Special Relativity in air.

If the universe was composed of still air, with no light or matter, would the speed of sound be the same for any observer, in any reference frame?

The only clock you have available works using sound, eg, the time for sound to travel from an emitter to a receiver.

If this is one unit of time, then time would slow if the clock moved through the air, because the distance travelled would be longer for a moving clock. The faster the clock moves, the slower the clock runs.

And when the speed of the clock reached the speed of sound, time would stop altogether, because the sound could never reach the reciever.

So the speed of sound would be the same, measured by any observer moving at any speed, because of this time dilation.

So doesn't special relativity apply to virtually any medium?