Sound Effects, STC & Rw Ratings calculation

📈 Acoustic Performance Ratings

🔬 Report-Calibration Anchors

Frequency Anchors

Transmission Loss at Anchors

Extrapolation Slopes

📜 Calculation Methodology

📖 User Guide

Getting Started

This calculator predicts the acoustic performance of single and double-leaf wall/partition systems using established acoustical engineering principles.

1. Choose a preset or configure your system type (single/double leaf)
2. Define material layers for each leaf (thickness, density, elastic properties)
3. Set cavity parameters if using a double-leaf system
4. Click Calculate to generate predictions
5. Review results including STC, Rw, and frequency-dependent TL values

Key Concepts

STC (Sound Transmission Class): Single-number rating per ASTM E413. Primarily reflects mid-to-high frequency performance (500-4000 Hz).

Rw (Weighted Sound Reduction Index): ISO 717-1 single-number rating with broader frequency range (100-3150 Hz).

C & Ctr: Spectrum adaptation terms that adjust Rw for specific noise types (pink noise vs. traffic noise).

Mass Law: TL increases ~6 dB per doubling of mass per unit area or frequency (below coincidence).

Coincidence Effect: Reduction in TL when acoustic wavelength matches bending wave in panel.

Mass-Air-Mass Resonance: Resonance frequency in double-leaf systems where TL is reduced.

Tips for Best Results

• For double-leaf walls, maximize mass and cavity depth for better low-frequency performance
• Use different thicknesses/materials on each leaf to avoid coincidence frequency alignment
• Add absorptive material in cavity to dampen resonances
• Typical residential walls: STC 45-55; Commercial: STC 50-60; Studios: STC 60+
• Engineering model provides estimates ±3-5 dB; lab testing required for certification

Standards & References

• ISO 717-1: Acoustics — Rating of sound insulation in buildings and of building elements — Part 1: Airborne sound insulation
• ASTM E413: Classification for Rating Sound Insulation
• ASTM E90: Laboratory Measurement of Airborne Sound Transmission Loss

❓ Frequently Asked Questions

Q: How accurate are these predictions?

Engineering predictions typically fall within ±3-5 dB of laboratory measurements. Accuracy depends on proper input data and idealized construction assumptions.

Q: Can I use this for certification?

No. Official ratings require laboratory testing per ASTM E90 or ISO 10140 standards. Use this tool for design estimation and optimization only.

Q: What's the difference between STC and Rw?

STC (ASTM) focuses on 125-4000 Hz, while Rw (ISO) covers 100-3150 Hz. Rw includes spectrum adaptation terms (C, Ctr) for different noise types. Both use contour-fitting methods but with different procedures.

Q: Why does adding insulation sometimes not help much?

Cavity insulation mainly dampens resonances. If the system is already well-damped or mass-limited, additional insulation provides minimal benefit. Increasing mass or cavity depth is often more effective.

Q: What causes the "coincidence dip"?

When the acoustic wavelength in air matches the bending wavelength in the panel, energy couples efficiently through the panel, reducing TL. Thicker/stiffer panels have lower coincidence frequencies.