US1689524A - Electromagnetic pick-up apparatus - Google Patents

Description

' Oct. 30, 1928. 1,689,524

P. R. FORTIN ELECTROMAGNETIC PICK-UP APPARATUS Original Filed July 21, 1924 lnVenb or- 2 aul -Fl. For-tin,

by %M His AGbor'ney.

Patented Oct. 30, 1928. e

U N I T E D S T A T E PAUL B. FOBTIN, OF

c 1,689,524 PATENT OFFICE.

SCHENECTADY, NEW YORK, ASSIGNOB/ '10 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTROMAGNETIC PICK-UP APPARATUS.

Application filed Ju1y 21,"1924, Serial No. 727,142. Renewed May 4, 1926.

produced by the violin, cello, and wind instruments are transmitted with comparative fidelity by the ordinary. type of microphone,

the same is not true of musical instruments of the percussion type, such as the piano. Thus, when the music of an instrument of the last mentioned type is picked up by 'a microphone placed in proximitv thereto and transmitted it is found that the tone obtained at the receiving end is far inferior to the original, the reproduction being in the nature of a tinkling or jingling? sound instead of the deep sustained note desired by the artist and characteristic of a fine piano. Furthermore, owing to imperfections inherent in present day radio circuits considerable distortion is suffered by the music during the transmission and reproduction processes so that these factors also contribute to the poor quality of the emitted product. Aside from mechanical and electrical imperfections a further disadvantage of the microphone system of picking up piano music resides in the fact that a microphone is unusually sensitive and subject to socalled room noises such as those caused by gusts of air, the rustling of garments and of papers used by the artists. Such noisescause the microphone to transmit so-called hissing sounds.

Attempts have been made to grade or regulate pianos to overcome some of the above mentioned difliculties on the theory that suitable modification of the values of the treble, bass and middle register with respect to each other would admit of a better microphonic transmission. Thus, in view-of the fact that f present-day loud-speakers and telephonic reproducing instruments in general tend to subdue the sounds of lower frequencies from approximately middle C on the piano down 5 it is necessary to use a piano in which the lower section has been made to sound 'several times as loud as the treble. Attempts to grade pianos in this manner has not been attended With any appreciable success particularly in view of the fact that inasmuch as the music as heard by the musician at the keyboard is distorted, the artist, even though convinced that the radio audience is getting perfect tones, cannot do his best work on an instrument which is non-responsive to his touch.

Another disadvantage attending the use of a microphone resides in the difiiculty of obtaining and maintaining a proper transmittingbalance between a plurality of musical instruments and soloists no matter how carefully arranged they may be with respect to the position of the microphone. There is always a tendency' for the soloist to drown out the instrumental accompaniment, particularly during the occurrence of loud phrases thus causing the vocal selection to monopolize the microphone. The only remedy consists in shifting the positions of the artists and instruments with respect to each other, which is, however, an obviously impractical expedient.

One of the objects of my invention is to provide a device which may be attached directly to some vibrating element of a musical instrument such as the sounding board or bridge of a piano and which will permit transmission of the music of the instrument either to a radio circuit for broadcasting purposes or to a reproducing or recording instrument of suitable type such as a loud speaker or phonograph record cutter without appreciable deterioration in quality.

Another object of my invention is to devise means for grading the picked-up music by merely regulating the current generated thereby and to efiect such regulation at a point remote to the studio so as to obviate, first, the necessity of grading the piano itself and secondly, the necessity of shifting the positions of the artists and instruments during a selection.

A still further object of my invention is to devise means by which both piano music and" vocal selections may be transmitted or recorded simultaneously over one circuit without the undesired predominance of either type of sound in the reproduced music.

a With these objects in view the invention consists substantially in the relation of 'elements, interdependent action of the same, and

associated circuit arrangement hereinafter more fully set forth as illustrated in the accompanying drawing and pointed out in the appended claims.

In the drawing,

Figure 1 shows a front View of a pick-up device constructed and applied in accordance with my invention.

Figure 2 is a side view, showing the disposition of the device upon the sounding board of a musical instrument.

Figure 3 illustrates a circuit arranged for amplifying the electrical output of the device or of a plurality of such devices for radio broadcasting, recording, or analogous purposes. It also shows a microphone circuit adapted for use in combination with the electrical circuit of the electromagnetic pickup devices.

The pick-up device shown in Figures 1 and 2 comprises essentially a dynamo or generator capable of producing current impulses. Referring to the specific construction of the instrument, 1 designates a magnet which should be preferably a horse-shoe or meter type of permanent magnet although an electromagnet of suitable design may be used in lieu thereof. The magnet is provided with pole pieces 31 and 32 attached to the magnet frame by screws 35.

In order to secure a symmetrical unitary structure and to facilitate the attachment of bearings and associated elements which otherwise would be difficult to secure to the hardened steel magnet frame, the air gaps at the top and bottom of the pole pieces are capped by bridges of non-magnetic material 33 retained in place by screws (not shown). As sociated with the upper bridge are cradles 34 also of non-magnetic m aterlal adapted to carry pivot screws 3 and 4 between which a coil of wire or simple form of armature 2 is disposed so as to be in inductive proximity to the magnetic pole pieces and capable of cutting the lines of force of the magnetic field. This coil may be of any suitable construction.

The magnet 1 is mounted upon a framework 5 having a vise-like clamping arrangement comprisin jaw cheeks 6 and 7 and screws 8 locked y nuts 9 by means of which system the body of the instrument may be disposed upon a relatively non-vibrating portion of the piano such as the rib-frame 1O of the casting supporting the sounding board 11, thus leaving the coil free to be connected with some actively vibrating element of the musical instrument. Such connection is offected by means of a stylus 13 which is carried by a lever 12 attached in turn to coil 2. The stylus is caused to rest upon the most actively vibrating portion of the piano such as the sounding board or, preferably, some element integral therewith such as the bridge inasmuch as the latter takes up more of the resultant sound than the former. For purposes of illustration and to avoid complication the bridge and sounding board may be represented as a single structure.

Associated with the stylus carrier 12 are adjusting screws 14; which may be used for causing the stylus to bite into the vibrating element of the musical instrument to the proper extent in order to insure transmission of the vibrations to the coil. A spring member 15 is used to cause the armature coil to a malntain its relative posltlon 1n the magnetic field. The action of spring 15 is aided somewhat by a rubber bumper 16 whose primary function, however, is to dampen the natural period of vibration or frequency of the spring arm, stylus, and other metal parts associated therewith, so as to prevent the occurrence of beats and other undesired sounds. The ends of the armature coil are led off by conductors 36 to binding posts 17, 18 located upon the magnet retaining frame 5 and suitably insulated therefrom as at 19 and from which posts connection may be made to suitable broadcasting, recording or reproducing instruments.

The instrument described above thus constitutes a unit which may be attached and detached at will. A plurality of such units may be distributed at various points on the sounding board of the piano. Thus, one may be disposed on the bass, one on the middle register and one on the extreme treble so that each tone field of the piano-is covered. The ordinary use of the piano is not interfered with by the presence of the device, but, of course, if desired, the pick-u may be removed at an time. It is to he understood that the deslgn of the clamp by means of which the pick-up is retained in place upon the musical instrument may be varied from that hereinbefore described and that the shape of the magnet and general configuration of the electromagnetic generator may be changed in order to. permit adaptation to various types of pianos, such as grand and upright and to other musical instruments all without departing from the scope of the invention.

The operation of thepick-up device of my invention is as follows: When the piano is played the vibrations of the sounding board are transmitted to the coil of the pick-up device through the intermediary of the stylus and lever system, thus causing a similar vi-. bration of the coil. This vibration of the coil in the field of the magnet produces a pulsating current which may be regarded as an electrical reproduction of the vibrations of the sounding board. The pulsating current so obtained may be amplified and transmitted to a distance for reproducing the musical sounds in a loud speaker of suitable design or it may be employed for radio broad-. casting purposes. The current may also be caused to actuate apparatus adapted to produce reproducible sound records such as those used on phonographs, the telegraphon'e and the like.

The method of using the pick-up device of the invention is-diagrammatically indicated in Figure 3 which shows a suitable circuit for amplifying the current obtained from such a device. Here, by way of illustration, two pick-up devices are used, one represented by the numeral 20 being disposed in the treble tone field of the piano and the other, 21, in the bass. It is to be understood that another pick-up niay be placed in the middle register and that if deemed advisable a plurality of pick-up devices constructed substantially as hereinbefore described may be positioned at different points in each or any tone field of the instrument Without departure from the scope of the invention. In the circuit illustrated the pick-up devices 20 and 21 are shunted respectively with rheostats 22 and 23 for regulating their individual outputs while another rheostat 24 is furnished for adjusting the joint output. The individual outputs of the pick-up devices 20 and 21 may also be regulated by providing their magnets with variable magnetic shunts.

The output of the pick-up devices is fed into an amplifying circuit. A resistance coupled amplifier circuit is shown in Figure 3, although, of course, any suitable circuit may be used. The circuit comprises input transformer 25 which is associated with therinput circuit of the first amplifying space current device 26 from which current is supplied successively to the remaining space current devices also indicated by 26. A. potentiometer 51 is provided for varying the grid bias on the first device. The cathodes of the space current devices 26 are provided with regulating rheostats 28 while cathode and plate current sources are indicated at 37. The circuit arrangement further includes coupling condensers 27, grid leak resistances 30 and coupling resistances 29. a The output of transformer 49 may be led to any desired type of recording or reproducing instrument 50 or it may be used directl for modulating high frequency currents or broadcasting purposes.

When it is desired to transmit or record vocal selections accompanied by piano music the electromagnetic pick-up devices of the invention may be used in combination with the ordinary microphone pick-up so that each category of sound may be picked up individually with exceptional purity and the combined output of all of the pick-ups brought together in a single circuit for recording or for broadcasting by ether waves. Such an arrangement is also shown in Figure 3 where the circuit of microphone 38 is arranged in such a manner as to be readily associated with the electrical circuit of the electromagnetic pick-updevices. The microup circuit from the electromagnetic pick-up circuit. at any time.

It is obvious that by the arrangement shown one is able to accomplish the equivalent of shifting the relative positions ofthe artists with respect to each other and with the piano in the studio during the performance. Themusic and solo will thus be balanced without disturbing the musician, as would otherwise necessarily result when it is foundimperative to shift the microphones around the piano. Furthermore, the respective outputs of the treble, middle register, bass and even of the microphone may be balanced and regulated electrically in the broadcasting orrecording instrument room without the necessity of handling the pick-up .devices themselves.

It will be appreciated that by means of the pickup device of the invention only the musical sounds produced by the sounding board of the piano will be transmitted since the hereinbefore mentioned room noises will not be able to affect the oscillating coil of the pick-up device to the same extentthat they are capable of influencing a microphone. What I claim as new and desire to secure by Letters Patent of the United States, is

1. In an electromagnetic pick-up device, the combination of a magnet adapted to be disposed in proximity to the sounding board of a musical instrument, an armature pivotally mounted in the field of said magnet, lever means adapted to transmit the vibrations of said sounding board to said armature to cause said armature to generate a pulsating current, said means comprising a stylus adapted to make contact with said sounding board and a lever connecting said stylus with said armature, resilient'means for maintaining the armature in the field of the magnet and damping means for suppressing the natural frequency of vibration of said lever field, and lever means adapted to make 0011- tact with the sounding board for transmitting the vibrations of said sounding board to saidcoil to produce a pulsating current in said coil proportional to the amplitude of vibration of said sounding board.

. vibration of each tone field of said board.

4. In a pick-up system, the combination of a percussive musical instrument having a soundin board divided into a plurality of tone fiel s, a magnet disposed in proximity to each of said tone fields, an armature pivotally disposed within the field ofeach of said magnets, lever means for conducting the vibrations of said tone fields to said armatures to generate current'impulses, and circuit means for combining and amplifying said current impulses.

5. In combination, a sound .producer having a relatively non-vibratory portion and a vibratory member, and a sound pick-up device therefor comprising a generator having a magnet fixed to said non-vibratory portion and a movable armature in the field of the magnet and a mechanical connection between said armature and said vibratory member whereby the generator is actuated solely by the vibratory movements of said member.

6. In combination, a sound producing instrument comprising a frame and a sounding board having a plurality of tone fields, a plurality of current generators each comprising a fixed part secured to said frame and a movable part, said movable parts being operatively connected with the sounding board in the respective tone fields, and means for adjusting the relative values of the currents produced by the several generators.

7. In combination, a musical instrument comprising a frame and a sounding board having a plurality of tone fields, a plurality of current generators each comprising a magnet secured to the frame and a movable coil arranged in the-field of the magnet, means connecting the coils with the sounding board in the respective tone fields, means for sepa rately varying the currents produced by each of the generators, and means for combining the generated currents in a single circuit.

In witness whereof, I have hereunto set my hand this 19th. day of July, 1924.

PAUL R. FORTIN.

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