US2225195A - Apparatus for the production of music - Google Patents

Description

Dec. 17, 1940. B. F. MIESSNER 2,225,195

APPARATUS FOR THE PRODUCTION OP MUSIC Filed Sept. 13, 1958 IN VEN TOR:

Patented Dec. 17, 1940 UNITED STATES APPARATUS FOR THE PRODUCTION OF MUSIC BenJamin F. Miessncr, Millburn Township, Essex County, N. J., assignor to Miessner Inventions, 1110., Township of Mlllburn, N. 1., a corporation of New Jersey Application September 13, 1938, Serial No. 229,650

17 Claims.

This invention relates to the production of music, and more particularly to that production involving the mechanico-electro-acoustic translation of the vibrations of tuned vibrators. While not in all its aspects necessarily limited therechanico-electro-acoustlc translation dispenses with, or at least renders secondary, the requirement for a resonator (e. g., a soundboard) to effect direct mechanico-acoustic translation from the vibrators. But, over and above that direct translation from the vibrators, the resonator of conventional instruments has performed additional functions of considerable importance in determining the characteristics of the output tones. One of these functions is the vibrational intercoupllng of the vibrators; and it has been pointed out that, even though the resonator is to be eliminated or reduced in its radiating or translational effectiveness, intervibrator coupling may very advantageously be retained. An object of the instant invention is to provide a novel and improved means for coupling the vibrators together in instruments of the class described.

In stringed instruments the resonator is conventionally a vibratile support on which the strings bear, for example through a bridge. It is an object of the invention to provide a vibratile string support of particularly simple nature and of small radiating propensity.

Another important function of the resonato of conventional instruments has been to influence the vibrational modes of the vibrators and the amplitudes of their vibrations, by vibratory reaction between vibrator and resonator. Itis an object of my invention to provide an. improved vibrator-coupling or -supporting means which carries out this influence.

The nature of this influence'depends on the predominant natural frequencies of vibration of the resonator in its several portions respectively most closely associated with the several strings v or other vibrators. It is an object of this invention to relate the natural frequencies of the several portions of the vibrator-supporting or conpling means to each other, and to the vibrator frequencies, in anovel manner. for the production of improved output tones throughout a wide pitch range.

While the vibrator-supporting or -coupling' means according to my invention preferably has small sound-collecting propensities, yet under some circumstances with the output loudspeaker of the instrument near the vibrators there may still occur acoustic or conductive feed-back from the loudspeaker, which may have the effect of producing sustained oscillations or at least distortion. It is an object of my invention to provide improved means for neutralizing, or suppressing the effect of, this feed-back.

Other and allied objects will more fully appear 10 from the following description and the appended claims. r

In the description of my invention hereinafter set forth reference is had to the accompanying drawing, of which: I

Figure 1 is a front elevational view of an upright electronic piano in which my invention is. embodied, the front portion of the. casing and the keys, action, conventional pedals etc. as well as many of the strings and pick-up electrodes being omitted for the sake of better illustration, and certain of the electrical components being purely schematically shown;

Figure 2 is a vertical cross-sectional view taken along the line 2-2 of Figure 1;

Figure 3 is a vertical cross-sectional view taken along the line I3 of Figure 1: Figure 4 is a substantially horizontal crosssectionalview taken along the line 4-4 of Figure 1; 39

Figure 5 is a view generally similar to Figure 4 but illustrating certain modifications of my invention: and

Figure 6 is a vertical cross-sectional view takenalong the line 6-4 of Figure 5.

Reference being had to Figures 1 through 4, there will be seen a vertical metallic plate or frame I having upper portion 2 and lower portion 3, and vertical side portions 4 and intermediate vertical reinforcing bars 5 Joining the up- 40 per and lower portions. A forwardly extending flange 6 may be provided aroundthe periphery of the frame to facilitate its attachment to a casing for the instrument, which casing is indicated as 1. Thelower frame portion 3 may be progressively upwardly widened in its central and righthand portions, and in its lower rlghthand corner it may be provided with a triangular aperture' Io. Along the bottom edge of the upper frame portion 2 and along the top edge of the lower frame portion 3 may be provided the respective forwardly extending ledges 8 and 8.

Strings I I, all for example substantially parallef-and vertically disposed, are strung from hitch pins ll in the lower frame portion 3 across 66 its ledge 9, up to and across ledge 8 and to conventional tuning pins not herein necessary to show. Either one or more than one string may be employed for each note of the instrument, there having been illustrated by way of example one string for each of the bass (lefthand) notes and two strings for each of the treble (central and righthand) notes. The string or strings for each note are adapted to be struck a little below the ledge 8 by a respective hammer, as indicated by the hammer 12 in Figures 2 and 3, and (excepting permissibly for the very most treble notes) to be damped by a respective damper, as indi-- cated by the damper l3 in Figure 3; the hammers and dampers may be controlled by a conventional piano action not herein necessary to show. Just above the ledge 9 the strings pass over and bear lightly on a bridge 55, being secured thereto as by conventional bridge pins Hi; the active portions of the strings lie between the bridge i5 and the ledge 8, and the bridge thus forms a support for the strings at the lower extremities of their active portions. The strings are of course tuned to progressive. fundamental frequencies, extending for example over a range of approximately six or seven octaves.

In the embodiment of the invention illustrated in Figures 1 through 4 the bridge i5 is secured to is desirably of somewhat compliant rather than rigid material, and it may further be advantageously characterized by at least some internal damping; wood, such as spruce or maple, may be mentioned as suitable material, though no unnecessary limi-tation thereto is intended. In genera], the support for the bridge provided by the plate 16, or the support for the strings provided by that plate together with the bridge, will be recognized as a cantilever support; and it will be understood that. by virtue of its compliance it is a vibratile support, and so serves to couple the strings together vibrationally.

The plate I 6 may be extended upwardly beyond the bridge 16 sufficiently to serve as a support for one or more translating systems having sensitive portions in spaced relation to, and responsive to the vibrations oi, the strings. While any type of translating system may be employed,

I have particularly illustrated herein translating systems of the electrostatic type, whose sensitive portions are in the form of electrodes adjacent the strings. In the figures one translating system is shown as comprising a strip 20 of insulating material, such as a phenol-resin composi-tlon product, secured to and extending forwardly from the plate l6 a little above the bridge IS; 'a respective electrode 22 for the string or strings of each note, preferably in the form of a screw having its head behind the respective string or strings and passing through the strip 20 and through an oversize hole 22a in the plate I8; and a conductor 24 electrically interconnecting the several electrodes 22, for example behind the plate [6.

By virtue of its position, this translating sys-- tem is responsive to the vibrationsof portions of the strings quite near their lower extremities; additional translating systems responsive to the vibratlons of more upward string portions may of course be provided to make selectively available a variety of oscillation and tone harmonic structures. Such an additional translating system may also if desired be carried by the plate l6 above the first translating system, to which it may be similar; it has been shown as comprising the strip 2! of insulating material, the electrodes 23 passing therethrough, and the conductor 25 for the electrodes 23 seen at-the righthand end of the strip 2| in Figure 1.

The sets of electrodes 22 and 23 of course form with the strings small capacities which are Varied by string vibration, and the capacity variations are caused to produce corresponding electric oscillations by the impression of a high voltage across each of the capacities through a high resistance. Thus the metallic frame 5, with which the strings make contact, has been shown as electrically grounded (i. e., connected to a reference potential); and the conductors 24 and 25 have been shown connected to first extremities of respective high resistances 26 and 27, of which the second extremities are connected together and to ground through a relatively high voltage source S. If the source S be a D. C. source, simple vibration-representing oscillations will be produced across the resistances 26 and 21; while if the source S be a high-frequency (super-audible) A. C. source, high-frequency oscillations, representing string vibrations by modulations corresponding to those vibrations, will be produced across the resistances. The oscillations across the resistances may be applied through respective condensers 28 and 29 to separate input channels 30 and 3| of an amplifier system A, the amplifier system being operated to demodulate as well as to amplify if the high-frequency course S be employed. Electrostatic shielding may be sufficiently disposed about the sensitive portions of all the apparatus feeding into amplifier system A, in well understood manner; it has been partially indicated schematically in Figure 1 as H.

In the amplifier system A, amplitude and phase controls may be included for the separate input channels, to provide harmonic structure control in the manner disclosed in U. S. Patent No. 1,906,607; and common output channel controls 34 and 35, for example for frequency characteristic and volume control respectively, may also be included. The common output channel 36 of the amplifier system may be connected, as by conductors 31, to a loudspeaker or other electroacoustic translating device 38. By way of example this has been shown as an electro-dynamic loudspeaker, disposed within the frame aperture 3a above-mentioned, and secured to the lower frame portion 3 and to the righthand side frame portion 4 as by brackets 39. A baflle for the loudspeaker has been shown in Figure 2 as formed by a front member 40 of the instrument casing.

In the case of soundboards of acoustic pianos, the predominant natural frequency of vibration varies somewhat from point to point along the bridge-i. e., between the portions respectively most closely associated with the various fre quency strings. Although of restricted degree, this variation of predominant natural frequency is of the same direction as that of the string frequencies-e. g., it is an upward variation toward the righ-thand or treble extremity of the instrument. In order that the vibratory reactions between the strings and the cantilever string strings and the conventional soundboard, I may arrange the cantilever string support to have a progressively increasing predominant natural frequency in a rightward (treble-ward) direction.

In Figures 1 through 4 I have illustrated two dimensional variations either or both of which may be employed to effect the natural frequency variation abovementioned. One of these is the progressive increase in the thickness of the plate I6, taken in a rightward direction, this increase best appearing in Figure 4. The other dimensional variation is a progressive decrease of the overhang of the cantilever string support (i. e., of the dimension from the rigid spacing strip 11 to the bridge); this appears in Figures 1, 2 and 3, wherein it will be seen that in the lefthand (bass) portion the plate ll overhangs the frame portion 3 for a considerable distance between the strip l1 and the bridge, and that the strip I1 is shaped and mounted to progressively reduce this overhang, ultimately to a very small distance in the righthand (treble) portion. It will be understood that the degree of each of these variations, the mathematical progression according to which .each is carried out, and the range of the scale over which each extends, may be varied within wide limits without departure from the broadaspect of a substantial progressive variation of the predominant natural frequency of the support from point to point. It will also be understood that each of the dimensional variations abovementioned, as well as the combination of the two, constitutes a progressive variation of the compliance of the string-supporting or -coupling system, downwardly toward the treble extremity.

In the very top bass or bottom treble regions of good acoustic pianos (or in general in the neighborhood of 100 cycles) the predominant natural frequencies of the soundboard, as I have observed them at points along the bridge, appear .to be approximately similar to the fundamental frequencies of the respectively associated strings; this fact I believe to be significant in contributing to the emciency and pleasing tonal qualities obtained from those instruments in this scale region. But this approximate similarity appears to be limited to about a one-octave range; and the entire range of variation of the natural fre- .quency of the soundboard is typically from about 100 to about 500 cycles, or only a little more than two octaves. Accordingly for the very low base strings the predominant natural frequencies of the most closely associated soundboard portions stay materially higher than the fundamental string frequencies, whereas for the higher treble strings the predominant natural frequencies of the soundboard stay materially lower than the fundamental string frequencies. The mentioned condition in the low bass I believe to be significant in contributing to the poor fundamental and lower partial development in the string vibration, since beneficial resonant reactions between string and soundboard occur at upper partials of the string vibration; and the mentioned condition in the higher treble I believe to be significant in contributing to the relative smallness of string vibrational amplitude, since any resonant effect is largely lost and a poor impedance match is established between string and soundboard.

At least largely to cure these conditions I may extend the range of variation of predominant natural frequency of the string-supporting or I -coupling means upwardly well beyond 500 cycles and preferably well beyond 1,000 cycles (at the treble extremity) and downwardly well below 100 cycles (at the bass extremity) so that the range is one of at least three and preferably of more octaves; thereby I may readily extend the range of approximate similarity, between that predominant natural frequency and frequency of the associated strings, to at least three octaves and in cases even further, obtaining over a very substantial portion of the whole scale the advantages conventionally obtained in a very restricted region only.

bridge from the spacing strip I], to establish compliances which, with the effective mass values of the plate l6, bridge l5, translating system portions 2!, 22, 23, 24 (when these are mounted on the plate l6 as shown), etc., will produce the desired predominant natural vibrational frequencies at the several points along the bridge. It may be mentioned that since the presence of the strings in their normal positions and tensions influences the effective parameters of the system (as by continually applying a rearward force to plate l6, contributing at least slightly to the effective total mass, etc.), observations of predominant natural frequency at various points are desirably made with the strings in place and under normal tensions.

It will be understood that the proper absolute values of the thicknesses and overhangs at various points will depend not only on the degree and extent of the desired variation of predominant natural frequency of the string-coupling or -supporting means, but also on the characteristics of the material of which the plate I6 is made, the

effective masses abovementioned, etc.; these values are, however, readily determined by test for any given material and under any given set v of other conditions.

and phase characteristics of the amplifying means until the bridge most freely executes sustained vibrations--of which the fundamental frequency may be'taken as the predominant natural frequency of vibration at the point in question.

Over and above the advantages abovementioned, the closer similarity of predominant natural frequency of the string-supporting means and the fundamental string frequency in the higher treble region further tends to reduce the relative prominence of the thud or rap components customarily noticeable in the higher treble tones as an incident. of tone inception. This component is caused essentially by the transient vibration of the supporting means at the predominant natural frequency of its portion most closely associated with the struck string, which vibration is translated to a considerable extent by all the electrodes in this region. The raising of that natural frequency to approximate the string'frequency tends to cause this component to be better obscured by the pure tone component, both because of the frequency change in itself, and because of an amplitude decrease 75 of the first component and an amplitude increase of the second.

The cantilever support need not be in the form ofa continuous platesuch as It. It may alternatively, for example, be in the form of a plurality of individual supporting members supporting the bridge i5 at frequent intervals along its length; this has been illustrated in Figures 5 and 6 by the narrow individual supporting strips or members 19, each secured in its lower portion to the back of the frame portion 3 through the spacing strip ll of earlier figures and extending upwardly to have secured thereto the bridge l5 and, if desired, sufficiently further to support one or more translating systems (e. g., strips 20 and 22). It will be understood that the supporting members i 9 serve essentially as springs; and they may be appropriately stiff metallic springs, although wood or other material with appreciable internal damping may be substituted if desired. While their absolute values will be dependent among other things on the material employed, the

thicknesses and overhangs of the several mem-,

bers l8 may be chosen in the manner of and for the results effected by the progressive dimensioning of the plate It in the earlier embodiment.

Although the sound-radiating and -collecting surfaces of the vibratile support in the instruments above described are small, the close proximity of the loudspeaker 38 may occasion some undesirable acoustic feed-back to the support and strings; moreover slight feed-back by vibration conduction to' the-support and strings may occur through the frame i of the instrument. To counteract or neutralize these feed-backs I have shown in both embodiments a plurality of electro-mechanicai translating devices mounted to vibrationally influence the support, and electrically supplied with output oscillations from the amplifier appropriate to subject the support to a vibrating force substantially equal and opposite to the feed-back forces influencing the support. These electro-mechanicai translating devices may be of any desired form; by way of simple illustration I have shown them as polarized elec-- tromagnets 43, positioned behind various portions of the plate It (in Figures 1 through 4) or behind various ones of the vibratile supporting members It (in Figures 5 and 6), preferably opposite bridge l5. They may be substantially rigidly mounted, on relatively heavymetallic brackets 42 terminally secured to frame portion 3 as by appropriate ones of the bolts I8, and their poles may be very slightly spaced from the back surfaces of respective armatures ll secured against the back of plate I8 and preferably eleo-' trically grounded, or from the back surfaces of the respective supporting members I! (in Figures 5 and 6) when the latter are of magnetic material. They may be supplied with output oscillations from the amplifying system A, preferably through adjustable filter and phase-controlling networks 48 (serving to control phase progressively as well as in respect of reversal) autismplitude controls 48; these may be individual to the several devices for the obtainment of the most accurate neutralizing effects. With a small numher, or even one, of these devices with carefully regulated oscillation supply thereto, there may be neutralized very large feed-back forces from the loudspeaker l8-such for example as may occur to string-supporting systems of as large areaas conventional soundboards and the like.

While I prefer to associate feed-back neutralizing devices with the vibratile string-supporting system, as described above for the device 43, I may alternatively employ neutralizing devices in association with the strings themselves. In, United States Patent No. 1,929,031 to me I disclosed feed-back to the strings of a mechanicoelectro-acoustic instrument; but that feed-back was to all the strings, which latter were uncoupled from each other. I have found that in a coupled-string instrument of the class herein described I may efiiciently suppress feed-back arising through the coupling system by associating an electro-mechanicai translating device with a restricted number of strings only, such as the strings-of a single note. This I have illustrated .in Figures 1' and 4 by the electro-mechanical translating-device 48 secured, just above and infiuencing the strings of one note, on the bottom of a cross-member 49 between the frame members 5; this may be connected, through a filter and phase-controlling network 45 and amplitude control 46 as above described for devices 43, to the output of the amplifier system A. By proper se-, lection of the strings involved and of the control adjustments, this structure may be made to suppress quite troublesome feed-backs.

While I have disclosed my invention in terms of particular embodiments thereof, I do not intend any unnecessary limitations by virtue of the details of those embodiments, which are illustrative rather than comprehensive. The scope of my invention is expressed in the following claims, in many of which 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 a plurality of progressively tuned vibratable strings and mecha-nico-electro-acoustic means for translating string vibrations into sound: the combination of a frame comprising aapair of support members between which said strings are strung; and stringcoupling means comprising a bridge disposed adjacent one of said support members and engaged by said strings, and vibratile means having a portion secured to said one support member, extending therefrom in cantilever to support said bridge, and having at most a small extension beyond said bridge.

2. In an electronic piano having a plurality of progressively tuned vibratable strings and mechanico-electro-acoustic means for translating string vibrations into sound: the combination of a frame comprising a pair of support members between which said strings are strung; and string-coupling means comprising a bridge disposedadjacent one of said support members and engaged, at progressive points therealong, by said strings. and vibratile means having a portion secured to said one support member, extending therefrom in cantilever to support said bridge, and having at most a small extension beyond said bridge, said string-coupling means being characterized, at points along said bridge associated with progressively higher-frequency strings. by progressively higher predominant natural frequencies of vibration.

3. In an electronic piano having a plurality. of progressively tuned vibratable strings and mechanico-electroacoustic means for translating string vibrations into sound: the combination of aframe comprising a pair of support members between which said strings are strung; and string; coupling means comprising a bridge disposed adjacent one of said support members and engaged, at progressive points therealong, by said strings,

and vibratile means having a portion secured to said one support member, extending therefrom in cantilever to support said bridge, and having at most a small extension beyond said bridge, a

the distance of said bridge from said secured portion progressively decreasing toward the extremity of said bridge with which the higher-frequency strings are associated.

4. In an electronic piano having a plurality of progressively tuned vibratable strings and mechanico-electroacoustic means for translating ness of said cantilever-extending means progressively increasing .toward the extremity of said bridge with which the higher-frequency strings are associated. I I

5. In an electronic piano having a plurality of progressively tuned vibratable strings and mechanico-electro-acoustic means for translating string vibrations into sound: the combination of a frame in which said strings are strung; and string-coupling means comprising a bridge engaged, at progressive points therealong, by said strings, and vibratile means having a portion secured to said frame and extending therefrom in cantilever to support said bridge, the distance of said bridge from said secured portion progressively decreasing, and the thickness of said cantilever-extending means progressively increasing, toward the extremity of said bridge with which the higher-frequency strings are associated.

6. In an electronic piano having a plurality ofprogressively tuned vibratable strings and mechanico-electro-a-coustic means for translating string vibrations into sound: the combination of a frame comprising a pair of support members between which said strings are strung; and string-coupling means comprising a bridge disposed adjacent one of said support members and engaged, at progressive points therealong. by said strings, and vibratile means having a portion secured to said one support member, extending therefrom in cantileverto support said bridge,- and having at most a small extension beyond said bridge, said cantilever-extending means having a compliance progressively decreasing toward the extremity of said bridge with which the higherfrequency strings are associated.

7. In an electronic piano having mechanicaelectro-acoustic means for translating string vibrations into sound: the combination of a plurality of progressively tuned strings: and stringcoupling means comprising a bridge engaged, at progressive points therealong, by said strings, and vibratile means supporting said bridge, said string-coupling means being characterized, at points along said bridge engaged by strings tuned to fundamental frequencies above 500 cycles, by predominant natural frequencies of vibration in excess of 500 cycles.

8. In an electronic piano having mechanicaelectm-acoustic means for translating string vibrations into sound: the combinationof a plurality of progressively tuned strings; and stringcoupling means comprising a bridge engaged, at

' progressive points therealong, by said strings, and

vibratile means supporting said bridge, said string-coupling means being characterized, at points along said bridge engaged by strings tuned to fundamental frequencies above 1,000 cycles, by predominant natural frequencies of vibration in excess of 1,000 cycles.

9. In an electronic piano having mechanicoelectro-lacoustic means for translating string vibrations into sound: the combination of a plurality of progressively tuned strings; and stringcoupling means comprising a bridge engaged, at progressive points therealong, .by said, strings, and vibratile means supporting said bridge, said string-coupling means being characterized, at points along said bridge engaged by strings tuned to fundamental frequencies below 100 cycles, by predominant natural frequencies of vibration below 100 cycles.

10. In an electronic piano having mechanicaelectro-acoustic means for translating string vibrations into sound: the combination of a plurality of progressively tuned strings; and stringcoupling means comprising a bridge engaged, at progressive points therealong, by said strings, and vibratile means supporting said bridge, said string-coupling means being characterized, at points along said bridge engaged by strings tuned throughout a fundamental frequency range of at least three octaves, by predominant natural frequenciesof vibration approximating the fundamental frequencies of the strings respectively engaging those, points. 11. In an electronic piano having mechanicoelectro-acoustic means for translating string vibrations into sound: the combination of a plurality of progressively tuned strings; and stringooupling means comprising abridge engaged, at

progressive points therealong, by said strings, and vibratile means supporting said bridge, said string-coupling means being characterized, at progressive points along said bridge, by predominant natural frequencies of vibration varying through at least a three-octave range.

12; In an electronic piano having a plurality of progressively tuned vibratable strings and mechanico-electro-acoustic means for translating string vibrations into sound: the combination of a frame in which said strings are strung; and string-coupling means comprising a bridge engaged, at progressive polnts'therealong, by said strings, and a plurality of vibratile supports having portions secured to said frame and extending therefrom in cantilever to supportsaid bridge at progressive points therealong, said vibratile supports being of progressive compliances.

, 13. In a musical instrument having a plurality of tuned vibrators and mechanico-electric means for translating their vibrations into electric oscillations and an amplifier for said oscillations: the combination of vibratile means vibrationally coupled to all of said vibrators; electro-acoustic translating means'supplied with oscillations from lations of phase and amplitude to produce a vibrational influence of said apparatus on said vibratile means opposing said feed-back influence.

14. In a musical instrument having a plurality of tuned vibrators and mechanico-electric'means for translating their vibrations into electric oscillations and an amplifier for said oscillations: the combination of vibratile means vibrationally coupled to all of said vibrators; electro-acoustic translating means supplied with oscillations from said amplifier and having a vibrational feedback influence on said vibratile means and vibrators; and feed-back opposing means, comprising a plurality oi! electro-mechanical translating devices variously associated with said vibratile means, and means connected between said amplifier and said devices for supplying to said devices oscillations of phase and amplitude to produce a vibrational influence of said devices on said vi bratile means opposing said feed-back influence. 15. In a musical instrument having a plurality of tuned vibrators and mechanico-electric means for translating their vibrations into electric oscillations and an amplifier for said oscillations: the combination of vibratile means vibrationally coupled .to all of said vibrators; electro-acoustic translating means supplied with oscillations from said amplifier and having a vibrational feed-back influence on said vibratile means and vibrators; and feed-back opposing means, comprising electro-mechanical translating apparatus immediately associated-with said vibratile means, means for supplying oscillations from said amplifier to said apparatus, and means included in said supplying means for controlling the phase and amplitude of said last-mentioned oscillations.

'16. In a musical instrument having a plurality 1o! tuned vibrators and mechanico-electric 1 means for translating their vibrations into electric oscillations and an amplifier for said oscillations: the combination of vibratile means vibrationally coupled to all of said vibrators; electro-acoustic translating means supplied with oscillat-ions from said amplifier and having a .vibrational Ieed-baclg influence on said vibratile means and vibrators; and feed-back opposing means, comprising a plurality of electro-mechanical translating devices variously associated with said vibratile means, means for supplying oscillations from said amplifier to each .of said devices, and individual means included in said supplying means for controlling the phase and amplitude of the oscillations supplied to each device.

1'7. In a musical instrument having a plurality of progressively tuned vibrators and mechanico-electric means for translating their vibrations into electric oscillations and an amplifier for said oscillations: the combination of vibratile means vibrationally coupled to all of said vibrators; electro-acoustic translating means supplied with oscillations from said amplifier and having a vibrational feed-back influence on said vibratile means and vibrators; and feed-back opposing means, comprising electro-mechanical translating apparatus immediately associated with a restricted number only of said vibrators, means for supplying oscillations from said amplifier to said apparatus, and means included in said supplying means for controlling .the phase and amplitude of th oscillations supplied to said apparatus.

BENJAMIN F. MIESSNER.

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