R-value ≠ STC
There is a common misconception that increasing thermal insulation is a way of returning privacy to the conference room and open office environment. If the sound escaping is leaving through the ceiling, and if the insulation is installed consistently, it might provide some benefit to reducing some of the sound travel. However, simply doubling the R-value of a wall or ceiling system will not double the STC because the sound transmission class is a measure of the entire system’s performance, of which the insulation is only a small component.
It is also important to remember sound levels measured in decibels are a logarithmic scale. Increasing the performance of a 35 STC wall system to hold back double the sound energy is only an increase to 38 STC, not to 70 STC. This is why a 55 STC door is so much more expensive than a 35 STC. The 55 STC holds back 100 times more sound energy than its lower-cost counterpart.
As an absorber, insulation will only have an effect on sound energy that actually reaches the material. Here again, ceiling insulation has no attractive power to draw in sound energy headed for the gap between the frameless glass doors of the boardroom. It is often better to investigate adding an entirely different class of acoustic treatment before trying to double down on the performance of a treatment already in place, or to try using thermal insulation as a barrier to contain sound.
Conclusion
It is safe to say the glass houses of modern conference rooms are with us for the foreseeable future. With office space at a premium in many markets, open-plan offices, tighter employee seating, and limited acoustical treatments are all design features that will be around for a while. Conversations in open spaces will continue to distract employees trying to focus on their work, while private conversations that should not be overheard will be an increasing concern of employers, employees, and legal organizations. Sound management, and especially sound masking, is an important part in the mitigation of sound for these new open and glass-enclosed office spaces.
Jeremy Krug has more than 15 years of experience as a professional audio engineer. He studied music performance at The Harid Conservatory and Colorado University (CU)-Boulder, and audio engineering at the CU-Denver. Krug served for almost a decade as the recording studio engineer for the School of Music at Washington State University, and has worked in both residential and commercial audio visual (A/V) integration. Krug joined the team at Cambridge Sound Management in 2014. He can be reached via e-mail as jkrug@cambridgesound.com.
