Concept of Damping
Damping is a straightforward concept defined as the rate at which something dissipates energy. Higher damping equals higher energy dissipation. Without decoupling, the most efficient way to isolate vibrations is to dampen. Dampening methods include constrained layer damping material or extensional damping.
CONSTRAINED LAYER DAMPING (GREEN GLUE COMPOUND)
In a constrained layer damping system, a damping product installs between two other (usually stiff/rigid) materials. An example would be Green Glue Compound sandwiched between two layers of drywall. To understand the concept of constrained layer damping, compare a Green Glue Compound assembly to rubbing your hands together to generate heat.
Think of the outside of each hand as the drywall, the inside of your hand as the Green Glue Compound, and the heat generated by rubbing your hands together as the damping effect. This is essentially what occurs in a wall with Green Glue Compound applied as sound tries to pass through the wall. The drywall layers flex laterally when sound waves hit the drywall placing the Green Glue Compound under considerable shear stress (stress created from lateral movement). As the Green Glue Compound shears, it generates heat, effectively turning the sound that caused the wall to flex laterally into heat. This energy conversion from vibration to heat is damping.
EXTENSIONAL DAMPING (VIBRADAMP)
An extensional damping system is when the damping product applies to the top of the surface. An example of this would be our VibraDamp. When bent (impact of sound against damping material), the constrained layer damping material will stretch (extension) and compress, allowing some of the sound energy to be converted into heat. Extensional damping products, while effective for their proper use, are best for lightweight materials like plumbing, duct, and sheet metal. Use of extensional damping products in wall, ceiling, and floor assemblies will provide no benefit.
DAMPING OF RESONANCE
The mass of a partition offers resistance to airborne sound at most frequencies. Typically a heavy partition will require a significant amount of noise to vibrate it. At some frequencies, however, it is extremely easy for airborne sound to vibrate the partition. This is the resonance point. Partitions with several layers of material (usually drywall or wood) can have increased resonance issues without alternating the thickness and material type, e.g. 1/2″ drywall for all layers of drywall. This resonance issue is minimized with the inclusion of a damping product like Green Glue Compound between the layers of material.
DISSIPATION OVER DISTANCE
The performance of a product is often only considered in terms of STC results from acoustic lab testing. Sound transfer that spreads throughout a structure cannot be properly tested in an acoustics lab. If the material or structure has low damping, the sound vibrations can travel from material to material for considerable distances, e.g. transferring into a wall, then to the ceiling and the floor above. If a structure has high damping, then the vibration dissipates quickly and cannot travel throughout the structure with ease.
Because of this, damping products like Green Glue Compound are vastly more crucial than lab tests show. Even in high STC assemblies, the Green Glue Compound will have considerable value in reducing the strength of the vibrations that do pass through the assembly from being able to travel throughout the structure with ease.