Sound Transmission Control and the Design of Wall Sections

Quick post here… I am looking into the issues surrounding the design of wall sections for sound transmission control. Here are the things I am considering in the design:

  1. Sound frequency is measured in Hertz (Hz). Hertz is defined as one cycle per second, and is typically applied to Sine waves.
  2. Sound is a compressive wave that is sent through a media, whether it is air (as we usually experience it), water or any other solid material.
  3. The control of sound therefore must happen as a means of dispelling the sound wave, which happens through the process of refraction.
  4. Absorption of the sound wave could also be considered as a type of refraction, through which the sound propagates through a given medium, but at a lesser intensity.
  5. First thing you should take into consideration in the design of a wall section is the expected sound levels of the rooms that you are blocking between. Since the spaces under consideration are normal office spaces, we will assume a sound rating level of 60dBa for a moderately loud office. The dB (decibel) level is a measurement that gives an indication of the loudness of the sound.
  6. The ultimate capability of the wall or any media to block sounds is its ability to handle a number of frequencies (through dispelling each sufficiently) within the expected range of frequencies that will be encountered.
  7.  From the early 1960’s, the range of sounds was determined according to what has become to be known as STC… the Sound Transmission Class.
  8. STC is determined through testing various assemblies of materials and comparing the reading of the sounds from one side of the material to the other side for a range of frequencies.
  9. The range of frequencies tested for STC ratings are from 125 Hz (Hertz) to 4000 Hz.
  10. Most complaints are generated due to sounds that are below the 125 Hz frequency level.
  11. The STC rating of each of the various frequencies are graphed and a curve is developed from the various points. The resulting curve is called the STC rating.
  12. A higher STC rating is usually better than a low one.
  13. The STC rating doesn’t correspond to the number of decibels the wall could stop.
  14. STC numbers can’t be added together, since they are a representative of a logarithmic indication.
  15. For an office application, an STC of 45 or over should be sufficient for most typically encountered situations.
  16. Green Glue ” is an adhesive that is used in many sound control applications.
  17. If a wall occurs along a curve, then Gyp. board that is flexible is needed. However, flexible gyp. board comes in 1/4 inches thick sections and has a lower STC rating than 5/8 inch thick drywall.
  18. I should not expect to get more of an STC rating than about 30 for a non-insulated wall with 1/2″ drywall.
  19. With a curving wall section that has an extended portion, the studs will need to be staggered to increase the sound refraction capabilities.
  20. To proceed, I called the USG to determine what they would recommend to get both the curve as well as the STC rating I am wanting to achieve. I will update this post as I get more information.

For this information, I consulted the following references:

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