WALLACE CLEMENT WAEE SABINE— HALL 



[Memoirs National 

 [Vol. XXI, 



the current at the four instruments. The two other chronographs were in charge of other observers, provision 

 being thus made for three independent determinations. After a test had been made of the absorbing power of 

 the whole audience — 157 women and 135 men, sufficient to crowd the lecture room — one half, by request, passed 

 out, 63 women and 79 men remaining, and observations were again made. On the following night the lecture was 

 repeated and observations were again taken, there being present 95 women and 73 men. There were thus six 

 independent determinations on three different audiences and by three observers. In the following table the first 

 column of figures gives the total absorbing power of the audience present; the second gives the absorbing power 

 per person; the initials indicate the observer. 



1 This is additional to the absorbing power of the scat and floor area covered by the person. Correction on this account makes the "abso- 

 lute" absorbing power per person 0.44 — that is, 0.44 of the absorbing power of a square meter of open window. 



E. H. H. 



In view of the difficulties of the experiment the consistency of the determination is gratifying. The average 

 result of the six determinations is probably correct within 2 per cent. 



The following passage illustrates the nicety of observation aimed at and attained in these 

 tests : 



Under certain circumstances the audience will not be compactly seated, but will be scattered about the 

 room and more or less isolated, for example, in a council room, or in a private music room, and it is evident 

 that under these conditions the individual will expose a greater surface to the room and his absorbing power 

 will be greater. It is a matter of the greatest ease to distinguish between men and women coming into a small 

 room, or even between different men. In fact, early in the investigation, two months' work — over three thou- 

 sand observations — had to be discarded because of failure to record the kind of clothing worn by the observer. 

 The coefficients given in the following table are averages for three women and for seven men, and were derhiced 

 from experiments in the constant-temperature room. 



Absorbing power of an audience 



Audience per square meter 0. 96 



Audience per person .44 



Isolated woman .54 



Isolated man -48 



Evidently, the absorbing power of an "isolated woman" as compared with that of an "iso- 

 lated man" must vary with the fashions in clothing. 



Along with this study of the absorbing power of different objects and materials went the 

 determination of a mathematical formula 8 — 



t = Tc-i- (a+x), 



in which t is the number of seconds the residual sound lasts^the "duration of audibility," — 

 jfc is a constant quantity depending on the size of the room, a is the absorbing power of the 

 bare walls, floor, and ceiling, and x is the increase of absorbing power due to the furniture and 

 audience. 



Studying rooms of different shapes and sizes, Sabine found that Jc is approximately 0.171F, 

 where V is the volume of a room in cubic meters. Then, knowing the absorbing power of 

 different surfaces and the area of these several surfaces, he could calculate, even in advance of 

 construction, how long the reverberation would last in a given auditorium. 



Of course this feature is not the whole of architectural acoustics, but it is one of the most 

 important parts, and it is the only part discussed in the following passage relating to the design 

 of Boston Symphony Hall, the first auditorium to be affected, in construction, by Sabine's 

 advice. It is greatly to the credit of the distinguished architects of this building, Messrs. 



8 This is the simple, approximate, formula to indicate the nature of the relation discovered. The exact formula is much too complicated for 

 useful reproduction here. 



