Interpreting Acoustic Lab Test Reports

When you receive an acoustic lab test report—whether for mineral wool, ceiling tiles, or wall panels—you are looking at a scientific document that translates physical properties into standardized performance metrics. In 2026, with the rise of AI-driven building simulations, accurately interpreting these reports is essential to ensure a product meets both building codes and real-world expectations.

1. The Core Metric: Sound Absorption Coefficients (α)

The most detailed part of any report is the table of sound absorption coefficients. These values represent the ratio of sound energy absorbed by the material at specific frequencies.

• Scale: Values range from 0.00 (total reflection) to 1.00 (total absorption).

• Frequency Bands: Standard tests measure frequencies from 125 Hz to 4000 Hz.

• Low Frequency (125–250 Hz): Difficult to absorb; requires thicker or denser mineral wool.

• Mid Frequency (500–1000 Hz): Critical for human speech.

• High Frequency (2000–4000 Hz): Crucial for clarity and "shimmer" in music or speech.

Note: Occasionally, you may see values slightly above 1.00 (e.g., 1.05). This indicates perfect absorption and is a result of laboratory diffraction effects.

2. NRC vs. SAA: The Single-Number Summaries

Because raw frequency data is complex, the industry uses two main averages:

• NRC (Noise Reduction Coefficient): The average of absorption at 250, 500, 1000, and 2000 Hz, rounded to the nearest 0.05.

• SAA (Sound Absorption Average): A more precise average across twelve 1/3-octave bands from 200 to 2500 Hz. If a report has both, the SAA is the more accurate representation of performance.

3. The "Mounting Type": Why It Matters

Acoustic performance is not just about the material; it’s about how it was installed during the test. A report that lists NRC 0.95 without a mounting type is misleading.

• Type A Mounting: The material is placed directly against a hard surface (the lab floor).

• Type E-400 Mounting: The material is suspended with a 400mm air gap behind it, significantly boosting low-frequency absorption.

4. Sound Attenuation: CAC and STC

If your goal is to stop sound from traveling between rooms (isolation), rather than reducing echo within a room, look for these metrics:

• CAC (Ceiling Attenuation Class): Measures the ability of a ceiling to stop sound from traveling through the plenum into the next room. A CAC of 35 or higher is considered high performance.

• STC (Sound Transmission Class): Measures the sound-stopping ability of a wall assembly. Mineral wool typically adds 5–10 points to an STC rating compared to empty cavities.

5. Summary Table for Quick Interpretation