The Science of Sound Part VII: Beating Flanking Paths


In dealing with sound transmission, there’s no substitute for quality construction materials: simple mass is what stops sound waves. Naturally, stud and drywall construction is going to have a higher STC than 1/4″ hardboard paneling. Extra attention to quality techniques will pay off in sound control and ensure a good fit for the partitions.

Above all, the best defense against flanking paths is careful planning in the early stages of the project. An excellent guide to recommended installation instructions is ASTM Recommended Practice E557* which includes such issues as:

  1. Flat, level floors
  2. Level track, suspended from a non-sagging structure
  3. Sealed, insulated plenum barrier
  4. Plumb end walls or adjustable jambs
  5. Indirect HVAC ducts

Using a screed when pouring a ballroom floor, for example, keeps the floor even and level for the seals. Building a barrier in the plenum above the partition track with a construction as good as the partition itself will prevent the sound from leaking over the top. The permanent walls in which the movable partitions intersect must be vertical and braced so that the horizontal pressure does not force the partition to become uneven.

Although wall insulation (glass or mineral wool) is not an effective barrier, adding it in the cavity of wall greatly improves its performance. It is also useful above the suspended ceiling to reduce reverberation.

Both the supply and return air ducts should branch from main lines outside the rooms containing movable partitions, rather than running directly from one side to the other. If this is not possible, using lined ducts with a zig-zag pattern will help somewhat.

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