Reading STC ratings is straightforward: a higher STC number indicates greater effectiveness in blocking sound transmission.
Understanding Sound Transmission Class (STC)
Sound Transmission Class (STC) is a single-number rating system used in the United States to measure the effectiveness of a building partition (like a wall, floor, or ceiling) in reducing the transmission of airborne sound. It is calculated based on sound transmission loss measurements over a range of frequencies relevant to speech.
Essentially, the STC rating tells you how much sound is stopped by a barrier. The higher the STC value, the better the material or assembly is at preventing sound from passing through it.
Interpreting STC Ratings: What the Numbers Mean
To "read" or interpret an STC rating, you need to understand the practical implications of different numbers. The provided reference gives clear examples related to speech intelligibility:
| STC Rating | Practical Meaning (Speech) |
|---|---|
| 25-30 | Speech can be easily understood through the partition. |
| 35-45 | Loud speech is audible but less intelligible. |
| 50-55 | Speech privacy is achieved at normal voice levels, but loud sounds are still audible through the wall. |
This table, based on information from Riverbank Acoustics, illustrates how higher STC ratings provide better sound isolation, moving from easily understood speech (low STC) to significant speech privacy (high STC).
Key Takeaways for Reading STC
- Higher is Better: Always remember that a higher STC number means the partition blocks more sound.
- Context Matters: The required STC rating depends on the application (e.g., bedroom wall vs. conference room).
- Speech is Key: STC is particularly relevant to blocking speech sounds. While it provides some indication for other sounds, its calculation is weighted towards frequencies common in human speech.
Understanding these points allows you to read and interpret STC ratings to assess how well a wall or barrier will reduce noise transfer.
