US2932231A - Tone generating apparatus - Google Patents

Description

April 12, 1960 B. F. MIESSNER TONE GENERATING APPARATUS Filed Nov. 29, 1955 INVENTOR. BENJAMIN F. MIESSNER M w United States Patent TONE GENERATING APPARATUS Benjamin F. Miessner, Harding Township, Morris County, N..I., assignor, by mesne assignments, to The Wurlitzer Company, Chicago, 111., a corporation of Ohio Application November 29, 1955, Serial No. 549,589

Claims. (Cl. 84-1.14)

This invention relates to tone generators, and more particularly to such generators for use in an electronic musical instrument and comprising fixed-free clamped reeds.

Fixed-free reeds are generally unsuited for use in an electronic musical instrument, particularly an instrument intended to produce piano tones, because of the normal inharmonic relationships between the various partial frequencies at which the reed vibrates when impulsively excited, as by percussion or plucking.

According to the present invention I employ an electrical system (comprising reed and pick-up) in which there are generated a series of partials harmonically related to the fundamental of the reed vibration, and with it I combine a mechanical system (comprising the reed and an exciting means therefor) by which there is substantially avoided the presence of any upper partials in the reed vibration itself.

It is an object of the invention to provide advantageous means and methods for creating, from the vibrations of a fixed-free reed, output tones having a rich development of upper partials harmonically related to the fundamental and substantially free of upper partials not so related.

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 had to the accompanying drawing, wherein the single figure is a side view of a fixed-free reed and percussive exciting means and pick-up therefor.

Reference being had to the drawing, the electrical system may be considered as comprising the reed (mounted and set into vibration as hereinafter described) and a pick-up therefor adapted in its action to generate a whole series of upper partials harmonically related to the fundamental frequency of the reed vibration. Such a pick-up may comprise a thin conductive element 13 (secured for example to insulating rail 14 as by screw 15) disposed in close spaced relationship to a peripheral portion (e.g., the free extremity) of the reed; the element 13 may for example lie in a plane parallel to that of the reed but preferably slightly displaced therefrom, and it may be abruptly swept past by the reed in each of the reeds higher-amplitude vibratory swings. Such a pick-up may be considered as highly non-linear, and the resulting generation of the harmonic series to be the result of its high non-linearity.

Specifically the illustrated pick-up is of the electrostatic type, whose capacity to the reed is oscillatorily varied by the reed vibration; and it will be understood that by suitable electrical circuitryeither D.C. polarizing, or highfrequency amplitude-modulating, or high-frequency frequency-modulating--connected to the reed and to the pick-up, the oscillatory capacity variations may be translated into electric oscillations (which, by suitable amplifying and electro-acoustic translating means, may be amplified and translated into sound). It is in such translation into electric oscillations that there is generated the series of harmonic upper partials mentioned above, such generation resulting from the structure above described.

The mechanical system may be considered as comprising the reed 10 extending from the rail or block 11 in which it is firmly secured (as by the screw 12), and an exciting action therefor which may be described as follows: A finger-operable conventional playing key 16 is pivotally mounted on a base 17, the key carrying an adjustable capstan 18 that is normally spaced from a felt pad 19 affixed to the lever arm 20. At one end this am is pivoted to the flange 21 which in turn is secured to rail 22 (as by screw 23), and at the other end this arm has secured thereto a hammer comprising a solid member 24 and, secured to that member, a reed-contacting member 25 hereinafter further described. Depression of the outer end of the playing key 16 of course imparts an arcuate movement to the lever arm 20, causing the member 25 to strike, and thus to excite, the reed.

In conventional percussive excitation devices for setting vibrators into decadent vibrations, the exciting device contacts the vibrator over only a small fraction of the vibrators length. In the case of a piano the felt-covered convex-shaped hammer head makes contact with the tensioned string over only a distance of approximately onequarter of an inch even for long strings and with maxi mum hammer velocity, and proportionately less for shorter strings and for lower hammer velocities; this is due to the radius of curvature of the hammer head and the relative hardness of the felt covering of the head. Similarly other percussive instruments such as bar chimes, xylophones, celeste, drums and the like are played with percussive hammers which contact the vibrator over a relatively minute segment of the vibrators length.

According to the present invention, I employ an exciting device which contacts thereed over a substantial fraction of the reeds length, and which is of a much higher degree of softness than is conventional. In this way the upper partials of the reed vibration are damped out during the brief interval of the hammers contact with the reed/and the reed is accordingly caused to vibrate with substantially no upper partials in its vibration, and thus substantially only at its fundamental frequency. This action of the mechanical system-which would be a useless one indeed if the output tone were to correspond becomes a highly useful one when combined with the electrical system of the nature and function above described.

A preferred form for the reed-contacting member 25 is a neoprene foam rubber pad between A and inch thick, the pad being cemented to the member 24 which may be made of wood. Foamed soft plastic materials, as well as very soft felts, may alternatively be used. It is of significance in achieving the most advantageous results that the hammer structure be so arranged and the included member 25 so formed that at the instant of contact of member 25 with the reed, its whole upper-shown surface uniformly engages the reed, so that its full action in damping out the upper partials of the reed vibration will take place.

The reed-contacting surface of the member 25 may have a length, along the reed, of between 10% and 30% of the reed length; widthwise it is preferably at least as wide as the reed. By reason of its long contact surface and its high yieldability, the member 25 acts more nearly like the conventional vibration dampers (tone-terminators) of a conventional piano than like the hammers of that instrument. It is of course to be understood that its action of damping out the upper partials of the reed vibration takes place during a temporary interval of contact with the reed-for the adjustment of the parts will, as usual, be such that even though the playing key remain depressed, the entire hammer will nevertheless drop back slightly after the member 25 has struck the reed, allowing the excited vibration of the reed (substantially pure fundamental, in view of the abovementioned damping out of the [tact with respect to a shorter reed. softnesses of the members 25 may be varied from the 7 upper partia-ls of the reed vibration.

upper partials) to take place without interference by the member 25. 1

The hammers mass and velocity are so proportioned that it remains in impulsive contact with the reed for only three fourths to one cycle of vibration at its fundamental frequency, whereby it imparts negligible damping for partial I. 6.27 times that of partial I, so that the hammer remains in contact with the reed during 6.27 times as many cycles as for partial I and therefore exerts a strong damping influence for partial II. Since partial II of the reed has a normal amplitude, for a hard hammer, of approximately six times that of partial I, the additional much higher damping and the much lower excitation of the soft hammer for partial II over partial I effectually eliminates partial II.

Partial III has a frequency which is 17.5 times and an amplitude which is about that of partial I. The hammer therefore remains in contact with the reed for 17.5 times as many cycles of vibration as for partial I and thus exerts a very strong damping influence for partial II.

For still higher numbered partial frequencies of the reed, the hammers damping influence is correspondingly still greater and the amplitude correspondingly lower.

Such damper-like hammers cannot be used in string pianos because they would so strongly damp out the higher numbered partials that the output tone would lack pianistic quality.

While the striking region on the reed may be anywhere between the fixed and the free end, I have found that the best striking point lies between the fixed end and the middle of the reed.

For the varying lengths of a full complement of reeds corresponding, say, to 6 or 7 octaves of a piano scale, the members 25 may all have a uniform length along the reeds. It is preferably, however, to vary that member length so as to provide a shorter absolute length of con- Further, the relative long (bass) to the short (treble) reeds. In the upper portion of the scale too soft a material (which will result in too long a period of contact with the reed) will cause some undesirable damping of the desired fundamental vibration of the reed; thus as a general proposition the softness of the member 25 may advantageously be graduated throughout the scale.

In, connection with this point it is pertinent that partial II of the reed vibration (the lowest of the upper partials), which is 6.27 times the fundamental in frequency, steadily rises in absolute frequency from the bass to the treble reeds. Thus (with ascending frequency) when a fundamental of LQOO cycles per second has been reached the accompanying partial II has a frequency of 6,270 c.p.s., which is well above the top fundamental frequency of a piano, and when a fundamental of 2,000 c.p.s. has been reached the accompanying partial II has a frequency of 12,540 c.p.s., which is beyond the audible output range of most amplifier-speaker systems. As to partial III, which is 17.5 times the fundamental frequency, it is readily seen that it reaches an absolute frequency of the order of 10,000 c.p.s. when the fundamentalfrequency is only some 570 c.p.s. For these reasons the softness and length requirements as to the member 25 become decreasingly important in the upper reaches of the scale.

It is the lower portion of the scale which requires the more exacting precautions as to the damping out of the In this region a very-soft material for the member 25, contacting the reed over approximately 20% of the reeds active length, damps out the upper vibration partials so effectively that the reed vibration is for all practical purposes purely sinusoidal. I have found by actual tests that there is not the slightest indication of transient dissonance (the most Partial II however, has a frequency which is prominent component of which may be expected to be the transient beat between partial II of the reed vibration, as tending to be translated by the pick-up, and the sixth partial of the Fourier series generated in the translation as above described), at and immediately after reed excitation (which is when such dissonance would be observed, if ever). On the other hand when a conventional hammer is used for the reed excitation, partial II is then excited in sufficient amplitude to produce a strong such dissonance, which the ear hears, inter alia, as a ragged or fuzzy modulation of the desired tone components in the initial portion of the tone-a characteristic, thoroughly undesirable, which is absent from conventional piano tones.

The actual softness of the members 25 best adapted for use in the important lower portions of the scale is of the order of that of the conventional damper felts employed in an ordinary piano (which are of course of an entirely different order of softness than, are the relatively hard hammers of that instrument).

While I have disclosed my invention in terms of, a particular embodiment thereof, it will be understood that unnecessary limitations are not thereby implied, since by the disclosure various modifications will be suggested to those skilled in the art. Such modifications will not necessarily constitute a departure from the scope of the invention, which I undertake to express in the appended claims.

This application is filed as a continuation-in-part of my co-pending application Serial No. 248,947, filed September 29, 1951, now abandoned.

I claim:

pulse exciting means for setting it into decadent free vibration, a mechanicoselectrical system consisting of a portion of the reed and a pick-up device in spaced rela-.

tion to and influenced by said portion for translating electric oscillations from the reed vibrations, means comprised in said mechanical system for substantially eliminating from the reed vibrations all of its own partial-frequency vibrations above the fundamental, and means comprised in said mechanico-electrical system for introducing into the oscillations translated from the fundamental reed vibrations a series of upper partials harmonically related thereto.

2. In combination in a musical instrument, a mechanical system comprising a fixed-free reed and single impulse exciting means for setting it into decadent free vibration, a mechanico-electrical system consisting of a portion 'of, the reed and a pick-up device in spaced relation to and influenced by said portion for translating electric oscilla tlons from the reed vibrations, means comprised in said mechanical system for substantially wholly damping out vibrations of the reed at all ofits own partial frequencies above the fundamental, and means comprised in said mechanico-electrical system for introducing into the oscillations translated from the fundamental reed vibrations a series of upper partials harmonically related thereto.

3. In combination in a musical instrument, a fixed-free reed, a hammer propellable to strike the reed, means comprised in the hammer and effective during its contact with the reed for substantially wholly damping out vibrations of the reed at all of its own partial frequencies above the fundamental, a mechanico-electrical system consisting of said reed and a pick-up device in spaced relation to and influenced by the reed for translating electric oscillations from the reed vibrations, and means comprised in said.

with the reed for substantially wholly damping out vibrations of the reed at all of its own partial frequencies above the fundamental, and means for translating from the fundamental reed vibrations electric oscillations containing a series of partials harmonically related to and including the fundamental, comprising an electric pick-up close to but out of the path of vibration of the reed and vibratorily passed by an edge portion of the reed, said pick-up being of an effective thickness, in the direction of reed vibration, smaller than the high-amplitude stroke of said portion of the reed.

5. In combination in a musical instrument, a n1echanical system comprising a fixed-free reed and single-impulse exciting means for setting it into decadent free vibration, means comprised in said mechanical system for substantially eliminating from the reed vibrations all of its own partial-frequency vibrations above the fundamental, and means for translating from the fundamental reed vibrations electric oscillations containing a series of partials harmonically related to and including the fundamental, comprising an electric pick-up close to but out of the path of vibration of the reed and vibratorily passed 6 by an edge portion of the reed, said pick-up being of an eifective thickness, in the direction of reed vibration, smaller than the high-amplitude stroke of said portion of the reed.

References Cited in the file of this patent UNITED STATES PATENTS

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