GENERAL PAPERS 47 



caused the echoes. Small mirrors attached to the walls as- 

 sisted in tracing the reflections. 



Experiments to improve the acoustics were then carried on 

 in accordance with the results of the analysis. Sounding 

 boards, or more properly, reflecting boards, of various kinds 

 were tested. 4 A flat board about five feet square was placed 

 at an angle over the position of the speaker. This proved to 

 be of small effect, as was also the case when a large canvas 

 sheet 12 by 20 feet was similarly mounted, although speakers 

 said the ease of speaking was increased when they stood under 

 the canvas. A parabolic reflector was then tried and gave 

 much better results, but it had several disadvantages. It was 

 necessary for the speaker to keep closely to the focus of the 

 parabola to have the sound proceed properly. Any movement 

 on his part would diminish the efficiency of the reflector. Also 

 the sound worked both ways, so that noises generated by the 

 audience were focused at the speaker's ears. The reflector 

 was suited only for a single speaker and would not serve for 

 concerts or plays where the entire stage was used. Further- 

 more it did not reduce the reverberation materially. 



A word or two should be added concerning the use of wires 

 in correcting acoustics. Wires attached in an auditorium have 

 practically no effect on the acoustics. Five miles of wire were 

 installed in one church and the acoustics still remained im- 

 perfect. Wires have much the same effect on the sound that 

 a fish line in the water has on water waves. To break up the 

 sound, the obstacle must be much larger than a wire; it must 

 have dimensions comparable with the wave length of the 

 sound." 



Canvases were then hung in various positions in the hall to 

 determine the effect of cutting off certain walls frum the action 

 of the sound. Absorbing materials were also hung at critical 

 points suggested by the analysis. The final provisional cure 

 was brought about when four large canvases were hung in the 

 dome. For the first time speakers could talk with compara- 

 tive ease without suffering great annoyance from echoes. 



*"The Use of Sounding Boards in an Auditorium," Physical Review, Vol. 1, 2 , 

 p. 241, 1913. Also a more complete article in The Brickbuilder, June, 1913. 



'"Inefficiency of Wires as a Means of Curing Defective Acoastics of Auditor 

 iums," Science, Vol. 35, p. 833, 1912. 



