Speed of sound in LBM is 340 m/s or 1500 m/s?

Hi
I simulation a acoustic wave in LBM as:
acoustic source: rho=rho0+rhos sin(omega t)
NI=101
NJ=101
nu lb=0.05
Cs^2=1/3

how can calculate the physical speed sound?
physical speed sound is 340 m/s or 1500 m/s or …?

Thanks