A VOICE AND EAR 313 



that used in the sound meter, the artificial ear ma\' be used to obtain 

 a measure of the relative loudness produced by different receivers. 

 Other weighting networks may be used to enable a direct meter reading 

 of other desired characteristics. 



While any single design of artificial ear can, of course, simulate only 

 a single ear condition, there appears to be no reason why a structure 

 of the type described cannot be made to simulate any ear by proper 

 changes in the dimensions of the passage and values of the acoustic 

 impedances without sacrifice of stable performance or the ability to 

 specify and reproduce it. As far as data on the characteristics of 

 human ears are at present available, the particular design described 

 gives a good approximation, both in its effect on the receiver and in 

 its own frequency characteristics, of a typical male ear. There is 

 indication that this artificial ear, in addition, may offer an equally 

 satisfactory substitute for the real ear in the measurement of open 

 sound fields. A further study of this possibility is being made. 



General Applications of the Artificial Voice and Ear 

 Equipment of the kind described offers many advantages, both in 

 aboratory investigation and in shop testing of instruments, as com- 

 pared with the methods that have been used heretofore. The artificial 

 voice and ear described have, of course, the advantages of exact 

 specification and control of the testing conditions, and of rapidity in 

 obtaining data which have been the principal arguments for the use of 

 previous voice and ear substitutes. In addition, instruments tested 

 by these new means are under nearly normal operating conditions. 



In laboratory investigations and development of instruments the 

 artificial voice, makes it possible to carry out tests, such as response- 

 frequency measurements with the same instrumentalities as are used 

 for speech tests. This is, of course, impossible with the real voice. 

 When used in conjunction with a high quality transmitter it permits 

 either the variation of talking intensity without change in quality, or 

 the maintenance of a constant output intensity from the artificial 

 mouth, even though the actual speaker's voice may be varied over a 

 wide range. Applications of this kind in exercising over a caller's 

 voice, control of which he himself is incapable, are invaluable in many 

 laboratory investigations. 



As applied to shop inspection practices, the desirability is obvious 

 of having a single testing means for all transmitters and receivers 

 regardless of type, which is identical in principle with the means of 

 testing used in the laboratory. The results of measurements made on 

 instruments, whether in laboratory, factory or repair shop, can be 



