To calculate the global acoustic insulation of an heterogeneours wall, it's necessary to come back to
the transmission loss of each element weighted by the corresponding surface.The formula used is :

$$ \tau = \frac{\sum_{i=1}^{q} S_i \tau_i}{\sum_{i=1}^{q} S_i} $$
with :

- \( S_i \) the surface of each element \( i \)
- \( \tau_i \) the transmission coefficient of each element \( i \)