Acoustic velocity

Hello all,

I am looking for a definition of acoustic velocity implemented in Comsol (Pressure acoustic/frequency domain - no flow). I want to make sure that what I am getting is exactly what I need. The Acoustic Module User Guide does not seem to have that definition. I really hope that it is defined as:

(u_ac)_i=[-1/(2*pi*f*rho)]*[dp/dx_i] with f being a frequency associated with a particular mode.

Can anybody help?

Thanks