2004-2006 Scion xB 1st Gen (bB / NCP31) — subwoofer box fitment

What we researched for this specific generation: where an enclosure actually fits, what the factory speakers are, how the factory audio is wired, and which real builds and commercial products exist for it. Confidence badges say how well each figure is sourced — this is research, not manufacturer spec.

Body styles covered: 4-Door Hatchback

Where a box actually fits

These are researched envelopes, not a guarantee. Measure your own vehicle — the numbers here tell you what to expect, not what you have.

Trunk Likely

Locationrear hatch cargo area, behind the rear seat
Outer bounding box37"W x 15"H x 15"(top) to 21"(bottom) D — the depth is EXPLICITLY LABELLED by the source as top-versus-bottom, and note it is deeper at the BOTTOM (21") than the top (15")
Known obstructionsThe hatch tapers inward toward the top, which is why the top depth is six inches shorter than the floor depth. Design the box to 15" if it is a full-height build; a box that only occupies the lower portion can use the full 21". A spacesaver spare and a foam rear floor sit under the floor panels — the rear speakers are reached by removing both, so a floor-mounted box should account for still needing spare-tire access.
Usable volume estimate2.5 ft³

Starting points

Suggested configurations for this vehicle, not prescriptions. Run the numbers in the Box Builder before you buy anything.

Budget

Subwoofers1x10" or 1x12" sealed
Box typesealed
Locationrear hatch area

Enthusiast

Subwoofers2x10" sealed — the source names this exact configuration as fitting the published space
Box typesealed
Locationrear hatch area

Competition

Subwoofers1x12" or 1x15" ported using the full 21" floor depth, accepting that the box then blocks the rear speakers and the spare
Box typeported
Locationrear hatch area

Door speaker fitment

Sizes and depths below are what research turned up for this generation. Confirm against your own vehicle before cutting or ordering — trim levels vary.

Front doors Likely

Factory speaker size6-1/2", 4 OHM, Pioneer. Replace with 6-1/2" or 5-1/4" — the source notes the 5-1/4" aftermarket selection is considerably larger, so downsizing is the better-supported option here. A mounting bracket is required for EITHER size.
Known obstructionsDRILLING IS REQUIRED, and this is the one real obstacle on the car: the factory speakers are held by RIVETS that must be drilled out, and then new screw holes must be drilled for the replacement. Standard drilling cautions apply — check for wiring, window mechanism, and depth before going in. Tools: Phillips screwdriver, panel tool, drill and 1/8" bit.
Adapter bracket neededYes, for both 6-1/2" and 5-1/4" — a bracket is needed regardless of which size you pick, because the factory mounting is riveted rather than screwed.
TweeterDash, alongside the centre-mounted gauge cluster. The source calls these easy to get to and specifically recommends a front component set on this car because of it.

Rear doors Likely

Factory speaker sizeNone — the xB has no rear-door speakers. Its rear pair sits at the back of the cargo area (see other_speaker_locations), which is unusual for a 4-door and is called out by the source as a deliberate break with convention.
Known obstructionsn/a
Adapter bracket neededn/a

Factory audio integration

Factory amp / premium audioNo factory amplifier and no premium-audio tier. A 6-speaker Pioneer AM/FM/CD system was standard across the whole run, and the only real change came in 2006: a revised head-unit design, a new steering wheel with built-in audio controls, a remote AUX input, and iPod control/charging/song-display through the receiver. So the integration job is simple electrically — but read the impedance note below before buying speakers, because this car's factory impedances are unusual in all three locations.
Adding subs without a head-unit swapYes — no factory amp in the path, so a universal line-output converter at the front speaker wires is the standard route, and the hatch build never touches the dash.
Head unitNo replacement needed

Known integration products

Mounting locations

Trunk Likely

37"W x 15"H x 15"(top) to 21"(bottom) D. Crutchfield's own read on that space is that it holds a pair of 10" subs in a sealed enclosure — a genuinely useful anchor, since it converts the raw dimensions into a build most people can picture. The first-gen xB is a car-audio favourite precisely because a car this small has a cargo box this square.

Build it for this vehicle

Each link opens the tool with this vehicle already selected.

Before you cut anything

Measure your own vehicle. Trim levels, factory subwoofer options, and mid-generation changes all move these numbers, and a box cut to a researched figure that does not match your truck is wasted wood. Where a badge reads Unconfirmed, treat the value as a starting point for your own measurement, not as an answer.