Why Go Ported?
The DDport was developed with the DDbox to increase the overall efficiency of the system and broaden the power response curve as discussed previously. In order to keep a 3-1 ratio of cone area to port area, use the following formula:
16 square inches of port area per cubic foot of box volume, make the port 18-20 inches deep. The port is tuned to the box volume, not the subs.
This generally tunes the box to the upper 30Hz area, with the vehicle transfer function extending the frequency another 10-12Hz or so. This is the most popular all purpose tuning.
If the system is primarily playing bass tracks and electronically massaged music, extend the port length in the 24-28 inch length. The box will lose a little upper frequency response while adding extending the low frequencies.
Once you determine how much space you have available, divide the sub(s) into that space. Don't cram the space, its better to error on the big side than the small side. A 10" sub will outperform a 12" sub if the space isn't big enough.
The proper combination of a vented enclosure coupled to a driver that is suited for this application can give a substantial increase in output for a given input power and yield outstanding SQ. A vented enclosure has increased output due to the fact that it has an increased effective radiating area.