US2949053A - Tone generator - Google Patents

Description

Augl5, 1960 c. w. ANDERsEN 2,949,053

TONE GENERATOR Filed June 1, 19=4 2 sheets-sheet 1 aa a6 Aug. 16, 1960 c. w. ANDERsl-:N v 2,949,053

' TONEy GENERATOR Filed Jun 1, 1954 United States Patent O TONE GENERATOR Clifford W. Andersen, De Kalb, Ill., assignor to The Rudolph Wurlitzer Company, North Tonawanda, N.Y., a corporation of Ohio Filed June 1, 1954, Ser. No. 433,564

9 Claims. (Cl. 841.0`6)

This invention is concerned generally with key actuated percussive instruments, and more particularly with a portable electronic piano utilizing vibrating reeds as tone generators.

For many hundreds of years the piano and its historical predecessors have utilized vibrating strings as tone generators. These string tone generators are stretched under substantial tension, and are subject to gradual detuning due to stretching of the strings, loosening of the mechanism holding the strings, changes in size with temperature, changes in the supporting and associated structure due to temperature and atmospheric changes, and due to corrosion of the strings which changes their physical dimensions.

The bass strings of a piano are of considerable length and therefore require that a piano be a large size instrument. The aggregate tension f all of the strings of a piano typically may run on the order of eighteen tons. This requires a large and massive supporting structure, commonly made of cast iron or the like, and further requires an instrument of large size. The cast iron or other massive supporting structure leads to great weight in a piano, the smallest pianos weighing on the order of five hundred pounds, and grand pianos weighing as much as fifteen hundred pounds or more. The minimum length of bass strings is on the order of three to four feet, thus requiring a piano dimension of at least this much in the direction of the bass strings, and grand pianos may be as much as nine feet in length to accommodate the long bass strings.

The large size and weight of conventional pianos makes them unsuitable for use in many homes, and seriously crowds student practice rooms. Eiforts have been made to reduce the size and weights of pianos by utilizing sound generators other than tensioned strings, or by changing the dimensions of the strings. These eiorts generally have been unsuccessful. I have found that by suitably shaping and dimensioning a vibratile metallic reed, the reed can be struck by a hammer and utilized as an electrostatic generator which when suitably electronically amplified and transduced produces sounds practically indistinguishable from those of a conventional piano. Such a musical instrument is adapted for the use of earphones as transducers so that the pianist may listen to his own playing without disturbing others in the vicinity. Of course, for general use a loudspeaker would be used rather than earphones.

It is an object of this invention to provide a portable electronic piano utilizing a vibratile reed and corresponding pickup as an electrostatic tone generator wherein the reed and pickup are so correlated as to produce: a proper balance of fundamental and harmonics.

A further object of this invention is to provide an electronic piano utilizing vibratile reed tone generators wherein the reeds are provided with a mount which will not absorb the reed vibrations and thereby damp the reeds.

A further object of this invention is to provide a vibrating reed electronic piano in which the reeds are so formed,

l of earphone plugs.

52,949,053' Patented Aug. 16, 1960 ICC as to insure vibration from a predetermined point, whereby more accurately to control their vibrational characteristics.

A further object of this invention is to provide a vibrating reed tone generator electronic piano wherein the reeds are reduced to a minimum size.

Yet another object of this invention is to provide a vibrating reed electronic piano having a pickup cooperable with the reeds which is of economical and readily fabricated construction.

A further object of this invention is to provide a vibrating reed electronic piano having a pickup cooperable with the reeds which provides a very large change in capacitance, thereby increasing the volume of the output and masking random noises. y

Yetanother object of this invention is to provide, in an electronic piano having vibrating reed tone generators, a pickup cooperable with the reeds which is shaped to produce a proper graduation of tonal volume along the length of the instrument.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings wherein:

Fig. 1 is a perspective view of a piano constructed in accordance with the principles of my invention with parts broken away for clarity of illustration;

Fig. 2 is en enlarged cross sectional View through the piano taken substantially along the line 2 2 of Fig. l;

Fig. 3 is a fragmentary horizontal sectional view taken substantially along the line 3--3 in Fig. 2;

Fig. 4 is an enlarged cross sectional view taken along the line 4-4 of Fig. 3 and showing the piano action;

Fig. 5 is a perspective view showing the cooperation of the reeds and pickup;

Fig. 6 is a sectional view showing the cooperation of one of the bass reeds and pickup and is similar to the center portion of Fig. 4 on an enlarged scale;

Fig. 7 is a view similar to Fig. 6 showing a treble reed and its association with the pickup;

Fig. 8 is a diagram illustrating the type of electrical wave produced by one of the reeds and the pickup; and

Fig. 9 is a view similar to Fig. 6 showing a modified form of the pickup.

Reference first should be had to Figs. 1 and 2 for a general understanding of the piano. The piano is indicated generally at 10 and comprises a case 12 of generally rectangular conguration having parallel end walls 14 and 16, a bottom -18 and a top 20 parallel thereto, and a rear wall 292. The top 20 is of lesser depth than the bottom 18, and a cover Z4 is hingedly connected at 26 to the front edge of the top 20. The cover is provided with a depending flange 28 which abuts an upstanding front wall 30. When the cover is tilted back to the dashed line position shown in Fig. 2 it cooperates with a tray 32 to form a music rack. When it is closed, it is inclined downwardly over the keyboard shortly to -be described.

The front wall 30 and depending cover ilange 28 are provided with complementary fasteners 34 of conventional construction for holding the cover closed, and a handle 36 is provided on the front wall 30 for carrying the piano.

An electronic amplifier 38 of suitable design is mounted within the case Ifor amplifying the oscillations generated by the reeds and pickups as hereinafter will be set forth. A loudspeaker 40 is positioned in the cabinet lbeneath the opening 42 which is covered by a cover plate 44 having suitable sound transmitting slots 46 therein. A pair of jack-s 48 is mounted adjacent the right hand end of the shelf 32 as `shown in Fig. l for the receipt Whena plug is associated with one of the jacks, the sound is audible only through the earphones, while the sound is audible both through the speaker and through the earphones when the earphone plug is associated with the other jack.

The piano as heretofore described is of relatively small size, being on the order of three feet long and two feet in depth, the height being substantially less than one foot. The weight of the piano is well under one hundred pounds, and it .thus will be appreciated that the piano is readily portable and can be placed on la table or desk for operation. Alternatively, wrought iron legs Sii of the type currently popular may be attached to the underside iof the piano `case by any suitable means such as screws, it being understood lthat Ithese legs probably would be used only for semi-permanent installations.

The piano is provided with a base or support 52 preferably constructed of wood and lying along the bottom 18. A keyboard 54 extends across the front edge of this base or support and comprises a plurality of keys 56 as shown in Figs. yl-4. The keys are pivoted on a fulcrum rail 58 by means of the usual balance key pins 60, and are provided with Ithe usual guiding front key pins 62 and a limit stop 64 of felt or other suitable -material.

The inner end of each key is provided with a raised portion 66 having a capstan screw 68 (Fig. 4). The extreme inner end of each key further is provided with a shelf 70 having a pad 72 of `felt or other suitable material thereon.

A main rail 74 extends across the keyboard between a pair of supporting brackets 76 secured to the base or support 52 -by any `suitable means such as screws 78. Butt flanges 80 are spaced along the main rail 74- and pivotally support the butts 82 of a plurality of hammers generally designated by the numeral 84 and further including hammer shanks 86, and hammer heads 88 having strikers 90 of felt or other suitable material. The underside of each butt 82 is provided with a pad 92 of suitable material such as felt and is engaged by the corresponding capstan screw 68.

A spring rail 94 extends between the brackets 76, being mounted thereon by means of auxiliary brackets or blocks 96. A plurality of springs 98 is spaced along the spring rail 94, `and each spring corresponds to one of the hammers 84. The end of each 'spring 98 is curled over as at 100, and the curled over end is received in a groove or slot 101 in a forwardly projecting portion 102 of the `corresponding hammer butt 82. Each spring thus urges the pad 9'2 of its hammer butt against the corresponding capstan screw 68, and all of the hammer Shanks are urged up against a felt pad 104 on the bottom of a hammer rail 106 extending between corresponding top portions of the brackets 76.

A generally rectangular reed and pickup supporting frame 108 is provided in the piano forwardly of the piano actions just described. This frame comprises a pair of end pieces 1110 of heavy steel, a back piece or rail 112 likewise of heavy steel and welded to the end pieces 110 at right angles thereto, and a front piece or rail 114 which likewise is of heavy steel and is welded between the end pieces 110. The treble end piece is slightly shorter than the bass end piece, and the front rail `114 is not quite parallel to the back rail 112, but rather tapers toward the back rail from the bass end of the piano to the treble end due to the physical sizes of the reeds as hereinafter will be brought out. It will be appreciated that the mass of the supporting frame 110 precludes any vibration thereof which would tend to damp the reeds or otherwise to affect tone generation adversely. A pair of rubber blocks 116 is mounted on the base or support 52 substantially at opposite ends of the piano, and the end pieces 110 rest on these blocks, suitable screws 118 passing through said end pieces and said blocks and being threaded into the support or base 52 for holding down the frame.

The front frame rail 1214 is provided with a raised portion 1'20, and a plurality of vibratile metallic spring steel reeds 1212 is spaced along this raised portion, each reed being mounted by means of a cap screw 124 passing through a widened base portion 126 of the reed and threaded into the raised portion 12d of the front rail 114. The reeds 122 necessarily vary in physical size from a maximum `at the base end of the piano to a minimum at the treble end. Reference to Figs. 6 and 7 reveals 4the difference in sizes, a bass reed being indicated at 12217 in Fig. 7, and a treble reed being indicated at 122i in Fig. 7. The thickness of the bass reeds preferably is greater than that of the treble reeds to limit the amplitude of vibration, and the width also may be greater to limit undesirable lateral vibration. The reeds are undercut as illustrated at 128 in Figs. 6 and 7, preferably by grinding, so that the reeds will vibrate from the undercut or shoulder portion out toward their free ends. Accordingly, the position at which the reed bases 126 are clamped by the heads of the cap screws 124 is not critical. The undercut portion or shoulder of each reed further has been found to delay the decay of vibration in a desirable manner.

In order to avoid making the bass and some of the other reeds too large, lead weights 13) are provided on the outer ends of these reeds. This causes the weighted reeds to vibrate at a lower frequency than they would without the weights. The weights also provide inertia which acts to eliminate high frequency harsh transients or partials which otherwise would be generated upon striking of the reed, and which would lead to a non-pianolike tone. The lead weights also delay the decay of vibra- I tion in a highly desirable manner. In addition to the foregoing, the lead weights simplify tuning of the reeds, as such tuning can be done merely by adding a little extra lead, or by tiling some off. The lead weights preferably are tapered on their sides as indicated at 132 in Fig. 5, and at their ends as indicated at 134 in Figs. 4-6.

This tapering provides physical clearance so that there.

is substantially no danger of striking the pickup now to be described.

The pickup comprises a plastic member 135 having a shelf portion 136 projecting forwardly toward the reeds 122. The outer edge of the shelf portion is of generally comb-like construction having a plurality of extending fingers 138. The plastic pickup 135 is secured on top of the back frame rail 112 by means of a series of cap screws 140 having washers 142 beneath their heads, the cap screws passing through the plastic member 135 and being threaded into the back rail 112. The plastic pickup 135 and the reeds 122 are so mounted that the reeds are coplanar with the bottom surface of the shelf 136 with the outer ends of the reeds fitting in the spaces between the lingers 138. As may be seen in Fig. 5 it is preferable that two bass reeds iit in the space between two of the fingers 138; The treble reeds likewise could be arranged with two per space, but it is preferred that the treble reeds be arranged with only one between each pair of fingers, and it is contemplated that the bass reeds also could be arranged with only one reed between a pair of fingers. The importance of the coplanar relation of the reeds and the bottom of the shelf 136 will be apparent shortly.

The top tand bottom surfaces, las well as the projecting end surfaces, of the `shelf 136 of the pickup are provided with a conductive coating 144. This conductive coating preferably comprises metal which may be plated, sput-k tered, deposited, or otherwise placed on the plastic. Various techniques for providing such metal coatings are known in other tarts, for instance the `art of manufacture of printed electrical circuits. Silver has been yfound to be a preferable metal for such coating due to its excel lent conducting characteristics and `due to the use of coating silver onto an insulating base. The coating is suliciently thin that only a small amount of metal `is heeded, and the cost of silver therefore is not prohibitive. The reeds 122 all are grounded through the frame 1108, and the conductive coating 144 of the pickup is conuected tto the input of the lampliiier 38'. It will be evident that a capacity eld exists between .the reeds and the conductive coating on the pickup when a potential is :applied to the pickup. When each reed is struck by its corresponding hammer to set the reed into vibration, the capacity field varies to produce oscillations which result in piano tones when properly amplified and transduced.

The thickness of the shelf 136 varies from end to end of the pickup 135. The thickness of the shelf is greatest at the bass end of the piano, and decreases to a minimum 'at the treble end. The thickness is correlated with the swing of the corresponding reeds` so that when the reeds swing upward from their rest position (this being coplanar -with the bottom of the shelf as previously noted) the reeds never swing above the top surface of the shelf. The entire lower half cycle of reed swing is beneath the shelf. As a result, a change in capacity is produced as illustrated in Fig. 8. The median line 146 represents the capacity between a reed and the pickup when the reed is at rest. When the reed swings down below the shelf, the capacity between the reed and pickup coating 144 changes by a maximum amount as indicated at 148. This change in capacity has been indicated as approximately a sine -wave for simplification of representation, but it is to be understood that the wave actually closely corresponds with the sound wave `generated by a vibrating piano string, such sound wave being complex and comprising a fundamental and series of harmonics. When the reed swings upwardly above its rest position, the capacity changes only very slightly as indicated at l150, and for all practical purposes this change can be ignored. The fundamental thus generated is strong and bears the proper relation to the harmonics to represent a piano sound.

AIt will be `apparent that if a reed were centralized with respect to the shelf 136 and conductive coatings 144, there would be no oscillation lgenerated except when the reed swung Ibeyond the upper and lower surfaces of the shelf. Each time the reed would swing beyond the extremities of the shelf in such manner a strong second harmonic would be generated, and the resulting sound would have a distinctly guitar-like quality. Placement of the reeds in the slots between the iingers engenders a maximum change in capacity for a given reed swing, thereby giving rise Ato :a reasonably strong initial signal so that random noises will be inaudible.

It has been noted previously that the front rail 114 progressively approaches the back rail 1=12 from the bass to the treble end of the instrument. This is` necessary due to the progressive decrease in length of the reeds, and it will be apparent from Fig. 6 that in addition to the progressively ydecreasing spacing between the front and .rear rails the upper projection 120 on which the reeds are supported Ibecomes progressively wider to position the reeds progressively closer to the pickup 135, the pickup being mounted directly on top of the back rail. The length of the shelf 136 of the pickup, specifically the iingers 138, also decreases from the bass to the treble end so that not too high `a percentage o-f the length of a treble reed extends into the space between adjacent fingers. rlhis maintains a proper balance among the various tones -generated by the several reeds of the piano.

It has been noted heretofore that the large change in capacity engendered by projection of the reed ends between the projecting fingers of the pickup renders background or stray noise substantially inaudible. The use of the relatively small pickup area of the coating 144, as opposed to a metallic bar which would have to extend to the back edge of the pickup element 135, further helps to eliminate background or stray noise. Such pickup or stray noise further is minimized by a conductive shield 152 preferably of aluminum, covering the top and back of the pickup and mounted on the support or base 52 by means of outwardly directed ears 154 (Fig. 3) which may be held down by screws or other suitable fasteners. It is to be understood that the shield 152 is suitably grounded.

It is well known that the various strings of a piano have dilferent vibrational decay characteristics; more particularly stated, the bass strings tend to vibrate much longer than the treble strings. Accordingly, dampers are provided to arrest the vibration of piano strings when the corresponding keys are released. The reeds utilized in my electronic piano likewise have different vibrational `decay characteristics. Accordingly, I have provided dampers for the reeds, and these are illustrated in Fig. 4.

Each damper is indicated generally at 156, and includes a damper lever 158 pivotally connected at 160 to a damper lever iiange 162, the damper lever iianges being spaced along the lower front edge of the main rail 714. A damper wire 164 extends from each lever 158 toward the back of the piano, and extends upwardly to support a damper head 166 having a suitable reed engaging pad 168 of felt or other material. The butt end of each damper lever is provided with a hook-like or substantially L-shaped wire 170 extending upwardly and overlying the felt pad 72 on the corresponding key shelf 70. Whenever a key is depressed, the shelf thus raises the butt end of the damper lever, and accordingly retracts the pad 168 from the corresponding reed so that that reed is free to sound. At the same time, the capstan screw engages beneath the hammer butt 82 to start the hammer head in motion toward the corresponding reed. The pad 64 beneath the outer end of the key engages the base or support 52, to stop the key before the hammer head pad engages the corresponding reed, and inertia of the hammer continues the hammer in motion to effect such engagement. The hammer then rebounds and is returned by the spring 98 against the capstan screw which holds the hammer partially depressed until the key is released. The spring 98 then returns the hammer to its rest position as shown in Fig. 4, and the damper is returned to damping position by a spring (not shown) encircling the pivot i.

In order to play forte, it is necessary to release all of the dampers. This is effected by means of a rod 172 (Fig. 4) extending completely across the piano and journaled in a graphite impregnated felt bearing 174 in a generally semi-circular groove 176 extending across the base or support 52, this base or support being provided with a rectangular channel or groove 178 in the vicinity of the rod 172. A bar 180 is welded longitudinally along the rod 172 and engages beneath the butt'end of all of the damper levers 158. A foot pedal 182 (Fig. 1) is provided for the piano and is detachably connected thereto by push pull control 184 of the type comprising a ilexible wire movable within a tiexible sheath. This control is so connected to the rod 172, as fully illustrated in my copending application Ser. No. 433,563, tiled June 1 1954, now Patent No. 2,888,851, and entitled Piano Action, as to effect counterclockwise rotation of the rod 172 when the foot pedal is depressed. This causes the bar 180 to cam under the bottom edge of the lever 158 to pivot each damper to released or retracted position and to ho'ld it there until the foot pedal is released.

It now will be apparent that the structure disclosed in this case causes the reeds to vibrate at a predetermined point, thereby actually controlling their pitch frequency and precluding the necessity of critical positioning of the holding means. The massive support of the reeds precludes damping thereof by the support bar, and therefore the support does not aiiect the vibrational characteristics of the reeds yThe lead weights on the reeds enable the reeds generating the lower tones to be constructed with a reasonable physical size. These Iweights also act to absorb or 7 eliminate hard transients or partals which tend to be generated when the reed initially is` struck. Furthermore, the lead weights lead to improved decay characteristics and simplify initial tuning of the reeds in allowing the reeds to be tuned by the addition of a bit more lead or by tiling off a bit of lead.

The cooperative relationship of the reeds and pickups whereby the reeds are coplanar with one face of the pickup and wherein the pickup is of sufficient thickness so that the reed does not pass beyond or through the pickup in one direction of vibration is important in producing proper piano tones. The balance of fundamental and harmonics achieved in this manner is substantially indistinguishable from that of a conventional piano.

The metal coating of the plastic pickup bar has several important advantages over a metallic pickup bar. insulating problems are greatly simplified, and in fact are substantially eliminated. The mounting structure therefor is simplified. The cost of production is lo'wered, and there is a lesser area which could pick up stray signals or noise.

The projecting teeth of the pickup extending between the reeds effects a greater volume change due to the greater change in capacitance than is achieved by any means in the prior art with which l am familiar. The effect varies with the length of the projection, and for this reason the length of the projection varies across the keyboard in order to produce a proper tonal balance among the bass, treble, and intermediate tones. The tonal balance further can be obtained and is inuenced by whether there are one or two reeds between each pair of teeth or projections, and this is borne in mind in determining the length of the projections to obtain proper tonal balance.

A modified form of pickup is shown in Fig. 9. This pickup is functionally similar to that previously described, and similar numerals with the addition of the suffix a are utilized to identify similar parts. The pickup 135e: comprises a metal plate, preferably aluminum, with a forwardly projecting shelf 13611 having slots 138a in which the reeds 122a vibrate. An insulating slab 137 spaces the pickup 135a from the back bar or rail 11251, and a grommet 139 insulates each cap screw 140a and washer 142a from the pickup. The pickup 135e may comprise a plurality of pieces arranged end to end and electrically interconnected, or may be made in one piece.

The specific example of the invention herein shown and described is to be understood as being for illustrative purposes only. Various changes in structure will no doubt occur to those skilled in the art, and are to be understood as forming a part of my invention insofar as they fall within the spirit and scope of the appended claims.

I claim:

1. An electronic musical instrument comprising a common reed support, a plurality of reeds with bases fixed on said common support and with vibratile tongues projecting in the same direction therefrom in side-by-side substantially coplanar parallelism from said support, a plurality of hammers respectively percussively engageable with the tongues of said reeds respectively to set said reed tongues in decadent free vibration, a plurality of manually engageable keys respectively operatively connected to said hammers for selectively moving said hammers into such percussive engagement with said reed tongues, a pickup member of comb-like conguration having a plurality of parallel teeth and an intermediate plurality of slots each opening at one end, means mounting said pickup member in opposition to said reeds substantially in a common plane therewith with the reeds projecting into the slots between the teeth, the teeth on opposite sides of a reed extending substantially the same distance therealong, there being at least one reed tongue in each slot, and each reed being closely adjacent a pickup tooth along 8 a longitudinal edge of said reed, said pickup teeth terminating at free ends short of the reed biases, the hammers respectively percussively engaging the reed tongues between the reed bases and the free ends ofthe adjacent pickup teeth, said reeds and said pickup member comprising electrostatic tone generating means, means establishing an electric potential between said reeds and saidr pickup 1 wherein the plane of said reeds is displaced from the` median plane of the pickup teeth, and wherein saidreeds vibrate asymmetrically about such median plane.

3. An electronic musical instrument as set forth in claim 1 and further including common means electrically grounding said plurality of reeds.

4. An electronic musical instrument as set forth in claim 3 wherein the common grounding means comprises the common reed support, said support being electrically conductive, and said reeds being mounted directly on said support in physical and electrical engagement therewith.

5. An electronic musical instrument as set forth in claim 1 wherein the reed tongues and the teeth of the pickup are substantially rectangular in cross-section and in outline to provide a sharp tonal reaction'.

6. An electronic musical instrument as set forth in claim 1 wherein the reed support and the pickup member' support comprise parts of a common support which is massive relative to said reeds.

7. An electronic musical instrument as set forth in claim l wherein the pickup member comprises an insulating base and an electrically conductive coating on surfaces thereof.

8. An electronic musical instrument as set forth in claim 7 wherein the coating is on the top, bottom andA References Cited in the file of this patent UNITED STATES PATENTS 1,915,858 Miessner June 27, 1933 1,950,859 Midgley Mar. 13, 1.934 2,027,074 Miessner Ian. 7, 1936 2,212,292 Kock Aug. 20, 1940l 2,243,542 Taylor et al May 27, 1941 2,246,855 Miessner June 24, 1941 2,275,252 De Muth Mar. 3, 1942 2,368,842 Kealoha Feb. 6, 1945 2,414,886 Miessner Jan. 28, 1947 2,456,321 Rhodes Dec. 14, 1948 2,581,963 Langloys Ian. 8, 1952 2,601,185 Van Den Bergh June 17, 1952 2,614,171 Fein Oct. 14, 1952 2,653,306 Piety Sept. 22, 1953 2,656,755 Miessner Oct. 27, 1953 FOREIGN PATENTS 401,537 Great Britain Nov. 16, 1933 140,814 Australia Apr. 16, 1951 1,072,352 France Mar. 17, 1954

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