FSTC window testingHere are 10 tips to improve the Sound Transmission Class (STC) between rooms. STC is described below the tips.

  1. Extend the wall to the structure. In office spaces, as a minimum extend the all above the acoustic tile ceiling.       The path through the ceiling tiles (CAC) may be the week path.
  2. Seal the wall at the perimeters and all penetrations with non-hardening caulk. Do not allow any gaps in the wall. All drywall seams should be taped and mudded (on each layer).
  3. Receptacle boxes should not be located back-to-back on opposite sides of a wall.
  4. Adding acoustical absorption in the air cavity +5 STC
  5. Double layers of dry wall on one side of a wall +3 STC
  6. Double layers of dry wall on both sides of a wall +5 STC
  7. Double air cavity of the wall +5 STC
  8. Change from single studs to staggered studs +10 STC (dual studs perform even better +15 STC)
  9. Add resilient channels to one side of wood studs +4 STC (be careful with resilient channels, they can be shorted if you connect directly to the studs)
  10. Add resilient channels to both sides of wood studs +8 STC

As with the ceiling, doors and windows can become a week path. All of the improvements done to a wall may have very little effect on the overall sound transmission is there is a weak path.

Be aware of HVAC system paths.  Two return diffusers connected by an unlined duct may be the weak path.  Open return grills may be a weak path when the wall between offices does not go to the ceiling.

Airborne noise isolation addresses noise sources such as televisions, stereos, human speech, etc.  The Sound Transmission Class (STC) is a single-number rating of the sound transmission performance for a partition tested over a standard frequency range. The higher the STC, the more efficient the partition is for reducing sound transmission between spaces.   The following is a list of STC descriptions which corresponds the single-number STC rating to a subjective evaluation of a typical listener. The STC descriptions are based on the audibility and intelligibility of speech between two spaces, and assume relatively low background noise. Keep in mind that the subjective descriptions below are based on typical human speech. Low frequency noise, such as from music, will be more easily audible than speech.

STC 30         Normal speech can be heard and easily understood
STC 35         Loud speech can be heard and easily understood
STC 40         Loud speech can be heard and moderately understood
STC 45         Loud speech is audible, but will sound “muffled.”
STC 50         Loud speech is difficult to detect. An occasional word may be understood.
STC 55         Loud speech is not audible.

FSTC test should be conducted in accordance with ASTM E336, Standard Test Method for Measurement of Airborne Sound Insulation in Buildings and ASTM E966, Field Measurements of Airborne Sound Insulation of Building Facades and Facade Elements. The FSTC is calculated using ASTM E413, Classification for Rating Sound Insulation.


Thank you for your interest in the Noise Engineers podcast.

Noise Engineers provides information and resources to help people address acoustical issues. In these episodes my goal is to provide resources, inexpensive tools, rules of thumb when dealing with acoustical issues. I would like to explain basic acoustic principles and answer any questions. I will describe actual projects to make this as practical as possible.

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