522 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



a direction depending upon the slopes of the attachment and the 

 horn. 



6. The end correction of the conical horn in these experiments is 

 shown to be approximately 0.7 times the radius. 

 Physical Laboratory, 



State University of Iowa. 



THE BINAURAL DIFFERENCE OF PHASE EFFECT 



G. W. STEWART 



ABSTRACT 

 The binaural difference of phase effect has become of increased 

 importance in recent years. The following are the new facts ob- 

 tained in recent experiments which are still in progress : 



1. For a frequency of 130 d. v. the ratio between the phase and 

 the apparent displacement from the median plane is approximately 

 unity. The ratio will be called the "displacement ratio." 



2. This "displacement ratio" is not the same for frequencies from 

 50 to 1,300 d. V. Present experiments indicate that this "displace- 

 ment ratio" can be expressed approximately in the following equa- 

 tion: 



Ratio=0.5+0.0037X frequency. 



3. This equation shows that the sensitivity of the ears as ex- 

 pressed by displacement is not strictly a time effect nor is it strictly 

 a phase difference effect. At the lowest frequencies mentioned the 

 change in displacement ratio is so slow as to indicate that, approxi- 

 mately, the displacement depends only on the phase and is indepen- 

 dent of frequency. But in the higher frequencies from 500 to 1,000 

 the displacement is approximately inversely proportional to the fre- 

 quency. This would represent equal sensitivity in equal difference 

 in time of arrival of the waves. 



4. When the sound listened to binaurally is complex, the tones in 

 the lower range will have a different displacement. This has been 

 verified and in addition it is found that the presence of an overtone 

 tends to decrease the sensitivity for the fundamental. It is also 

 found that if the overtone is faint enough, both tones are displaced 

 together in accord with the displacement of the fundamental. In 

 a similar manner if the fundamental is sufficiently faint, the dis- 

 placement of the entire tone is that of the overtone. 



Physical Laboratory, 

 State University of Iowa. 



