General rules of thumb for controlling noise between spaces:
  •  A wall must extend to the structural deck in order to achieve optimal isolation. Walls extending only to a dropped ceiling will result in inadequate isolation.
  •  Sound will travel through the weakest structural elements, which, many times, are doors, windows or electrical outlets.
  •  When the mass of a barrier is doubled, the isolation quality (or STC rating) increases by approximately 5 dB, which is clearly noticeable.
  •  Installing insulation within a wall or floor/ceiling cavity will improve the STC rating by about 4-6 dB, which is clearly noticeable.
  •  Often times, specialty insulations do not perform any better than standard batt insulation.
  •  Metal studs perform better than wood studs. Staggering the studs or using dual studs can provide a substantial increase in isolation.
  •  Increasing air space in a wall or window assembly will improve isolation.
Changes in STC/Changes in Apparent Loudness:

Changes in STC RatingChanges in Apparent Loudness
+/- 1
Almost imperceptible
+/- 3
Just perceptible
+/- 5
Clearly noticeable
+/- 10
Twice (or half) as loud

Recommended Ratings
Weaknesses - What You Should Know
The difference between STC and NRC
STC Ratings for Various Wall Assemblies
STC Ratings for Masonry Walls

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