XV.The measurement of transmission and reflexion of sound by partitions of various materials.—I.Felt-like materials

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Abstract
The present paper is part of a study of the transmission and reflexion of sound by various partitions, and relates mainly to partitions of a felt-like nature. The method used is on the general lines of that due to F. R. Watson. The partition is clamped over an aperture in the wall between two adjacent sound-proof rooms, in one of which a source of sound, in conjunction with a paraboloidal mirror, directs a fairly uniform beam of sound obliquely on to the partition. Measurements of intensity are made in the transmitted and reflected beams and at various other points within the rooms. A description is given of the electrical equipment used in the production and measurement of the sound-field. The actual arrangement has the advantage that under certain conditions the exploration of the sound- field is not affected by inconstancy of the current operating the loud-speaker source, nor by gradual drift in the efficiency of the amplifiers employed. Tests were carried out to determine if there was any reaction on the source when a test material was placed over the aperture, but no appreciable effect was observed. A detailed study of the field of sound in the two rooms was made both with and without a partition over the aperture. The results of this exploration showed that transmission and reflexion ratios were almost independent of the positions in the beam at which the measurements were made. A number of partitions were tested, and the consistency of the results is indicated in graphical form. The transmission of sound through felt was specially investigated. Four partitions of hair-felt, each of 0·58 in. thickness, were employed, and the transmission through one, two, three, and four layers was studied. A number of frequencies ranging from 250 to 1600 vibrations per second were used, and curves are given showing the results obtained. A comparison is made between these results and those obtained by P. E. Sabine who used a reverberation method.

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