US2032435A - Musical instrument with electric sound reproduction system - Google Patents

Description

March 3, 1936. N. A. 'PALMGREN MUSICAL INSTRUMENT WITH ELECTRIC SOUND REPRODUCTION SYSTEM Filed July 16, 1952 INVENTOR ATTORNEY /V/1 s ARV/o PALM'GRE/V Patented Mar. 3, 1936 PATENT OFFICE MUSICAL INSTRUMENT WITH ELECTmo SOUND REPRODUCTION SYSTEM Nils Arvid Palmgren, Goteborg, Sweden Application July 16, 1932, Serial No. 622,993 In Sweden February 8, 1932 1 Claim. (Cl. 84-1 The present invention relates to musical instruments associated with electric sound reproduction systems and is applicable to all types of instruments having a series of mechancal vibratory systems or vibratory bodies, such as strings, or the like, tuned to acoustic frequencies and consisting wholly or in part of electrically conductive material.

.An object of the invention is to provide an instrument having a wider range both as to volume and timbre than hitherto known types, and which will, therefore, permit the volume and timbre of the difierent tones to be adapted to the most varied requirements.

A further object of the invention is to provide an instrument which can be inexpensively manuiactured and which will he of light weight and require but small space.

wan these and other objects in view the invention consists mainly in that one or more electrodes or the like are disposed near the vibratory bodies and electrically insulated from them, so

that the electrodes form electrical condensers together with the vibratory bodies.

Several forms of the invention are illustrated in the accompanying drawing, in which:

Figure, 1 shows in diagram the principle of the electrical part of the instrument.

Fig. 2 is a diagram of a form of the invention, the mechanical arrangement of whichv is illustrated in Figs. 3, 4 and 5;

3 being a vertical section through the instrument,

Fig. 4 a section along the line 5-4 in Fig. 3 and Fig. 5 a section along the line 5-5 in Fig. 3.

Referring now to Fig. 1, the numeral i denotes a body capable of being set in vibration. Near the body I is an electrically conductive body, or

electrode, 2 which is electrically insulated from the vibratory body through an air gap, and thus together with this body forms an electrical condenser. The body I is in a suitable manner connected to a source ofelectric energy 4, for instance a generator, a battery or the like. The electrode 2 is connected to a resistance 3 offering a relatively great impedance to alternating current. The resistance and the source of energy are connected in the manner shown in the diagram so that the electric capacity of the condenser formed by the vibratory body and. the electrode will form part of an electric circuit in series with the resistance. Ii the vibratory body is now set in vibration, there will be a flow of electrons to and from the electrode 2 in a similar manner as in a capacitance microphone. This current will give rise to a variation in potential between the terminals 5 and 6 of the resistance 3.

In the form of the invention illustrated in Fig. 2, two sections of electrodes 2 and 2 are disposed near the vibratory body I and each covers a part of this body. Either one of these elec trodes, or both simultaneously, can be connected to the primary or" an audio frequency transformer 8 by the battery 1. The secondary oi the transformer is connected to a resistance 9 from which a movable contact ill leads to the terminal 5. Any desired voltage can thus be obtained between the terminals 5 and 6.

The above described circuit diagram is shown applied to the form of the invention illustrated in 1 Figs. 3, 4.- and 5. in this form of the invention a number of strings l are mounted under tension on a frame it, in such a manner that they can be tuned to different audible frequencies. The strings can caused to vibrate by blows from hammers l2 manipulated from the keys ll. Behind the strings are disposed two electrode sections 2 and 2 These electrode sections together cover the greater part of the length of the strings, and the fundamental vibrations of the strings will, therefore, cause great variations in capacity. On the other hand, the variations in capacity due to the harmonics will be very small. Especially will this be so for the even harmonics. This will result in a softer tone and a deeper timbre than that of the tone emitted directly by the string. A tone, in which the harmonics are louder relative to the fundamental, is obtained if the electrode covers only a portion of the length of the string at the vicinity of the end of the string, as all harmonics have a common node at the end of the string, while the only anti-node of the fundamental is situated at the middle of the string. If, for instance, only the section 2* is connected, the four first harmonics will be very pronounced and will be even louder relative to the fundamental than when transmitted direct to the ear from the string. If only the section 2 of the electrode is active mainly the fundamental and the second harmonic will be amplified. The timbre of the instrument can, therefore, be altered by means of the two-way switch IS. The arm of the two-way switch is connected to the transformer 8, which is in its turn connected to the battery 1. The other pole of the battery is electrically connected to all the strings I. The potentiometer 9 is connected across the secondary of the transformer, The movable contact III of the potentiometer is actuated from a pedal l3 so that, when the pedal is It is apparent from Fig. 8 that the electrode,

section 2" for example covers a diflerent pro--, portion of the length of the diflerent strings: In this manner it is possible to accentuate the harmonics of strings relatively lacking in harmonics and to damp them instrings richer in harmonics. As illustrated in Fig. 3, 29% of the length of the shortest string, but only 24% o! the length of the longest string, is covered by the electrode 2 Fig. 4 shows how the distance between the string and the electrode can be varied along the length of the same string. The distance is small at the bottom of the string and greater at the top. In this manner it is possible to adjust the relative sound volumes when connecting the different electrode sections or to adjust the volume of a certain harmonic, or certain harmonics,

relative to the fundamental.

Fig, 5 illustrates the manner in which the distance between the strings and the electrode electrode has no resonance in the acoustic trequency range or that its resonance is so suppressed that it will be aperiodic. In the special iorm of the invention described above it should be noted that the transformer 8 should have a high primary inductance and low capacity between the turns in order to obtain the greatest possible volume. 1

It only the electrode 2" is used, the additional advantage is obtained in the form or the invention described that the hammers I 2 strike the strings at a part not covered by an active electrode.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

In a musical instrument, the combination of a plurality of tuned, electrically conductive strings; means for vibrating said strings at their respective fundamental and partial frequencies, an. electrode positioned adjacent to said strings and forming electrical capacities with said strings, the electrode uninterruptedly covering a greater part of each string in which part the string vi- 343

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