e transmitter must be used in free space where the flow of
air particles is unimpeded. “Pick-up” from the rear of the mi-
crophone is eliminated by the design and construction of the
unit.
PART II — OPERATION
6. Microphone Assembly.
—e Type 77-A uni-directional
microphone is shipped with the stand flange attached by means
of three screws to the microphone mounting yoke. e suspen-
sion fitting is shipped in an envelope in the box with the micro-
phone unit.
(a) Stand Mounting.
—If it is desired to mount the microphone
unit on a program stand, it is necessary merely to screw the mi-
crophone (using the stand flange) securely to the stand column.
See Section 9. List of Parts and Accessories, for the type of stand
recommended for this purpose.
(b) Suspension Mounting.
—If it is desired to suspend the mi-
crophone overhead, the stand flange must be removed from the
microphone mounting yoke and replaced with the suspension
fitting, which contains the eyelets for cord attachment. e fit-
ting must be attached securely to the yoke by means of the three
screws formerly used for mounting the stand flange.
NOTE.—When the microphone is suspended, see that its
weight is carried on the suspension fitting, with no
strain on the cable.
(c) Cable Connections.
—e microphone is shipped with the
microphone cable already connected at the microphone termi-
nal board. is terminal board is rendered accessible for inspec-
tion or service by taking out the three screws located about the
microphone screen mounting flange and removing the screens.
(d) Phasing.
—When more than one microphone is used in a
single pick-up, it is possible that the output of the of the various
microphone circuits may not be in phase when fed into a com-
mon circuit. e microphone circuits include the microphones
themselves, microphone pre-amplifiers, microphone attenua-
tors (mixers) and the necessary connecting lines. e output of
the microphone attenuators (mixers) when fed into the overall
attenuator (mixer) must be in phase, or varying degrees of dis-
tortion will result, depending on the relative placement of the
microphones. If two microphones are placed close together, the
result will be practically zero output if their circuits are out of
phase at the overall mixer.
To check the phasing of two or more microphones connected
in a single pick-up, place the units close together, two at a time,
with the attenuators (mixers) turned to the off position. Turn on
the attenuator of one microphone to some arbitrary position
where the output will be distinctly audible or register definitely
on the volume indicator meter, if such a device is used. Talk into
the microphone and note the output volume. Now, without dis-
turbing the setting of the attenuator of the microphone just
used, turn on the attenuator of the second microphone to the
same setting. Talk into the two microphones and note the result.
If there is an increase in volume, the microphones are in phase.
If there is a decrease in volume, remove the screen of one mi-
crophone and reverse the connections at the microphone cable
terminal board. If more than two microphones are employed,
using one microphone as a reference, check the other units
against it, one at a time, in the manner outlined above. If any
are found to be out of phase, reverse the cable connections, at
the microphone cable terminal board, of the lesser number of
microphones necessary to bring all the units into phase. A
thirty-foot cable is furnished as part of the microphone equip-
ment. e microphone plug must be furnished by the customer.
For microphone connections refer to Figure 4, Schematic
Wiring Diagram.
7. Technique of Uni-Directional Microphone Placement.
—
e proper placement of the microphone is essential in order
to realize fully its inherent advantages. For this reason, the fol-
lowing instructions should be carefully studied, and close at-
tention should be given to the results of any special placement,
with a view toward future improvement of technique. ese in-
structions can, of course, serve only as a guide, and a study
should be made to determine the best microphone placement
for each condition.
(a) General.
—e Type 77-A uni-directional microphone has
a pick-up angle of approximately 150 degrees. e source of
sound, speaker, announcer, actor or musical instrument, should
not be placed closer to the microphone than 2 feet, and a dis-
tance of from 3 to 4 feet is to be preferred. At shorter distances
Figure 4—Schematic Wiring Diagram of Microphone
Summary of Contents for 77-A
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