When evaluating soundproofing materials, two key metrics are used: OITC (Outdoor-Indoor Transmission Class) and STC (Sound Transmission Class). Both measure how well a building element (like walls, windows, or doors) blocks sound, but they assess different frequency ranges and real-world conditions. Understanding OITC vs STC ratings helps in selecting the right materials for effective noise control.
What Is STC (Sound Transmission Class)?
STC measures a material’s ability to block mid-to-high-frequency sounds (125 Hz to 4000 Hz), such as voices, TV noise, and office chatter.
Key Features of STC:
- Best for indoor soundproofing (walls, doors, windows).
- Higher STC = Better sound blocking (e.g., STC 50+ is excellent for privacy).
- Does not account for low-frequency noise (traffic, bass, machinery).
Common STC Ratings:
- STC 25-30 – Thin walls (basic privacy).
- STC 40-50 – Good for offices & homes.
- STC 50+ – High sound isolation (studios, theaters).
What Is OITC (Outdoor-Indoor Transmission Class)?
OITC evaluates a material’s ability to block low-frequency sounds (80 Hz to 4000 Hz), such as traffic, airplanes, and construction noise.
Key Features of OITC:
- Designed for outdoor-to-indoor noise (highways, airports).
- More accurate for real-world impact noise (trucks, subwoofers).
- Typically lower numbers than STC due to low-frequency emphasis.
Common OITC Ratings:
- OITC 25-30 – Standard windows (some traffic noise).
- OITC 35+ – High-performance soundproofing (urban areas).
OITC vs. STC: Key Differences
| Feature | STC | OITC |
|---|---|---|
| Frequency Range | 125-4000 Hz | 80-4000 Hz |
| Best For | Indoor noise (speech, TV) | Outdoor noise (traffic, aircraft) |
| Low-Frequency Performance | Weak | Strong |
| Typical Use | Walls, doors, partitions | Windows, exterior walls |
Which Rating Should You Use?
- For indoor noise (offices, homes) → STC is sufficient.
- For traffic, airports, or loud machinery → OITC is more reliable.
- For full-spectrum soundproofing → Combine both ratings in material selection.
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Conclusion
Choosing between OITC and STC depends on your noise concerns. STC works well for speech and everyday sounds, while OITC is better for low-frequency outdoor noise. For optimal soundproofing, consider materials tested for both ratings to ensure maximum noise reduction.