In our last post, we discussed design strategies for achieving optimal office speech privacy. We also introduced the Speech Privacy Potential (SPP) Calculator, which helps you fine-tune the appropriate STC rating for a room type and desired level of privacy.
While the SPP calculator provides guidance on selecting the right NC (Noise Criteria) levels for different spaces, the user still needs to determine the appropriate STC rating based on the project’s specific partition design. In this post, we’ll go deeper into typical partition STC ratings, helping you understand how they impact pricing, wall thickness, and overall speech privacy in your space.
1. What is the STC?
STC (Sound Transmission Class) is a key measure used to evaluate how well a partition reduces sound. Developed in the 1960s, it’s calculated based on laboratory testing in accordance with ASTM E90.
However, real-world performance tends to be slightly lower due to variables like construction flaws or unsealed gaps. In the field, we measure performance using NIC (Noise Isolation Class) or ASTC (Apparent STC), and these values typically differ by around 3-5 points. This variation helps determine how much sound travels through a partition.
2. Key Factors That Impact STC Performance
STC (Sound Transmission Class) is a key measure used to evaluate how well a partition reduces sound. Developed in the 1960s, it’s calculated based on laboratory testing in accordance with ASTM E90.
However, real-world performance tends to be slightly lower due to variables like construction flaws or unsealed gaps. In the field, we measure performance using NIC (Noise Isolation Class) or ASTC (Apparent STC), and these values typically differ by around 3-5 points. This variation helps determine how much sound travels through a partition.
3. Improving STC with Specialized Materials
Specialized materials and systems can be strategically used to further improve sound isolation:
Isolators: Products like resilient channels or neoprene clip systems decouple the gypsum board from the studs without significantly increasing the thickness of the wall, leading to STC increases of 5 to 10 points.
Gypsum Board Layers: Adding layers of gypsum board is one of the most cost-effective ways to improve STC. This improvement is based on the principle of mass law: greater mass equals higher sound isolation. Doubling the number of layers of gypsum board can increase the STC rating by approximately 5 points.
Gypsum Board Type: Standard 5/8-inch thick Type X gypsum board is the typical material used for sound-isolating partitions. Using sound-dampening boards (ex: Certainteed SilentFX, Pabco QuietRock ES, or Gold Bond SoundBreak XP) can increase STC ratings by 5 to 10 points.
4. Practical Insights: How These Improvements Affect Your Design
Achieving desired levels of office speech privacy requires a nuanced approach. When considering improvements to your wall designs, it’s important to understand how different configurations impact the STC rating. While certified laboratory tests provide useful benchmarks, real-world results can vary based on specific building conditions. In our next post in this series on speech privacy, we discuss common construction site observations that have material impacts on measurable sound isolation performance.
We hope this information helps with your detailed design. Stay tuned for Part 3 of the office speech privacy where we discuss common installation challenges.
If you have any questions or need further assistance with using the SPP calculator, feel free to reach out!
