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Critical Frequency Calculator




Understanding Critical Frequency in Acoustic Insulation

The critical frequency is a key parameter in building and material acoustics. It occurs when the bending wavelength of a panel equals the acoustic wavelength in air. At this point, the bending wave speed equals the speed of sound in air, leading to a drop in sound insulation performance.

Critical Frequency Formula

The critical frequency (fc) can be calculated using the following equations:

$$ f_c = \frac{c_0^2}{2\pi}\sqrt{\frac{\rho_s}{B_p}} = \frac{c_0^2}{\pi} \sqrt{\frac{3\rho_s(1-\nu^2)}{E h^3}} $$

  • ρs: Mass per unit area (kg/m²)
  • E: Young's modulus of the material (Pa)
  • ν: Poisson's ratio (dimensionless)
  • h: Thickness of the material (m)
  • c0: Speed of sound in air (m/s)

Why Critical Frequency Matters

When designing walls, floors, or partitions, accounting for the critical frequency helps optimize sound insulation performance depending of the frequency radiation of the noise source. Near this frequency, sound transmission increases due to coincidence effects.

Further Resources

Reference: Sound Insulation – Carl Hopkins

For complete transmission loss calculations of various materials, try our interactive module: AcouVApp Insul.


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