US2487420A - Electroacoustical musical instrument - Google Patents

Description

Nov. 8, 1949 c. c. BROWN 2,487,420

ELECTROACOUSTICAL MUSICAL INSTRUMENT Filed Feb. 10, 1947 2 Sheets-Sheet 1 Fig. i.

I )1 w nter Charles C. Brown By 2mm Nov. 8, 1949 c. c. BROWN 2,487,420

ELECTROACOUSTICAL MUS ICAL INSTRUMENT Filed Feb. 10, 1947 2 Sheets-Sheet 2 I11 vellto r V Charles C. Brown 60 Fig. 5.

II2 y Patented Nov. 8, 1949 ELECTROACOUSTICAL MUSICAL INSTRUMENT Charles C. Brown, Los Angeles, Calif.

Application February 10, 1947, Serial No. 727,507

6 Claims.

This invention relates to electro-acoustical musical instruments of the piano or organ type provided with a keyboard on which the keys are operated or played in the customary fashion, but in which the tones are produced electro-acoustically.

It is the main object of this invention to provide as compact an instrument as possible, which may be folded for transport and may be carried by the operator himself, while presenting the appearance and giving the performance of an ordinary piano.

It is a further object of the invention to substantially improve those means which are producing the electrical oscillations to be converted into sound oscillations.

It is a further object of the invention to simplify themechanical means for producing oscillations while maintaining as far as possible the character of the tones produced.

It is a further object of the invention to provide means capable of being assembled on a small space in direct vicinity of the keyboard.

It is finally a further object to simplify the conversion of mechanical oscillations into electrical oscillations and to produce a resulting oscillation capable of being treated with conventional means for producing the sound picture.

Further objects will be apparent from the following specification.

One embodiment of the invention and several modifications are shown in the accompanying drawings. It is to be understood however, that said embodiment and said modifications are to be regarded as examples serving mainly the purpose of explaining the principles on which the invention is based and that these principles may be incorporated into other embodiments or modifications some of which have been mentioned or foreshadowed in the following specification. The construction or use of modifications and further embodiments based on the principles as explained is, therefore, not necessarily a departure from the invention.

In the drawings:

Figure 1 is a perspective view of a musical instrument of the piano type;

Figure 2 is a perspective view of a case serving as a housing for the electrical equipment and as a case for accommodating the instrument during transport;

Figure 3 is a front view of the keyboard chest, when folded;

Figure 4 is a sectional elevational view of the keyboard chest illustrating diagrammatically the 2 apparatus and the electrical connections which are used.

Figure 5 is a sectional partial view of a modification.

One of the main objects of the invention consists in providing a foldable piano-like instrument which may be moved without difficulty by one man and which does not occupy much space during transport. The general construction of the instrument is, therefore, shown in Figures 1 and 2, illustrating a modification when set up ready for use, while Figure 3 shows the instrument when folded for transport.

It will be seen that the instrument comprises a keyboard chest it which is divided into two sections H, H forming separate units connected by hinges R4. The front side of the chest may be provided with a shiftable lock plate 34, and the pin 35. The division of the keyboard chest into separate units permits the use of a keyboard 33 of 88 keys as customary on a piano and on similar instruments.

The chest is supported on feet l5 hinged at Hi to the bottom of the keyboard chest and braced by means of pivoted brace members H.

The pedals l8, I9, 28 are mounted on a separate block 2! which is connected with the instrument by means of a cable 22, provided with a plug which is inserted into a suitable connector (not shown) at the back of the chest of the instrument.

The entire electric sound producing equipment is contained in a case 25 according to the modification shown in Figures 1 and 2 which is subdivided into two compartments 26, 21 by means of a partition wall 28. The upper compartment 26 in the example shown contains the amplifier, speaker and all other equipment mounted on a suitable base box 38 which contains the connections and to which cables 29, 30 with suitable plug connectors 3!, 32 are leading. One of these plug connectors is inserted into a socket provided on the keyboard chest, for connection with those units which are associated with the key, while the second cable 30 is connected with the mains or with the available source of supply current.

The amplifier and speaker box 38 and case 25 are preferably placed into a position which is suitable with respect to the acoustic effect, either below or above the instrument or at some other suitable place. An outlet (not shown) may be provided for connection with a public address systern.

When folded for transport the two chest sections which may be locked, if necessary, form a single box as shown in Figure 3 which may be inserted into the lower compartment 21. Suitable guiding ledges 39 may be provided for this purpose. The space between the guiding ledges may be used for storing smaller parts such as the pedal block and the like.

The keyboard chest l essentially comprises a closed portion 4| and an open section 42 and contains either that part of the electro-acoustic equipment which is associated with the keys or as shown in Figure 4, practically all of said equipment.

Section 4| ends in a stepped portion or border ledge 43 on the side of the keyboard which reaches down towards the keys Ml which are pivoted at 44 on a lug 45 depending from the top board of section 4|. White and black keys are treated alike as regards the connection with the sound producing mechanism, merely the location of the upper surface and the length of the projecting part on the board being changed in the customary way.

The front section 46 of the keys covers the open section 42 of the chest completely, so that the keyboard is an exact replica of a piano keyboard. The front wall 48 may form or hold a stop bar 47 for the keys.

The rear section of the keys actuates a damping mechanism to be described below.

In the space below the keys the electro-acoustic tone production device is located which is mounted on a supporting board 52 held on a highly compressible and yieldable layer 53 preferably made of sponge rubber, or of other shock absorbing non-oscillating material. The board and the shock and oscillation absorbing compressible elastic layer may be fixed to the bottom board 54 of the chest In in any desired manner either by means of glue or cement or by mechanical means. It is, however, to be understood that the electro-acoustic tone producingv and damping mechanism is fixed on the supporting board 52 and not to the bottom board 54 so that shocks or oscillations imparted to the mechanism are not transmitted to the bottom board. No reaction is, therefore, produced which might interfere with the production of sound oscillation.

The supporting board carries uprights 5B, 58 of wood or metal below each key fixed by mechanical means such as screws, and projecting toward the keys. The uprights 56 form a series,

one upright or a pair being arranged below each key. The uprights 58 may either be separate units arranged below each key or instead of such a series a cross bar (as shown in Figure 4) mounted transversely with respect to the keys may be arranged. This cross bar 58 carries a tuning fork .60 for each key which is fixed thereon by means of a stem at the closed end of the tuning fork which passes through a hole in the cross bar. Said stem is provided with screw threads and carries nuts 62 firmly gripping the cross bar on both sides. The tuning fork is thus held in a horizontal position in substantial parallelism to the key 40 above it. It is tuned to the tone corresponding to the key with which it is associated.

It will be understood that a tuning fork is used in order to produce the oscillation which corresponds to the desired tone. Instead of a tuningfork a reed .may be used which is tuned to the corresponding tone, and which has to be mounted in such a way that the oscillation is not deformed or influenced by the fixation means, and that the oscillating length is well defined. This may be 4 accomplished by mounting it between two cross bars.

The tuning fork is best made of metal, but is not magnetized.

The tuning fork 60, in order to make it oscillate, is struck by a mallet 1|] consisting of a spherical or cylindrical head 7| carried by an arm l2. This arm is pivoted on a pivot pin 13 carried by an upright :56 or between two such uprights. The arm 12 has an extension M at the end of which a counterpoise 15 is mounted which holds the said head against the lower surface of the key 48. The head consists either of soft material or is lined with soft material. The counterpoise T5 is of such weight not only to counterbalance the head but to impart to it a tendency towards upward movement. The counterpoise, therefore, serves the multiple purpose of holding the head in the desired position of contact with a key, of taking up some of the energy imparted to the head upon depression of a key and of breaking the downward movement of the head li when it has fulfilled its purpose. The latter effect may be obtained by arranging the stop 41 in such a way that it will act as a stop for the counterpoise.

It will, therefore, be clear that upon depression of the key the head ll will strike shortly against the tuning fork 68 and will thus produce oscillations of the desired frequency.

A further part of the mechanical arrangement of the instrument consists in the damping mechanism associated with the rear section 50 of the key Ad. This mechanism comprises the damping pad W5 consisting of leather, sponge rubber or similar relatively soft materiaL'pressed against the tuning fork. This pad is merely removed when the tuning fork is struck by the mallet. The damping pad is fixed on a head 77 mounted on an arm l8 whose fulcrum 79 may for instance be formed between points or knife edges (not shown) within a hole, recess or cut portion of the cross bar 53. The outer end 80 of the arm carries a pin 8| sliding within a slot 82 of a link 83 pivoted at 8 to the key section 50.

It will be manifest that when the key 40 is depressed and the tuning fork is struck by the mallet the rear section 50 moves upwardly and the link 83 will lift pin 8| and the end 80 of arm 18 and will thereby lower head 11 and move it away from the tuning fork 6|).

A damping pad lifter 85 is moreover provided in the chest which comprises a cross wire 86 passing below the ends 8|! of the arms 18, and which is capable of lifting said arms when operated. This cross wire is supported on depending arm sections 81 joined to horizontal sections 88, which are pivoted on a post depending from the top board of the closed chest section 4|. The other end of the horizontal section 88 is pivotally connected (at 89) with the core 9| of magnets 92, which are operable by depressing the left pedal H5. It will be clear that only a small number of magnets is necessary to operate the transverse wire or wires 86 which lifts all the arms 18 as soon as this pedal is depressed. The magnets in this case are energized, the cross wire or wires 86 raises the ends of the arms 18 and removes the damping pads 76 from the fork Ell, the pins 8| moving within the slots 82 of the links 83 during such action.

The arms 18 are either slightly weighted at or near the end 80 carrying the pin so as to move downwardly with the link 83 after having been lifted, or the pin 8| is inserted into the slot 82 with some friction which is suflicient to produce a downward movement of the arm which applies the damping pad 16 when link 83 moves downwardly, while this friction is easily overcome by the pull of magnet raising the cross wire or wires 86 by means of lifting levers 85. It will thus be clear that the two mechanisms for lifting the arms 78 are capable of independent action. It will also be clear that these mechanisms permit holding and transportation of the chest without requiring any adjustment.

The electrical arrangement includes the tuning fork 60 one prong of which forms one plate of a condenser I00, while the second condenser plate is formed by a member 99 which is mounted on the board 53. This second member 99 consists mainly of a strip of metal facing preferably the inside of the prong.

It will be understood that the length of the strip 99 which determines the capacity of the condenser Hi will have to be adjusted in accordance with the frequency, such adjustment depending to a large degree on the width of the prongs on the tuning fork, and on other circumstances. It is preferable to arrange the strip 99 between the prongs of the tuning fork 60 because it is a well known fact that the vibrating prongs when struck'hard have a tendency to spread, and this would lead to a striking of the prongs against the plate 99, which is to be avoided.

The condenser I00 formed between the prongs and the member 99 is connected with a so-called padder formed by a small adjustable condenser Illl provided with means for adjusting the capacity of the circuit. By means of a lead 94, these condensers are connected with the grid Ifll of a I-IF oscillator Hi2 which is of any well known type and connected and operated in a well known manner. The HF oscillations produced in the oscillator are modulated by the oscillations produced in the circuit 94, 95, 99, BI] in a Well known manner. The connections shown correspond to one of the customary methods of operating and modulating an oscillator and are not part of this invention. Any well known method will produce the same result and it is deemed unnecessary to describe or show these well known oscillator arrangements in detail.

In certain cases the metal strip H2 may be made of a thickness corresponding tothat of the prongs of the tuning fork and it is then placed in front of the end ill of the prongs as shown in Figure 5 of the drawings. The condenser is in this case formed by the two end faces of the prong and strip respectively, and is changed by the oscillations of the prongs. denser may be used if necessary to increase the total capacity of the circuit.

The tuning fork 60 is connected with ground I04 by lead 95, one of the screws 62 serving as a binding post.

The modulated oscillations generated in the oscillator arrangement are transmitted to an amplifier H6 which contains a demodulator and the necessary number of audio amplifying stages. This amplifier is of the usual well known type. According to Figures 1 and 2 it is contained in case 25, but in the modification shown in Figure 4, the amplifier is arranged in the section II of the keyboard chest in the space beneath the keys and between the magnets 92. It is preferable to arrange a plurality of amplifiers and oscillator units one for every octave or for a small number of octaves in order to fit the carrier frequency and the amplifier arrangement including the audio transformers to the range of oscillations A parallel conw which forms the output of the corresponding section of the keyboard.

The demodulator and amplifier arrangement is a conventional arrangement which needs no specific description.

The speaker may be arranged within the chest but it is preferably a separate unit placed on the keyboard and emitting in the desired direction.

The action of one of the pedals has already been described. The other pedals H3 and H4 for decreasing or increasing the tone intensity are electrically operated by either adding or switching off amplifier stages or by switching in or out resistances in the audio circuits. Both methods are well known and do not form part of this invention. The application is merely indicated diagrammatically.

Changes in the general construction and especially in the electric or mechanic equipment do not necessarily affect the principles on which this invention is based.

I claim:

1. Afoldable electro-acoustical musical instrument of the type having a piano keyboard, mechanical means associated with each key of the keyboard for producing mechanical oscillations and means for converting said mechanical oscillations into electrical oscillations, said instrument comprising an elongated chest of substantially flat prismatic shape divided lengthwise into sections along a transverse dividing line, subdividing the keyboard, said sections being hinged to each other along the transverse dividing line, said chest having a closed and an open portion, the latter carrying the exposed portion of the keys of the keyboard and the aforesaid mechanical and electrical means associated with each key.

2. A foldable electro-acoustical musical instrument of the type having a piano keyboard, mechanical means associated with each key of the said keyboard for producing mechanical oscillations, means for converting said mechanical into electrical oscillations, a damping device for each of said mechanical means and means for operating the same, said instrument comprising an elongated chest of substantially fiat prismatic shape divided lengthwise into sections along a transverse dividing line, subdividing the keyboard, said sections of the chest being hinged to each other along the transverse dividing line, said chest having a closed and an open portion, the latter carrying the exposed portion of the keys of the keyboard and the aforesaid mechanical and electrical means associated with each key, said closed portion containing substantially the damping device operating means including the means to connect them with the keys, and electromagnetic means housed in said closed portion for operating the damping device of all the keys in common.

3. A foldable electro-acoustical musical instrument of the type having a piano keyboard, mechanical means associated with each'key of the said keyboard for producing mechanical oscillations, means for converting said mechanical into electrical oscillations, a clamping device for each of said mechanical means and means for operating the same, said instrument comprising an elongated chest of substantially flat prismatic shape divided lengthwise into sections along a transverse dividing line, subdividing the keyboard, said sections of the chest being hinged to each other along the transverse dividing line, said chest having a closed and an open portion, the latter carrying the exposed portion of the keys of the keyboard and the aforesaid mechanical and electrical means associated with each key, said closed portion containing substantially the damping device operating means including the means to connect them with the keys, electromagnetic means housed in said closed portion for operating all the damping devices of all the keys in common and operating means for said electromagnets, including a source of current, connecti-ng cables and a pedal provided with a switch,

the latter forming a separate unit connected with the foldable chest of the said connecting cables for operating the damping means from a point outside the chest.

4. A foldable electro-aooustical musical instrument of the type having a piano keyboard, mechanical means associated with each key of the said keyboard for producing mechanical oscillations, means for converting said mechanical into electrical oscillations, a damping device for each of said mechanical means and means for operating the same, said instrument comprising an elongated chest of substantially fiat prismatic shape divided lengthwise into sections along the transverse dividing line, subdividing the keyboard, said sections of the chest being hinged to each other along a transverse dividing line, said chest having a closed and an open portion, the latter carrying the exposed portion of the keys of the keyboard and the aforesaid mechanical and electrical means associated with each key, said closed portion containing substantially the clamping device operating means, the latter including means to connect the same with the keys, electro-magnets housed in said closed portion and operating the damping devices for all the keys in common, a separate pedal block containing a pedal with a pedal switch forming a unit and operating means for said electro-magnets including a source of 8 current and connecting cables leading to said magnet for operating the damping means from a point outside the chest.

5. A folclable electro-acoustical musical instrument as claimed in claim .1 comprising supporting feet for each section of the chest hinged to said section for a folding movement of the feet bringing them alongside the said section.

6. A casing for the transportation and reception of 1a foldable electro-acoustical musical instrument as claimed in claim 5 said casing being divided into two compartments, means for amplifying and for converting electrical oscillation produced in the chest into acoustical oscillations, said means being housed in one compartment of said casing, the said second compartment being adapted to receive the folded chest, spacing ledges in said second compartment for holding the folded chest when inserted at a distance from the wall of the casing, thus providing a further compartment for receiving the cables and the pedal block.

CHARLES C. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,027,475 Hanson May 28, 1912 1,663,238 Bilhorn Mar. 20, 1928 2,187,251 Severy Jan. 16, 1940 2,226,900 Dickerson Dec. 31, 1940 FOREIGN PATENTS Number Country Date 423,121 Great Britain Jan. 25, 1935 492,762 Great Britain Sept. 27, 1938

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