Subwoofer box for a Chevy Avalanche
The Avalanche is a Suburban-based crew cab with a short bed and a midgate that opens the cab into the bed. It is still a favorite for custom audio — and the midgate is what decides where the box can go.
Where the sub goes
- Under the rear seat. The usual spot: the cushion flips up and a long, low box sits on the floor, like in a Silverado crew cab. One or two shallow subs fit.
- Behind the rear seat. That is the midgate. A box there works only if you never open it.
- Bed storage bins. The lockable bins in the bed sides are tempting, but they are outside the cab, get wet and do not get the cab’s bass lift.
The H2 SUT has the same midgate idea — see the Hummer H2 guide.
Pick a sub for this spaceThe calculator opens with the vehicle and the space from this guide and lists the subs that fit there, each with its box. Then adjust the size to your own vehicle.
Example: under the rear seat
Ready-made boxes for the 2002–2013 Avalanche are about 45″ wide, 13¾″ front to back and 6″ high; one listing is 48 × 16¾ × 6″. Take 45 × 13½ × 6″. With ¾″ walls the inside is 43.5 × 12 × 4.5″ — about 1.4 ft³ gross: two shallow 10″ sealed at the small end of their range (0.5–0.9 ft³ each) or two 8″, firing up. With only 4.5″ inside, the sub’s mounting depth decides everything: the ready-made boxes take subs about 4½″ deep or less. Measure your truck — and measure again with the seat folded for the midgate.
Cab gain
With the midgate closed the Avalanche cab behaves like a crew cab: it lifts the deep bass, so a sealed box sounds deep. With the midgate and the rear window open, the cab joins the bed and most of that lift is gone.
Design it for your Avalanche
Enter the measured space, pick a shallow sub from the database and compare sealed and ported; the calculator checks that the sub and port fit, draws the box and gives you the cut list and DXF.
Model it for your own subResponse in your car, cone excursion and port air speed — free, no signup.Open the calculator →FAQ
Where does a subwoofer go in a Chevy Avalanche?
Most often under the rear seat: the cushion flips up and a long, low box fits on the floor, as in a Silverado crew cab. Behind the rear seat is the midgate, so a box there blocks it. Some owners use the lockable bins in the bed sides, but they are outside the cab and get wet.
Does the box get in the way of the midgate?
When you open the midgate, the rear seat folds forward. A box under the seat has to be low enough for the folded seat to clear it — measure with the seat folded before you build.
What size sub fits under an Avalanche rear seat?
Usually two shallow 10″ or one 12″ in a sealed box. The inside height under the seat is the limit, so check the sub’s mounting depth.