The graph presents the sound level in dB(A) as the sound power level without room attenuation for the combination of grille and damper DWN. The value of Vk on the graph is that for the grille without damper.
Ps = Pressure loss in Pa
Vk = Effective velocity of the corresponding grille (see selection tables SH(V)N, AH(V)N, ALG, SPN-V, SPN-VH, SDN-V and SDN-VH)