US1564209A - Electrical circuits for the production of musical tones - Google Patents

Description

Dec. 8, 1925- 1,564,209

|. B. CRANDALL ELECTRICAL CIRCUITS FOR THE PRODUCTION OF MUSICAL TONES Filed June 9, 1921 P Sheets-Sheet 1 &

Dec. 8, 1925- 1,564,209

I. B. CRANDALL ELECTRICAL CIRCUITS FOR THE PRODUCTION OF MUSICAL TONES //"v/hy 5. Cranda/A Mai; A?

Patented Dec. 8, 1925.

STATES PATENT orrrce.

IRVING B. CRANDALL, OF WYOMING, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y.,

A CORPORATION OF NEW YORK.

ELECTRICAL CIRCUITS FOR THE PRODUCTION OF MUSICAL TONES.

Application filed June 9,

To all whom it may] concern:

Be it known that I, IRVING 1%. CHANDALL, a citizen of the United States, residing at lVyoming, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Electrical Circuits for the Production of Musical Tones, of which the following is a full, clear, conelse, and exact description.

This invention relates to electrical circuits for producing alternating currents of different frequencies, and also to arrangements for converting such currents into tones of varying pitch.

The invention has for an object the product-ion of tones which vary widely in pitch and at the same time are controlled as to volume.

A further object is to produce electric oscillations of variable frequency and to control their amplitude at different frequencies.

In accordance with the invention a source of electric oscillations is provided with means for changing the frequency, for example by changing a capacity or a c011- denser in a tuned circuit, and simultaneously with the operation of the frequency changing means, a resistance in shunt across the output circuit, or in series therewith, or both, is varied to control the amplitude of the oscillation currents. This circuit is particularly useful, when connected to a telephone receiver or other device for converting electrical energy into sound energy, for the purpose of testing the sensitivity of the ear to tones of different pitch.

Oscillation generators frequently have the characteristic of producing currents of a greater amplitude at one frequency than at another. For example, the output energy may increase as the frequency is increased. In order to compare the sensitivity of the ear to a tone of one pitch with that of another pitch, it is desirable to be able to control easily the sound energy of the various tones used in testing. If a receiving device is used which acts to uniformly convert electrical energy into sound energy at all frequencies, it'is then necessary only to provide means for giving a constant supply of electrical eaiergy, with means for changing the energy by a known amount from a predetern'iined amount which may be taken as a standard. It is very difficult,

1921. Serial No. 476,169.

however, to design a receiver which will not be more responsive to some frequencies than to others. This invention provides means adapted not only to correct for changes in electrical energy output, but also to correct. for non-uniform translation through the receiver.

The above and other objects of the invention will be more fully understood from the following detailed description taken in connection with the accompanying drawings, in which Fig. 1 shows the invention in a circuit employing a mercury arc oscillator, and Fig. 2 shows a modified form employing a vacuum tube oscillator.

Referring to the drawings by reference characters, the evacuated mercury are device 10 and its associated circuit provide an oscillation generator operating on the principles outlined in Vreeland Patent No. 973,826, dated October 25, 1910. The tube 10 contains a cathode 11 and oppositely positioned anodes 12. A battery or other source 13 supplies direct current through an inductance .15 and resistances 16 between the cathode and anodes. Vindings 18 and 19 serve the purpose of shifting the ionization current between the cathode and anodes to produce oscillations, and also serve as primary windings for the secondary winding 20, which is connected to the work circuit.

The windings 18 and 19 in conjunction with a series condenser such as that shown at 22 also serve to control the frequency of the oscillations. A plurality of con densers like those shown in the drawing at 22,, 22 22 and 22, are employed for changing the frequency, one of these condensers being selectively thrown into the circuit by closing the contacts 26,, 26 26 26 etc., of a plurality of keys A, B, M, N, etc., which, if desired, may be arranged as the keys of a musical instrument. The letters A, B, etc., represent the keys used for the lower frequencies, and the letters M, N, etc., represent the keys for the higher frequencies. For the lower frequencies it is desirable to have the windings 18 and 19 connected in series, as shown in the drawing, and for the higher frequencies to have them connected'in parallel, a relay 2% being employed to change the windings from series to parallel relationship.

naeaaoe In order to purify the tones of harmonics or other undesired frequencies, a parallel resonant circuit for each frequency is connected across the secondary portion of the output circuit. For the frequency represented by the key A this resonant circuit comprises" the condenser 28 and the inductance 30 The inductance 30,, may be used for all of the lower frequencies represented by the keys A, B, etc., a separate condenser such as 28,, 28 etc., being used with each of the keys of this series. For hi her frequencies an inductance 30 is substituted for 30,, and this is employed in conjunction with condensers 28 28 etc., for the series of frequencies beginning with the key M. These keys are provided with additional contacts 3%,, 32 etc., which close a circuit through relay 24: and relay 33 for changing windings 18 and 19 to the parallel arrangement and for changing from inductance 30 to 30 Each key is provided also with a contact for connecting adjustable resistances 35,, 35 35 35 etc., across the secondary circuit. The method of adjusting these resistances will be described later.

The secondary circuit is also connected to a receiver R, which may be specially designed to uniformly convert electrical oscillations into sound waves, or may have a non-uniform translating characteristic. In the latter case, if desired, a correcting circuit may be employed comprising a parallel resonant circuit in series with the receiver,

having a condenser in one branch and an inductance 42 and resistance 44 in the other branch, and a series resonant circuit across the line having a condenser 46, inductance 48 and resistance 50 in series. These circuits are tuned to the frequency at which the receiver is 'most sensitive, and tend to cut down the current at this frequency and to some extent at adjacent frequencies. This arrangement is disclosed in the copending application of E. C. Vente. Serial No. 482,729, filed July 6, 1921, and need not further be described here. A current measuring instrument 52' may be placed in the circuit connecting the oscillator to the receiver R.

The operation of this circuit when used in ear analysis is as follows:

First, assuming that the receiver R or the receiver and its correcting network, if the latter is employed, have a uniform translating characteristic, the resistances 35 35 35 35 etc., may be initially adjusted so that at each frequency the same current is shown in the meter 52. This condition may be taken as a standard, and for comparison of the sensitiveness of the ear at different frequencies, a tone of one frequency,,produced by the standard amount of current as above described, is listened to. Another key may then be quickly depressed, and if the apparent loudness of this tone is different from that of the first tone, the corresponding resistance may be adjusted manually until the apparent loudness is the same. The relative difference in tone intensity may be determined from the readings of the meter 52 at the two adjustments, or the resistances 35 may be calibrated in any desired units for giving a direct indication. It will be seen, therefore, that a curve can readily be made showing the amount of sound energy necessary at a plurality of frequencies to give the same apparent loudness.

If a receiver is employed which has a nonuniform translating characteristic and no correcting network is used, the amount of current necessary to give uniform sound intensity at various frequencies with a given receiver can be determined by known laboratory methods, and the resistances 35 may beinitially adjusted so that the required current may be immediately supplied when the respective keys are depressed. In this case it is desirable to calibrate the resistances with relation to some value of output sound energy arbitrarily taken as a standard. In this way the resistances 35 take care of irregularities both in the source of oscillations and in the receiver.

Referring now to Fig. 2, a three-electrode vacuum tube oscillator is employed comprising the oscillator tube 55 and the amplifier tube 56, which is connected between the oscillator and the transformer 57. Oscillations are produced by reason of an inductive feed-back comprising one or more of the windings 58, 59 and 60 in the input circuit of tube 55 and the windings 58, 59 and (50 in the output circuit. For controlling the frequency condensers 65 65 etc., may be selectively connected across the winding 58, or a plurality of the windings 58, 59 and 60,-as the case may be. As shown in the drawing, the lower frequencies, represented by keys A, B, etc., use only the windings 58 and 58. Another series of keys beginning with M use the windings 58 and 59 in series and windings 58' and 59' in series. Still another series of keys not shown may use all three windings in series. Tuned circuits comprising condensers 28 28 28 etc., and inductances 30 ,'30 30, etc., are employed for filtering, substantially as in Fig. 1. For controlling the amplitude of the current, series resistances 7 5,. 75,;,, etc., and parallel resistances 76... 76 ,-76m. etc., may be employed. instead of the single resistances shown in Fig. 1. By using both series and shunt resistances the impedance of the secondary circuit to the amplifier 56 may be maintained constant. The operation of the circuit of Fig. 2 is substantially the same as that of Fig. 1.

While two embodiments of the invention of said oscillations, and means mechamcal ly connected with said first means including an adjustable resistance for operation simultaneously therewith for controlling the amplitude of said oscillations.

2. In combination, a

, ond means being unequally efiicient at differa source of electric waves ent frequencies, and means operably connectedwith said frequency changing means for varying the current to correct said inequality.

4. In combination, a source of electric oscillations, manually operable means for changing the frequency of said oscillations, and preadjustable means including an adjustable resistance for determining the amplitude at each of a plurality of frequencies.

5. In combination, a telephone receiver, for energizing said receiver, means for regulating the frequency of said waves, and means mechanically connected to said first means for operation I simultaneously therewith for regulating the mentioned means.

, keys for varying a tuned circuit for frequency, and means including ,an adjustamplitude of said waves.

1 6. In'combination, a telephone receiver, a source of electric waves for energizing said receiver, means for regulating the frequency, means mechanically connected to said first means for operation simultaneously therewith for controlling the amplitude of said waves, and means for controlling the amplitude of said waves independently of second 7. In combination, an oscillation genera-.

' I tor having a tuned circuit, a plurality of reactance element in saidchanging the oscillation source of electric os source of electric oscillations, means connected to said source for able resistance controlled by said keys for varying the amplitude of said oscillations.

8. In combination, an oscillation generator havinga tuned circuit, a plurality of keys for varying a reactance element in said tuned circuit for changing the oscillation frequency, mean including resistance controlled by said keys for varying the amplitude of said oscillations, and means operable independently of said keys for varying the amplitude of said oscillations.

9. In combination, an oscillation generator. means forvarying the frequency of said oscillations, a resistance in the output circuit of said generator, and means mechanically connected with said first means for operation simultaneously therewith for varying 'said resistance.

'10. In combination, an oscillation generatorhaving a tuned circuit, a plurality of condensers adapted to be selectively connected in said tuned circuit, and means for controlling the amplitude of said oscillations simultaneously with the selection of said condensers respectively.

11, In combination, tor, means for varying the frequency of sa1 oscillations, a plurality of circuits selective to individual frequencies, and means for simultaneously connecting any one of said selective circuits to said generator and adjusting said generator to produce a corresponding frequency. v

12. In an apparatus for testing the sen-sitiveness of the ear to sounds-means to produce sustained tones each of said tones having a different frequencv but the same intensity, means to vary the intensity of said tones to produce the same apparent loudness to the ear for all frequencies, and means to measure the variations in intensity for each frequency. 7

13. In an apparatus for testing sensitiveness to sound, means for producing tones of different frequencies, and means for preadjusting said tone producing means to -obtain the same constant intensity at all frequencies.

an oscillation generafor producing tones of for preadjusting toeqnal constant nessto sound, means various frequenc es, means said tone producing" means ass intensity at all frequencies. and means for varying the intensity of said tones.

Inwitness whereof, I hereunto subscribe my name this 7th day of June, A. D. 1921.

IRVING B. CRANDALL.

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