Radio broadcast .. (1922-30)

There Are No Noisy B Batteries By E. E. HORINE National Carbon Company THE appearance of the usual block type B battery is more suggestive af a paving brick than a fine musical instrument, yet in radio-telephony the B battery becomes one of the most versatile musical instruments known. On occasion, it reproduces perfectly the music of a violin, a French horn, or an entire symphony orchestra, for everything heard from a radio set, whether it be speech, or music, or code signals, proceeds directly from the B battery to the ear of the listener. True, the immediate source of sound is the telephone receiver, or loud speaker. But these devices do not generate the sound; they merely serve to transform electrical energy into sound, much as the electric lamp transforms electrical energy into light. In the case of the lamp, the real source of light is the generator in the power station; with the telephone receiver, the actual source of sound is the B battery, for it supplies the current which operates the receiver. The work done by the B battery in reproducing sound is rather complicated, and to get some idea of its nature, it will be necessary to touch lightly upon the subject of sound. Sound is a wave motion, consisting of alternate layers of compressed and rarified air. Sound waves may be generated by any vibrating body. In radio receiving sets, they proceed from the vibrating diaphragm of the telephone receiver. Each sound in nature has a wave-form which differs in shape from the wave-form of every other sound. These wave-forms are usually quite complex, and the difference between them is sometimes minute, but it is the tiny variations in the shape of the waves which enable the ear to distinguish between musical instruments, or to identify individuals by the sound of their voice. When a sound wave strikes a diaphragm, the compressed layer of air pushes it in one direction, and the rarified layer pulls it back in the opposite direction. If the diaphragm is properly constructed, and is sensitive enough, its motions will follow accurately the waveform of the sound. The illustrations (Figs, i to 5) were made by recording the motions of such a diaphragm. The motion of the diaphragm is transferred by suitable mechanical devices to a small mirror, on which is concentrated a beam of light. As the mirror swings back and forth due to the motions of the diaphragm, the spot of light reflected from the tiny mirror also swings back and forth on a sensitive photographic film, which moves past the mirror at a uniform speed. The moving spot of light is thus made to trace on the film a permanent record of the sound wave. These records were made by Professor Dayton C. Miller in his laboratory at Case School of Applied Science, and will serve to illustrate the manner in which sound waves from various sources differ from each other. Fig. i is a reproduction of the sound wave produced by a tuning fork vibrating 256 times a second (Middle C). This is an example of a pure tone, consisting as it does of the fundamental only. It is a pure sine curve, and is, perhaps, the simplest sound wave in nature. The curve in Fig. 2 is somewhat similar to that of Fig. i , but it will be observed that there is a series of overtones superimposed on the fundamental, appearing as minor ripples on the main curve. It is the number, amplitude and position of these overtones that give "quality" to the sound, and enable the ear to identify the instrument producing it. This particular record was made by a violin. Fig. 3, was produced by a French horn. Here the overtones almost overshadow the fundamental, which accounts for the peculiar booming quality of the sound produced by this instrument. Figs. 4 and 5 are records of the human voice. Both were made by the same individual, Fig. 4 being produced by the sound "do", and Fig. 5 by pronouncing the vowel "ee". These curves are comparatively simple, representing as they do a single sound preceding from only one instrument or voice. The complexity of the curve which results from blending the individual wave-forms of seventy or more instruments all playing at once is simply beyond comprehension! And yet, if a