Bauhaus-Universität Weimar

Titel:
Collected Papers On Acoustics
Person:
Sabine, Wallace Clement
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit39364/23/
14 
REVERBERATION 
Early in the investigation it was found that measurements of 
the length of time during which a sound was audible after the source 
had ceased gave promising results whose larger inconsistencies could 
be traced directly to the distraction of outside noises. On repeating 
the work during the most quiet part of the night, between half-past 
twelve and five, and using refined recording apparatus, the minor 
irregularities, due to relaxed attention or other personal variations, 
were surprisingly small. To secure accuracy, however, it was neces¬ 
sary to suspend work on the approach of a street car within two 
blocks, or on the passing of a train a mile distant. In Cambridge 
these interruptions were not serious; in Boston and in New York 
it was necessary to snatch observations in very brief intervals of 
quiet. In every case a single determination of the duration of the 
residual sound was based on the average of a large number of 
observations. 
An organ pipe, of the gemshorn stop, an octave above middle c 
(512 vibration frequency) was used as the source of sound in some 
preliminary experiments, and has been retained in subsequent work 
in the absence of any good reason for changing. The wind supply 
from a double tank, water-sealed and noiseless, was turned on and 
off the organ pipe by an electro-pneumatic valve, designed by Mr. 
George S. Hutchings, and similar to that used in his large church 
organs. The electric current controlling the valve also controlled 
the chronograph, and was made and broken by a key in the hands 
of the observer from any part of the room. The chronograph em¬ 
ployed in the later experiments, after the more usual patterns had 
been tried and discarded, was of special design, and answered well 
the requirements of the work — perfect noiselessness, portability, 
and capacity to measure intervals of time from a half second to ten 
seconds with considerable accuracy. It is shown in the adjacent 
diagram. The current whose cessation stopped the sounding of the 
organ pipe also gave the initial record on the chronograph, and the 
only duty of the observer was to make the record when the sound 
ceased to be audible. 
While the supreme test of the investigation lies in the consistency 
and simplicity of the whole solution as outlined later, three pre¬ 
liminary criteria are found in (1) the agreement of the observations
        

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