ARCHITECTURAL ACOUSTICS 



113 



musicians of critical taste the importance of considering these 

 facts is obvious. 



A further point of which account must be taken is the 

 composite character of a musical tone. The quality of a 

 tone depends on the relative intensities of the overtones, 

 and it has been customary for physicists to regard these 

 relative intensities as dependent simply on the source of 

 sound. Primarily, of course, this is true. But while the 

 source determines the relative intensities of the issuing sound, 

 their intensities as heard depend not merely on that but 

 also to a surprising degree on the room itself. Thus with 

 an 8-foot organ-pipe for which the overtones were pro- 

 nounced in an empty room the introduction of felt reduced 

 the ratio of the ist upper partial to 

 the fundamental by 40 per cent., 

 that of the 3rd upper partial by 

 50 per cent., and that of the 4th by 

 60 per cent. 1 



With a 6-inch pipe, on the other 

 hand, the effect was to accentuate 

 the overtones, whereas all notes below 

 the 6-inch fundamental were purified. 

 The effect of an audience was still 

 different, viz. to purify all notes up 

 to C^ 512, and to have very little 

 effect on tones above this. For C^ 64 

 the first overtone was decreased 65 

 per cent, relative to the fundamental 

 and the second 75 per cent. 



The musical effect will thus be 

 injured or improved according to 

 circumstances. The mixture stop in 

 an organ is designed to be rich in 



overtones, the night-horn stop to be specially pure, and it 

 may happen that the room in which they are sounded will 

 completely alter the intended effects. To determine the 

 balance must lie with musicians, and it is important that the 

 judgment of musical authorities should be gathered in available 

 form. 



The necessity for extending the investigation to cover the 

 whole musical scale has been demonstrated. Examples of the 

 results obtained by Sabine are most conveniently given by 

 the following curves : 



Fig. 3 shows the absorbing power of an audience for different 



notes. The lower curve represents the absorbing power per 



person, the upper curve the absorbing power per square metre 



as ordinarily seated. The ordinates are fractions of one square 



8 



C, Cj C3 C4 Cg Cq Cv 



Fig. 3. — The absorbing power 

 of an audience for different notes. 



