relatively adjacent the high-note extremity, of the keyboard and instrument, and the speakers have been accordingly so illustrated. I have found this arrangement markedly to enhance the naturalness of pianistic performance by an instrument of this type. No claim, however, is made to this arrangement of speakers in this particular application.

In the instrument so described it will be appreciated that there is a substantial acoustic-vibrational influence exerted by the loudspeaker on the strings; the very close adjacency of the loudspeaker to the restricted resonator portion (which is vibrationally coupled with the strings) causes this influence to be of the same order as would a moderate adjacency of the loudspeaker to a more complete resonator (e. g., soundboard). In

any instrument wherein this substantial influence or feed-back to the strings is present I have found that the securing of the mechanico-electric translating (i. e., electrode) means to the resonator portion (i. e., vibratile system) has the peculiar and highly beneficial function of markedly suppressing the effect of that feed-back i. e., a regenerative or self-oscillatory tendency of the system, which would be of a prohibitive order were the translating means secured to relatively rigid portions such as the plate I. In such an instrument as that disclosed in U. S. Patent No. 1,912,293 to me, above mentioned, the like securing of the translating means-while otherwise beneficial-did not perform this additional function, in view of the substantial absence of feed-back, resulting from joint restriction of the resonator portion and comparative isolation therefrom of the loudspeaker. The beneficial function above described is performed in the currently described instrument by reason of the participation of the translating means (or at least the sensitive portions thereof) in the appreciable composite vibration of the resonator portion and strings which is produced by the compressional waves from the loudspeaker-so that in spite of appreciable vibrational amplitude the sensitive spacings between (or relative positions of) the translating means and the strings tend to remain constant.

It is of course true that the resonator portion vibration may stimulate individual strings into small individual vibrations of their own, so that those strings to that extent depart from the composite vibration of resonator portion, strings and translating means; these individual string vibrations can of course influence the translating means. While without special attention to this phenomenon a large suppression of the feed-back effect is obtained as outlined in the preceding paragraph, this effect "is even more perfectly suppressed by proper further arrangement of the translating means in such positions longitudinally of the strings that they do not have a strong response to these feed-back-produced individual string vibrations. Ordinarily I find these vibrations to be predominantly at relatively high-numbered partial components of the strings, so that their amplitude is as great very close to the string end as it is nearer the string center; for efficient intended translation, however, the spacing of the translating means from the mean string position tends to be greater, and the influence of a high-numbered partial component vibration therefore less, the further that means is from the string end. Accordingly the desirable longitudinal position for the translating means is at an appreciable distance from the string end; and the cured as to vibrational joint observance of this specification and that of securing the translating means to the resonator portion, in an instrument with appreciable loudspeaker-to-strings feed-back, insures a surprising absence of effect of the feed-back-i. e., of regenerative and self-oscillatory tendencies.

While I have disclosed my invention in terms of a preferred embodiment thereof, it will be understood that no unnecessary limitations are intended by virtueof the details of that embodiment; for modifications, many of them wide, which will suggest themselves to those skilled in the art may fall within the true spirit and scope of the invention. In many of the claims hereunto appended I undertake to express that scope broadly, subject however to such proper limitations as the state of the art may impose.

I claim:

1. In an electronic piano having vibratable strings: a bridge to which said strings are semovement; vibratile means supporting said bridge for both linear and rocking response of said bridge to string vibrations; and pick-up electrode means passing through and supported by the same bridge and extending into spaced relationship to said strings.

strings a bridge to which said strings are secured as to vibrational movement; vibratile means supporting said bridge for both linear and rocking response of said bridge to string vibrations; a portion integral with and extending from said bridge under said strings; and pick-up electrode means passing through and supported by said portion and extending into spaced relationship to said strings.

4. In an electronic piano having vibratable strings: a bridge contacted by and supporting said strings; and pick-up electrode means carried by the same bridge, the surface of said bridge between said electrode means and the region of contact of said strings therewith being slotted to a substantial depth.

5. In an electronic piano having vibratable strings: a bridge contacted by and supporting said strings; and pick-up electrode means carried by the same bridge, said bridge being of wood but containing in at least a surface layer portion a substantial percentage of oil.

6. In an electronic piano having vibratable strings and a plurality of vibratile ribs; stringbridge means secured to said ribs and having said strings secured thereto as to vibrational movement; and adjacent bridge means and pickup electrode means carried thereby. at least said string-bridge means extending about and being secured to three surfaces of each of said ribs.

"7. In an electronic piano having vibratable strings: string-bridge means contacted by and supporting said strings; adjacent bridge means;

a common vibratile support for both said bridge tive second ends formed for tool manipulation whereby to adjust said spaced relationship.

8. In an electronic piano including a pair of adjacent, substantially parallel and similarly tuned strings: a pick-up electrode screw for said strings, the axis of said screw being substantially centered between, and substantially normal to the plane of, said strings; and a conical head on said screw adjacent said strings.

9. In an electronic piano having a series, of

pairs of vibratable strings tuned to progressive frequencies: pick-up means for said strings comprising a plurality of electrode screws having conical heads respectively substantially centered with respect to said pairs of strings, the apex angles of said conical heads being progressively more acute toward the treble extremity of said string series.

10. In an electronic piano having a plurality of strings tuned to progressive frequencies: means for translating electric oscillations from the vibrations of said strings, including pick-up electrodes respectively associated with said strings and electrical connections between said electrodes; and filter means, at least partially interposed in saidconnections, for progressively attenuating predetermined components in the oscillations translated from progressively more extreme-frequency strings.

11. In an electronic piano having a plurality of impulse-excitable strings tuned to progressive frequencies: means for translating electric oscillations from the vibrations of said strings, including pick-up electrodes respectively associated with said strings and electrical connections between said electrodes; and filter means, at leastpartially interposed in said connections, for progressively attenuating predetermined transient components in the oscillations translated from progressively higher-frequency strings.

12. In an electronic piano having a plurality of vibratable strings tuned to progressive frequencies, and an amplifier: means for translating electric oscillations from the vibrations of said strings, including pick-up electrodes respectively associated with said strings, electrical con nections between said electrodes, and means connecting said electrodes to the input of said amplifier; resistances serially interposed in said connections; and a frequency-discriminating shunt circuit connected to an electrode remote from said amplifier-connecting means.

13. In an electronic piano including mechanico-electro-acoustic translating means having a negligible damping reaction: a vibratable string influencing said translating means; and a. thin coating of damping material surrounding said string whereby an appreciable damping reaction of said translating means is simulated.

14. In an electronic piano including mechanico-electro-acoustic translating means having a negligible damping reaction: a vibratable string influencing said translating means; and a thin coating, surrounding said string, of elastic material characterized by at least some internal trio-- I tion, whereby an appreciable damping reaction "said string, whereby an appreciable damping reaction of said translating means is simulated.

16. In an electronic piano including vibratable strings and mechanico-electro-acoustic translating apparatus influenced by but having a negligible damping reaction on said strings: a vibratile structure supporting and vibrationally coupled with said strings; and sound-absorptive material secured on at least portions of the surface of said structure, whereby an appreciable damping reaction of said translating means on said strings is simulated.

17. In an electronic piano including vibratable strings and means for translating electric scillations from their vibrations: a vibratile structure supporting and vibrationally coupled with said strings; an electro-acoustic translating device responsive to said oscillations and exerting asubstanti'al vibrational influence on said vibratile structure; and sound-absorptive material secured to at leastmortions of the surface of said structure, whereby said vibrational influence is substantially reduced.

18. In an electronic piano including vibratable strings, means for efiecting impulse excitation thereof, and mechanico-electro-acoustic translating means responsive to said strings: means for varying the strength of said excitation, and means, connected and operated concomitantly with said strength-varying means, for varying the efficiency of said translating means.

19. In'musical tone production from a damped tuned vibrator, the method of control of apparent tone damping rate whichcomprises effecting an impulse excitation of-the vibrator, efiecting a mechamco-electro-aco'ustic translation from the resulting vibrations of the vibrator, and controlling the strength of said excitation and the efiiciency of said translation in inverse relationship to each other.

20. In an electronic piano including vibratable strings and mechanico-electro-acoustic translating means responsive thereto: a terminally pivoted and upwardly biased pedal; and volume-control means, electrically connected with said translating means, mechanically connected with said pedal, and operated by depression of said pedal to finitely reduce the efliciency of said translating means.

21. In an electronic piano including vibratable strings and mechanico-electro-acoustic translating means responsive thereto: a terminally pivoted and upwardly biased pedal; a plurality of resistances; a plurality of contact means respectively connected with said resistances, and progressively responsive to depression of said pedal to progressively shunt said resistances across an electrical portion of said translating means.

22. In an electronic piano including vibratable strings, hammers movable to excite said strings, and mechanico-electro-acoustic t r a n s l'a tin 3 means responsive to said strings: a pedal; means connected with and operated by the pedal for reducing the range of movement of said hammers; and volume-control means, electrically connected with said translating means, mechanically connected with said pedal, and operated by operation of said pedal to finitely reduce the emeiency of said translation.

23. In an electronic pianoincluding vibratable strings, pickup electrode means in spaced rela tion thereto "nd forming a capacity therewith, means for c arging said capacity, and an electronic amplifier: an input resistance and an input condenser for said amplifier; a resistance for said charging means; an electrostatic shielding enclosure for said resistances and condenser; and sealing means surroundingsaid resistances -sociated therewith: means for shielding said sensitive portions comprising a substantially nonconductive member; a coating of appreciably conductive material carried by the surface of said member; and a metallic conductor interconnecting a plurality of intermediate portions of said coating.

25. In an electronic piano including vibratable tuned strings and an amplifier for string-vibration-representing oscillations: a vibratile system supporting and vibrationally coupled to said strings; an electro-acoustic translating device fed by said amplifier and exerting a substantial vibrational influence on said strings through said vibratile system; and mechanico-electric translating means feeding said amplifier, and having sensitive portions in spaced relationship to and responsive to said strings and carried by said vibratile system for vibrational influence by said electro-acoustic translating device jointly with said strings.

26. In an electronic piano including vibratable tuned strings and an amplifier for string-vibration-representing oscillations: a vibratile system supporting and vibrationally coupled to said strings; an electro-acoustic translating device fed by said amplifier and exerting through said vibratile system a composite vibrational influence on said strings and individual vibrational influences on the several strings; and mechanico-electric translating apparatus feeding said amplifier, and having sensitive portions in spaced relationship to and responsive to said strings and carried by said vibratile system for vibrational influence by said electro-acoustic translating device correspending with said composite string vibrational influence, said sensitive portions being so positioned longitudinally of said strings that they are substantially unresponsive to said individual string vibrational influences.

27. In a musical instrument including a vibrator and means for translating sound from the vibration thereof: the combination of an exciting system for said vibrator, including means for effecting excitation of said vibrator at different strengths; and means, controlled by said exciting system and inversely responsive to the strength of said excitation, for varying the efiiciency of said translating means.

BENJAMIN F. MIESSNER.

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