S 51 53 55 56 56 5s 6o 62 63 65 66 67 5s

& x & x 16 3-oell Lightweight Concrete Masonry Unit A No Center Srout - 2& ibs/biook B Center &routed + *5 Rebar

C Center ©routed + #5 Rebar + 2 Coats Flat Oil Base Paint Each Side

A 34 31 37 36 37 3& 41 45 43 44 4& 41 52 52 54 55 45 B 35 33 37 37 41 40 44 45 41 54 57 60 64 66 7O 73 4& O 36 37 31 44 46 41 54 54 57 51 62 66 61 71 75 75 55

transmission loss values of concrete panels used in wall or floor construction. Note the difference in the grouted block data between painted and nonpainted conditions. Blocks are intrinsically porous and must be sealed with a bridging (oil-based) paint to achieve their full potential.

High Transmission Loss Constructions

An important study was undertaken by Sharp (1973) to try to develop construction methods that would achieve transmission loss ratings 20 dB or more above the mass law. In this work several techniques were utilized, not normally seen in standard construction practice but which could easily be implemented. These included spot lamination, which has been previously discussed, and point mounting. The point mounting technique he devised was to use 1/4" (6 mm) thick foam tape squares between the gypboard and the stud and then to attach the sheet with drywall screws through the tape into the stud. This technique resulted in panel isolation that approaches the theoretical point mounting discussed in Eq. 9.54. A triple panel wall having an STC of 76 utilizing these techniques is shown in Fig. 10.11. This wall has a relatively low transmission loss value of 33 dB in the 80 Hz band.

Figure 10.11 High Transmission Loss Wall Construction (Sharp, 1973)

Double Wood Stud Wall

2x4 Studs Separated by a 3" Cap

Outside Layers 3/S" + 1/2" Drywall on 1/4" Foam Tape

Inside 5/S" + 1/2" + 5/£>" Drywall on 1/4" Wood Squares

All Layers Spot Laminated at 24" OC and Strewed

Through Mounts - 2" Batt Insulation in all Cavities o o

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