A wedge subwoofer box is bought on three numbers, and two of them are not the ones people measure. Because the cabinet is deep at the floor and shallow at the top, one depth figure tells you nothing. Measure the space at the floor, measure it again at the height the top of the box will sit, and take the width where the box will finally rest rather than where it goes in.
This guide walks through those measurements behind a truck seat, where wedges live most often, and finishes with how to work out a wedge cabinet's volume from its outside dimensions so you can check a listing before you order.
Key Takeaways
- Measure two depths: at the floor, and at the height of the top of the cabinet. On our wedges the difference between them is the height times the tangent of 20 degrees, about 4.7 inches on a 13 inch tall ten and 5.5 on a 15 inch tall twelve.
- Measure with the seat in the position it will live in. A reclining seat closes the gap you just measured, and a folding seat changes angle through its travel.
- Take the width where the cabinet sits, not at the door. Wheel wells, seat brackets and jack storage narrow a cab toward the back wall.
- Volume of a wedge is the trapezoid area of the side times the internal width. Worked example below lands within 0.01 cubic feet of a listing.
Why does a wedge need two depth measurements?
Because the back of the cabinet slopes. On a Proline X wedge the front baffle is vertical and the rear panel is raked at 20 degrees, so the box is deepest at the floor and shallowest at the top shelf. The Alpine S2-W10 sealed wedge, for example, is 11.10 inches deep at the base and 6.37 at the top, on a cabinet 13 inches tall.
A seat back slopes the same way, which is the whole idea, but not necessarily at the same angle or from the same starting point. So the question is not "how deep is the space behind my seat?" It is two questions: how much floor is there between the seat base and the back wall, and how much room is there at the height where the top of the box will sit?
If the floor depth is generous and the top depth is tight, the wedge fits where a square box would not. If both are tight, no shape saves you and the answer is a shallower cabinet, which we come to at the end.
Step one: measure the floor depth
Put the seat where it will live. On a crew cab bench that is usually fully upright; on a bucket seat it is wherever the driver actually sits, not all the way forward. Then measure along the floor from the back wall of the cab to the nearest part of the seat base or its bracket. That is your maximum depth at the base.
Check it at three points across the width, because cab floors are rarely flat and seat frames are rarely symmetrical. Use the smallest figure. If the seat folds forward for access, measure with it back in place, since that is where it spends its life.
Step two: measure the depth at the top of the box
Decide how tall the cabinet is. Our single-driver wedges run 11.75 inches tall for an eight, 13 for a ten, 15 for a twelve and 18 for a fifteen; duals are a little taller. At that height off the floor, measure horizontally from the back wall to the seat back. That is your maximum depth at the top.
Now recline the seat one notch and measure again. If the owner ever uses that notch, the smaller figure is the real one.
Step three: measure the width where the box will sit
Widths lie at the door. A truck cab is widest at the opening and narrows toward the back wall, where the wheel-well humps, the seat-belt anchors and any jack or tool storage intrude. Measure between the two nearest obstructions at the depth the cabinet will occupy, at floor level and again at the top of the box.
Our single-driver wedges are cut up to 29.5 inches wide and duals up to 32, so most full-size cabs take a single easily and a dual with care. A mid-size cab often does not, and that is a fact to know before you fall for a dual.
Step four: check the driver's depth, not just the box's
The shallow edge of a wedge is where the driver's magnet lives. On our builds the minimum top depth is solved from the magnet's clearance against the raked wall at the top of the cutout, which is why two wedges of the same nominal size can differ by an inch or more at the top. A shallow-mount driver gets a shallower cabinet; a big motor pushes the top depth out.
If you are bringing your own driver, the listing's stated depths already account for it. If you are comparing a universal box, take the driver's mounting depth, add the thickness of the baffle it will bolt through, and make sure that total clears the raked wall with room to spare at the top of the cutout. Our cabinets carry a double 1.5 inch baffle, so on a Performance Optimized wedge that allowance is built in.
How do you work out a wedge box's volume?
Treat the side of the cabinet as a trapezoid and multiply by the width. Internal volume in cubic inches is the internal width, times the internal height, times the average of the two internal depths. Divide by 1,728 for cubic feet, then subtract the driver's displacement for the net figure the alignment actually sees.
Here is the JL Audio 12W3v3 sealed wedge worked from its listed outside dimensions of 23.75 wide, 14.5 tall and 13.5 deep at the base tapering to 8.25 at the top. The sides drop into dados inset half an inch from each edge, so the internal width is 21.25. The top and floor take 1.5 inches, so the internal height is 13.0. The front is a four-layer stack with the double baffle, so 3.0 inches comes off each depth, leaving 10.5 and 5.25.
If you would rather not do it by hand, the wedge subwoofer box calculator takes the outside dimensions and both depths and does exactly this, and our subwoofer airspace calculator takes internal dimensions, and the sealed box calculator turns a driver's parameters into the volume it wants. For what to do with the answer, sealed versus ported with the data is the next read.
Proline X single-driver wedge heights and the taper each produces at a 20 degree rake.
| Driver size | Cabinet height | Taper, floor depth minus top depth |
|---|---|---|
| 8 inch | 11.75 in | about 4.3 in |
| 10 inch | 13 in | about 4.7 in |
| 12 inch | 15 in | about 5.5 in |
| 15 inch | 18 in | about 6.6 in |
What if the space is smaller than any wedge?
Then stop trying to make a wedge fit. A regular cab with the seat against the back wall has no depth to give at any height, and the answer there is a down-fire cabinet under the seat or a Micro Series shallow-mount build. Some trucks have a vehicle-specific enclosure cut to the cab already, which removes the measuring altogether.
Our behind-seat truck subwoofer guide covers the drivers that suit those shallow spaces, and what fits in your vehicle covers the cab configurations in more detail. If the numbers come back with room to spare, the wedge subwoofer boxes are cut to the driver you own, sealed and, for many twelves and tens, ported.
Measured and still not sure? Call 931-563-5151 and talk to an SQ-judge tech, or send us the space and the driver through the contact page and we will tell you whether anything in the line fits before you order.
Frequently asked questions
How deep is a wedge subwoofer box?
How do I measure behind a truck seat for a subwoofer box?
How do you calculate the volume of a wedge box?
Will a wedge box fit behind a crew cab seat?
Is a wedge or a down-fire box better behind a truck seat?
About the Author
Scott Welch is a Multi Time IASCA National and MECA World Sound Quality Champion, an active SQ judge since 2019, and the owner of Audio Intensity in Tullahoma, Tennessee. He cuts every Proline X enclosure on the shop's CNCs and tunes every customer system before it leaves. Audio Intensity is the original US importer for Goldhorn DSP and an authorized dealer for Prodigy, Crescendo, Image Dynamics, Wavtech, Tru Technology, and more.
