An investigation into the reproducability results of the European ILT programme.

In an inter-laboratory test programme (ILT) for the measurement of airborne sound insulation of lightweight walls, reproducibility values of up to 12dB were obtained from the sound reduction index measured in 21 participating laboratories. These high reproducibility values were for a test structure composed of lightweight plasterboard panels, forming a double wall, mounted on separate metal 'C' channels. This paper presents possible reasons for the large reproducibility values for the double wall using experimental investigations and theoretical models using Statistical Energy Analysis (SEA). Whilst the sound reduction index (SRI) does take into account the different test wall areas and reverberation times of the respective laboratories involved, some factors which may influence the measured SRI values are not. It is suggested that the principle factor which may have effected the SRI values of this test programme for the double wall was the lining material of the test aperture in the various laboratories which can provide a flanking transmission path between both sides of the double wall. Other factors are discussed which may also play a contributory role in causing differences in the measured SRI values such as sill/reveal size, aspect ratio, panel-channel connections and workmanshi