Maybe a variety of explanations might help?
From Eminence:
Vas/Cms
Vas is an equivalent volume of air that has a compliance equal to that of the driver’s moving system. Vas can be calculated as follows:
Vas = ρc2Cas
where Cas is the acoustic compliance of the driver’s suspension. Vas is one of the trickiest parameters to measure because air pressure changes relative to humidity and temperature — a precisely controlled lab environment is essential.
Cms is measured in meters per Newton. Cms is the force exerted by the mechanical suspension of the speaker. It is simply a measurement of its stiffness. Considering stiffness (Cms), in conjunction with the Q parameters gives rise to the kind of subjective decisions made by car manufacturers when tuning cars between comfort to carry the president and precision to go racing. Think of the peaks and valleys of audio signals like a road surface then consider that the ideal speaker suspension is like car suspension that can traverse the rockiest terrain with race-car precision and sensitivity at the speed of a fighter plane. It’s quite a challenge because focusing on any one discipline tends to have a detrimental effect on the others.
From Kaya Sound:
Vas (Liters)
The air inside the cabinet has its own compliance. When you try to compress the air inside a box, you will encounter resistance. If the box is small, the air is harder to compress and therefore less compliant, and if the box is larger, the air is easier to compress, therefore more compliant. In conclusion, Vas describes the volume of the air inside the cabinet, where the compliance of the speaker matches the compliance of the air inside the box.
- If you are making an acoustic suspension box, you can tell that the volume of the box will be something less than Vas .
- If it’s larger than Vas, it would be an infinite baffle
Sonix Electronix
Vas: This is the amount of air that has the same stiffness as the subwoofers suspension. The greater the rating, the lower the stiffness and larger recommended enclosure. It is measured in Liters.
