International projectionist (Oct 1931-Sept 1933)

February 1933 INTERNATIONAL PROJECTIONIST 29 wave-length of a water wave is the distance between the crest of one wave and the crest of the next wave. This distance remains the same as long as the wave continues, even though the wave becomes so small as to be hardly perceptible. All waves produced do not have the same wave-length. A small pebble dropped into a pond will produce a wave of short wave-length, but a large stone will produce a wave of correspondingly longer length. In sound the wave-length is dependent upon the frequency of the source. Similarly, in sound the wavelength of a sound wave is the distance between the point of maximum compression of one wave to the point of maximum compression of. the next wave. This is illustrated graphically in Figure 2. (See also Figure 1.) Sound travels at different speeds in different substances, thus it travels at a much higher speed in water and steel than in air. We are interested only in sound traveling in air, where it travels about 1,100 feet a second. An illustration of the fact that time is required for sound to travel from one place to another is shown by a steam whistle at a distance of several hundred yards. If it is observed when blown, it will be noticed that the steam can be seen coming from the whistle a considerable length of time before the sound of the whistle is heard. Sounds of all frequencies, or pitches, travel at the same speed. Therefore, if we divide the speed at which sound travels by the frequency, we will obtain the wave-length of the sound wave. A knowledge of wave-length is necessary for the proper construction and location of baffle boards and horns, and will be discussed in more detail later on. Speech. — The sounds of speech are divided into two classes, vowels and consonants. The vowel sounds are used in the pronunciation of the letters "a," "e," "i," "o," "u," and sometimes "y," in the formation of words. These letters are also used in combination to indicate other vowel sounds. The pitch frequencies of the vowel sounds in male voices range from 110 cycles to 140 cycles. For female voices the range is from 230 to 270 cycles. The characteristics frequencies, or overtones of the vowel sounds, however, reach frequencies of 3,300 cycles. So important are these overtones that the pitch frequency can be entirely eliminated without noticeably changing the sound sensation produced on the human ear. The full range of frequencies used in vowel sounds is from 110 cycles to 4,800 cycles. The pitch frequency of the vowel sounds is produced when air is blown through the vocal cords. The vocal cords are two muscular ledges in the air passage of the throat. When these muscles are taut there is a narrow slit between them, which sets the air passing through into oscillation. The sound produced by the vocal cords is changed by the cavities of the mouth. The shapes iif liie (cavities continuously chyngc as a person speaks, making it possible for him to produce a wide variety of sounds, all of very nearly the same pitch frequency. Consonant sounds are usually produced without the aid of the vocal cords. Most of these sounds are produced by the lips and teeth, as in the pronunciation of "th," "s," and "f." The range of frequencies covered by consonant sounds is from 200 to 8,000 cycles, but most consonant sounds have frequencies of less than 6,000 cycles. Hearing. — The actual mechanism of hearing is not very well understood, but certain facts regarding the ability of the ear to register sounds of various frequencies have been determined very accurately. The range of frequencies which the average person can hear is from about 20 cycles to 17,000 cycles, but a comparatively large amount of sound energy is required before the ear can detect sound of extremely low or extremely high frequencies. The ear is most sensitive to frequencies between 500 cycles and 7,000 cycles; also, the ear is most sensitive to changes of pitch and changes of intensity of sound in this same band of frequencies. MATTER AND ENERGY.— The recording and reproduction of sound involves the use of energy in many forms, and matter in general. Everything with which we come in contact in our daily life is in some way related to energy and matter. Matter is anything which has size, shape and weight, that is, anything capable of occupying space. All matter is believed to consist of small particles, called molecules, which are in rapid motion, but travel only through very short distances. Matter is believed to hold its shape due to the mutual attraction of the particles. There are three classes of matter: solids, liquids, and gases. In solids the particles are relatively close together and, although the particles are in motion, the motion is of a very orderly nature, and considerable force is required to separate them or change the order of their motion. In liquids the motion of the particles is still very orderly, but the particles slide over each other with less difficulty, and they move at greater speeds than do the particles of solids. In gases the particles move more or less at random, and can be considered as knocking one another around, which give the gas a tendency to expand as pressure is released. The gases of the air are compressed by the weight of the air above, and as we go farther up from the surface of the earth the air is less dense. Energy is work, anything that arises as the result of work, or anything which can be converted into work. Such a statement is not clear in itself, but it will serve as a starting point for a discussion of energy. For greater clarity, energy can be classified into many different forms, the most common of which are mechanical energy, sound energy, heat energy, electrical energy and chemical energy. Energy cannot be created or destroyed. SUN -ARC CARBONS FOR PERFECT PROJECTION "Best by Test" BIG SAVING COMPLETE SATISFACTION BETTER LIGHT SLOWER BURNING • CARBON SAVERS (patent pending) free of charge. 2 Savers for each Theatre. Burn Hilow and High Intensity down to 2 Inches and less. CARBONS FURNISHED READY FOR USE WITH THE SAVER. No inconvenience whatsoever for the operator. HIGH INTENSITY CARBONS 13.6 are furnished 22 Inches long. They burn 8 minutes to one inch, as compared with 4% and 5% minutes, respectively, of other brands. Hi-Low Carbons (for 60-85 amps.) are precratered. They deliver 56 lumens per Ampere, as compared with 51 and 49 lumens, respectively, of other brands. SAMPLES ON REQUEST CARBON PRODUCTS, INCORPORATED 324 W. 42nd St., New York City