422 BELL SYSTEM TECHNICAL JOURNAL 



125 c.p.s. Pure Tone Test No. 4 Crew No. 1. 1000 c.p.s. Voltage Level (db) 



Fig. 16 — Loudness balance data sheet. 



marks were used for recording the observers' judgments, a cipher 

 indicating the 125-cycle tone to be the louder, and a plus sign denoting 

 the reference tone to be the louder of the two. No equal judgments 

 were permitted. The figures at the head of each column give the 

 voltage level of the reference tone impressed upon the receivers, that is, 

 the number of decibels from 1 volt, plus if above and minus if below, 

 and those at the side are similar values for the tone being tested. 

 Successive tests were chosen at random from the twenty-seven possible 

 combinations of levels shown, thus reducing the possibility of memory 

 effects. The levels were selected so the observers listened to reference 

 tones which were louder and softer than the tone being tested and the 

 median of their judgments was taken as the point of equal loudness. 

 The data on this recording chart, combined with a similar number 



