Horizontal seal To achieve optimum sound attenuation, a double-shell construction is used. Working on the jack principle, telescopic, flexible, spring- loaded double seals press against the ceiling track and the floor; the spring sections can take up eventual uneven ness of the bulding. The load exerted by each panel does not overload the floor but is sufficient to give the Variflex system enough stability to avoid its displacement even when subjected to pres sure.