US1772374A - Signaling system - Google Patents

Description

Aug. 5, 1930. J. WEINB ERGER w 7 SIGNALING SYSTEI. Film; lay 3, 1923 ahoento'z JULUS WEINBERGER Patented Aug. 5, 1930 UNITED STATES PATENT OFFICE JULIUS WEINBERGER,.OF NEWYORK, N. Y., ASSIGNQR, TO RADIO CORPORATION OF AMERICA, A CORPORATION or DELAWARE SIGNALING SYSTEM Applicationfiled May 3, 1923.: Serial Name- ,298,

The object of this invention is to provide audio frequency vacuum tube amplifier circuits, used in combination with a loud speaker (or similar electro-acoustic device) which produce an improved quality of performance of the system.

It is well known that the grid voltage-plate current characteristic of a vacuum tube is, in general, not a straight line but acurve. Over a small portion of this curve it may be regarded as a straight line, and alternating voltages impressed, on the grid may be substantially reproduced in undistorted form by currents in the plate circuit, provided such voltages are small relative to the entire range of the characteristic curve. a

When the voltage impressed onthe grid becomes appreciable, relative to the total voltage which would be required to swing theplate current from zero to maximum, the effect of the curvature of the characteristic is to give rise to harmonics in the plate current. That is, if a voltage having a frequency of 800 cycles be impressed-onthegrid of a tube,

of appreciable amplitude, the current in the plate circuit will contain this fundamental frequency plusnumerous harmonics thereof (1600, 2400, 3200 cycles and so on) in increas- V f mg proportion to the fundamental as'the amplitude of the voltage impressed on'thegrid is increased. Should the tube be used as an amplifier to feed a loud speaker, these harmonics will produce objectionable shrillness in the sounds emitted by the loud speaker.

The undesirable effect thus produced may be greatly alleviated cuits diagrammatically shown by Way of eX- ample in Figs. 1, 2 and'3. V

Figure 1 shows one simple method of carrying out this invention. vIt is my object therein to provide an element connected to the loud speaker, in this case a condenser,

which will tend to progressively short-circuit the loud speaker for'the higher frequencies, and thus progressively allow less and less current due to harmonics to flow through the loud speaker, the higher the frequency of these harmonics. In this figure, 1 is a vacuum tube amplifier, 2 an input transformer for audio frequencies, 3 a loud speaker and 4 a such as a filter,in the loud speaker, whichwill produce an effect only above a certain 1 frequency, f In music, (and also in speech) the fundamental, requencles mostemployed lie ordinarily bea by the use of the circondenser connected: in, parallel therewith. The value of this condenser is best :found by trial, and varies with the particular loud speaker used. I have? found, however, that for vacuum tubes'having an output impedance (or internal resistance) of the order of 20,000:ohms, the best condenser is approximately determined by making it of suchvalue that its reactance is equal to. thereactance ofrthe loud speaker at a frequenc of about 1200 cycles. For example, wit speaker having an inductance of 4 henries, a

suitablecondenser would be about 0.005 microfarads. Higher or lower values of capacity maybe used without departing from the spirit of; the invention, which consists in the connection of an electricalelement in a vacuum tube loud speaker circuit for the purpose of selectively adjustin the current passed through the loud spefi er at different: frequencies.

a loud An improved methodof carryingout the invention is to use a more complex net work, parallel or 1n series. with low about 2000 cycles; .Harmonics of these frequencies, present in; the original sound, give it its quality; However, it is in general the harmonics having frequencies consider Jablyabove 200 0 cycles, whlch, when'gehrated by an amplifying;t ube-,fgive rise to the objectionable shrillness.

If a high pass filter is made which passes relatively little in therange offrequenciesbelow 2000 cycles,-

Figure 2. Here the Y but progressively more in the range above this, and connected in parallel to the loud Zspeaker, the same results 7 (to improve the performance of the filter) replaces the condenser 4 of Figure 1. It is obvious that a said filtering means being said" harmonics, whereb noises produced harmonics,

acrosssaid filterin means.

prises sufiiciently dulations 1n addition filtering said harmonics from said amplified undulations and converting said amplified i in its normal operation,

. connected to said amplifier,

monies producing undesirable noises in the 7 loudspeaker; a

harmonics, whereby produced in said loudspeaker by jsaid harloudspeaker,

low pass filter in series with the loud speaker may be designed so as to produce the same 7 result as a high pass filter in parallel. Fig. 3 discloses this type of a filter.

The scope ofthe invention is not limited to the combination of a vacuum tube amplifier with a loudspeaker only, but to the combination thereof with any output circuit from which it is. desired to progressively keep higher harmonic currents'which may be produced due to distortion by the vacuum tube.

Having described my invention, what I claim is: 1 a

1. The method of converting electrical undulations into audible signals which comamplifying said electrical undulations to produce undulations into sound vibrations.

2. Inthe art of electrical reproducing, the method ofimproving the quality of sound vibrations produced which comprises overamplifying the electrical undulations to be reproduced, said over-amplification resulting amplified electrical [unin the production of dulations and harmomcs' of said undulations, separating said harmonics from said amplified undulations, and converting said amplified undulations intosound vibrations.

3. In a radio receiving system having a vacuum tube 'audio frequency amplifier constructed and arranged to produce harmonics a loudspeaker device filtering means connected across the terminals of said loudspeaker; said filtering means being to eliminate the noises monies. H

4. In 'a radio-rece1v1ng system having a vacuumtub'e audio frequency amplifier constructed and arrangedto produce harmonics in its normal operation,

a loudspeaker'device connected to'said amplifientliesaid harmonicsf producing undesirable noises in the a filtering means -conne'cted across the terminals of 1 designed to absorb to eliminate "the in said loudspeaker by said an impedance connected INBERGER,

and

, 'JULTUS wharmonics of said unj to said undulations,

the said hardesigned to absorb said said loudspeaker,

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