SABINE. — ARCHITECTURAL ACOUSTICS. 61 



paratively empty, with hard wall surfaces, for example plaster or tile, 

 and having in it comparatively little furniture, the amount of rever- 

 beration for the sounds of about the middle register of the double- 

 bass viol and for the sounds of the middle register of the violin will be 

 very nearly though not exactly equal. If, however, we bring into the 

 room a quantity of elastic felt cushions, sufficient, let us say, to 

 accommodate a normal audience, the effect of these cushions, the 

 audience being supposed absent, will be to diminish very much the 

 reverberation both for the double-bass viol and for the violin, but will 

 diminish them in very unequal amounts. The reverberation will now 

 be twice as great for the double-bass as for the violin. If an audience 

 comes into the room, filling up the seats, the reverberation will be 

 reduced still further and in a still greater disproportion, so that with an 

 audience entirely filling the room the reverberation for the violin will 

 be less than one third that for the double-bass. When one considers 

 that a difference of five per cent in reverberation is a matter for ap- 

 proval or disapproval on the part of musicians of critical taste, the 

 importance of considering these facts is obvious. 



This investigation, nominally in regard to reverberation, is in reality 

 laying the foundation for other phases of the problem. It has as one 

 of its necessary and immediate results a determination of the coeffi- 

 cient of absorption of sound of various materials. These coefficients 

 of absorption, when once known, enable one not merely to calculate 

 the prolongation of the sound, but also to calculate the average loud- 

 ness of sustained tones. Thus it was shown in one of the earlier 

 papers, though at that time no very great stress was laid on it, that 

 the average loudness of a sound in a room is proportional inversely 

 to the absorbing power of the material in the room. Therefore the data 

 which are being presented, covering the whole range of the musical 

 scale, enable one to calculate the loudness of different notes over that 

 range, and make it possible to show what effect the room has on the 

 piano or the orchestra in different parts of the register. 



To illustrate this by the example above cited, if the double-bass 

 and the violin produce the same loudness in the open air, in the bare 

 room with hard walls both would be re-enforced about equally. The 

 elastic felt brought into the room would decidedly diminish this re- 

 enforcement for both instruments. It would, however, exert a much 

 more pronounced effect in the way of diminishing the re-enforcement 

 for the violin than for the double-bass. In fact, the balance wiU be so 

 affected that it will require two violins to produce the same volume 

 of sound as does one double-bass. The audience coming into the room 

 will make it necessary to use three violins to a double-bass to secure 

 the same balance as before. 



