The L'Anse sentinel., 1923-02-09
PRESERVING TONE
IN LOUD SPEAKER
How This Can Be Done and the
Maximum Amount of Ampli-
fiCation Obtained.

/
Of every radio novice, us with one of
these instruments greater range Of the
received signals is obtained and the
necessity Of wearing the head phones
Is eliminated. The loud speaker also
permits d greater number of people to
| hear the concert, as with head phones
the number hearing the concert is
limited to the supply of head phones,
while with the amplification the num-
ber of people hearing the concert Is
limited to the range of the device.
There are several problems involved
In obtaining the maximum amount Of
amplification, and yet at the same time
preserving the original tone so that 1t
will retain Its pleasing qualities.
Most of these problems are involved
IN tile maintenance of the quality Of
the received tone, as 1t Is compara-
lively simple matter to amplify the
received signal sufficiently.
| III order to eliminate or minimize
loud speaker distortion, 1t Is necessary
to know the y causes involved. The
source Of the trouble may be In the
amplifier, In the loud speaker itself,
or in both.
Amplifier distortion may be caused
by unequal voltage transformations in
the coupling transformer at different
radio frequencies, by the operation Of
the amplitier tube ut the wrong point
of Its characteristic and by overload
Ing the tube to the point of saturation.
For good amplification Of telephone
signals, the inter-stage transformer
should be capable of giving a uni
form transfer Of voltage from about
200 to 5000 cycles per second. A good
many transformers now in use do not
do this, and their operation is one Of
the principal causes for unsatisfactory
signals. For any particular plate vol
tage applied to the amplifier tube there
Is corresponding value of negative
grid voltage which should be applied
in order to operate upon straight por-
tlOn of the characteristic curve and
thus secure uniform amplification.
For connecting to the loud speaker,
especially when using a power tube
for the last stage, 1t Is preferable to
use an intermediate transformer with
the proper constants, instead Of plac-
ing the loud speaker directly in the
tube plate circuit This keeps wind
ing and prevents the polarizing effect
that it would have upon the dia-
phragm.
A two-stage amplifer will general
ly give enough intensity to operate a
loud speaker In an ordinary living
room, while the loud speaker mechan-
ism itself may be of the head tele-
phone type with a suitable horn. Some
receivers operate very well at moder-
ate intensities, but when very strong
signals are applied to them they vi
brate so violently that the diaphragms
hit the pole pieces and produce harsh
sounds instead of good reproduction
Of the original signals. To handle the
proper amount of energy, therefore,
the construction must be such that rea-
sonably strong vibrations will not
force the diaphragm to its limit of
travel. The material and shape Of the
diaphragm are also important in de-
termining the resultant tone qualities,
since whatever natural periods of vi
bration 1t may have will bring out GER
tain tones In greater proportion than
they should be to the remaining tones
Of musical selection.
The size, shape and material Of the
horn are likewise important factors
In the final result. The high natural
period of small horn will tend to ac-
centuate the higher tones to the ex-
clusion of the lower ones. The ma
terial from which the horn Is made
should be some substance which will
not vibrate and produce rattling
sounds.
Thus we see that In order to pro-
duce combination Of amplifer and
loud speaker which will give pleasing
results, II Is necessary to choose the
various parts with care and assemble
them so that they will give a true re-
production Of the original signals.
Test Buzzer for Crystal Detector Set.
Those who have crystal detectors
when asking the usual question, "How
can best improve my set?" are usu-
ally Immediately told to get vacuum
tube detector outfit. This Is out of
tie question for many Of the crystal
set owners, since a six-volt battery
costs In the neighborhood Of $50 and
with the IS V. Il. and other accessories
the price of the unassembled parts
comes to at least S30
In order to get the best possible
"point" on crystal II Is absolutely nee
essary to use test buzzer.
Any buzzer or bell which depends on
battery current for operation will do,
although the higher-pitched buzzers
cola for radio ,yorL oviya n ,,,uch hot