A VOICE AND EAR 295 



Requirements for an Artificial Ear 

 In considering a substitute for the human ear, the general require- 

 ment is that it shall respond, as does the human ear, to sounds of 

 various frequencies, amplitudes and lengths of duration. Further- 

 more, its reaction on the source of sound, whether that sound be 

 produced by a receiver held against it or by a source at a distance 

 from it, shall be the same as that of the human ear. 



As in the case of the artificial voice, the artificial ear may con- 

 veniently be considered as consisting of two parts, the ear coupler and 

 the measuring equipment. Based on the above general considerations, 

 the ear coupler should meet the following more specific requirements: 



(1) It should have the same impedance at every audible frequency as 



a real ear, either in the open air or with the receiver held 

 to it. 



(2) The pressures developed in the ear coupler should be the same at 



every audible frequency as the pressure developed in a real 

 ear. 



For the measuring equipment, the requirements are as follows: 



(1) For steady state conditions it should be capable of giving an 



indication at every audible frequency proportional to the 

 pressure in the coupler over a range of pressures as great as 

 that experienced by a real ear. 



(2) It should respond to sound of short duration as does a real ear. 



(3) It should be possible to change the response to various frequencies 



in any manner required by means of suitable electrical net- 

 works. 



(4) It should respond to complex sounds as does the real ear. 



The artificial ear should be completely specifiable, reproducible, and 

 constant in performance. 



At the present time it is not possible to meet rigidly all of these 

 requirements, either for an artificial voice or ear. Development work 

 has progressed to a point where it can be stated that the requirements 

 have been met sufficiently well to enable the production of both an 

 artificial voice and ear w^hich are close simulations of the real voice 

 and ear and which will be satisfactory as substitutes in almost all of 

 the laboratory or shop tests for which a real voice and ear have been 

 largely used. 



Description of the Artificial Voice 

 The schematic arrangement of the artificial voice referred to is 

 shown in Fig. 1. As indicated, electrical energy may be supplied 



