SEVENTY-FIVE YEARS OF THE TELEPHONE 233 



of amplification. Furthermore, the carbon transmitter has been made to 

 behave well with respect to position, use and time. 



The 1950 receiver, invented prior to World War II, involves a radically 

 new structure — a receiver having a composite diaphragm with an outer an- 

 nular portion of magnetic material and an inner circular part of domed 

 impregnated fabric. This invention was stimulated by the analytical demon- 

 stration of the benefits of a diaphragm of low dynamic mass. A paper^^ 

 published in the January 1951 issue of this Journal gives the theory of this 

 receiver and describes the manner in which it was developed and designed 

 to have the projected performance. That presentation shows the high level 

 which the technology of the design of such devices has now reached. 



From Curve D of Fig. 4(b), it is seen that this latest receiver is 5 db more 

 efficient than the 1937 design and reproduces a wider frequency range. The 

 dropping of the response at the lower end is intentional to avoid increasing 

 the interference from power systems. ^^ 



By these extensive studies in theory, the development and application of 

 physical and subjective measurements, and the advanced technology of de- 

 sign, the present generation of the descendants of Bell's transmitter and 

 receiver approach in their performance the inherent limitations of the struc- 

 tures and materials, with the compromises that are chosen in the interests 

 of quaUty and cost of production, and ruggedness and uniformity in use. 

 As embodied in the 1950 set, the efficiencies of conversion of the transmitter 

 and receiver are now so high that, on the shorter loops, losses are automat- 

 ically introduced in order to avoid the delivery of sounds of too great loud- 

 ness to the ear of the listener. 



Design for Production 



Since the war, production of the instruments of the 1937 type handset 

 reached a rate of around five million a year apiece. This production has 

 demonstrated that devices of such sensitivity and refinement in design can 

 be made in large quantity with closely controlled quaUty and at low cost. 

 The analytical quantitative approach to design in the case of these instru- 

 ments has been an important factor in the adaptation of these designs to 

 quantity production with present manufacturing techniques. Such produc- 

 tion may call for changes from the designer's ideas as to the properties of 

 the materials, their fabrication or the tolerances to be met. With the ana- 

 lytical quantitative approach to design, the effect of such changes can be 

 readily evaluated, and proper judgments reached as to whether such com- 

 promises with the design are justified in the interests of control of product 

 and lower costs. Such judgments can be made without the necessity of ex- 

 ploring the range of possibihty by a series of models. 



Furthermore, to carry out such kind of production, many of the meas- 



