Acoustic ohm

Abstract: A method for obtaining a wide range of calculable impedance values has been developed. Three telescoping tubes are used, one being acoustically “infinite” in length. This “infinite” tube is used as a convenient, calculable impedance terminating the device. The effective lengths of the remaining two sections are varied to adjust the input impedance, whose value may then be calculated in terms of that of the “infinite” section. A unit having an input section 1 inch in diameter and an “infinite” section 0.130 inch in diameter has been constructed. The range of impedance values obtainable is best described in terms of a resistance‐reactance plot. On such a plot the range at 800 c.p.s. for the 1‐inch diameter unit includes the impedance values enclosed by a circle having its diameter on the resistance axis and determined by the points R = 0.194 acoustic ohm, X = 0 and R = 342 acoustic ohms, X = 0. The theory is developed, and measured and calculated impedance values for several conditions are compared.