ACOUSTICAL INSTRUMENTS 



411 



sities over which we desire to make measurements of this character is 

 very wide. Reverberation measurements are preferably made over a 

 range of at least 60 db and the level range of orchestral music covers 

 about 75 db. Several instruments designed for such purposes have 

 been described recently.^^ In the instrument described by Wente, 

 Bedell and Swartzel the level is recorded by a stylus on waxed paper. 

 The recorder can be adjusted to give either a short or a long time 

 average. At the higher speeds it is capable of following changes in 

 intensity at the rate of 840 db per second and fluctuations in intensity 

 of about 100 per second. The instrument may be adjusted so that the 

 full scale covers a range of 30, 60 or 90 db. 



Loudness Measurements 



The preceding discussion was restricted to the purely objective or 

 physical aspects of sound. In certain types of acoustical problems, as 

 in the study of noise, we are, however, interested in subjective charac- 

 teristics, but we do not yet have instruments which respond to an 

 acoustic stimulus in the way the brain does through the ear. In fact 



20 



100 500 1000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 9 — Auditory chart. 



^^ Hunt, Jour. Acous. Soc. Amer, 6, 54 (1934). Wente, Bedell and Swartzel, Jonr. 

 Aeons. Soc. Amer., January, 1935. 



