Downfire formula?

[BigPerm 0]

If you're building a downfire enclosure, how do you calculate the distance from the floor?

I've searched and haven't found a definitive answer. All i've found is calculations for

woofer sag and "just do 3"-4" from the floor."

Half the radius, or plus 5% of Xmax... What?

Help please! Thank you.

[Adrian_D 520]

Some say you only need it to be high enough to clear the surround under excursion. 3-4" seems like good measure imo.

[KU40 173]

To be a smartass, you calculate the distance from the floor with a ruler.

But really, Adrian has it. It obviously needs to be more than the xmax of the sub, but a few inches is good. I'd say basically as much as you can afford to get the airspace you need under the seats, because there will be some sound effects from having the sub too close to the floor, or any surface (even back firing into a trunk for example).

[BigPerm 0]

To be a smartass, you calculate the distance from the floor with a ruler.

I knew I was doing something wrong.

For future searches, I found some other info that basically said the opening that

allows the sound "out" must be as large as, or larger than the SD of the sub.

Thanks for the responses.