Indirect sound transmission with joist and solid floors

Field values of airborne sound insulation of floating joist floors are considerably lower than laboratory values. To investigate this difference the indirect transmission past such a floor with an average airborne insulation of 43 db has been measured in the field by a method previously described. The transmission past a similarly situated floating concrete floor, insulation 49 db, has also been measured for comparison. In both cases the value of airborne insulation was found to be determined mainly by flanking transmission and it appears that the higher insulation of the concrete floor in the same structure is due to the junction of the floor with the walls attenuating the flanking energy. There is little indirect insulation with the joist floor since it connects with the walls at very few places.