US2626991A - Tone control system - Google Patents

Description

Patented Jan. 27, 1953 UNITED STATES. PATENT OFFICE.

SchaferjWaltvorth, N. Y., assignors to Stromberg-Qarlson Company, a cgrp'oration of New York Application June 16, 1948, SerialNo, 33,316

2. C ims- 1 Thepresentinventlon relates toa tonecontrol system, and: more particularly to such a system especially adapted for use. in a radio broadcast receiver or in a. sound system.

It has been found that reproductionofmusic bya. radio receiver or other sound amplifying system is enhanced if the bass portion of the audio frequency spectrum is accentuated relatively to the middle and treble portions of the; musical scale. In; general, however, accentuation of the bassportion of the frequency spectrum tends to render reproduction of speech boomy and sometimes practically unintelligible.

One; solution of. this. problem is to provide a relatively rapid transition from a high bass level to a substantially lower level for the middle and treble portions of the frequency spectrum. The simplest type ofcircuit arrangement for securing relative accentuation of the bass frequenciesu-tilizes a. combination of resistance and capacitance. This arrangement is not entirely satisfactory, however, since the response curve obtained with it has a gradual slope downward frpm the bass level to the level of the middle and treble portions of the frequency spectrum.

a ob c f he. se nv n n, er fore to provide an improved tone control system which the. transition from the bass level to the level of themiddle. and treble portions. of the frequency spectrum is: relatively sudden,

Itiisanother object of the present invention to provide a tone control system which is capable of attenuating the upper and middle portions of the frequency spectrum without a substantial effectupon the lower portion thereof.

An additional object of the present invention is to provide an improved, tone control system of simple and inexpensive construction, which is. capable of substantially enhancing the reproduction of musical program matter without any. deleterious effect upon the reproduction or intelligibility of speech.

Theabove and other objects are realized in accordancewith present invention by providing a source of signals extending over a wide band of frequencies. Means are provided for transmitting the upper portion of this frequency band with substantial attenuation, and for transmitting-the lower portion of the frequency band without appreciable attenuation. Means are also provided for transmitting the portion of the frequency band intermediate the upper and lower portions in such a manner as toprovide a relatively sudden transition from the level of the lower portion to the level of the upper portion.

Byway of example, let it be assumed that the frequency. spectrum. tobe covered extends from to 10,000 cyclesper s co In Order to ur improved; musical reproduction, it is desirable to, substantially accentuate the, frequencies in he, r gion bet e n 0 and 1 y les e second with respect to the frequencies above this ran e. If unsatisfactory reproduction of speech is to be avoided, however, the relative accentuation of the bass frequencies should lie entirely below approximately 300. cycles per second. Such per-.. formance. is readily obtained with the arrangements in accordance with the present invention.

The above and other objects and features of the present invention will be better understood by referring to the following description taken in connection with the accompanying drawing, in which like components are designated by like reference numerals, and in which:

Fig. 1 is a schematic circuit diagram of one embodiment of the present invention;

Fig. 2 represents schematically a modified embodiment of the present invention; and

Fig. 3 shows graphically the performance realized with the embodiments of Figs. 1 and 2.

Referring to Fig, 1 of the drawing, there is shown a tone control system comprising input terminals l and 2 and an electron discharge de- Vice 3 having a control electrode 4, a cathode 5,

and an anode 6. Input terminal I is coupled to control electrode a by a capacitor l. A resistor 8 is connected betweencontrol electrode 4 and line 9, which is connected to input terminal 2 and which may be grounded as indicated at 10. Cathode 5 is connected to line 9. Anode 6 is connected through a load resistor II to a suitable source of positive potential, as indicated at l2.

Connected between anode 6 and line 9 is a series network comprising a capacitor l3, a resistor l4, capacitors l5 and I6, and a resistor IT. A resistor l8 and a potentiometer iii are connected in series between the junction 20 of resistor l4 and capacitor l5, and junction 2| of capacitor I6 and resistor H. A capacitor 22 is connected between junction 23 of resistor l8 and potentiometer l9, and junction 24 of capacitors I5 and 16. The movable arm or slider 25 ofpotentiometer I9 is connected to a first output terminal 26, the second output terminal 2'! being connected to line 9.

In operation, resistors 14 and i8 and capacitors i5 and 22 form a T network. This network by itself would provide a response curve which would accentuate the bass portion of the frequency spectrum relative to the remaining frequencies, but which would have a pronounced dip or in some cases a cancellation resulting in zero response at an intermediate frequency, as forexample, at approximately 300 cycles persecond. However, by returning this network through the capacitor l6 rather than directly to line 9, the dip in the response curve is substantially eliminated. The capacitance of capacitor I6 is ChQSen to secure the maximum cancellation of this clip. The general level of the upper portion of thefrelquency spectrum. may be set by asuitable choice of the value 01' resistor l1. Increasing the value of this resistor decreases the relative degree of bass accentuation and also decreases the insertion loss of the network as a whole. Potentiometer I9 may be used to adjust the relative degree of bass accentuation, maximum accentuation being secured when the movable arm 25 is at the top of potentiometer I9. When slider 25 is at the bottom of potentiometer l 9, there is a marked loss in the bass portion of the frequency spectrum, due to the fact that capacitors I5, 22 and I6 are effectively in series with resistor I 1, acting as the load resistor.

In one particular embodiment of the circuit arrangement of Fig. 1, the following values of circuit components were found to operate satisfactorily:

Resistor 8 megohms 4.7 Resistor II ohms 390,000 Resistors l4 and I8 do 220,000 Resistor l1 do 7,000 Potentiometer l9 do 500,000 Capacitors 1, l5 and 22 microfarads 0.01 Capacitor I6 d 0.2 Vacuum tube 3 Type 6AV6 When the above values were employed in the embodiment of Fig. 1, the measured response curve was substantially that represented by curve 28 of Fig. 3. It will be observed that substantial accentuation of the bass frequencies is achieved and that there is no appreciable effect upon the middle and upper portions of the frequency spectrum.

Referring now to Fig. 2 of the drawing, it will be noted that the portion of the circuit to the left of capacitor I3 is identical with that of Fig. 1, which was described in detail above. A series network comprising a resistor 29 and a potentiometer 30 is connected between capacitor l3 and line 9. A capacitor 3| is connected between the movable arm or slider 32 of potentiometer 30, and line 9.

Capacitors 33 and 34 are connected between the junction 35 of capacitor 13 and resistor 29, and line 9. A shunt network comprising a resistor 36 and a capacitor 31 is connected between arm 32 of potentiometer 30 and the junction 39 of capacitors 33 and 34. Junction 39 is also connected to output terminal 26, output terminal 21 being connected to line 8.

In operation, resistors 29 and 36 and capacitors 3| and 34 constitute a network which attenuates the middle and upper portions of the frequency spectrum. Capacitor 33 provides a by-pass around this network for certain of the middle and high frequencies. The degree of accentuation of the bass portion of the frequency spectrum may be varied by potentiometer 30, which controls the effective reactance of capacitor 31 and increases the resistance in series with capacitor 3|. Maximum bass response is obtained if potentiometer 30 has a high resistance value. The capacitance of capacitor 3| serves to remove the dip or cancellation which otherwise would be present in the response curve.

Curve 40 of Fig. 3 represents the approximate response curve which was achieved with the embodiment of Fig. 2, employing the following values of components:

Resistor 8 megohms 4.7 Resistor ll ohms 360,000 Resistors 29 and 36 do 270,000 Potentiometer 30 megohms 5.0

4 Capacitors 1 and I3 microfarads 0.01 Capacitors 3| and 34 do 0.003 Capacitor 31 do- 0.001 Capacitor 33 d0 0.0005 Vacuum tube 3 Type 6AV6 It will be noted that curve 40, like curve 28, is substantially free from any appreciable dip in the middle-frequency region thereof, and that the embodiment of Fig. 2 provides marked bass accentuation and a relatively sudden transition to the level of the middle and upper portions of the frequency spectrum.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a system for transmitting a relatively wide band of audio frequencies, means for substantially attenuating the middle and upper portions of said frequency band without appreciably affecting the lower portion of said frequency band, comprising: a three terminal network having an input terminal, an output terminal and a common terminal; a series path including two impedance elements between said input and output terminals; a pair of series-connected capacitively reactive impedance elements connected in shunt with one of said two impedance elements; and another capacitively reactive impedance element and another impedance element connected in series between the common connection between said capacitively reactive impedance elements and said common terminal.

2. In a system for transmitting a relatively wide band of frequencies, means for substantially attenuating the middle and upper portions of said frequency hand without appreciably affecting the lower portion of said frequency band, comprising: a three terminal network having an input terminal, an output terminal and a common terminal; a series path including two impedance elements between said input and output terminals; a pair of series-connected capacitively reactive impedance elements connected in shunt with one of said two impedance elements; another capacitively reactive impedance element and another impedance element connected in series between the common connection between said capacitively reactive impedance elements and said common terminal, and a path of adjustable impedance between said output terminal and the connection between said another capacitively reactive impedance element and said another impedance element.

GARRARD MOUNTJOY. CURTISS R. SCHAFER.

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

UNITED STATES PATENTS Number Name Date 1,698,269 Konheim Jan. 8, 1929 2,037,285 Tasker Apr. 14, 1936 2,113,003 Van Slooten Apr. 5, 1938 2,121,150 Jarvis June 21. 1938

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