What is the difference between ASTM STC and ISO Rw?

ASTM provides the Sound Transmission Class (STC) rating, while ISO provides the Weighted Sound Reduction Index (Rw). Both measure sound insulation but use slightly different methodologies, and ISO adds correction terms (C, Ctr) for different noise types.

Why does Thailand use ASTM transmission loss standards?

Thailand historically adopted ASTM standards due to U.S. trade influence, familiarity among engineers, and their integration into local building codes and regulations.

ASTM vs ISO Transmission Loss Measurements in Thailand | Acoustic Laboratory Thailand

ASTM vs ISO Transmission Loss Measurements: Why Thailand Follows ASTM Standards and What the Future Holds

At Acoustic Laboratory Thailand, an ISO17025 accredited acoustic laboratory, we are often asked about the differences between ASTM and ISO transmission loss measurements. While both frameworks are internationally recognized, Thailand has historically adhered to ASTM standards. Let’s explore why this is the case, what the differences are, and whether Thailand might adopt ISO in the future.

What Is Transmission Loss Testing?

Transmission Loss (TL) measures how well a construction element—such as a wall, door, floor, or window—blocks sound. Higher TL values mean better noise control, crucial for comfort, productivity, and privacy. TL testing is essential for building acoustics, industrial noise control, and product development.

ASTM Transmission Loss Standards

ASTM standards, developed by the American Society for Testing and Materials, are widely used in North America and Asia. In Thailand, they are the foundation for acoustic performance regulations.

ASTM E90 – Laboratory measurement of airborne sound transmission loss
ASTM E413 – Classification of sound insulation (STC)
ASTM E336 – Field measurement of sound insulation

ISO Transmission Loss Standards

The International Organization for Standardization (ISO) standards are used widely in Europe and other global markets. They emphasize Rw values and correction factors (C, Ctr) to adapt to real-world noise spectra.

ISO 10140 series – Laboratory measurement of sound insulation
ISO 16283 series – Field measurements
ISO 717 – Rating of sound insulation (Rw, C, Ctr)

ASTM vs ISO: Practical Differences

Although ASTM’s STC and ISO’s Rw often yield similar numbers, the differences matter in contracts and regulations.

Comparison chart of ASTM vs ISO transmission loss standards, showing ASTM with STC and ISO with Rw and spectrum corrections. — Visual comparison of ASTM and ISO approaches to transmission loss.

Key differences include spectrum adjustments (included in ISO, not ASTM), regional usage (ASTM in North America and Thailand vs ISO in Europe), and reporting expectations.

Infographic table comparing ASTM and ISO transmission loss measurement standards, covering ratings, procedures, spectrum adjustments, and regional usage. — Detailed infographic table contrasting ASTM and ISO standards.

Why Thailand Adheres to ASTM

Thailand’s preference for ASTM is rooted in:

Historic U.S. trade and construction influence
Familiarity among local engineers and contractors
Regulatory alignment with ASTM standards
Consistency across Southeast Asian projects

Will Thailand Switch to ISO?

With globalization, more European investment, and regional integration, a shift toward ISO is possible. However, for now, ASTM remains the regulatory anchor. A practical solution may be dual reporting, where both ASTM (STC) and ISO (Rw) values are provided for international projects.

Conclusion

Currently, Thailand continues to follow ASTM standards for transmission loss. However, with international cooperation increasing, we may see more ISO-based projects in the future. At Acoustic Laboratory Thailand, we provide both ASTM- and ISO-compliant testing, ensuring that our clients meet local codes while preparing for global requirements.

Contact us today to learn more about acoustic testing services in Thailand.