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What is Flanking?

Flanking is when sound vibrations pass through a structure 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, however, in the field flanking cannot be ignored. With enough flanking, the performance gains of sound isolation products can be entirely lost.

Flanking

Products To Treat Flanking

  • Electrical boxes leave 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 restore the mass and provide damping. – SpecSeal SSP Putty Pads
  • The significant loss in mass from recessed lighting must be restored. The QuietBox fully restores this lost mass. Also, resilient installation is possible with the GenieClip LB. – QuietBox
  • Plumbing pipes and sheet metal duct work are lightweight so they will conduct energy easily. Adding mass and damping to these surfaces will isolate the vibrations. – VibraDamp
  • Much of the resonance in duct work can be resolved with flex duct. In tighter areas or areas with more stringent performance requirements, we suggest an airtight centrifugal fan. – Fantech Centrifugal Fan
  • 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. – GG Acoustical Sealant
  • The gaps around the perimeter of the door slab will limit the performance of any door to around 20 STC. The door seals will limit loss to around 1 STC point. – View the ADB and PDS Door Seals
  • Even the highest performing solid wood door fully sealed will max out at STC 30. 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. – 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. – 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 rolled Iso-Sill resolves this obvious flanking issue. – Iso-Sill

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