Distance behind port

[bernie]

Purchased a 12: sub, amp, and 3" flared port. Building my own forward firing enclosure. Have a few questions:

If my port requires 12" length how deep does my enclosure need to be for correct clearance...is it 1/2 the dia?, 1 x the dia?, or??

When determining the overall box size, I know I need to account for the volume of the port but what about the area taken by the cone, magnet, etc?

I'm confused about the insullation -- I've learned that this has the same effect as a box of 10-15% larger. I've also heard this is only true with sealed enclosure not for vented. If it is true for vented, does this % (and what is that number) get subtracted from the calulated box volume?

Please advise -- I'd like to keep the depth to a minimum but need these answers to continue.

Thanks

[Pete Schumacher ®]

> Purchased a 12: sub, amp, and 3" flared
> port. Building my own forward firing
> enclosure. Have a few questions:

> If my port requires 12" length how deep
> does my enclosure need to be for correct
> clearance...is it 1/2 the dia?, 1 x the
> dia?, or??

> When determining the overall box size, I
> know I need to account for the volume of the
> port but what about the area taken by the
> cone, magnet, etc?

> I'm confused about the insullation -- I've
> learned that this has the same effect as a
> box of 10-15% larger. I've also heard this
> is only true with sealed enclosure not for
> vented. If it is true for vented, does this
> % (and what is that number) get subtracted
> from the calulated box volume?

> Please advise -- I'd like to keep the depth
> to a minimum but need these answers to
> continue.

> Thanks

Your port can have bends in it to get to the right length. If you have a 3" diameter vent, you need about 3" of clearance between the port end and a box wall.

If you add fiberglass to the inside of the enclosure, you need to make sure that the vent area is clear of stuffing so that air flow is unimpeded.

[Chris Roemer]

> Your port can have bends in it to get to the
> right length. If you have a 3" diameter
> vent, you need about 3" of clearance
> between the port end and a box wall.

> If you add fiberglass to the inside of the
> enclosure, you need to make sure that the
> vent area is clear of stuffing so that air
> flow is unimpeded.

WinISD ( <A HREF="http://www.linearteam.org">www.linearteam.org</A> ) has enough "slack" built in that you can generally ignore the space lost to the driver. I've also read that stuffing with glass/polyfill only makes a "sealed" box look bigger to the driver. Many folks don't line a vented sub box at all, it's operating at too low a frequency to really matter much. Most any 12" "sub" worth its salt will probably be happier with a 4" dia. port to avoid chuffing.