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ARCHITECTURAL ACOUSTICS 



two stations. The master unit contains an amplifier, microphone, loud 

 speaker, and a talk-listen switch. The remote unit consists of a micro- 

 phone, loud speaker, and talk-listen switch. In some of these systems 

 the loud speaker with suitable electrical compensation is also used as a 

 microphone. Additional stations and appropriate switching systems may 

 be added for communicating between a number of rooms. The voice 

 currents are carried in two ways: in one by direct wire, and in the other 

 by using a high frequency carrier on the power mains. The latter system 

 does not require wiring but has the disadvantage that in large buildings 

 having several separate systems cross-talk may occur. 



J. Radio Receiver Operating in a Living Room^'' . — The radio receiver and 

 phonograph represent by far the largest number of complete reproducing 

 systems. For this reason, the performance of a radio receiver in a room 

 is an extremely important problem. Equations 12.4, 12.5 and 12.6 for 



n^ 



/ POSlTlONSl 



PLAN VIEW 



(/I 10 



u 



IT 0, 



Fig. 12.12. Apian view of a living room with a radio receiver. The graphs show the response 

 frequency characteristics for various positions in the room. 



the direct and reflected sound are applicable to a radio receiver in a room. 

 In the case of a theatre it is possible to adjust the loud speakers so that the 

 direct sound is the same in all parts of the auditorium. It is not practical 

 to arrange the loud speakers in a radio receiver so that there will be no 

 variation of the direct sound with distance. In view of the rather small 

 distances and relatively small volume of the room this is not very important. 

 It is important, however, that the directional characteristic be independent 

 of the frequency and sufficiently broad to send direct sound into all listen- 

 ing areas. 



The response frequency characteristics of a good radio receiver taken 

 at various listening positions in a typical living room are shown in Fig. 12. 12. 



" Olson and Massa, " Applied Acoustics," 2nd Ed., p. 401, P. Blakiston's Son and 

 Co., Philadelphia, 1939. 



