In the February issue of The Construction Specifier, we published the article, “Using Gypsum Wallboard for Acoustical Control,” by Ashwin L. Himat. The piece dealt with new drywall products designed to reduce noise. However, one reader was concerned there was a bigger picture to keep in mind. Steven Zalben, AIA, NCARB, LEED AP, wrote:
The use of acoustical sealant to reduce sound transmission was only cursorily mentioned. Using an appropriate sealant on both top and bottom plates, and sealing all perimeter joints of all layers, is as important—possibly, more important—than the mass. The mass primarily addresses the structure-borne sound, while sealing primarily addresses airborne sound.
We asked the article’s author to respond.
Mr. Zalben’s feedback on the use of acoustic sealants along wall and ceiling edges for dampening airborne sound transmission is quite valid. It is important to incorporate these sealants into all aspects of the gypsum-board-finishing process, and also to apply acoustical putty around all electrical boxes to prevent similar airborne sound transmission.
The function of gypsum board sealant is similar to that of the viscoelastic polymer used as the middle layer in laminated noise-reducing gypsum boards—both convert sound energy into thermal energy. The image below helps illustrate the sound transmission paths that could be present in most buildings.
I would further like to emphasize adding mass with layers of drywall to dampen airborne sound has its disadvantages. For instance, it is not as effective for improving the sound transmission class (STC) rating of the wall system, and it reduces the footprint of the usable space. Decoupling methods using resilient channels also have their limitations, as they are easy to short-circuit during installation. The newer concept of a laminated noise-reducing gypsum board achieves high STC ratings without any of the limitations that often result from adding extra layers of drywall or using resilient channels.