Explanation of Flanking

Flanking is when sound vibrations pass through a structure (conduct) along an indirect path. These paths are most common through framing connections, electrical outlets, recessed lights, plumbing pipes, and duct. Lab tests cannot account for flanking and should not because of the varying levels of flanking in any assembly. Regardless, real life flanking occurs in every real world structure and cannot be ignored. With enough flanking, the performance gains of sound isolation products can be entirely lost.

Flanking

PRODUCTS TO TREAT FLANKING

  • Electrical boxes are generally unsealed and create a loss in mass that must be restored to maintain high STC ratings in the assembly. Putty pads on the back of the boxes will seal the box, restore the mass, and provide some damping. – Recommendation: SpecSeal SSP Putty Pads
  • The significant loss in mass from recessed lighting must be restored. The QuietBox fully restores this lost mass. Resilient installation (to further reduce flanking) is also possible with the GenieClip® LB. – Recommendation: QuietBox
  • Plumbing pipes and sheet metal duct work conduct energy easily as they are inherently lightweight. Adding mass and damping to these surfaces will reduce the vibration transfer. – Recommendation: VibraDamp
  • A gap that makes up 1% of a surface can allow 50% of the sound to pass through it. It is crucial to seal any gap in an isolation assembly. Read Importance of Seal Quality for more info. – Recommendation: GG Acoustical Sealant
  • The gaps around the perimeter of the door slab will limit the performance of any door to around 15-20 STC. A loss upwards of 15 STC points. Using perimeter door seals for all 4 sides of the door can limit loss to around 1 STC point. – Recommendation: ADB and PDS Door Seals
  • Even the highest performing solid wood door fully sealed will max out at STC 30. A DIY door based on common design recommendations found in online forums maxes out around STC 37, but with significant resonance issues. The IsoDoor and IsoDoor HD will push performance into the high 40’s STC and low 40’s OITC – a rating several times better than a thick solid wood door. – Recommendation: IsoDoor, IsoDoor HD
  • Framing for soffits, ceiling fans, projectors, plumbing, acoustical grid ceilings, sway bracing, and other similar items can be decoupled with an L bracket resilient clip. – Recommendation: GenieClip® LB
  • Even with double or staggered stud walls, the bottom plate and top plate of the framing are still significant sources for flanking. The GenieMat® FIS resolves this obvious flanking issue. – Recommendation: GenieMat® FIS