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The Critical Frequency appears when the bending wavelength is equal to the acoustic wavelength (or the celerity of the bending wave is equal to the sound celerity) :
with :
- the mass per square meter (m²)
- the Young Modulus (Pa)
- the Poisson Modulus
- the thickness (m)
- the sound celerity (m/s)
References : Sound Insulation - Carl Hopkins
And to calculate the complete transmission loss of materials, use
AcouVApp Insul