If you are looking for a 2015 gmc sierra subwoofer box, you've probably already realized that while the truck itself is a beast, the factory sound system is a bit of a letdown. Whether you have the Bose upgrade or the base system, the low-end frequency is usually pretty thin. It lacks that punchy, "feel it in your chest" bass that makes a long drive or a workday much more enjoyable.
The 2015 GMC Sierra is a fantastic platform for audio upgrades, but it does present some unique challenges. You aren't working with a trunk; you're working with a cab where every inch of floor space matters. Most guys want to keep their back seats functional, which means we're almost always looking at the space under the rear bench. Let's get into what you need to know to get the right box for your rig.
Understanding the Space Constraints
Before you go out and buy the biggest subs you can find, you have to look at your cab configuration. The 2015 gmc sierra subwoofer box requirements change depending on whether you have a Crew Cab or a Double Cab. The Crew Cab is much more forgiving. It has a flatter floor and more depth under the seat. The Double Cab, on the other hand, is a bit of a tight squeeze.
One thing you'll notice quickly is the floor hump. GMC didn't make the floor perfectly flat back there, so a generic, rectangular box you'd throw in an old SUV isn't going to sit right. You need a vehicle-specific enclosure that is molded or cut to contour around that floor shape. If the box doesn't fit snugly, it'll slide around, rattle against the seat brackets, and probably sound like garbage because it isn't decoupled from the floor properly.
Sealed vs. Ported Enclosures
This is the age-old debate in the truck world. When choosing your 2015 gmc sierra subwoofer box, you have to decide what kind of listener you are.
Sealed boxes are generally smaller. Since space is at a premium under the seat of a Sierra, a sealed setup is often the easiest way to go. They provide a very tight, accurate bass. If you listen to rock, metal, or country, you'll probably love a sealed box. It hits the notes precisely without much "reverb" or lingering boominess. Plus, you can usually fit two 10-inch or even two 12-inch subs in a sealed configuration without needing a seat lift kit.
Ported boxes are for the guys who want to be heard down the block. They are more efficient, meaning they can get louder with the same amount of power. However, ported boxes require more internal air volume. Getting a ported 2015 gmc sierra subwoofer box to fit under the seat without making the seat unusable is a trick. Usually, if you go ported, you might have to stick to a single 10-inch sub or look into a seat lift.
The Down-Firing Advantage
You'll notice that most high-quality boxes for this year of Sierra are "down-firing." This means the subwoofers actually face the floor rather than the bottom of the seat. There are a few reasons why this is the way to go.
First, it protects your gear. If you have people sitting in the back or if you throw tools and bags on the seat, you don't want the seat foam pushing down onto the subwoofer cone. A down-firing box uses the legs of the enclosure to create a gap between the sub and the floor, keeping the moving parts safe.
Second, down-firing can actually help with the "loading" of the sound. When the sound waves hit the floor and bounce back up, it can create a slightly deeper, richer tone in the cab. It also helps hide the equipment from prying eyes. When someone looks through your window, they just see a carpeted hump under the seat instead of expensive speakers.
Materials Matter: MDF vs. Fiberglass
Most of the prefab boxes you'll find online are made of MDF (Medium Density Fiberboard). It's the industry standard because it's dense, doesn't resonate much, and is relatively cheap. If you go this route, make sure the box is at least 5/8" thick, though 3/4" is better for larger subs.
If you're going for a high-end custom build, you might see some fiberglass work. Fiberglass is great because it can be molded exactly to the floor of your 2015 Sierra, maximizing every cubic inch of air space. The downside? It's much more expensive and labor-intensive. For 90% of truck owners, a well-built MDF box that is carpeted to match the interior is the sweet spot for value and performance.
Do You Need a Seat Lift?
This is a question that comes up a lot when people start looking for a 2015 gmc sierra subwoofer box. A seat lift kit is basically a set of spacers that raises the rear bench by one to two inches.
If you are trying to fit "full-size" subwoofers—meaning subs that aren't the "shallow mount" variety—you're probably going to need a lift. Full-size subs have much larger magnets and need more mounting depth. They also usually require more air space to move properly.
However, shallow-mount technology has come a long way. Companies like JL Audio, Alpine, and Kicker make shallow subs that sound incredible. If you don't want to mess with the geometry of your seats (which can sometimes make the sitting angle a bit awkward for tall passengers), a shallow-mount box is your best bet.
Choosing the Right Subwoofer Size
In a 2015 Sierra, you're usually choosing between 8s, 10s, or 12s.
- Dual 8-inch subs: Don't sleep on these. They are incredibly punchy and fit into very small boxes. If you like fast, tight bass, dual 8s can surprise you.
- Dual 10-inch subs: This is the "Goldilocks" setup for most Sierra owners. You get a good balance of deep lows and punchy mids, and they fit under the seat relatively easily.
- Single or Dual 12-inch subs: This is for the bass heads. If you want the truck to rattle, you want 12s. Just keep in mind that air space is your enemy here. A 12-inch sub in a box that is too small will actually sound worse than a 10-inch sub in a properly sized box.
Installation Tips
Once you get your 2015 gmc sierra subwoofer box, the installation is pretty straightforward, but there are a few things to keep in mind.
First, check your clearance. Even if the box fits, make sure the subwoofers have enough "excursion" space. If the rubber surround of the sub is hitting the floor every time the bass hits, it's going to wear out the speaker and sound like a clicking noise.
Second, think about your amp placement. A lot of guys try to cram the amp under the seat next to the box, but these trucks get dusty and the air circulation under the seat isn't great. If you can, mount the amp on the back wall of the cab behind the rear seat. It's out of the way, stays cooler, and makes for a much cleaner-looking install.
Lastly, don't forget the sound deadening. The 2015 Sierra is a quiet truck, but once you add a real subwoofer, you're going to find every loose clip and plastic panel in those doors. Putting a bit of deadening material on the floor under the box and behind the rear seats can make a massive difference in how clean the bass sounds inside the cab.
Final Thoughts
Upgrading to a dedicated 2015 gmc sierra subwoofer box is probably the best bang-for-your-buck upgrade you can do for your truck's interior. It changes the whole vibe of the drive. You don't have to go overboard and shake the mirrors off, but filling in that bottom end of the music makes everything from podcasts to heavy metal sound "complete."
Just remember to measure twice, consider your cab size, and decide if you're willing to sacrifice a little seat height for bigger bass. Whatever you choose, it's going to be a massive step up from that weak factory setup. Reach for a box that's built specifically for your year and model, and you'll save yourself a massive headache during the install.