PHYSICAL MEASUREMENTS OF AUDITION 



155 



the top. The .r-axis gives units above threshold for sound A and the 

 ^-axis gives the units above threshold of the sound B when the two 

 sound equally loud. In this case, the spectra are somewhat similar 



<b qR.M.S. Pressure Arb. Units 





400 800 1200 1600 

 Frequency 



2000 2400 



CQ 



~*50 



40 



$30 



$20 



$10 



10 20 30 40 50 60 



Units above threshold Sound A 

 Fig. 4 



and we have a straight line of slope 45 passing nearly through the 

 origin. The two sounds are thus of practically equal loudness w r hen 

 they are the same number of units above threshold. In Fig. 5 we 

 have similar data for two sounds which have quite different spectra 

 as is indicated by the two charts at the top. The curve for C means 

 that it was a practically continuous spectrum. It was produced 

 by a device for making the "swishing" type of noises which are usually 

 so prominent in office rooms. The curve representing the relation 

 is not straight, since for values of intensity near the threshold, the 



