silencer duct

Hi

I want to simulate insertion loss for ventilation ducts. I need to define inlet and outlet pressure so i can calculate insertion loss by its difference.
There is a similar sample "perforated muffler" for this situation.
there is a definition for acoustic power
P_in = intop_in(2*p0^2/(2*acpr.rho*acpr.c)) Total acoustic power at the inlet

P_out = intop_out(2*p*conj(p)/(2*acpr.rho*acpr.c)) Total acoustic power, outlet

TL 10*log10(P_in/P_out) Transmission loss

Are these formulas suitable for calculating sound pressure or i need to use anything else?

Regards