Evening star., 1924-07-13
PROBLEM IS FOUND
IN LOUD SPEAKER
Its Use in Radio Concert
Work Not Always Regard
ed With Favor.
long ago. when broadcasting

Not long ago, when broadcaSting
was more or less of Il novelty, it
was common with many enthusiastic
expermenters to entertain their
friends with radio concert. After
the loud speaker had been induced
to operate, the congratulations of the
guests were made with effort. the
more candid of the critics declaring
that if the barnyard chorus coming
from the horn was radio, they would
be content with a phonograph.
There were many fans, it is true
who overlooked the obvious imper-
fections in the reproduction of the
human voice. The marVelousness and
mystery of radio itself was quite Suf
ticient to outweigh any shortcomings
of the loud speaker. Recently the
demands have become more critical
and the radio public have been in
SiStent that the loud speaker should
not be the cause of imperfect re-
production.
Different Loud Speakers.
Sooner or later you will wish to lay
aside the headphones and attach a
loud speaker to your radio, so that
the younger folks can dance by the
music and the whole family can en-
JOY the programs without the in
convenience of wearing headphones.
When this time comes you will be
confronted with the problem of Sc.
lectinE loud speaker that Will
faithfully reproduce. without distor-
ton or noise, the quality OF the radio
programs that you have been enjoy
ing with the headphOnes.
In its present usage. the term loud
speaker is applied generally to cleo
trODhonlC devices amnlDVlng
means of distributing sound over an
area. 1t is possible to divide loud
speakers into three separate and dis
tinct classes, however:
/. Those which make use of exist
Ing telephone receivers by means of
rubber conncters or clamps to attach
pair OF phones to horn.
>. The type of speaker that uses
a single telephone receiver equipped
with cap to permit its being fast
ened to the small opening of a horn.
in this class can be included the
numerous loud speakers that incor-
porate "A telephone of some sort in
the base of the horn.
B. The loud speakers constructed
on the Solenoid principle, in which
the current act on a coil placed in
the field of Il strongly energized mag
net
Excellent in Limited Way.
The first and second types of loud
speakers are excellent in their own
limited way. However, there are a
few serious faults that entirely pre-
vent them from being considered as
frStclass loud speakers. One is that
they cannot be used on very strong
signals without causing the diaphram'
to strike the pole pieces of the small
fixed magnet and produce a rattle
IN the loud speaker.
Another SPri0nS limit a tn
class of loud speakers is that when
high b battery Voltages, such as are
common lns most audio frequency
amplin~rs, are used a DC current
flows through the windings of the
phone and eNerts a strong downward
pull on the diaphragm This causes
the metal diaphragm to be drawn
out of shape and will cause the loud
speaker TO have hollow or tinny
sound.
The vibration of the metal dia-
phragm toward and away from the
poles Of the magnet in the unit will
cause the air gap to vary. This, in
turn, VIII cause the Impotence (alter-
mating current reSistance) of the loud
speak to vary and has a great deal
to do with the proper operation of
the receiving set itself on weak or
distant signals. The impotence of
the loud speaker has it's function in
the tuning and balancing of the re-
celVeT. and if it is fiuctuating will
have its effect in upsetting the ac-
curdte tuning of 4 receiver.
Not Necessary in Third Type.
In the third type Of loud speaker
this factor need not be considered.
as the air gap is constant and fuc-
tuations of current through the wind
ings Of the loud speaker do not
change the impotence of the circuit
The DC current from the B battery
doeS not act on the diaphragm of
loud speakers such as the Thorophone,
ana less distortion may be expected.
AT the same time the third type of
reproducer will not rattle or freeze"
on extremely loud signals, yet will
give a greater amount of sound on
extremely weak or faint signals. A
mica diaphragm, one of the most
perfect substances known for sound
reproduction. is used, whereas in
most of the other classes Of speakers
metal diaphragm must be used, re-
suItlng IN a greatly inferior tone
quality.
shape of Horn n Factor
The particular shape of the horn
has great deal to do with the per-
formance of any loud speaker From
theoretical point of view a. straight
norm is better than a curved one and
the amount of increase in the size
or the horn in proportion to IFS
length must be very carefully calcu-
lated for best results. When this is
once obtained the horn can be curved
into most any shape without DESTROY
ing its amplifying value or tonal
qualities
The material of which the horn is
composed is very important in re-
gard to the quality of music that
VIII be received and with the faithful
ness with which the sounds are re-
produced. A horn made of wood ~
paper mache gives a purer tone tban
metal one, which is liable to pro
duce braSSy ovortones or vibrations
Horns made of some inert material,
Such as thorlte. which will not vi
brate or absorb the sound wayes
nave been found to be the most salts,
factory for loud speaker use