equipment primarily in an audiovisual presenta-
tion. You will be responsible for selecting,
setting up, and operating this equipment in a
variety of situations. These could range from
auditoriums and conference rooms to class-
rooms and offices. This section presents infor-
mation on the components of an audio system
and a representative type of audio recorder. You
will gain practical experience as you perform
your duties.
AUDIO SYSTEM COMPONENTS
Before you can effectively operate any type
of audio equipment, you must understand the
basic principles and the individual components
that go into an audio system. These individual
components will be discussed first. They are
(1) microphones, (2) amplifiers, and (3) loud-
speakers.
Microphones
The function of a microphone is to change
sound (mechanical) energy into electrical energy
which then is passed on to the amplifier. The
variations in sound waves are converted into
corresponding electrical variations. Since the
development of the first crude telephone
transmitter or microphone by Bell in 1875, many
types of microphones have been invented but
most have been discarded and now only a few
are used to any extent. In a microphone two
things are important: sensitivity and fidelity.
Sensitivity is the degree of electrical variation for
a given intensity of sound wave. Fidelity is the
ability to reproduce the audiofrequencies in
their proper relative magnitude without
generating other frequencies in the process. In
most of your work, the second requirement is
more important because the microphone is
primarily used so much in narrations. You
should use a microphone that can reproduce the
audiofrequencies and get high-quality sound. If
the sensitivity is low, the electrical output can be
increased by using additional amplifiers.
MICROPHONE TYPES.—Two types of
microphones are in current use in most facilities.
They are the crystal and the dynamic.
Crystal.—The crystal microphone is of
medium sensitivity and gives good fidelity at
speech frequencies. It is widely used in public
address work and radio other than broadcasting.
Dynamic.—The dynamic microphone con-
sists of a coil attached to a diaphragm which
holds the coil suspended in the field of a cobalt
permanent magnet. The speech waves cause the
diaphragm to vibrate and move the coils in the
field of the magnet and thus generate a voltage
in the coil. This assembly is almost universally
used for high-quality sound. Thus, the dynamic
microphone is especially suited for use in
recording and in public address systems.
G U I D E L I N E S F O R M I C R O P H O N E
PLACEMENT.—In recording sound, you must
have the proper placement of the microphone.
If it is necessary to record speech in a room
that is too “lively” (as in most classrooms and
offices), the microphone should be brought as
close as permissible to the speaker. In extreme
cases, any sound-absorbing materials that may
be available, such as coats, blankets, or burlap,
could be suspended at the sides of the
microphone about 3 feet away. Sound-
absorbing material may also be placed on the
floor and ceiling to absorb, as much as possible,
the reflected sound coming from these direc-
tions. It is not necessary to absorb the reflected
sound coming toward the back of a directional
microphone.
Remember that in sound recording you can-
not always place the microphone in the most
advantageous position for ideal sound pickup.
As a consequence, the microphone position is
often a compromise, Remember to consider the
position of both temporary and permanent
acoustical materials when placing the micro-
phone. It may be possible to improve sound
reproduction by simply moving the position of
the temporary acoustical materials. The follow-
ing rules will prove helpful in microphone place-
ment.
Never place the microphone next to
reflecting surfaces, such as tabletops and bare
walls.
7-35
