The measurement of sound reflection and transmission at right-angled bends in rectangular tubes

Equipment for measuring the sound reflection and transmission at discontinuities in ducts is described. It has been used for measurements of the sound propagation along right-angled bends in rectangular tubes. The characteristic reflection and transmission factors and the impedance matrix of the equivalent four-terminal electrical circuit are derived from the measurements for different frequencies and compared with the zero-order approximation derived from theoretical wave acoustics. Results are given also for a particular asymmetrical discontinuity. The general method and simplifications of the technique for loss-free and symmetrical discontinuities are confirmed.