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Solving the Floor/Ceiling Sound Puzzle - Assembly Components
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| Apr 08, 2014 |
With multifamily projects on the rise, understanding how components of a floor/ceiling assembly impact sound control has never been more important. It may surprise you to know that even with a properly selected and installed sound control mat and underlayment, an improperly installed resilient channel or channel type may be the difference between achieving sound code minimum or not. In this multi-part series, we will help you solve the acoustics puzzle by first reviewing the components of a floor/ceiling assembly and then discussing flanking paths and proper floor isolation/sound deadening mats.
Assembly Components
To ensure that the floor/ceiling assembly does not adversely impact a properly installed sound control system, it is important to understand the role each component plays in sound control.
Truss Type and Subfloor – Gypsum board, the subfloor, poured underlayment, and the floor truss make up the mass of the system. According to the Mass Law, the greater the mass, the greater the sound energy (sound wave) required to transmit through it. In addition to mass, the subfloor and truss also reduce sound transmission by adding stiffness to the system. A stiffer floor will transmit less sound when high end ceiling products and sound control mats are used.
Insulation – Insulation provides sound absorption in the joist spaces which helps absorb sound waves as they pass through the system. It should be noted that sound absorptive material is very important within the joist cavity, but there is a law of diminishing returns. In other words, doubling the thickness of insulation will not double the degree of improvement realized from the initial thickness.
Resilient Channel – The resilient channel is also a very significant part of the system both for STC and IIC. It effectively de-couples the ceiling from the joists therefore creating a vibration break. Over the years there have been a number of resilient channels appear on the market that vary considerably in performance. For this reason, it is imperative that well performing channel be used in the various floor/ceiling and wall systems. There are some excellent resources available that discuss resilient channel. Two to reference include, "Quantitative Comparisons of Resilient Channel Designs and Installation Methods" published by Veneklasen Associates and JGL Acoustics' "Resilient Channel Update".
Hangers – Besides the use of resilient channel, there are now other products on the market that can be utilized to hang a resilient ceiling. Rubber clips and spring systems have been developed by multiple manufacturers. Several of the products perform as equals to good quality, well installed resilient channel. Some products perform better than resilient channel. Make sure to thoroughly evaluate the sound test reports for these products or call Maxxon's Acoustical Specialist, Josh Jonsson - (800) 356-7887, for further thoughts on this topic.
Gypsum Board – The gypsum board is also significant as it completes the cavity, which results in a reactive air space within the truss cavity when resilient channel or acoustical hangers are present. Air space alone can increase STC and IIC performance, although fiberglass insulation further enhances the performance of the air space. The gypsum board also provides a dead load which is necessary for the resilient channel to work properly, and as mentioned above, the gypsum board further increases the mass of the system. Adding a second layer of drywall to the floor/ceiling assembly has historically added 1-2 STC and IIC points to a traditional wood frame floor/ceiling assembly’s performance.
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