Microphone control system

March 18, 1941. i. r. goshaw 2,235,518

MICROPHONE CONTROL· SYSTEM Filed Aug. 27, 1938 2 Sheets-Sheet 1

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March 18, 1941.

I. R. GOSHAW MICROPHONE CONTROL· SYSTEM

Filed Aug. 27. 1938

2,235,518

Sheets-Sheet 2

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Patented Mar. 18, 1941

2,235,518

UNITED STATES PATENT OFFICE 2,235,518 MICROPHONE CONTROL SYSTEM

Irl R. Goshaw, Beverly Hills, Calif., assignor to Radio Corporation of America, a corporation of Delaware Application August 27, 1938, Serial No. 227,054

Claims.

This Invention relates to talking motion picture apparatus and particularly to a boom system for placing a microphone in its optimum position for detecting a moving source of sound or 5 different sound sources within a prescribed area, such as a motion picture set.

Accompanying the photographing of motion pictures, sound is picked up by a microphone, and it has been the general practice to suspend the ¹⁰ microphone on the end of the telescoping cross arm of a boom, the microphone being raised, lowered and moved horizontally by movement of the cross arm. So as not to unnecessarily move the microphone during recording, the boom is ¹⁵ generally placed so as to position the microphone at some fixed position where all the sounds may reach it with comparable energy and a similar frequency response if the microphone is always directed at the particular source of sound, re20 gardless of its position on the set. To change the microphone’s direction, it must be rotated so as to follow the movement of a sound source about the set or to shift from one source to another in different parts of the set.

Several methods of and means for accomplishing the rotation of a microphone at the end of a boom have been suggested and patented. The use of a motor for accomplishing this result is disclosed in U. S. Patent 1,924,679, 30 this practice, however, having the fault of creating electrical disturbances caused by the operation of the motor, which are picked up by the immediately adjacent microphone. An advance over the motor control is shown in U. S.

Patent 2,122,778. This improvement employs a purely mechanical system which, although eliminating electrical motor disturbances, does create wind reaction and complicates the mechanism of the boom structure, as it is necessary to provide 40 means for extending and withdrawing the operating cables, as shown in the patent. Other mechanical systems have been employed, such as square shafts and bevel gears which may be rotated by the boom operator to rotate the micro45 phone.

The present invention eliminates the motor and all mechanical devices and permits the microphone to remain absolutely fixed while effective rotation thereof is obtained. The oper50 ator need only rotate a knob on a dial similar to a ridio receiver to follow the sound source about the set without actually moving the microphone in any respect. The boom structure is rimyiHfled since only the usual dectrical cable 55 extension from the microphone is required. The (Cl. 179—1) electrical circuit used is based upon the disclosure in U. S. Patent to L. J. Anderson, No. 2,173,219, of Sept. 19, 1939, and the microphone is of the type shown in U. S. Reissue Patent 19,115 of March 13, 1934. 5

An object of the invention, therefore, is to simplify a microphone boom construction while providing means for accomplishing all the necessary movements of the microphone.

Another object of the invention is to obtain ¹⁰effective rotation of a microphone mounted on the end of a boom without any physical movement of the microphone.

Another object of the invention is to reduce interference with the pick-up sensitivity of a ¹⁶microphone.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the claims appending herewith, the invention itself, its objects 20 and advantages, the manner of its organization and the mode of its operation will be better understood by referring tp the following description read in conjunction with the accompanying drawings forming a part thereof, in which:

Figure 1 is a side elevation of a movable microphone boom embodying the invention;

Figure 2 is a circuit diagram employed in Fig.

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Figures 3, 4 and 5 are characteristic curves of the microphone used in the invention.

Referring now to Fig. 1, a truck having wheels a and 6, crosspieces 7, and braces 8 and 9 has mounted thereon, a column member i i. Pivoted and rotatable on the column 18 is cross arm 92 having a telescoping endpiece 13 at the end of which is mounted a microphone cradle support IS resiliently supporting, by rubber bands or springs 86, 87, 18 and 89, a microphone pre-amplifier 2 8 and microphone 22. The cradle, micro- 40 phone and amplifier are not rotatable in. any manner with respect to the end of the arm 13.

To the left of the column 8 8, the arm 12 has mounted thereon a traveling counterweight 26 hung on a roller block 25. The arm 93 is extend- 45 ed and withdrawn within the arm 12, and the weight 26 moved correspondingly to balance the arm 83, by actuating a bell crank 26 operating on a wheel 2T rotatable about the pivot point 28. Two cables shown by the dotted lines ar® 50 also employed for this purpose. One end of one of the cables is attached to the inner end of arm 13 at 36, from which the cable extends around a pulley 81 at the left-hand end of the arm (2, around a pulley 32 on the block 25, a pulley 88 W

2,235,518 at the end of the arm 12, and then to point 34 •where it is attached to the block 25. The other cable is attached at 36 to the arm 13 and extends around a pulley 37 at the right-hand end of arm 5 12, around actuating pulley 27, to a pulley 38 on the block 25, to a pulley 39 attached near the pivot point of the arm 12, and then to a point 40 where it is attached to the block 25. Thus, . rotation of the pulley 27 in one direction will 10 extend the arm 13, and rotation of the pulley 27 in the other direction will withdraw the arm 13, the weight 24 traveling along the left-hand end of the arm 12 to counterbalance the weight of the microphone and associated elements as their dis15 tance varies from the column if.

The pick-up leads from the microphone are contained in a cable 42, which is attached to the arm i3 at 43, then extends over a pulley 44 at the right-hand end of arm 12, then around one 20 of a pair of pulleys at 45, over a pulley 46 mounted on the traveling block 25, then back over another pulley at 45, and to the column 11, where it is attached at 47. The cable ¢2 then extends to a dial 50, the output of which is fed into an 25 amplifier 51 and then to a recorder 52. Thus, the extension and withdrawal of arm 13 do not cause any slack in the cable 42, since the traveling block 25 takes up the slack automatically. For positioning the microphone, therefore, the 30 truck is first placed, then the pulley 27 rotated to extend the microphone, after which the arm 12 may be rotated on the column 81 to further position it. Thereafter, the microphone may remain absolutely fixed with respect to a certain 35 scene, the action being followed solely by the turning of a knob 54 at the dial 50. Although an amplifier 21 has been shown positioned adjacent the microphone 22, this is not a necessity and this amplifier may be positioned on the column 40 ί i or Included in the amplifier at 51.

Referring now to the circuit employed to produce the rotational results above-described, reference is made to Fig. 2 wherein the microphone 22 is shown as comprising a pair of slightly 45 crimped conductive ribbons 60 and 61 mounted at right angles to one another between respective magnets 62, 63 and 64. The microphone ribbon 60 is connected through transformers 66 and 67 with the input of a vacuum tube 68 having a 50 biasing resistance 69 and bypass condenser 70 In its cathode circuit. The output of ribbon 61 is similarly connected through transformers 70 .and 71 to the input of a vacuum tube 72 having biasing resistance 13 and the bypass con55 denser 74 in its cathode circuit. It will be noted that the input to tube 72 is connected in phase opposition to the input to tube 68.

The outputs of tubes 68 and 72 are capacityresistance coupled by condensers 68' and 72' and 60 resistances 69' and 73’ to respective tubes 76 and 77 through respective potentiometer resistances 78 and 79, these last resistances being arranged in circular formation so that sliders 80 and 81, respectively, may be operated sfinultane⁶⁵ ously through a connection 83. The other terminals of resistances 78 and 79 are connected together and to ground at 87. The connection 83 has a pointer 84 mounted thereon for cooperation with a dial 85. Thus, by the turning of ⁷⁰ the knob 54 (see Fig. 1), sliders 80 and 81 are moved over their respective resistances in such a manner that when one resistance is entirely out, the other resistance is entirely in, and vice versa, thus making either ribbon 60 or 61 effec75 tive. Intermediate positions utilize both ribbons simultaneously and produce intermediate patterns, as will be described.

The output of the potentiometer 50 is impressed on tubes 76 and 71, mentioned above, amplified therein and transmitted through trans- 5 former 89 for transmission to a recorder or other load circuit.

Referring now to Figs. 3, 4 and 5, when the pointer 84 is to its extreme left position, the microphone characteristic will be in accordance 10 with Fig. 3 and will, therefore, be directional to a sound source positioned in the neighborhood of 45° with respect to the front position of the microphone. With the dial pointer 84 in the extreme right position, the microphone character- 15 istic will be in accordance with Fig. 4, or at an angle of 90° with respect to the characteristic of Fig. 3, since the ribbons 60 and 61 are at right angles. With the pointer 84 in its central position, the characteristic of the microphone 22 is 20 shown in Fig. 5. Intermediate positions of the pointer will provide the microphone with intermediate characteristics. This variation of 90° is satisfactory for the majority of sets since the characteristics are circular though greater varia- 25 tions are obtainable with different settings of the microphone ribbons. It is to be understood that separate microphones positioned at right angles may also be employed without departing from the spirit of the invention. 30

Thus, without actual physical or bodily translation of the microphone 22, effective rotation thereof is obtained by the simple manipulation of the knob 54 on the dial 50, which eliminates wind resistance and disturbances caused by move- ⁸⁵ment of the microphone while simplifying the boom structure itself.