293,822. Boyd, F. A. April 13, 1927. Sound - magnifying appliances. - Two or more expanding conduits e, d of different length, adapted to amplify different ranges of frequency in desired proportions, are equalized in effective length by a straight piece n. The conduits c and n, d may open into a common horn c, Figs. 2 and 3, which may be at right-angles to d. Each conduit may be formed with right-angle bends, and may expand step-wise at the bends instead of continuously. Specification 178,147 is referred to in the first Provisional Specification.
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