US 3418417 A
Description (OCR text may contain errors)
Dec. 24, 1968 I 1-1.5. RHODES ELECTRIC Pumo INCORPORATING MULTI-COMPONENT TUNING FORKS Filed June 24. 1965 2 Sheets-$heet l 7 INVENTOR. 7
llneow H. B. RHODES Dec. 24, 1968 ELECTRIC PIANO INCORPORATING MULTI-COMPONENT TUNING FORKS Filed Jun 24, 1965 2 Sheets-Sheet 2 INVENTOR. [40040 8. RHODES Anne/vans United States Patent Filed June 24, 1965, Ser. No. 466,534 7 Claims. (Cl. 84-115) This invention relates to an electric piano or the like, in which tone generators are provided in the form of multi-component tuning forks. In addition, the invention relates to an acoustically-integral connection between a cylindrical tine and an element with which such tine is associated in fixed-free relationship.
The present invention constitutes an improvement over the apparatus described and claimed in my prior Patent No. 2,972,922, issued Feb. 28, 1961, for Electrical Musical Instrument in the Nature of a Piano. Reference is hereby made to such patent for a description of the basic principles of operation of the present type of electric piano.
In the above-cited patent, the relatively rigid portions of the tuning forks (tone generators) were specifically described as being integral castings. In accordance with the present improvement, however, such relatively rigid portions are not integral castings but are instead formed of two or three interconnected elements. In addition, such elements are preferably formed of different materials. With such an arrangement, very important benefits are achieved including greatly reduced manufacturing costs, and reduced weight.
In electric pianos of the type described in the cited patent, and in certain other instruments, it is necessary to connect a cylindrical piano wire (or like cylindrical element) to a base member in a critical manner which will permit sustained vibration of the piano wire yet will not result in fatiguing and consequent breakage of such piano wire after long use. The general manner of connection may be referred to as fixed-free, because one end of the piano wire is fixed and the other end thereof is free to vibrate. It will be appreciated that if such one end of the wire is not rigidly attached to the base (in acoustically-integral relationship) there will be no true tuning fork operation, and there will be insufficient dwell or sustaining of the generated tone. It will also be understood that if the manner of mounting is such that breakage occurs after sustained periods of use, the necessity for repair and replacement of various components of the instrument will be greatly increased, and customer satisfaction will be drastically decreased.
In view of the above, it is an object of the present invention to provide a very light-weight, low-cost, multicomponent tuning fork adapted to serve as a tone generator in an electric piano (or the like) such as the one described in the above-cited patent.
An additional object is to provide an improved manner of mounting the base or fixed end of a cylindrical piano wire to the base region of the tuning fork, thereby achieving extremely important advantages including minimization of the possibility of breakage of the piano wire as the result of fatigue.
These and other objects will become apparent from the following detailed description taken in connection with the accompanying drawings in which:
FIGURE 1 is a vertical sectional view illustrating an electric piano incorporating a tuning-fork tone generator constructed in accordance with the present invention;
FIGURE 2 is an enlarged fragmentary view of the upper region of the showing of FIGURE 1, portions being broken away to illustrate the manner of connection of the various components of the tuning fork;
3,418,417 Patented Dec. 24, 1968 ice FIGURE 3 is an exploded view of the tuning fork;
FIGURE 4 is a fragmentary side elevational view illustrating the means for preventing relative rotation between the cross-member portion of the tuning fork and the relatively rigid leg thereof;
FIGURE 5 is a transverse sectional view on line 5-5 of FIGURE 2; and
FIGURE 6 is an enlarged fragmentary sectional view illustrating the inner end of the cylindrical piano wire (tine or reed) as mounted in the cross member of the tuning fork.
The present invention will be specifically described in connection with only one of the numerous keys (and related apparatus) in an electric piano, it being understood, however, that the various other keys are similar to the one described and illustrated herein, as set forth in the above-cited patent. Because the lower-pitched tone generators are preferably provided with counterweights at the outer ends of the relatively rigid inertia-bar portions thereof, the tone generator described herein is of such lower-pitched variety. It is emphasized, however, that the principles set forth hereinafter apply to all of the keys of the instrument.
Referring particularly to FIGURE 1, the apparatus may be seen to comprise a plurality of horizontal support elements 10, 11 and 12 which may be suitably mounted above a horizontal bottom element 13, for example by means of upwardly-extending end elements one of which is shown at 14. The various elements 10-14 support all of the components of the electrical musical instrument.
Mounted on the horizontal bottom element 13 is a piano key 16 having an outer portion 17 adapted to be struck (depressed) by the pianist. The key also has an inner portion 18 adapted to actuate a hammer element 19 which is pivoted at 21 to the support element 12. As described in detail in my co-pending patent application Ser. No. 225,917, filed Sept. 24, 1962, for a piano action, depression of the outer key portion 17 effects upward pivotal movement of hammer element 19 in a vertical plane until the hammer head 22 engages the tine or reed 23 of the associated tone generator 24. Furthermore, and also as described in such co-pending patent application, upward pivotal movement of the hammer effects downward movement of an associated damper means 25 until it no longer contacts the tine or reed 23.
Proceeding next to a detailed description of the multicomponent tuning-fork tone generator 24 of the invention, this comprises two legs one of which is formed by the above-indicated tine or reed 23 and the other of which is formed by an inertia bar element 26 having a much greater mass. Legs 23 and 26 are connected to each other, in acoustically-integral relationship, by means of a crossbar or cross-member 27. Such member 27 may be regarded as forming a portion of the base of a tuning fork because the two legs 23 and 26 extend therefrom and vibrate freely at their portions remote from the cross-member 27. The member forming inertia bar 26 extends for a substantial distance past the connection to cross-member 27, thereby providing an additional base portion 28 which serves as a means for mounting the tone generator to the aboveindicated support 10 or other suitable support.
As stated in detail in the cited Patent 2,972,922, the low-mass leg 23 and high-mass leg 26 of the tuning fork are tuned or resonated to each other. Although the lowmass leg 23 comprises a cylindrical section of piano wire or the like, the plane of vibration does not vary or rotate (as is normal with cylindrical tines) but instead extends through the high-mass leg 26. Fine tuning of the tone generator 24 is readily effected by merely sliding along the cylindrical wire 23 a helical compression spring 29 which is bent or twisted at the midportion thereof in order to insure against undesired movement.
The full advantages of the present type of tuning-fork tone generator are not achieved unless such tone generator is substantially isolated (vibrationally) from the support therefor, as by springs, felt or other resilient means. As described in detail in my co-pending patent application Ser. No. 421,148, filed Dec. 16, 1964, for Apparatus for Mounting a Tone Generator, and for Positioning the Same Relative to a Transducer, a particularly advantageous manner of mounting the tone generator 24 is achieved by extending screws or other fasteners 31 and 32 (FIGURE 2) into the support 10 through holes 33 and 34 in the tone generator portion 28. In addition, and very importantly, springs 36 and 37 are mounted around the screws 31 and 32 to maintain portion 2-8 spaced above support 10.
The described manner of mounting not only substan tially isolates the tone generator from the support 10, but also facilitates adjustment of the tone generator relative to a mechanical-electric transducer 38 which is disposed adjacent the free end of the wire 23. Such transducer is preferably of the electromagnetic variety, incorporating a permanent-magnet core 39, a coil 40, and support means 41 for adjustably connecting the core and coil to element 11 or other support. The coil '40 is suitably electrically connected to an amplifier 42 and loudspeaker 43 so that the vibrations of the tine 23 will be reproduced in the speaker as desired.
The high-mass leg 26 of the tuning-fork tone generator, including the base portion 28 which is an extension of such leg, is formed of a relatively light-weight (low specific gravity) metal such as extruded aluminum bar stock (e.g., No. 6061T6). For example, the bar stock may be substantially square in section, the dimension of each side of the square being inch. Rigidly mounted at the free end of the working or musical portion 26 of the bar 2628 (that is to say, the portion to the right of cross-member 2 7 as viewed in FIGURES 1 and 2) is a counterweight 45 which is preferably formed of a relatively heavy (high specific gravity) metal such as steel. Desirably, counterweight 45 is also formed of a section of bar stock, having the same cross-sectional size and shape as element 26.
-In order to rigidly secure the counterweight 45 to the free end of the leg or inertia bar 26, such elements are provided with corresponding cylindrical bores 46 and 47. A rivet 48 formed of a soft ductile metal, preferably aluminum, is then inserted through such bores 46 and 47 (in close-fitting relationship) and hammered against a suitable back-up element. This not only causes the inner end 49 (FIGURE 2) of the rivet to be upset, but also causes substantially the full length of the rivet to expand and thus lock with the cylindrical walls of bores 46 and 47. It follows that the counterweight 45 is locked to inertia bar 26, and cannot rotate relative thereto. It is to be understood that other methods of connection may be employed, for example screws, epoxy resin, etc.
The size of the counter-weight 45 may be reduced considerably, while still maintaining the correct tuned or resonated relationship to the tine 23 struck by the hammer, by recessing or indenting a portion of the leg 26 between the counterweight and the cross-member 27. Thus, a suitable recess or indentation 51 may be provided in the underside of the inertia bar 26.
It is emphasized that, for the higher-pitched notes, no countenweight 45 (and no recess 51) is employed. Instead, the inertia bar is relatively short as described in detail in the cited Patent No. 2,972,922.
The cross-member (or base component) 27, which constitutes an important element of the present invention, is shown as a rectangular metal bar which (for example) has the same cross-sectional shape and size as do bars 26 and 45. Stated more definitely, the cross-member 27 isa bar of relatively soft metal the surface region of which is caused to be relatively hard but less hard than the piano wire 23. Preferably, bar 27 is a ferrous metal or alloy, such as cold-rolled mild steel, which is case hardened to a substantial surface hardness less than that of the reed 23.
As an example, the mild steel forming cross-member 27 may be No. B1113, provided with a 0.005 inch case and drawn back to number 30 or 35 Rockwell hardness. The piano wire forming tine 23 is substantially harder, for example on the order of 5 6 Rock-well. The relative hardnesses are important, as will be described below, to the mounting of the tine or reed (piano wire) 23 in the crossmember 27.
Cross-member 27 may also be formed of a hardenable steel such as 'No. C1137, which has been tempered (heat treated) to about a 30 or 35 Rockwell hardness. Such hardness exists throughout the steel, yet the steel is surficiently tough to withstand the tine-insertion operation to be described hereinafter. Very importantly, a hardenable steel of the indicated type is also cheap, being much less expensive than (for example) spring steel.
In order to rigidly secure cross-member 27 to bar 26- 28, such member is provided at the upper end thereof with an internally-threaded axial bore 52 adapted to receive the lower shank region of a cap screw 53. The cap screw extends through a cylindrical bore 54 (FIGURE 3) which is formed in bar 26-28 parallel to bores 33, 34 and 46. Bore 54 separates the working or vibrating portion 26 of tuning fork from the base region 28 thereof.
As best shown in FIGURES 3 and 4, the upper end of the cross-member 27 is dished or recessed in such manner that the corners of such end are upwardly protuberant and sharp, forming teeth which are designated by the numeral 56. When the cap screw 53 is inserted through bore 54 and. into bore 52, and is threaded downwardly by a forceable threading operation, the teeth 56 (which are hard because of the above-indicated hardening operation) bite into the underside of the soft aluminum bar 26- 28 and effectively insure against any movement or rotation of the bar 27. Thus, and because the underside of the head of cap screw 53 is preferably serrated, the described assembly achieves, in a simple manner, a very elfective acoustically-integral connection between bar 27 and bar 26-28.
It will be appreciated that breakage of one or more tines, even after the piano has been in use for a year or more, is an extreme source of annoyance and customer dissatisfaction, particularly since replacement of tines has previously been a tedious process normally resulting in long delays. With the present invention, breakage of tines has been reduced to substantially zero. Furthermore, even if a tine should break, the problem of replacement is greatly minimized because it is merely necessary to remove the cap screw 53 and then replace an assembly 23-27 by reinserting such cap screw.
Referring particularly to FIGURE 8 of the cited Patent No. 2,972,922, there is illustrated what was previously regarded as the optimum manner of mounting a cylindrical tine to the base region of a tuning fork of the present general type. As is described in detail in such patent, the end of the tine is made frustoconical and is driven into a cylindrical bore in the base until there is close cont-act between the outer (surface) region of the base and a portion of the frustoconical surface. The tine was not driven into the bore sufliciently to cause the cylindrical region of the time to engage the cylindrical wall of the bore.
For many years, it was thought by the present inventor and his associates that the driving of the tine into the tuning fork base until the cylindrical tine surface engaged the cylindrical wall of the bore in the base would be undesirable for a number of reasons. In the first place, it was believed that such driving would eifect fracture of the rigid base, which was formed of cast iron or aluminum. In the second place, it was believed that such a degree of insertion of the tine would reduce the efiectiveness of the acoustically-integral relationship between the tine and base because there would then be no concentration of force at the outer (surface) region of the base. It is emphasized that to provide effective (long-dwell) vibration of the tine, with minimized damping action, there should be a very tight and close contact between the tine and the outer base region (the base region denoted generally by the reference numeral 29 in FIGURE 8 of Patent 2,972,922).
It was long believed that such manner of mounting the tine could not have any substantial deleterious effect upon the life of the tine, because the taper of the frustoconical surface was extremely slight (on the order of one degree as stated in the cited Patent 2,972,922 at column 4, line 38). Such slight taper provided such a minute reduction in the diameter of the tine that it was believed the tine life would not be adversely affected to any material extent.
According to the present invention, the small-diameter tine 23 is constructed in substantially the same manner as described in the cited patent, being a cylindrical piano wire having a frustoconical end portion 57 which is slightly tapered (for example, about one degree on each side as stated in the patent). It is to be understood that the degree of taper illustrated in the drawing is greatly exaggerated. The end portion of cross-member 27 remote from bar 26-28 is provided with a cylindrical bore 58 the size of which is so related to the diameter of the cylindrical main body of tine 23 that such main body may only be inserted in the bore 58 in a very tight force-fit relationship.
The tine or reed 23 is forced into bore 58 until the cylindrical surface of the tine engages the cylindrical wall of the bore. Because the core of cross-member 27 is formed of relatively soft material such as cold-rolled mild steel, or of a hardened steel, such forcing of the tine into the member 27 cannot effect breakage of such member. Because at least the outer region of bar 27 is hardened but is still less hard than the tine 23 itself, there will be a very close and tight contact between member 27 and tine 23 at the region 59 (FIGURE 6) adjacent the face of the member 27. This, as stated above, is important in causing the tine to vibrate effectively and with a long dwell, in the absence of undesired harmonics. Very importantly, there will be no stripping of the tine material as it is driven into the bore 58 because the tine is itself harder than even the hard region 59 of the member 27.
If the member 27 were not hard, the relationship shown in FIGURE 6 would not produce sufiicient dwell. This is because there would then be a minute (a fraction of 0.0001 inch) gap at region 59 which would cause a damping action.
The relative diameters of cylindrical elements 23 and 58 are critical. Element 23 should be substantially larger than bore 58, :by about 0.003 inch to about 0.006 inch. Thus, for example the diameter of bore 58 may be 0.070 inch, whereas that of tine 23 may be 0.075 inch.
The present construction greatly minimizes breakage of tines in response to fatigue stresses caused by long-continued vibration because there is no concentration of stresses adjacent the region 59. It has been discovered that even the minute reduction in diameter effected at the face (indicated at 29 in Patent 2,972,922) caused a stress concentration which tended to increase the possibility of breakage of the tine. In the present construction, on the other hand, bending and stresses are equally distributed along a very substantial length of tine, so that there is no stress concentration and no substantial tendency toward breakage.
In summary, the present invention has not only drastically reduced the weight and manufacturing costs of the tone generators 24 but has also substantially eliminated the problem of breakage of tines, even after long use. Furthermore, the present invention has eliminated the problem of breakage of the cross-member portions of the tuning forks during assembly. In addition, the invention has made it possible to replace assemblies comprising reeds 23 and cross-members 27 by merely removing and reinserting a cap screw 53.
The foregoing detailed description is to be clearly understood as given by way of illustration and example only, the spirit and scope of this invention being limited solely by the appended claims.
1. An electric piano, which comprises:
a piano action,
a mechanical-electrical transducer adapted to be utilized relative to the delivery of musical signals to a loudspeaker, and
a vibratory assembly comprising:
an elongated high-mass leg formed of metal,
an elongated flexible metal low-mass leg,
means to mount said high-mass leg on a support in cantilevered relationship therefrom,
a rigid metal connector element separate from said high-mass leg and having a transverse bore adjacent one end thereof,
said connector element being formed of metal which has been case hardened to make the surface region thereof hard in the vicinity of said transverse bore,
one end of said low-mass leg being inserted in press-fit relationship into said transverse bore whereby to cause said low-mass leg to be closely adjacent said case-hardened surface region of said connector element,
said low-mass leg having a hardness greater than the hardness of said rigid metal connector element,
means to connect said case-hardened connector element to said high-mass leg in acoustically integral relationship and in such manner that said low-mass leg is generally co-planar with said high-mass leg,
said low-mass leg being adjacent said transducer whereby vibrations of said low-mass leg in the common plane of said highmass and low-mass legs will generate a signal in said transducer,
said low-mass leg being disposed to be struck by the hammer portion of said piano action in the plane of said high-mass and low-mass legs whereby to vibrate in said plane.
2. The invention as claimed in claim 1, in which said case-hardened connector element has a surface hardness on the order of 30 to 35 Rockwell.
3. The invention as claimed in claim 1, in which said low-mass leg is a piano wire.
4. The invention as claimed in claim 3, in which said piano wire has a hardness on the order of 56 Rockwell.
5. The invention as claimed in claim 3, in which said case-hardened connector element has a surface hardness on the order of 30 to 35 Rockwell, and in which said piano wire has a hardness on the order of 56 Rockwell.
6. The invention as claimed in claim 1, in which said high-mass leg is not hardened.
7. An electric piano which comprises:
a piano action,
a mechanical-electrical transducer adapted to be utilized in the delivery of musical signals to a loudspeaker, and
a vibratory assembly comprising:
an elongated high-mass leg formed of metal, said high-mass leg having an aperture therethrough relatively adjacent but spaced from one end thereof,
an elongated flexible metal low-mass leg, said lowmass leg being harder than said high mass leg,
means to mount said one end of said high-mass leg on a support in such manner that said highmass leg is at least partially acoustically isolated from said support and also in such manner that said high-mass leg projects outwardly from said support in cantilevered relationship, and with said aperture clear at said support, a rigid metal connector element having an internally-threaded axial bore in one end thereof,
said connector element also having a transverse bore in the other end thereof and which receives one end of said low-mass leg in tight press-fit relationship, said connector element being less hard than said low-mass leg, the surface of said connector element being harder than said high-mass leg,
a screw extended through said aperture in said high-mass leg and tightly threaded into said axial bore in said connector element to secure said connector element to said high-mass leg in acoustically-integral relationship,
said connector element being so turned that said low-rnass leg is generally parallel to and co-planar with the cantilevered portion of said high-mass leg,
said low-mass leg being disposed adjacent said transducer whereby vibration of said lowmass leg will generate an electrical signal in said transducer,
said low-mass leg also being disposed to be struck by the hammer portion of said piano action in the plane of said high-mass and low-mass legs whereby to vibrate in said plane.
References Cited UNITED STATES PATENTS 8/1960 Anderson 84l.04 2/1961 Rhodes 841.l5 6/ 1962 Meissner 841.04 2/1963 Meissner 84-1.04 11/1965 Meissner 841.14
ARTHUR GAUSS, Primary Examiner.
H. A. DIXON, Assistant Examiner.