International projectionist (Oct 1931-Sept 1933)

January 1933 INTERNATIONAL PROJECTIONIST 17 ment. The piccolo, for example, is shown at the top and to the right of this group of brackets. Its range, in frequencies, is from 512 to 4,608 cycles per second. That is, sound from the piccolo will produce anywhere from 512 to 4,608 waves of compressed air in each second. The violin is shown to have a frequency range of from 192 to 3,072 cycles per second. A number of other instruments are listed, of which the bass viol reaches the lowest note, 40 cycles, and the piccolo, as said, the highest at 4,608. In this same group of brackets, between the musical scale and the piano Iceyboard, is a group of five brackets — the five lowest — showing the range of the human singing voice. Bass, baritone, tenor, alto and soprano are shown, the liuman bass reaching as low as 80 cycles, and the soprano as high as 1,152. Importance of Harmonics But this is not all there is to sound. The little ripples, or harmonics, are of the greater importance. If they did not exist, all notes of the same frequency would sound alike no matter what instrument played them or what voice sang them. Excepting the bass viol, the kettledrum and the piccolo, every instrument and voice shown on this chart can produce "middle C" — 256 cycles per second. Yet this note does not sound the same when sung by a bass and by a soprano, played by the violin and by the piano. In each case it will carry with it a different pattern of those small ripples called harmonics, which distinguish one instrument or voice from another. To the light of the piano keyboard there is the number 10,000, with the notation, "harTTionics of musical instruments," indicating that some of the smaller ripples are so small that with sound traveling at 1,000 feet per second, 10,000 of them can crowd into one second; obviously then, some of these very small waves that follow so rapidly upon each other are little more than one inch long. At the extreme left of the keyboard is the number 16, with the notation, "Point at which sense of feeling begins before sense of hearing"; — this refers to the lowest notes of a large organ which, as everyone knows, seem to be felt quite as much as they are heard. These waves, of which only 16 arrive in one second, are more than 60 feet in length. Auditory Limits At the far left of the keyboard are the figures 12.000 and 16,000, the upper limits of hearing for older and for young NEW DUOVAC 205-D TUBE THE marked improvement in 1. It is not susceptible to breaksound quality caused by the in down when temporarily overloaded, troduction of the Duovac thoriated 2. Due to the fact that there is no tungsten filament -242 with a mo coating on the thoriated tungsten lybdenum plate, which by this time filament, the heating period is alhas entirely superseded the old type ^^^^ instantaneous and uniform. 211-E oxide-coated tube with nickel o tt. ^u • . j . m 1 ^ ^1 • ^ »• u o. Ihe thoriated tungsten filament plate, prompted an investigation by , , ^ , , fu T?- r»» ? T\ can stand momentary overloads as the Engineering Dept. of Duovac ^. , ^^ j^^ ^^^^ ^ Radio Tube Corp. into the possibil ^ ity of incorporating the same im 4. Thoriated tungsten type tubes provements into the oxide-coated ^re, as a rule, far more uniform in filament type 205-D. general characteristics and thereExperiments on the design of such ^ore practically eliminate the deliba tube were begun several months erate selection of tubes, after the introduction of the 242, 5. The use of molybdenum plate and although various obstacles had will permit a considerable overloadto be overcome to make this type ing of the tube without causing pertube conform to the characteristics manent damage. In other words, of the oxide-coated filament 205-D, molybdenum plate permits degassithe developmental and experimental fication to a greater extent than does work has been brought to a satisfac a nickel plate, and therefore does tory conclusion and the new tube not liberate gas when overloaded, placed on a production basis. The sandblasted rough surface of The advantages of this new Duovac molybdenum plates allow cooler op205-D tube are as follows: eration at all times. General Rating New Duovac 205-D Tube Filament Current 1.6 1.6 1.6 amps. Filament Voltage 4.5 4.5 4.5 volts Plate Voltage 250 300 350 volts Negative Grid Voltage 15 20 25 volts Plate Current 22 25 28 mills Mutual Conductance 1,650 1,700 1.700 micromhos Amplification Constant 7 7 7 Thank You! Our appreciation is extended to all those who in commenting on the present series of articles by Mr. Nadell made suggestions which will prove valuable in outlining a new series bv the same writer. — Editor. persons, respectively. There are sound vibrations of higher frequency than can be sounded on instruments. Sound vibrations of at least 100,000 cycles can be created artificially, and have been shown to be deadly to insects and to small animals like mice. But these figures—12,000 and 16.000— mark the shortest waves of sound that human ears can hear. They lie above the limits of any ordinary musical instrument, above even the more important harmonics. The chirping of some insects lies in this region of many thousands of sound waves in one second. Below the keyboard are five groups of arrows, properly labelled, showing the frequency range of theatre sound systems, of radios, phonographs, telephone instruments and telephone circuits, etc. The fourth of these groups from the top is perhaps of greatest interest to the projectionist. It shows that a "hill-anddale" cut record is capable of recording from 30 to 10,000 waves of sound per second, while the lateral-cut disc commonly used in theatres of today is restricted to a range of from 60 to 6,000. At that, the theatre-type record is far superior to that of an old-fashioned phonograph (the bottom group), which was limited to from 256 to 3.000 cycles. Again, the fourth of these groups from the top shows that the film sound track has no lower limit, being capable of recording one wave a second or one an hour — if the loud-speakers (third group from the top) could reproduce them or the human ear hear them — and has an upper limit of 8,500 waves of compressed air per second. The projectionist may be interested in studying some of the other limits shown in these five groups of arrows. Underneath them, again, it is indicated that the sound of Niagara Falls has a frequency of from 40 to 50 waves per second, thunder and distant gun fire of from 20 to 40. The average male speaking tone is shown as 128 cycles, the average woman's as one octave higher, or 256 cycles. These figures, of course, refer to the TONE of the voice. Every sound spoken has its own frequency: 's' and 'f sounds in the deepest male voice do not have a frequency below 3,000 cycles, and their harmonics may run up to 8,000. It is the melody behind the voice, so to speak, that is pitched at the low figures given at the bottom of this chart. At the extreme right of the chart, beside the first and second group of arrows, the squeak of a door is placed