What Is the Acoustic Sound Absorption & Noise Reduction Coefficient (NRC) Calculator?
The Noise Reduction Coefficient (NRC) is a scalar index rating the sound absorption properties of architectural surfaces.
How Does the Acoustic Sound Absorption & Noise Reduction Coefficient (NRC) Calculator Work?
Absorption coefficients measured at 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz are averaged and rounded to the nearest multiple of 0.05 according to ASTM C423.
Acoustic Sound Absorption & Noise Reduction Coefficient (NRC) Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
ASTM C423 standard Noise Reduction Coefficient averages mid-frequency sound absorption coefficients and rounds to the nearest 0.05 increment.
How to Use the Acoustic Sound Absorption & Noise Reduction Coefficient (NRC) Calculator
- Enter reverberation room absorption coefficients measured at 250, 500, 1000, and 2000 Hz.
- Read the standardized NRC rating and ISO absorber class.
Step-by-Step Example Calculation
Standard 25mm Fabric-Wrapped Acoustic Wall Panel
Input Values:
Understanding Your Result
NRC = 0.00: 100% sound reflection (smooth glass, polished concrete).
NRC = 0.70 - 0.85: Quality office and classroom acoustic panels.
NRC ≥ 0.90: High-performance recording studio and auditorium sound absorbers.
Factors That Affect the Result
- Material porosity, flow resistivity, panel thickness, and air cavity depth behind the absorber.
When Should You Use This Calculator?
- Specifying ceiling tiles, acoustic wall panels, recording studio baffles, and open-plan office acoustics.
Assumptions & Limitations
- NRC omits bass frequencies below 250 Hz (use low-frequency bass traps for sub-bass control).
Frequently Asked Questions
Calculation Accuracy & Reference Note
Conforms to ASTM C423 and ISO 11654 architectural acoustic testing standards.