Some acoustic and telephone measurements

In the present paper, a brief description of some of the work carried out in the Research Section of the British Post Office is given. Part 1 is devoted to electro-acoustic and acousto-electric measurements of instruments. In Part 2 various voice-ear measurements on microphones and receivers are described. Part 3 deals with some mechanical tests by means of which rapid acceptance tests and estimates of the commercial life of instruments can be made. The question of the measurement of the efficiency of apparatus and circuits in actual use is discussed in Part 4.