SCIENTIFIC RESEARCH APPLIED TO THE TELEPHONE 253 



which have an important bearing either upon an understanding of the 

 operation of these instruments or upon their practical design. In 

 addition to the development of many methods of measurement and 

 testing applicable to laboratory research and development, of very 

 great importance has been a development of the testing methods 

 which permit of a better final evaluation of the developments based 

 upon the results of this activity. 



Instruments as Electromechanical Structures 



The telephone transmitter itself is a complex mechanical and 

 electrical structure. Its general method of operation can be described 

 qualitatively in relatively simple terms, but the operation of few 

 structures is more difficult to define in definite quantitative terms and 

 relationships. For example, we are concerned with acoustical prob- 

 lems such as those involved in the air connection between the lips of 

 the speaker and the diaphragm of the instrument. This air con- 

 nection may involve a short column of air as in those instruments 

 which have a telephone mouthpiece. Connection between the column 

 of air and the working parts of the transmitter may be partially closed 

 by a perforated section. When we come to consider the operation of 

 the instrument itself, there is involved the mechanical vibration of the 

 diaphragm as it operates on the carbon, and further, the whole question 

 of electric conduction in the small mass of granular carbon itself. 



In the case of the receiver which converts telephonic currents into 

 speech sounds, we have very similar acoustical, mechanical and 

 electrical problems with the exception, of course, of the mechanical 

 and electrical problems introduced by the carbon of the transmitter. 



A large amount of research work has been carried on in the Labora- 

 tories relating broadly to the transmitter and the receiver as electro- 

 mechanical physical structures. The theory of these devices as 

 vibrating systems has been developed so that their overall performance 

 can be related to the various structural features. Consequently, our 

 development and design engineers are now enabled to predetermine 

 by calculation how certain modifications in structure will affect the 

 physical performance of the instrument. In other words, the design 

 process has become very much less "cut and try." 



Research has been undertaken and substantial progress has been 

 made on a study of microphonic action in carbon. In order to develop 

 a complete theory of the operation of the transmitter, it is necessary 

 to understand fully what takes place between each carbon granule in 

 the carbon chamber. 



