Subwoofer box for a Silverado or Sierra: crew cab, double cab and regular cab
In a Silverado or a Sierra there is no trunk: the box goes under the rear seat or behind the front seat, and the cab style decides how much room there is. The good news is that a pickup cab is small, and a small cab makes a small box sound big.
Where the sub goes, by cab
| Cab | Usual spot | Typical subs |
|---|---|---|
| Crew cab | Under the rear seat — the cushion flips up | Two 10″ or 12″ shallow or low-profile, sealed |
| Double cab / extended cab | Under the rear seat, or a thin box behind it | One or two shallow 10″ |
| Regular cab | Behind the seat, wedge box | One or two shallow 8″ or 10″ |
Under-seat boxes are long and low and often down-firing (the sub faces the floor) or face the rear wall. A down-firing sub needs clearance below the cone for its travel and for the air — at least an inch, more for long-throw subs.
Generations matter
The space under the rear seat and behind the seat changes from one generation to the next — 1999–2006, 2007–2013, 2014–2018 and 2019 on — and between cab styles. A box built for one usually does not fit another. The GMC Sierra shares the cab with the Silverado of the same generation, so a box made for one generally fits the other. Measure your own truck, and make a cardboard mock-up to check that the seat still latches.
Example: two 10″ under a crew-cab seat
Say the space under the rear seat is 50″ wide, 14″ deep and 9″ high. With ¾″ walls the inside is 48.5 × 12.5 × 7.5″ — about 2.6 ft³ gross. That is enough for two shallow 10″ subs sharing one sealed box, but the inside height of 7.5″ limits the mounting depth — check the spec sheet. Set the number of subs to 2 in the calculator and it sizes the box for both.
Cab gain: why small boxes work
A pickup cab is a small, closed space. Below roughly 60–70 Hz it acts like a pressure chamber and lifts the deep bass a lot — more than in a sedan. A compact sealed box that measures modestly outside can sound deep inside the truck, which is why most truck builds are sealed. A ported box in a crew cab is tuned a little higher than in a sedan.
In the calculator choose “Pickup, crew cab” or “Pickup, regular cab” as the vehicle to include this in the predicted response.
Build tips for trucks
- Shallow and low-profile subs are designed for small sealed boxes — use the manufacturer’s recommended volume as a starting point.
- Carpet the box to match the floor and keep the seat-belt buckles and the seat latches clear.
- Screw the box to the floor or to the seat brackets so it does not slide around under the seat.
Design it for your truck
Pick your cab type, enter the space under or behind the seat, choose your subs from the database, and the calculator shows the response in your cab, draws the box (a wedge too, if the space is angled) and gives you the cut list and DXF. See also under-seat and truck boxes.
Model it for your own subResponse in your car, cone excursion and port air speed — free, no signup.Open the calculator →FAQ
What sub box fits under the rear seat of a Silverado crew cab?
Usually a long, low box with two 10″ or two 12″ shallow or low-profile subs. The height under the seat is the limit, so check each sub’s mounting depth against the inside height of the box. The space differs between generations, so measure your truck.
Can I put a sub in a regular cab Silverado or Sierra?
Yes, behind the seat in a thin wedge box with one or two shallow 8″ or 10″ subs. The space is only a few inches deep, so slide the seat forward and measure at the top and at the floor.
Does a sub box for a Silverado fit a Sierra?
The Silverado and the Sierra of the same generation share the cab, so a box for one usually fits the other. Boxes are not interchangeable between generations or between cab styles.
Do I need a big box in a truck?
No. The small cab of a pickup strongly lifts the deep bass, so a compact sealed box sounds much deeper inside the truck than it measures outside. That is why most truck builds are sealed.