Concept of Decoupling
The basic decoupling definition is to separate objects. Decoupling to isolate sound is most commonly done with resilient sound clips, resilient channel, or specialty framing like double stud or staggered stud walls. Sound vibrations will transfer easiest from material to material rather than through open space. An example of this would be sound transfer from drywall to framing and then to the drywall on the other side. Stop this transfer with acoustic decoupling by reducing the number of connections (resilient sound clips) or by breaking the path entirely (specialty framing).
USING RESILIENT SOUND CLIPS TO DECOUPLE
Quality resilient sound clips are small metal and rubber pieces that attach to the framing with screws. Metal furring hat channel inserts into the clips with drywall is fastened to the channel. Clips provide acoustic decoupling by suspending the drywall on the furring hat channel about 1-1/2″ from the framing. Not all clips are equal, only the well engineered clips with a soft rubber base can achieve results meeting or exceeding double stud walls. Other than the design of the clip, the two reasons resilient clips perform so well are 1) the minimal number of connections between the framing and drywall, and 2) the flex allowed in the channel within the wide 48” span between each clip.
The increase in performance by using resilient sound clips (GenieClip® RST) is significantly better than the performance of a staggered stud wall and nearly equal to the performance of double stud walls with three inch spacing. Resilient sound clips also provide an affordable alternative for achieving a high rating in a decoupled ceiling without setting up independently framed joists, i.e. room within a room design.
USING FRAMING TO DECOUPLE
The room within a room concept, acoustic decoupling the framing from the existing structure, is a powerful way to isolate sound with minimal use of isolation products. Double stud framing a room with three inch spacing between walls will generally perform slightly better than a GenieClip® RST system. Extending the spacing to six inches will provide noticeably superior performance over any resilient clip system with most gains in the lowest frequencies. A true room within a room design will have independent stud walls and independent ceiling joists. The performance of staggered stud walls is not as significant as assumed by most. A standard framed wall with Green Glue Compound will rate about as well as a staggered stud wall. The double wall framing of each side of the wall might not touch the other side, but the studs are still ultimately connected to the top and bottom plates.
The issue of flanking (sound transferring indirectly through framing) is a problem with double and staggered stud walls. The top and bottom plate of the wall still tie directly into the framing above and beneath the wall. Resolve flanking through the top plate by decoupling it from the ceiling joists using the GenieClip® LB. The GenieClip® LB should be spaced every 2′ along the top plate with a clip on each end. Using Green Glue Compound in a double or staggered stud wall has considerable value because of the flanking issues common with this framing method.
VALUE OF INSULATION IN DECOUPLED ASSEMBLIES
In coupled assemblies, meaning the drywall or wood fixes to the framing, the sound will pass through the assembly with ease. This transfer will occur mainly through the framing connections effectively bypassing the insulation in the open cavities, reducing the value of the insulation considerably. In decoupled assemblies, the sound transfer through the framing is reduced significantly. The remaining path of travel for the sound is directly through the mass of the assembly as well as the open cavities. Because of this, the importance of the insulation in the assembly is much greater.