The Monmouth inquirer., 1925-05-07

speech under comparatively uncritical
conditions, it would not do at all for
-broadcasting. In the first place, it
would be far too noisy. That is. the
average transmitter produces a GER
tain amount of continuous hiss and
crackle which would be intolerable in
~high-grade ~broadcasting. So that,
when carbon grain transmitters are
used, it is necessary TO fill them with
a special grade of carbon and to S
very small currents through the a
bon so that they-the transmitters-
will produce a minimum Of such OBJ
jectionable noise. Otherwise the de-
sired Velvety silence when the artists
are not singing will be missing and
the audience will be distracted and
annoyed by the hiss of the transmit
ter.
A second. objection to ordinary tele-
phone transmitters is that they exag-
gerate certain frequencies of the voice
or music very markedly because the
vibrating diaphragm or metal sheet
Of the telephone transmitter against
which one speaks responds most Wig
N~orusly, or ''resonates," at certain fire.
q~uencies or pitches. This is not &C
ceptable in sending out music. Par
ticularly dangerous would be the ef-
feet of such Partially for certain
notes if the transmitters were used
for sending out an orchestral selec-
ton. Some instruments would be
partly suppressed and others exagger-
ated. thus spelling the effect. So that
It becomes necessary to use a tele-
phone t~ransmitter which has a dia-
phragm which responds as evenly as
possible to notes Of all pitches. One
way of doing this is to use a thin and
powerfully stretched diaphragm Of
steel or some other strong material
which will respond equally to all usual
tones. Another way is to use the so
called glow microphone" where the
vibrating element is a small column
of glowing gas through which a small
electric current is passing. Yet other
methods are available, but most of
them not particularly simple.
Microphone Picks Up Sounds in Studio
The telephone t%ransmitter used for
pickup in the studio has to be suit
ably mounted and wired up to the
rest of the equipment.
The amount of power which it is
possible to get from these high-grade
telephone transmitters is nearly al
ways very small. and it becomes nee
essary to amplify it by means of a
powerful amplifer. This amplifer
must also be free from noise-produc-
ing tendencies and must amplify notes
of all pitches equally. Both these re-
~quirements are very difficult to meet.
Either resistance-coupled ampliiers
have to be used, or else the greatest
care has to be taken in the design
of the special transformers used in a
transformer-coupled amplifer for this
work. Ordinary ampiiiers would not
serve at all, as is sometimes evident
when listening to the music" ema
mating from a badly designed broad
casting station.
A suitably designed ampiiier of
elaborate construction is found in the
control room of Broadcast Central,
Stations WY and WIZ of the Radio
Corporation of America at Aeolian
Hall, New York City. This amplifer is
really two ampliiers, one at the top Of
the case, and the other at the bottom.
Special relays permit either amplfier
to be used at will so that there is
always a spare ampliier available IN
case a tube burns out or some other
defect develops in one Of the ampfi-
fiers. The control engineering at
tendant 1t these amplifers is perforce
chained to his post during the entire
performance listening to every note
that goes ont through special 'moni-
sets" and maintaining loudness
and quality of the music by the suit
able controls which are provided. He
has a number of special colored
signaling lamps before him on the
control room amplifer so that he
knows just what is going on in the
studio and whether the transmitter
which he controls is actually con the
air" (that is, transmitting) or not.
Clearly c~arelessness and simplicity
have no place in either the design or
the supervision of the pickup trans
mitter and control room amplifier Of
a satisfactory broadcasting station.
The broadcast listener would do we'll
when he is especially pleased by the
clarity and excellence Of an evenings
performance to remember something
of what has been done by brain and
Drawn" in reproducing in his home the
intricate and yet delightful melodies
and sounds which make up the broad
cast program.
(To be continued)
o1-.e- -u. ra1o