The Wrangell sentinel., 1923-04-05
PRESERVING TONE
 IN LOUD SPEAKER
How This Can Be Done and the Maximum Amount of Anlpli-
 fcaiion Obtained.

of every radio novice, as 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 alsU permits Il greater number of people 10 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- Der of people hearing the concert Is limited to the range of the device.
 There are several problems involved in obtaining the maximum amount o1 amplitication, and yet at the same time preserving the original tone SD that il will retain its pleasing qualities.
 Most of these problems are involved n the maintenance of the quality of the received tone. as it iS q compara- lively simple matter to amplify the received signal sufficiently.
 In order to eliminate or minimize loud speaker distortion, 1t is necessary to know the 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 o1 the amplifier tube at the wrong point of it's characteristic and by overload tnfr tho fnh ha fo hn Int af I'm. ian
 For good amplification of telephone signals, the inter-Stage transformer should be capable of giving uni form transfer of voltage from about POO 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 amplifer tube there is corresponding value of negative grid voltage which should be applied in order to operate upon a straight DOT tlon of the characteristic curve and thus secure bIniform amplitication.
 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 amplifier 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 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 req sOnably strong vibrations will not force the diaphragm to it's 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 vii bration it may have will bring out cer- tain tones in greater proportion than they should be to the remaining tones of a musical selection.
 The size, shape and material of the horn are likewise important factors in the final result. The high natural period of a 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 a combination of amplifier and loud speaker which will give pleasing results, it is necessary to choose the various parts with care and assemble them so that they will give true re- production of the original signals.