Box Design Steps
Step 4: Port Length
The sound of the system is somewhat tunable, via changes to the port length. As we learned in the Why Go Ported section, the port area needs to be in proper ratio to the cone area, so the DDBox system uses variations to the port length as primary means of tuning frequency mods.
Refer to the DDBox site chart to 23" long. This will enable a DDBox/sub combo to have effective bass response in the car, down into the low 30s. The DDBox plays all types of music very well and is a perfect tune to begin advanced dial in of your system after the subs break in.
The "break-in" period refers to the time it takes for the speaker's spiders to loosen up, allowing more excursion. We build speakers with very strong suspensions so they can be enjoyed for years, as they loosen, the bass will become deeper and louder.
After the break-in, the tuning frequency can be lowered by adding length to the port, try 4 inch increments. Conversely, the tuning can be raised by shortening the port.
Step 4.1: Variations on tuning
Some users have specific, frequency enhanced, types of music they like to play. Some even like the way body panels, windshields and non-cartilage types of body parts flex to the beat, some cars offer a complete beat down to those occupants. These applications might skip straight to a longer port length, adding 6 inches to the tuning frequency charts. Some upper frequency response in the 60-80Hz range may be affected.
This added port length also works well for applications where there is poor acoustic loading in the vehicle, or in open room applications like DJ systems and home applications. The increased port mass helps to enhance the low frequency extension.
Some users would like to cut down on box volume knowing their DD system exceeds their dynamic range expectations. The port area can be reduced by 25%, to 12 square inches per cubic foot and using the lower range of DDBox sizes for a given subwoofer diameter. There is a slight sacrifice in maximum output but some very compact designs can be realized that sound amazing on source material once called music.