. The Bell System technical journal. Telecommunication; Electric engineering; Communication; Electronics; Science; Technology. 144 BELL SYSTEM TECHNICAL JOURNAL of spherical shells; this part was thereby made very rigid so that it should move as a unit up to high frequencies. Construction of the Driving Coil For the driving element of loud speakers either a moving coil or a moving armature is commonly used. The latter is in general satis- factory if driven at a small amplitude. However, where large powers are involved, the moving coil drive can be much more simply con- structed so that it is f
. The Bell System technical journal. Telecommunication; Electric engineering; Communication; Electronics; Science; Technology. 144 BELL SYSTEM TECHNICAL JOURNAL of spherical shells; this part was thereby made very rigid so that it should move as a unit up to high frequencies. Construction of the Driving Coil For the driving element of loud speakers either a moving coil or a moving armature is commonly used. The latter is in general satis- factory if driven at a small amplitude. However, where large powers are involved, the moving coil drive can be much more simply con- structed so that it is free from amplitude distortion; it has the further advantage of having a resistance nearly constant with frequency and a practically negligible reactance. These were the primary reasons for our choosing this type of drive. The coil that was used in the re- ceiver consisted of a single layer of aluminum ribbon inch wide and inch thick wound on edge as shown in Fig. 4. The turns were held together with a film of insulating lacquer about inch thick, thor- oughly baked after the winding was completed. This type of coil has the following advantages. It is self-sup- porting, no spool being required; 90 per cent of the volume of the coil is occupied by metal; the distributed capacity between turns is small, giv- ing a coil whose impedance varies only slightly with frequency ; the metal is continuous between the cylin- drical surfaces, allowing heat to be conducted rapidly outward from the center of the winding and diminishing the possibility of any warping of the coil; it can be accurately made to dimensions, thus permitting small clearances between the coil and the pole pieces. Small clearances not only permit the use of a comparatively small magnet but they facilitate the dissipation of heat. This latter effect is shown in the curves of Fig. 5. These curves give the temperature of the coil as a function of the power input for the coil in open air {A), and when it i
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
