The Transmission Loss of Double Stud Walls with Layers of Gypsum Board Installed inside the Wall Cavity

A demising wall assembly that is frequently being specified for mid-rise and high-rise building constructions is a double steel stud wall assembly with one or more sheets of fire rated gypsum board installed inside the wall cavity between the rows of studs, creating a triple leaf wall. Locating the gypsum board inside the wall cavity can sharply decrease the transmission loss below the 200 Hz one-third octave band due to the creation of two mass-air-mass resonances centered around the 80 Hz one-third octave band. For the walls tested as part of this study, this decrease in the transmission loss was 14 to 17 dB. One theory for why gypsum board is being specified inside the wall cavity is the belief that the gypsum board in the wall cavity maintains the transmission loss of the wall even if residents create small holes in the outer gypsum board layers by hanging decorations on the wall or securing furniture to the wall. To disprove this theory, an increasingly larger number of holes were drilled into the gypsum board on both sides of a wall to determine the effect on the transmission loss. It was found that a significant number of holes, well in excess of normal use of a wall needed to be drilled into the gypsum board before the transmission loss was affected.