Loud Speakers and Microphones* 



By E. C. WENTE and A. L. THURAS 



In ordinary radio broadcast of symphony music, the effort is to create 

 the effect of taking the Hstener to the scene of the program, whereas in 

 reproducing such music in a large hall before a large gathering the effect 

 required is that of transporting the distant orchestra to the listeners. Lack- 

 ing the visual diversion of watching the orchestra play, such an audience 

 centers its interest more acutely in the music itself, thus requiring a high 

 degree of perfection in the reproducing apparatus both as to quality and 

 as to the illusion of localization of the various instruments. Principles of 

 design of the loud speakers and microphones used in the Philadelphia- 

 Washington experiment are treated at length in this paper. 



AS EARLY as 1881 a large scale musical performance was repro- 

 ■ duced by telephone instruments at the Paris Electrical Exhibition. 

 Microphones were placed on the stage of the Grand Opera and con- 

 nected by wires to head receivers at the exposition. It is interesting 

 to note that separate channels were provided for each ear so as to give 

 to the music perceived by the listener the "character of relief and 

 localization." With head receivers it is necessary to generate enough 

 sound of audible intensity to fill only a volume of space enclosed 

 between the head receiver and the ear. As no amplifiers were avail- 

 able, the production of enough sound to fill a large auditorium would 

 have been entirely outside the range of possibilities. With the advent 

 of telephone amplifiers, microphone efficiency could be sacrificed to 

 the interest of good quality where, as in the reproduction of music, 

 this was of primary interest. When amplifiers of greater output power 

 capacity were developed, loud speakers were introduced to convert a 

 large part of the electrical power into sound so that it could be heard 

 by an audience in a large auditorium. Improvements have been made 

 in both microphones and loud speakers, resulting in very acceptable 

 quality of reproduction of speech and music; as is found, for instance, 

 in the better class of motion picture theaters. 



In the reproduction, in a large hall, of the music of a symphony 

 orchestra the approach to perfection that is needed to satisfy the 

 habitual concert audience undoubtedly is closer than that demanded 

 for any other type of musical performance. The interest of the listener 

 here lies solely in the music. The reproduction therefore should be 



* Third paper in the Symposium on Wire Transmission of Symphonic Music 

 and Its Reproduction in Auditory Perspective. Presented at Winter Convention of 

 A. I. E. E., New York City, Jan. 23-26, 1934. Published in Electrical Engineering, 

 January, 1934. 



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