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Medium Quality

6" 05O nmj Solid Concrete Panel 75 Ibs/sq Ft (365 kg/sq m; R-11 C3.5" or ®tO mm^ Batt Insulation 1 Layer 5/£>" (16 mmj ©ypsum Board

High Quality

6" (150 mmj Solid Concrete Panel

0.15" (A mm) DeFleotion Heoprene Isolators

High Quality

6" (150 mmj Solid Concrete Panel

0.15" (A mm) DeFleotion Heoprene Isolators

Structural Stiffness

The achievement of a high IIC rating in a given floor-ceiling system does not guarantee that noise will not be a problem or that the sound of walking will not be audible in the units below. The IIC test measures the reaction of a floor system to the impact of a series of 1.1 lb (0.5 kg) weights dropped on the surface. Although this may model the noise of a heel tap, it does not represent the full effect of the loading and unloading under the weight of a walker. When a person steps or even stands on a floor, it will deflect under the static and dynamic load of his weight, as we discussed in Chapt. 12. If the underside of the floor is exposed to the room below, a sound generated by this motion will radiate directly into the receiving space. Noise generated by floor deflection sounds like low-frequency thumps, whereas heel clicks have a spectral character largely dominated by the high frequencies.

Three mechanisms are available to improve this condition: 1) increase the stiffness of the floor system, 2) increase the structural damping, and 3) increase the vibrational decoupling between the floor and the ceiling. In concrete structures both the stiffness and damping increase with slab thickness. For the 6" (152 mm) concrete slab required to achieve an STC of 53-55 structural deflection is rarely a problem for moderate spans. In wood structures the most common type of minimum quality construction consists of 1.5" (38 mm) lightweight concrete on plywood on joists with ceilings of drywall on resilient channel. This construction

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