SABINE. — ARCHITECTURAL ACOUSTICS. 67 



pipes and started the chronograph, the writer and the other observers 

 each had a key which was connected with the chronograph to record 

 the cessation of audibility of the sound. The results of the experi- 

 ment are shown on the lower curve in Figure 2. This curve gives the 

 coefficient of absorption per person. It is to be observed that one of 

 the points falls clearly off the smooth curve drawn through the other 

 points. The observations on which this point is based were, however, 

 much disturbed by a street car passing not far from the building, and 

 the departure of this observation from the curve does not indicate a 

 real departure in the coefficient nor should it cast much doubt on the 

 rest of the work, in view of the circumstances under which it was 

 secured. Counteracting the perhaps bad impression which this point 

 may give, it is a considerable satisfaction to note how accurately the 

 point for C4 512, determined six years before by a different set of ob- 

 servers, falls on the smooth curve through the remaining points. In the 

 audience on which these observations were taken there were 77 women 

 and 105 men. The courtesy of the audience in remaining for the 

 experiment and the really remarkable silence which they maintained 

 is gratefully acknowledged. 



The curve above discussed is that for the average person in an audi- 

 ence. An interesting form in which to throw the results is to regard 

 the audience as one side of a room. We may then look at it as an 

 extended absorbing surface, and determine the coefficient per square 

 meter. Worked out on this basis the absorption coefficient is in- 

 dicated in the higher curve. It is merely the lower curve multiplied 

 by a number which expresses the average number of people per 

 square meter. It is interesting to note that the coefficient of ab- 

 sorption is about the same from C4 512 up, indicating over that range 

 nearly complete absorption. Below that point there is a very great 

 falling off, down to Ci 64. The curve is such as to permit of an extra- 

 polation indicative of even less absorption and consequently greater 

 reverberation for the still lower notes. Without entering into an elab- 

 orate discussion of this curve, two points may be noted as particularly 

 interesting. The first is the nearly complete absorption for the higher 

 notes, a result which at first sight seems a little inconsistent with 

 the results which will be shown later on in connection with the absorp- 

 tion by felt. The inconsistency, however, is only apparent. The 

 greater absorption shown by an audience than that shown by thick 

 felt arises from the fact that the surface of the audience is irregular 

 and does not result in a single reflection, but probably, for a very large 

 portion of the sound, of multiple reflection before it finally emerges. 

 The physical conditions are such that they obviously do not admit of 



