Space between the port and the rear wall?

[Dammed 12]

The title says it all. How much space should I have between my port and rear wall?

My port will have a 9,5" x 20.5" surface area, the enclosure is 20 cu.ft., I will be using two Fi Q 18" powered by a Hifonics XX Colossus II amplifier that will deliver about 3000W rms.

The reason I ask is that I don't have enough room for the tuning I want, so I want to make it as close to the intended tuning as possible. I was thinking that 8" will be enough if I make the end flared and the wall "pointy" to reduce turbulence. Would this be enough?

Picture of how I was thinking about making the enclosure:

[shizzzon 461]

since the enclosure is basically dual chambered, you would divide the port width in half = 4.75" and that's the minimum space to be used between the back wall and end of port wall.

If you make the space that size, your port length will increase by several inches decreasing port tuning.

If you make the space larger, it will slightly increase tuning compared to lengthening it as said above.

[Dammed 12]

Yeah I know the tuning will be lower if the length of the port increases and vice versa.

Ok, thanks for the info mate. I will be making the port as it is pictured with about 8" space. I believe it would be a good way to reduce air turbulence. Or should I build it differently?

Edited March 23, 2010 by Dammed