NRC
A single-number rating (0-1) averaging a material's absorption at 250, 500, 1000, and 2000 Hz.
The Noise Reduction Coefficient (NRC) is a simplified, single-number rating that averages a material's absorption coefficients at four frequencies: 250, 500, 1000, and 2000 Hz. The result is rounded to the nearest 0.05.
NRC provides a quick comparison between materials but has significant limitations: • Ignores low frequencies (below 250 Hz), critical for music and bass control • Ignores high frequencies (above 2000 Hz) • Two materials with the same NRC can perform very differently • A 2" panel and 4" panel might have similar NRC but vastly different bass absorption
For serious acoustic treatment, always examine the full frequency-dependent absorption coefficient data rather than relying solely on NRC. The rating is most useful for general comparison of materials in speech-frequency applications (offices, classrooms).
NRC values typically range from 0.00 (very reflective) to 1.00 (highly absorptive). Values above 1.00 are rounded down to 1.00 for NRC purposes.
Formula
NRC = (α₂₅₀ + α₅₀₀ + α₁₀₀₀ + α₂₀₀₀) / 4- α₂₅₀ = Absorption at 250 Hz (coefficient)
- α₅₀₀ = Absorption at 500 Hz (coefficient)
- α₁₀₀₀ = Absorption at 1000 Hz (coefficient)
- α₂₀₀₀ = Absorption at 2000 Hz (coefficient)
Practical Example
2" rigid fiberglass panel
α: 0.22, 0.82, 1.00, 1.00 → NRC = (0.22 + 0.82 + 1.00 + 1.00) / 4 = 0.76 ≈ 0.75NRC 0.75 sounds good, but note the weak 0.22 at 250 Hz. Thicker panels needed for bass.
Standards: ASTM C423
Related Terms
Absorption Coefficient · Bass Trap
術語表 ·
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