Apparently the speed of any wave can be deduced mathematically utilising some properties of the medium.
Speed of light in vacuum is given by the Maxwell’s formula (http://en.wikipedia.org/wiki/Maxwell’s_equations)
The speed of sound c is given by the Newton-Laplace equation: (http://en.wikipedia.org/wiki/Speed_of_sound)
That doesn’t mean that speed of sound in air or the speed of a transverse wave in a lake are constant irrespective the observers motion. If that was so, one could ‘weave’ a relativity theory for every type of wave and medium.
So just because the speed of light (SOL) is deduced mathematically, one can’t assume that it is constant to all observers.
The speed must be with reference to the medium upon whose parameters and conductivity the calculations were done.