The box will lose a little upper frequency response while adding extending the low frequencies. If the system is primarily playing bass tracks and electronically massaged music, extend the port length in the 24-28 inch length. This is the most popular all purpose tuning. This generally tunes the box to the upper 30Hz area, with the vehicle transfer function extending the frequency another 10-12Hz or so. The port is tuned to the box volume, not the subs.
In order to keep a 3-1 ratio of cone area to port area, use the following formula:ġ6 square inches of port area per cubic foot of box volume, make the port 18-20 inches deep. The DDport was developed with the DDbox to increase the overall efficiency of the system and broaden the power response curve as discussed previously. We also found that inside the vehicle the combo of a compact box and low compliance subwoofer had an effective bass response down into the low 30s while still having great punch in the upper sub bass ranges, resulting in a sub system that could play all types of music very well. The vehicle itself offers additional loading to the system, and the transfer function will make the system play an octave lower than the tuning frequency. This design approach allowed the subwoofers to not have to completely rely on the box for their loading. It was determined that keeping the moving mass low, energy high and using a suspension with high restoring force to help control cone motion, was the recipe for success. Once we had the box worked out we set about designing the subwoofers to work in it. Through many hours in the woodshop and many scratch pads of calculations we finally determined the appropriate balance of port surface area to internal box volume that would work exceptionally well with high power, handling high excursion subwoofers.
We decided to base our box design efforts around the tuning range of 35Hz – 40Hz which allows the substage to be very effective in the frequency range that provides listeners with the most impact. Instead of engineering our subwoofers then designing boxes around them, we engineered a high efficiency type of ported box then designed our subwoofers to optimize the box energy. In order to get the most bass performance from the available space we needed to think outside of the normal box, so we took a different design approach than some other subwoofer manufacturers. We designed the DD Box to meet the needs of listeners desiring big bass that didn’t have the cargo room for a wall of subwoofers.The research that led to the development of the DD Box is at the core of our subwoofer design philosophy, and the outstanding performance of our subwoofers in a DD Box is what many people call “That DD sound”. The DD Box is more than just a style of box it’s a scalable system that every DD subwoofer is designed to work with.
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