The effects of some laboratory designs and mounting conditions on reduction index measurements

Abstract The effects of typical transmission laboratory designs on measured reduction indices are investigated. First the influences of test frames, test openings with deep apertures and mounting conditions are examined separately for some common wall types. The result of a limited test series is then discussed. The test was run in five laboratories. The reduction indices were measured for two lightweight walls, each one mounted in two different ways. For frequencies above coincidence the test results imply that for lightweight walls mounting and laboratory design are of secondary importance. For walls which are heavy compared to the test frame or flanking walls the losses at the edges are important. For frequencies below coincidence the measured reduction indices varied considerably between different laboratories. Mounting conditions, apertures and frames are found to influence the results.