Under-seat and truck subwoofer boxes
Updated October 13, 2026
In a regular-cab or crew-cab pickup, a Jeep or a car without a trunk, the box has to fit a space that was never meant for it. The design starts with the space, not the subwoofer.
1. Measure the space
- Measure width at the top and at the bottom, height, and depth at the floor and at the top — seat backs and rear walls are rarely vertical.
- Check what moves: seat rails, the seat's tilt or fold travel, seat-belt buckles, the jack, wiring.
- Make a cardboard template of the side profile and test it in the cab. It takes ten minutes and saves a sheet of MDF.
2. Shape the box to the space
Behind a truck seat the box is usually a wedge — deeper at the bottom than at the top. Under a rear seat it is long, wide and shallow. The calculator supports an angled (wedge) box: give it the limits and it fits the dimensions to the volume you need and accounts for the angled panel in the plans.
3. Choose the sub to suit
- Shallow-mount subs need half the mounting depth of a regular sub and are designed for small sealed boxes. Often the only option under a seat.
- Two smaller subs (two 8″ or two 10″) often fit a long, low space better than one 12″.
- Check the mounting depth in the manual against the inside depth of the box — at the shallow end if the box is a wedge.
4. Sealed or ported?
Under-seat and behind-the-seat boxes are usually sealed: there is rarely room for a ported box and its port, and the small cab of a truck lifts the deep bass a lot. A small cab acts like a pressure chamber below about 60–70 Hz, so a compact sealed box can sound much deeper inside than it measures outside. If there is room — under the rear seat of a large crew cab — a ported box tuned a little higher than in a sedan can work well.
5. Under the front seat
Compact powered subs and small sealed boxes under a front seat play mostly into the footwell; that position adds noticeably to the upper bass and less to the deep bass. The calculator has a placement setting for “under the front seat / in the footwell” that applies this to the predicted response.
Design it for your truck
Choose “Pickup, regular cab” or “Pickup, crew cab” as the vehicle and the placement in the cab, enter the space, and the calculator shows how the sub will sound in that cab and draws a box that fits.