We know the speed of light. Einstein found a limit to his theory of special relativity.
But what is the maximum speed of sound?
The speed of sound depends on its medium. It is a mechanical wave. Vibration in the medium causes the molecules in the medium to collide with each other to transfer energy.
That is, the faster the molecules in the medium are packed, the faster the sound travels.
It is not practical to take every available object and check the speed of sound with it. So which way ..?
As usual, physics found its way there. Using the fundamental constants that make up the physics of the universe, they discovered the maximum speed of sound in the universe !!! They found this by calculating the mass ratio of protons to electrons. That is, the rest mass of the proton is equal to the constant obtained by dividing the rest mass of the electron.
36 KM / sec or 22 miles / sec. This is about 2 times the speed of sound through a diamond.