US1893892A - Piano with reaction loud speaker - Google Patents

Description

Jan. 10, 1933. J. H. HAMMOND, JR 1,893,892

PIANO WITH REACTION LOUD SPEAKER Original Filed June 13, 1929 4 Sheets-Sheet l A TTORNEY.

Jan. 10, 1933. J. H. HAMMONI D, JR 1,393,892

PIANO WITH REACTION LOUD SPEAKER Original Fil'ed June 13, 1929 4 Sheets-Sheet 2 A TTO Y.

Jan. 10, 1933. J. H. HAMMOND, JR 1,893,892

- PIANO WITH REACTION LOUD SPEAKER Originl Filed June 13, 1929 4 Sheets-Sheet s RADIO RECEIVER ATTORN Y.

A 1.7 IZENTOR. 1% I Jan. 10, 1933. J, H, HAMM N R 1,893,892

PIANO WITH REACTION LOUD SPEAKER Original Filed June 13, 1929 4 Sheets-Sheet 4 "'21 INVENTOR.

7 MW L zlm 2 3 6 a m M x Q ATTORNEY Patented Jan. 10 1933' UNITED STATES mama rarer OFFICE.

PIANO WITH REACTION LOUD SPEAKER Application filed June 13, 1929, Serial No. 370,484. Renewed October 6, 1932. i

This invention relates to musical instruments of the percussive type, and more particularly to a piano having sound propagating and reenforcing means associated therewith. I

In accordance with the present invention a sound propagating device, such as the so called loud speaker-which is capable of converting electrical vibrations into compressional waves, is applied to a portion of the sounding board of a piano which is substantially inactive for each of the notes of the musicalscale. The loud speaker may thus be utilized for the reproduction of programs without interfering with the operation of the piano orv the reenforcing qualities of the sounding board.

The invention further provides for magnetically picking up-the vibrations of the strings of the piano, amplifying the same and applying the amplified energy to the loud speaker whereby the volume emitted by the piano may be controlled within the range of the amplifier.

The invention also provides for amplify- -ing the vibrations of the various strings as groups and for independently controlling the amount of amplification of each group.

A further feature of the invention is the utilization of the reactance of the loudspeaker to impart vibrations to the sounding board of a piano whereby the sounding board is utilized for reenforcing the vibrations propa- 5 gated by the loud speaker.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

. Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof, in which Fig. 1 is a diagrammatic view of the pickup and amplifying means showing the locamodified form of support for the speaker unit;

Fig. 7 is a sectional view of a further modified support;

Fig. 8 is a bottom plan view of the piano showing the reenforcing ribs; and

Fig. 9 is a side elevation of the piano broken away to show the reenforcing ribs.

Like reference characters denote like parts in the several figures of the drawings.

In the following description and in the claims parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring tothe drawings more in detail, the invention is shown as applied to a grand piano 10 having the usual keyboard 11, strings 12 and sounding board 13, Above the sounding board 13 is mounted a metallic frame 14 (Fig. 4) on which strings 12 are 8 mounted. Said strings are supported from bridges 15 and 16 which are secured to the sounding board of the piano in the usual manner.

Sounding board 13 is provided with a circular opening 20 below which is mounted a.

frame 21 (Fig. 2) formed partly cylindrical and partly conical. This-frame is bolted to the sound board 13 and to an annular ring 17 by means of bolts 18. In the cylindrical 9 portion of frame 21 is mounted a cylinder 22 of magnetic material inside of which is a winding 23 mounted on a magnetic core 24. Associated with the end of cylinder 22 is an annular ring 25 of magnetic material, which is separated from coil 23' by a ring 26 of nonmagnetic material. A coil 27, of comparatively fine wire, is supported in any convenient manner as by cup-shaped member 28 and is free to move within rin 25. Said member -28 is rigidly mounted to t 1e apex of the cone 30, the periphery of which is secured between sounding board 13 and frame 21. Screw 32 is carried in core 24 and serves as a guide for insuring the proper alignment of-coil 27 with respect to ring 25. Gone 30 may be of any suitable material such as heavy paper which is capable of transmitting compressional wave vibrations to the surrounding medium. The entire unit is supported by spring means I such "as a block 35- of sponge rubber from A speaker of the so called dynamic type which comprises a moving coil mounted in the field of an electromagnet. This form of loud speaker, is shown by way of example only and not as a limitation upon the scope of the invention. As shown in Fig. 2, the coil 23 is supplied with direct current from an A- C. main through a rectifying device 41. Condensers 42 are connected across'the A. O. main 40 in the usual manner and are. grounded to a frame 21 as by conductor 43. It is obvious that any suitable type of rectifying device may be employed for rectifying the alternating current from'main 40 and applying same to coil 23 for producing the powerful magnetic field which is required in a speaker of this type. The armature coil 27 is connected through switch 45 with a secondary 46 of an audio frequency transformer 47 (Figs. 1 and 2). Switch 45 maybe operated by lever 50 which is pivotally secured to the frame of piano 10 and is operated by plunger 51 connected to pedal 52'.

A plurality of magnetic pickups 55 are mounted over the various strings of the piano and are designed to be actuated by the action of said strings for producing a pulsating electrio current. As shown more in detail in Figs. 2 and 3 these pick-up devices consist of a pluralit of segments 56 each of which is located directly above the strings comprising a single note of the piano. Segments 56 are separated by magnetic insulating segments 57 and are mechanically secured together in any suitable manner as by casing 58; A pair of windings 59 and; 60 which may be wound in the form of a single coil, as shown in Fig.

3, are carried on each group of segments. One of said windlngs of each group, for ex 27 of the loud speaker.

ample, winding 59 is connected through a variable resistance 61 and choke 62 to battery 63, sifid battery being provided with a common return wire 64 to each group 55. The windings of each group, are connected through individual resistances .61 so that the amount of current flowing in each winding 59 can be individually adjusted. Windings 60 of the various pick-ups are connected to the grids 65 and filaments 66 of a plurality of space discharge devices 67. A battery 68 may be-employed for maintaining said grids at the proper potential. The plates 7 O of said space discharge devices are joined through a resistance 71to a common source of plate current, such as battery 72. The output circuit of space discharge devices 67 is coupled to the input circuit of amplifier 73 in any suitable manner, such as by condenser 74 and impedance 75. The output circuit of amplifier 73 is connectedto the primary of audio frequency transformer 47.

Although a particular form of amplifier has been illustrated byway of example, it is obvious that the invention is not limited thereto and that any desired type of amplifier may be employed for separately amplifying the current Variations induced in coil 60 by the vibration of strings 12 and applying the amplified energy to the armature coil 27 of the loud speaking device.

In the operation of the above described apparatus the current flowing in coil 59 from attery 63 produces electromagnetic lines of force in segments 56 thereby nroducingamagnetic field in which the strings 12 of the piano are positioned. The strings in effect form the armature of the electromagnet and their spacing from the coil pieces of the electromagnet determines the reluctance of the magnetic path. The field produced in segments 56 by the current in winding 59 accordingly varies in strength in accordance withthe vibrations of the adjacent strings. This varying magnetic field induces an electric current in coil 60 which is amplified by space discharge amplifiers 67 and 73 and applied through transformer 47 to the armature coil This coil is thus caused to vibrate in the magnetic field produccd by the electromagnet 23 and to thereby reproduce the vibrations of strings 12.

The amount of amplification of each oup of'strings can be determined by the positions of resistances 61 which governs the amount of current flowing in the various coils 59. It is accordingly possible to amplify a given group of notes, for example, the treble notes, a greater amount than the notes of another group, whereby any desired effect may be reproduced. The action of the amplifier is controlled by foot pedal 52 which may be the magnetic pick-up device to be fed back into the loud speaking device. This energy is again mechanically transferred to the strings 12 by the action of the compressional waves produced by the loud speaker whereby a regenerative eflfect is obtained. By properly adjusting the various elements it is accordingly possible -to produce a sustained note which will continue as long as the key is depressed.

' The reactance of the frame 21 of the loud speaking device is mechanically transmitted through said frame to sounding board 13 whereby the sounding board is caused to vibrate at the frequency of a note being emitted and toreenforce the vibrations produced by the vibrating cone .30. In order to permit the sounding board adjacent the loud speaker to vibrate more readily a slot 80 may be formed in said sounding board adjacent thepoint of support at the sideand-the front of the piano as shown in Fig. 4.

As a further means of transmitting the vibrations from frame 21 'to the various parts of the sounding board a plurality of ribs 81 may be positioned on the under-surface of said sounding board extending radially from opening 20 to the various parts of said sounding board. These ribs serve to more efficient- 1y transmit the vibrations of the frame and cause the entire sounding board to operate as a unit. I

A modified manner of supporting the loud ding board is shown in Fig. 6 as comprising a plurality of springs 82 which are secured to the lower I portion of said unit and are fixedto the frame of the piano and to a stationary member 83 by screws 84. Said stationary member may be supported from brace 37 in any convenient manner.

A second modification which may be utilized in place of the rubber sponge 35 of Fig. 2 isshown in Fig. 7 and comprises a plurality of spiral springs 85 which are mounted on base member 36 and extend between said member and frame 21.

I In additionto utilizing the lohd speaker device for amplifying the notes produced by the piano, it may be used in connection with a radio receiver in the manner illustrated in Fig. 5. For this purpose armature coil 27 1s connected through the output transformer 86 to the output circuit of the radio receiver Coil 23 of the speaker may be supplied with direct current by rectifier 41 in the manner illustrated in Fig. 2. It is obvious,

therefore, that the loud speaking device may be utilized either in connection with a radio receiver or in connection with the piano itself. It is preferably located at a nodal point on the sound board so that the normal operatioiithereof will not be'interfered with in playing a selection on the piano.

The nodal point of the sounding board may be determined in any well known manner, as for example, by placing a powdered material, such as sand, on the sounding board and playing the piano. The sand then collects at the nodal areas leaving the anti-nodal areas substantially clear.

The relative amounts of amplification of the various pick-ups 55 can be predetermined and the resistances 61 set at the desired value. The piano is then played in a normal manner and the amplifying apparatus is controlled by foot pedal 52. When this pedal is depressed for a loud note the amplifying device is brought into operation and the sound waves are amplified and reenforced in the manner above pointed out. The device will be utilized as a straight amplifying arrangement for merely amplifying the various notes, or by a suitable adjustment of the various parts may be caused to regenerate for producing a sustained note. In the latter case the sustained note would be maintained while the key is held down and the string is free to vibrate. When the key is released the felt stop will come in contact with the string in a manner well known in the piano art and will interrupt further vi.- bration thereof. It is accordingly possible in accordance with this invention to cause a piano to emit an undamped note of a duration which is dependent upon the length of time the key'is depressed.

While certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes in the forms and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. In a system of electrical amplification of sound waves, a piano, a sounding board connected therewith, a magnetic sound reproducing means having an armature and a chassis, said chassis being rigidly secured to said sounding board whereby the reaction from saidarmature on said chassis is directly transmitted to said board for reenforcing the sound waves produced by said armature.

2. In combination with a piano having a sounding board, a loud speaker having a chassis and a movable armature, and means for mounting said chassis on said sounding board whereby the reaction thereof is trans mitted to said sounding board.

3. In combination with a piano having a sounding board, a loud speaker having a chassis and a movable armature, means for mounting said chassis on said sounding board whereby the reaction thereof is transmitted to said sounding board, and means for, partially supporting the weight of said loud speaker whereby said sounding board remains free to vibrate.

4. In combination with a piano having a sounding board, a loud speaker mounted adjacent said sounding board at a nodal point thereof.

5. In a piano, a sounding board, a diagonal brace extending across a corner of said sounding board, said corner being free from support other than said bracev and a loud speaker mounted on said sounding board between said corner and said brace.

6'. In a piano, a sounding, board, a brace extending diagonally across a corner of said sounding board, said sounding board having slits \at said corner whereby said corner is substantially free to vibrate and a loud speaker mounted on said sounding board between said corner and said brace.

7. In combination with a piano, a sounding board, a loud speaker secured to said sounding board and ribs secured to said sounding board and arranged in a radiating position with respect to said loud speaker whereby vibrations are readily transmitted to the various parts of said sounding board.

In testimony whereof I have hereunto set my hand. v 7

JOHN HAYS HAMMOND, J R.

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