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A MICROPHONE BOOM

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					                       A MICROPHONE            BOOM

                         ELMER    C.   RICHARDSON*


  When sound motion      pictures were first produced in the Holly-
wood  studios, the sets were small, and no great difficulties were en-
countered in concealing microphones within the set, so that sound
could be satisfactorily picked up.
   As the sets became larger it became necessary to use a plurality
of microphones, and to fade from one circuit to another as the actors
moved  about. This operation of fading from one microphone to
another contributed to errors in recording which while excusable a
year ago would be highly criticized today.
  To obviate the use of plural microphones several devices were
used.  For instance, a microphone was sometimes suspended from
the ceiling by means of a cord and moved about with a long pole,
an operation quite obviously called "fishing." Some studios had
their property departments construct supporting arms or booms
which would facilitate the quick placement of microphones. Most
of these pieces of equipment were hurriedly made and crudely con-
structed and none too satisfactory in their operation.
  The Metro-Goldwyn-Mayer Studios, after some experimentation
with a microphone boom of this type, designed and built a boom
of the type illustrated in Fig. 1, which operated quite satisfactorily.
This   boom    consisted of a substantial base supporting a vertical
column which in turn supported a lever arm having an adjustable
portion which could be extended or retracted at will by operating
a cable drum by means of a crank from the floor. The under-
balanced portion of the boom and the weight of the microphone
was counterbalanced by a fixed counterweight and the boom operated
upon its vertical and transverse axes by an operating lever, as shown
in the illustration.
  While there are some sound engineers who object to the use of
moving microphones, many of the best technicians are convinced
  *
      Mole-Richardson, Inc., Hollywood, California.   (Read before the Society
at Washington.)
                                                                           41
42                             ELMER    C.    RICHARDSON                    [J. S.   M.   P. E.


that the inherent limitations of the microphone can be overcome by
silently moving the microphone to maintain it in a proper relation
to the sound source,          and by properly manipulating the                   fader.




          FIG.   1.   Microphone boom designed by Metro-Goldwyn-Mayer.




                 FIG. 2.   Extension tube    carrier,   Type   M-R   103-103A.

     As   is   true with   many     of our problems, the general principle in-
volved in this design         is   simple; the real problem, however, was to
July, 1930]                A MICROPHONE BOOM                        43

construct this piece of apparatus so it would operate with a degree
of silence which would in no wise interfere with sound recording.
  In the type illustrated, the sliding tube was operated by two
leather-faced friction rollers, which were rotated
                                                by a cable which
was wound over a capstan sheave.           The whole apparatus worked
quite silently,  but there   still        slight snapping sound as
                                     remained a
the wires of the cable changed their position on this capstan. To
overcome this difficulty, another type of extension tube carrier
was designed. (Illustrated in Fig. 2.) In this case, the extension
tube rolls in and out of the fixed tube, supported on a leather-faced




              FIG. 3.   Microphone boom, Type     M-R   103-103A.


rollerhaving an eccentric adjustment for centering purposes, but
instead of being moved by friction it is moved by a direct pull from
a cable attached to the rear portion of the sliding member and op-
erating in the annular space between the stationary and sliding
tubes. This cable passes back to a simple sheave supported at the
fulcrum point of the fixed tube and down to the operating drum.
It is wound around the operating drum several turns and passes
around another simple sheave at the fulcrum point, returning through
a sheave in the rear of the fixed tube, and is rigidly fastened to the
44                            ELMER   C.   RICHARDSON                 [J. S.   M.   P. E.



sliding member. This construction gives a positive motion to the
sliding tube with a construction which introduced no serious prob-
lems of extraneous noise. This type of boom (M-R 103) is illus-
trated in Fig.      3.

  A   number     ingenious suspensions for the microphones have
                 of
been worked out, such as hanging the microphone on rubber suspen-
sion loops and mounting upon sponge rubber shock absorbing mecha-
nisms.   One of the most successful mountings was worked out in
the Pathe Studios by suspending the microphone from the center
of a rubber diaphragm about six inches in diameter.    By means




          FIG. 4.        Microphone boom, Type   M-R   103- A (extended).


of these various rubber suspensions all "telegraphed" sounds were
withheld from the pickup circuit.
  Since the microphones have certain directional characteristics
many of the studios have taken advantage of this and constructed
suspensions which allow the microphone to be faced at will by the
operator.  In this way, for instance, if a conversation is being carried
on between two persons, the microphone may be faced from one to
the other, giving better recording results than would be the case
if the microphone were held in a constant
                                             position.
July, 1930]                   A MICROPHONE BOOM                     45


  Practically every major studio on the West Coast, and some of
the studios in New York, have been using these booms with good
success.
  A demand         arose for an automatically counter-balanced micro-

phone boom which could be operated from the top of a camera
booth. To meet this situation, the M-R Type 103-A boom was
developed. The same principles of design for moving the tele-
scoping portion have been incorporated in this boom as in the Type
M-R         but the counterpoise is mounted on a carriage which
         103,
slideson the rear portion of the fixed tube supported by leather-
faced rollers and operated by means of a sheave system working on
the principle of a double block and fall. The counterpoise moves
outward one foot when the sliding tube and microphone are extended
three feet. This gives the advantage of always maintaining the
boom in a state of balance, and by underslinging the boom from
its fulcrum bearing the boom will always return to a horizontal

position    when    it is   released.
  This     boom  mounted on a tripod which may be elevated (see
                   is

Fig. 4), and has a number of advantages which have been well ac-
cepted by the studio operating personnel.
   It does      not matter whether or not one objects to the use of the
moving microphones (other technicians are probably more familiar
with the pros and cons of that subject), the fact remains that micro-
phones must be placed. In the Hollywood studios, a picture of any
size iscarrying an overhead charge of from ten thousand dollars
a day up. Every minute gained in the production time is money
saved.  If you have ever observed sound operators trying to place

microphones by means of rope suspensions, fishing, etc., it is quite
obvious that a device such as has here been described has a very defi-
nite place in sound motion picture production.

				
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