Bauhaus-Universität Weimar

Collected Papers On Acoustics
Sabine, Wallace Clement
all that could be expected in view of the difficulty under which the 
observations were conducted and the limited time available. One 
point in particular falls far off from this curve, the point for C3256, 
by an amount which is, to say the least, serious, and which can be 
justified only by the conditions under which the work was done. 
The general trend of the curve seems, however, established beyond 
reasonable doubt. It is interesting to note that there is one point 
of maximum absorption, which is due to resonance between the 
walls and the sound, and that this point of maximum absorption 
lies in the lower part, though not in the lowest part, of the range of 
pitch tested. It would have been interesting to determine, had the 
time and facilities permitted, the shape of the curve beyond C740 96, 
and to see if it rises indefinitely, or shows, as is far more likely, a 
succession of maxima. 
The experiment was then directed to the determination of the 
absorption of sound by cushions, and for this purpose return was 
made to the constant-temperature room. Working in the manner 
indicated in the earlier papers for substances which could be carried 
in and out of a room, the curves represented in Fig. 7 were obtained. 
Curve 1 shows the absorption coefficient for the Sanders Theatre 
cushions, with which the whole investigation was begun ten years 
ago. These cushions were of a particularly open grade of packing, 
a sort of wiry grass or vegetable fiber. They were covered with 
canvas ticking, and that, in turn, with a very thin cloth covering. 
Curve 2 is for cushions borrowed from the Phillips Brooks House. 
They were of a high grade, filled with long, curly hair, and covered 
with canvas ticking, which was, in turn, covered by a long nap 
plush. Curve 3 is for the cushions of Appleton Chapel, hair covered 
with a leatherette, and showing a sharper maximum and a more 
rapid diminution in absorption for the higher frequencies, as would 
be expected under such conditions. Curve 4 is probably the most 
interesting, because for more standard commercial conditions ordi¬ 
narily used in churches. It is to be observed that all four curves 
fall off for the higher frequencies, all show a maximum located 
within an octave, and three of the curves show a curious hump in 
the second octave. This break in the curve is a genuine phenomenon, 
as it was tested time after time. It is perhaps due to a secondary


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