Evening star. [volume] (Washington, D.C.) 1854-1972, 1922-05-20
Expert Advice on Radio
Article Cooperation of Head Phones

amount of current which will flow
through varies according to the de-
gree that the granules are pressed
together or are in contact.
When one speaks into the transmitter
mouthpiece the sound waves from the
voice cause the diaphragm, B, to vi
brate and this vibration, transmitted
through the bar. C, produces corre-
spending movement Of the receptacle,
d. thus alternately pushing the gran
ules together and allowing them to sep
arate. exactly as a pebble inside or a
drum will dance or jump about II the
head is struck. or an object on the
piano will jump about when the in
strument is played.
Current in Carbon.
AS a result. the current flows
through the carbon as the granules are
pressed together or ceases as they fali
apart, and so the sound waves OF the
voice against the diaphragm produce
the varying electrical currents in the
wires connected to the transmitter.
The receiver is even more simple.
This consists of an earplece, or holder,
A. figure 2. with thin diaphragm b.
placed close to. but not touching, bar
of iron, c. which is wound with coil
of fine wire. d. connected through the
wires, Il, to the set. AS every one
knows. a bar of iron will become trans
formed into a magnet when current OF
eiectrlclty Is sent tnIouSh WI VI
wire surrounding it and the moment
the current is shut off the magnetism
will cease 1t is this principle which
is used in the telephone receiver
If we imagine the transmitter a'read!
described. or the wires to the receiving
sci attached to the coil of the phone.
ID. we can understand that each time
the current flows through the WIRE the
core or bar. c. will be magnetized ana
will draw or attract the diaphragm. b:
and the instant the current is smut OH
and the bar loses its magnetism the
diaphragm will spring back. Each time
this occurs the diaphragm produces
sound and so the electrical impulses
or waves passing through the cor
around the core produce corresponding
sound waves by means OF the dia-
phragm.
Why Sounds Vary.
If these currents are merely inleI-
rupted electrical waves the SOUNDS
given off by the diaphragm Will be
merely sharp. buzzing sounds. such as
one hears when spark signals OF the
dot and dash telegraph codes are pelhe
received But if the varying electrical
waves are produced by music: the hu-
man voice or other means, the S.pla-
tions of the diaphragm in the receiver
nroduced nv these varying electrical
waves will be exact reproductions OF the
original sounds which varied the elec-
trical waves. -
For. lust as the voice in the trans
,,,i,te, nrnduced vibrations of the dia-
uhragm. which. by means of the carbon
gran,Iles were transformed INTO vary
ing electrical impulses. SO these I'M
nr,ises flowing through the coil of WIRE
about the core in the receiver VIII De
Transformed into vibrations OF the dia-
phragm, which moves BACK anu ioi III
in unison with them.
Thus. the sound waves entering , .te
transrnitter phone are changed INTO
electrical waves by mechanical means.
md the electrical waves entering the
nhone receiver are again changed INTO
sound waves by mechanical means.
Won can also readily understand that
Il makes no difference whether these
electrical waves from the transrnltter
are carried to the receiver over wires
of through the air, for so long as they
reach the receiver and flow through the
coil of wire about the iron core tney
will produce the same results.
Copyright. 1922