US2772594A - Apparatus for producing chime tones - Google Patents

Description

P. H. ROWE APPARATUS FOR PRODUCING CHIME TONES 2 Sheets-Sheet 1 Filed March 28, 1952 6 Amp/[filer 1, 401. Eon E,

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Dec. 4, 1956 P. H. ROWE 2,772,594

APPARATUS FOR PRODUCING CHIME TONES Filed March 28,- 1952 2 Sheets-Sheet 2 mmmmmn F mmmmm .mmmmh 1 401. H; Home,

IN V EN TOR.

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United States Patent APPARATUS FOR PRODUCING CHIME TONES Paul Henry Rowe, Los Angeles, Calif., assignor to Maas- Rowe Electromusic Corporation, Los Angeles, Calif., a corporation of California Application March 28, 1952, Serial No. 279,352

2 Claims. (Cl. 841.11)

This invention relates to electrical musical instruments, and particularly to a device for adding harmonics to sonic currents.

In electrical musical instruments, presence of harmonics is necessary in order ot produce richness of tone. Structural alteration of complex wave generators (i. e., vibratable rods or tubes) can be made in order to control the harmonics generated, and to bring the partials of the wave generator into harmonic concord. One example of such an arrangement is described in United States Letters Patent NO. 2,588,295, issued in the name of Paul H. Rowe, and entitled Apparatus for Producing Chime Tones and Method of Tuning Musical Bars. It is an object of this invention to make it possible to add harmonies by an electrical system, thereby obviating the complex wave generator.

It is another object of this invention to utilize a saturable reactor in order to add harmonic content to a simple sonic current.

It is still another object of this invention to provide a system for electrically adding harmonic content to a sonic current, together with means for controlling the relative intensities of these harmonics.

It is still another object of this invention to provide an electrical system for producing complex wave forms in which there are no electron tubes, thereby providing a system that requires substantially no maintenance.

It is still another object of this invention to make it possible, in a simple manner, to add concordant harmonies to a wave form generator, such as a tuning fork.

It is still another object of this invention to provide a simple system for producing complex wave forms in which the relative intensities of the harmonics with respect to each other as well as to the fundamental may be easily controlled, whereby typical wave forms of Well known physical tone generators, such as piano strings, can be synthesized.

It is yet another object of this invention to provide a system of this character in which tuning of the several harmonics is automatically accomplished.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of several embodiments of the invention. For this purpose there are shown a few forms in the drawings accompanying and forming part of the present specification. These forms will now be described in detail, illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invetnion is best defined by the appended claims.

Referring to the drawings:

Figure l is a diagrammatic view of a system embodying the present invention;

' Fig. 2 is a diagrammatic view of one section of a modified form of this invention; and

' Figs. 3, 4, and 5 are views similar to Fig. 2 illustrating further modified forms of this invention.

2,772,594 Patented Dec. 4, 1956 In the form illustrated in Fig. 1, a plurality of pick- up coils 10, 11, and 12 are adapted to generate Wave forms corresponding to the actual vibrations of tone bars 13, 14, and 15. For this purpose, the tone bars are of magnetic material, and influence the pick-up coils respectively in a known manner. These bars are each capable of free vibrations that may be of a simple sine wave form corresponding to the fundamental frequency of a tone to be produced. Any appropriate means may be provided selectively to bring any one or more of these tone bars into vibration. Tone bars 13, 14, and 15 may be simple tuning forks, for instance. As many tone bars and corresponding pick-up coils are provided as there are notes in the instrument, but only three sets are illustrated in Fig. l as representative of a larger number.

A saturable core reactor comprising a toroidal core 17 and a coil 16 wound thereupon is connected to each pick-up coil in order to vary the induced wave form from a pure sine Wave. The core 17 may be a small Permalloy ring of continuous ribbon-like material that is readily saturable. Such a saturable core reactor adds odd harmonies of the fundamental when a pure sine wave current is applied to coil 16. The harmonics produced by the saturable core reactor are precisely multiples of the fundamental, and accordingly, no tuning problems are presented when this structure is used.

As the applied pure sine wave is increased in magnitude, saturation effects become greater, and accordingly, the relative harmonic content increased. Thus, if the current induced in the pick-up coils is small, very little distortion will result. However, if the current is large, the wave form as altered by the saturable core reactor will be greatly distorted, corresponding to the production of harmonics of considerable intensity relative to the fundamental.

A saturable reactor for each pick-up coil is provided. Each of the saturable reactor coils is connected in series with its associated pick-up coil. Reactor coil 16, for instance, is connected to pick-up coil 12 by a connection 18. Each series connected pick-up coil and reactor are connected across connections 19 and 20 that are common to the entire system. A variable resistor 21 completes the circuit, it being connected between the common connections 19 and 26.

Connections 19 and 20 also serve to connect an amplifier 22 across the variable resistor 21. The amplifier 22 may cooperate with sound channels, such as sound reproducers, or the like (not shown). t is apparent that the wave form produced by the combination of each pick-up coil 12 and saturable reactor coil 16 will be directly applied to the amplifier 22.

The variable resistor 21 controls the amplitude of the current through pick-up coil 12, saturable reactor coil 16, and the resistor 21 in series. Accordingly, as above described, the intensity of the odd harmonics relative to the fundamental are thereby controlled. Vibrating characteristics of physical tone generators can be thus synthesized by this control.

The variable resistor 21 controls all of the series connected saturable reactor coils and pick-up coils, since it completes the circuits therefor. Separate saturable reactor coils are required for each fundamental tone, since otherwise cross modulation would occur. However, only one resistor 21 is required, since it is a linear circuit element. Furthermore, it can be assumed that for each tone of a physical tone generator the characteristics of which are designed to be synthesized, the relative proportion of harmonics to the respective fundamentals is substantially constant. Accordingly, no loss of generality occurs by the use of only one control element, and a simple type of control is thereby permitted.

In the form illustrated in Fig. 1, variation in the value of the resistance of resistor 21 to control relative proportions of harmonics also causes variation in the effective composite signal sent to the amplifier 22. Thus, if it is assumed that the bar is vibrated with uniform amplitude whereby the pick-up coil 12 generates an electromotive force having a constant maximum amplitude, it is apparent that change in the value of resistor 21 shifts the relative voltage drops in the series circuit. Since the connections 19 and 20 are not shifted, the effective signal sent to the amplifier 22 upon such a change is also varied. Thus, if the current is reduced by increasing the value of resistor 21 to diminish harmonic content, the signal to the amplifier is increased, and increasing harmonic content reduces the signal to the amplifier 22.

Such a result may be undesirable from an artistic point of view. The artist may desire that the volume be increased as the harmonic content is increased. For this purpose, there is illustrated in Fig. 2 a tone generating system in which the volume of the signal is maintained constant, or increased, or decreased to a lesser extent as the relative harmonic content is increased.

The tone bar 15, pick-up coil 12, and saturable reactor coil 16 are provided as in Fig. 1. However, in this instance, the variable resistance comprises a pair of parallel connected elements 23 and 24. The resistance 24 is permanently connected across common connections 25 and 26. A movable arm 27 of insulation material carries a contact member 23 cooperable with the resistance 23 selectively connecting a portion of the resistance 23 across the lines 25 and 26. Accordingly, the current through the saturable reactor coil 16 is controlled by the value of resistance 23 and 24 in parallel. If the value of the resistor 23 is not beyond the order of magnitude of the resistor 24, it will have some effect upon the resistance of the resistors 23 and 24 in parallel. Movement of the contact member 28 to insert a smaller portion of the resistor 23 in the circuit causes the effective resistance of the resistors in parallel to be reduced. Accordingly, the current in the saturable reactor coil 16 is increased, and the amount of harmonic content is also increased. Moving the contact 28. to insert a greater resistance in the circuit correspondingly causes a reduction in harmonic content. a

The arm 27 carries. another contact member 29 in sulatedly mounted with respect to contact member 28. This member 29 cooperates with the resistor 24, and serves to tap off between a connection 30 and the common connection 26 an increasing voltage value as the resistance 23 is reduced. The connections 30 and 26 may energize the primary winding 31 of a transformer 32 coupling with an amplifier.

By this construction, and by properly choosingthe values of the resistances, and their respective characteristics, decreasing the relative harmonic content can be accomplished without decreasing the effective amplitude of the signal supplied to the amplifier. In fact, by proportioning the elements properly the amplitude of the signal applied'to the amplifier can be made actually to increase as the relative harmonic content increases.

In the forms just described primarily odd harmonics re produced, the strongest harmonic being the third.

For musical tones, a strong second harmonic content is.

often desirable. A substantial amount of even harmonics can be produced in asaturable reactor by introducing. a direct current component in addition to the pure sine wave. In Fig. 3, there is illustrated a device that will increase the proportion of second harmonics by the introduction of a direct current in the coil. For this purpose, a resistance 33 is connected across a direct current source, such as a battery 34. A movable contact member 35 cooperates with the resistor 33, and, serves to insert a direct current energization through the. coil 36. For this purpose, the. contact member connects, with one side of a pick-up coil 37 through a common connection 38; a connection 39 connects the other side of the pick-up coil to the saturable reactor coil 36. The other side of the coil 36 connects with a common connection 40. Between a connection 41 on the stationary side of the resistance 33, there is provided a variable resistance 42 similar to resistance 21 illustrated in Fig. l.

Adjustment of the resistance 42 controls not only the amplitude of the sine wave current supplied to the coil 36, but also the direct. current supplied to the coil 36, since the. resistance. 42 is in series with that circuit branch tapped by contact member 35'. Control of the second harmonic with respect to the third harmonic is effected by adjustment of the position of the contact member 35. Accordingly, resistance 42 controls the magnitude of both iarmonics with respect to thefundarnental, and contact member 35 controls primarily the relative amplitudes of the second and third harmonics.

Fig. 4 illustrates a system .for introducing a direct current component in saturable reactor coil 43 by utiliz ing the current generated in the pick-up coil 44. Thus, the system is similar to that illustrated in Fig. l with a variable resistor 45 and rectifier 46 connected in parallel and between the coil 43 and the pick-up 44. The rectifier 46 may be of the selenium or germanium type. By virtue of this arrangement, the rectifier branch supplies a direct current component, or a half wave on alternate half cycles, while the resistance branch 45 continuously supplies the sine wave to the coil 43. Adjustment of the variable resistor 45 controls the relative amplitudes. of the odd and even harmonics. Reducing the value of the resistance 45 corresponds to suppressing he second and other even harmonics with respect to the third and other odd harmonics. Adjustment of resistor 47, as before, controls generally the combined harmonic content with respect to the fundamental.

In the system in Fig. 4, addition of odd harmonics is accomplished not only by biasing the core to saturation by a direct current component, but also by the very nature of a half sine wave. Analysis of such a wave will show that it is inherently rich in odd harmonics.

in Fig. 5, a system is illustrated in which full wave rectification is achieved. With other conditions constant, a full wave rectification will produce odd harmonics with twice the magnitude as would be achieved with half wave rectification. In the present system, a pick-up coil 49 is provided with a central or neutral tap from which a common connection 50 leads. A rectifier 51 and variable resistor 52 connected in parallel lead from one side of the pick-up 49 and connect with the saturable reactor coil 53. Series connected resistor 54 and rectifier 55 connect with the other side of the pick-up 49 and the coil 53. The resistors 52 and 54 can be adjusted so that the coil 53 can receive substantially only rectified current, and the second harmonic is large in comparison with the fundamental.

In the form of Fig. 5, the second harmonic is due primarily to the full wave rectification. The coil 53 having a saturable core '56 serves to add other harmonics. Resistor 57 as before serves to control. the harmonic content generally.

The inventor claims:

1. In an electrical musical instrument: a plurality of parallel circuits, each including in series, means for producing sonic impulses, a saturable reactor energized by said means for adding harmonics to said impulses; a parallel connected rectifier and first variable impedance means, and a second variable impedance means; a common impedance in series with all of the parallel circuits; and means cooperating with said common impedance for translating said impulses to sound.

21., In an electrical musical instrument: a plurality of parallel circuits, each including. in series means for producingsonic impulses, a saturable reactor energized. by said means for adding harmonics to said impulses; the

circuit having a pair of branches one branch including a first rectifier utilizing a portion of the impulse produced by said means, and another branch including in parallel a rectifier and an impedance element and utilizing another portion of the impulse produced by said means; a common impedance in series with all of the parallel circuits; and means cooperating with said common impedances for translating said impulses to sound.

Fichandler Oct. 23, 1934 Vierling Jan. 7, 1936 6 Wrathall May 7, 1938 Williams Jan. 30, 1939 McCreary July 27, 1948 McCreary Nov. 30, 1948 Rowe Mar. 4, 1952 McMahon June 17, 1952 OTHER REFERENCES Magnetic Amplifiers, by McClure, Westinghouse 10 Engineer, vol. 10, issue 5, pp. 201-205, September 1950.

The Variation in High-Frequency Resistance and Permeability of Ferromagnetic Materials Due to a Superimposed Magnetic Field, by Webb, 1. R. B, vol. 26, No. 4, April 1938, pp. 439-440.

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