THE LOUDSPEAKER

Radio Record, Volume I, Issue 14, 21 October 1927, Page 2

THE LOUDSPEAKER

A WONDERFUL DEVICE Yo compress an entire orchestra into a tiny circular sheet (the diaphragm of a loudspeaker) this is the audacious demand of the modern radio engineer when he insists. that the loudspeaker shall reproduce perfectly for the broadcast listener the concert which is being given at some broadcast station studio. The problem is really a comparatively recent one. While telephone receivers have been known for fifty years, they were generally adapted only to reproduce the voice feebly and with fair accuracy at best. It was necessary to press them to the ear to understand well, and they failed to reproduce music with any reasonable degree of satisfaction. If it was attempted to make loudspeakers of them, they rattled and distorted the music badly. A new electric and acoustic technique has had to be developed to meet the reqnirements of an effective loudspeaker. Only after considerable research and development has it become possible to produce such devices which will accurately follow their vocal masters at the broadcast studio. Difficulties To Overcome. A jittle consideration will indicate wh the construction of a satisfactory loudspeaker is so difficult. It must faithfully reproduce all sounds from freqgencies as low as fifty vibrations or cycles per second {corresponding to the deepest tones of the organ and piano) to frequencies as high as eight or ten thousand cycles per second, corresponding to the highest overtones of the violin or piccolo and certain of the overtones of the spoken consonants ‘'s" and "£2? It must be capable of producing

soft, pure notes and also extremely loud notes, so that the expression and meaning of musical conrpositions or oratorical efforts shall not be lost. It must accurately reproduce, in correct proportion, the voice and its piano accompaniment, or the various instruments which blend into an orchestral ensemble. And, when finally produced, it must be a sightly or even ornamental article, since its place is generally in the home. Don’t Blame Transmission. Great care is taken at high-grade broadcasting stations to ensure accuracy of quality in the concerts sent out from such stations. In fact, a great deal of the distortion imputed by some listeners to the station is really due to their unsuitable londspeakers. The experience is often repeated of listening to an exquisitely rendered concert from a definite station on one receiving set, only to. be amazed at its poor quality on a near- | by receiving set. It is for this reason | that the listener should suspend judgment on the quality of a concert until he has proven beyond doubt that his receiving set is correctly designed and used, and that his loudspeaker is a good example of a reliable product. The method of supervising the quality of transmission by ear and ey2 at some big station is most interesting. The supervising engineer listens to the quality of the music on a suitable receiving set, and at the same time watclies 2 wavering line of light on the oscillograph mirror whereby he can tell the strength and, to a great extent, the quality of the outgoing concert. The broadcast listener would be amazed at the extreme complexitv of the sound waves shown on the oscillograph mirror. They look’as complicated as a cross-sec-tion of a line of ocean waves in a bad storm, and it is really one of the great achievements of science that such complicated sounds should be reproducible at all, much less by so simple a physical structure as a circular sheet or diaphragm. _ Ingenious Constriiction. Loudspeakers in general include a strong magnet, which is either a permanent steel magnet or, in a few cases, an electrically excited magnet, which requires battery current for its functioning. There is also a coil of wire, generally wound over the permanent magnets, through which flow the electric currents, which carry the music in the ‘form of regular or irregular fluctuations of these currents. In some loudspeakers, an iron diaphragm is set into motion by the variation of magnetism catsed by the incoming electrical currents catrying the music. In others, diaphragms of mica or other material are set into motion by mechanical systems attached to them, which, in turn, are controlled by varying magnetic pulls on a steel or iron movable part of the system.