explain VAS?

[murderedtahoe 10+ year member]

ive read about what VAS mean, but still isnt sure on its importance. so my question is, whats so important about vas as far as enclouser size go. i know that subs with larger vas need an bigger enclouser, but why is this?i noticed that vas on 18" woofers get ridiclious thats why 18s need such large boxes. what roll does vas play within subwoofers?

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[ciaonzo 5,000+ posts]

A driver's suspension has a certain springyness (not a real word) that is equivalent to a certain volume of air. You could blow up a balloon to represent that volume of air and feel the springyness of it. A sealed enclosure will have it's own springyness based on it's volume of air and it will act upon the driver's springyness in different ways based on how large that volume of air is relative to the driver's Vas. You can vary the enclosure size to act upon the drivers Qts and change the Qtc of the system (sub and enclosure working together). If you make the enclosure smaller than Vas you will drive the Qtc upward, maybe too high, and you will have peaky bass. If you make the enclosure larger than Vas the driver will be operating in a free-air fashion and the Qts of the driver will dominate. Qtc can never be less than the Qts of the driver so it only does so much to make the enclosure larger before it does no good at all. You can look at the Vas and Qts figure for the driver to get ballpark idea of what the enclosure volume might be.

This isn't everything, it's just a simple version.

 

[murderedtahoe 10+ year member]

A driver's suspension has a certain springyness (not a real word) that is equivalent to a certain volume of air. You could blow up a balloon to represent that volume of air and feel the springyness of it. A sealed enclosure will have it's own springyness based on it's volume of air and it will act upon the driver's springyness in different ways based on how large that volume of air is relative to the driver's Vas. You can vary the enclosure size to act upon the drivers Qts and change the Qtc of the system (sub and enclosure working together). If you make the enclosure smaller than Vas you will drive the Qtc upward, maybe too high, and you will have peaky bass. If you make the enclosure larger than Vas the driver will be operating in a free-air fashion and the Qts of the driver will dominate. Qtc can never be less than the Qts of the driver so it only does so much to make the enclosure larger before it does no good at all. You can look at the Vas and Qts figure for the driver to get ballpark idea of what the enclosure volume might be.
This isn't everything, it's just a simple version.

wow man thanks good breakdown!

 

[Papermaker85 5,000+ posts]

go to CAF and read my description... it will give you a excellent idea...

 

[murderedtahoe 10+ year member]

go too caf? car audio facts?