Proline X
Performance Optimized Down Fire Wide Sealed 10" Enclosure | PowerBass XL-1040T
SKU: PO 10-S DFW XLT
- Alignment: 0.546 cu ft net. Qtc 0.748, Fc 53.8 Hz, F3 51.0 Hz
- Down Fire Wide: 41"W x 12"D x 4.9375"H, 3" shallower than the standard 21.05 x 15 cabinet, for under rear seats
- Driver: PowerBass XL-1040T, 350 W RMS, 7.5 mm Xmax, 3.4 in mounting depth, single 4 ohm
- Rear Venting: Vented rear motor, pole vent may be fully obstructed
- Standoffs: Included, 1.75 in, uninstalled. Installed height 6.6875 in
Financing available. Choose Shop Pay Installments at checkout.
Performance Optimized Down Fire Wide Sealed 10" Enclosure | PowerBass XL-1040T
More enclosures cut for PowerBass subwoofers: PowerBass Subwoofer Boxes
Proline X Performance Optimized Down Fire Wide 10" Sealed
Under rear seat fitment for trucks and SUVs. Cut for the PowerBass XL-1040T
The Down Fire Wide Format
Down Fire Wide is the Performance Optimized answer to a specific problem: the space under the rear seat of a truck or SUV, or a narrow cargo floor, is long and shallow, and a 21.05 by 15 inch Down Fire cabinet will not go in it.
So the cabinet is turned sideways. This one runs 41 inches wide by 12 inches deep by 4.9375 inches tall. It is the same XL-1040T, in a cabinet 3 inches shallower front to back than our standard 21.05 by 15 inch XL-1040T cabinet and about 20 inches longer. The airspace given up in depth is recovered along the length, so the driver still gets a properly sized chamber rather than a compromised one.
Which one to choose. If you have 15 inches of depth, the standard 21.05 by 15 inch cabinet is the pick: it is shorter end to end and stands 4.9 inches tall. If depth stops at 12 inches and you have 41 inches of run, this is the cabinet that fits. Measure the depth first. Under seat spaces vary widely between cab configurations, and depth is almost always the limiting dimension.
Performance, Performance Optimized, and Micro
Proline X builds three tiers of Down Fire enclosure. The difference is not finish or materials, it is whether the cabinet was designed for a category or for a driver, and how much of the fitting work is already done for you.
| Performance | Performance Optimized | Micro Series | |
|---|---|---|---|
| Fitment | Universal. Accepts any subwoofer that clears the published cutout and mounting depth. | Woofer specific. Cut for one named subwoofer, with cutout, mounting depth, magnet clearance and displacement drawn in CAD from that driver. | Woofer specific. Cut for one named subwoofer. |
| Footprint | Sized to the driver diameter. 24.5 by 13.5 inches on the 10 inch. | Shared 30 by 15 inch platform on most builds. Down Fire Wide variants like this one run long and shallow for under seat fitment. | Compact per driver footprint. 21.5 by 14.5 inches on the 10 inch. |
| Front baffle | Single, 3/4 inch. | Double layer, outer layer machined as a flush recess. 1.5 inch. | Double, 1.5 inch. |
| Driver mounting | Solid flange. You drill your own mounting holes. | 8/32 threaded inserts, stainless machine screws included. | 8/32 threaded inserts, stainless machine screws included. |
| Joinery | V-groove and dado, CNC cut. | V-groove and dado, CNC cut, perimeter cross brace. | Stack fab, dowel reinforced. |
| Published alignment | Modeled Qtc profiles across a range of drivers. No single response curve. | A real predicted Qtc and F3 for that exact driver, calculated from its own Thiele-Small parameters. | Target alignment described in the listing. |
| Carpet | Gray standard, black optional. | Plush black. | Plush black. |
| Warranty | 1 year limited. | 1 year limited. | 2 years. |
Feet ship with every tier, uninstalled on purpose. Mount them where your floor wants them for a down fire install, or leave them off and run the cabinet front firing or up firing. The orientation is yours to choose.
This page is a Performance Optimized enclosure. The cutout, the cabinet height and the airspace all come from the PowerBass XL-1040T's own published numbers. A Performance box fits your subwoofer. A Performance Optimized box was built for it.
Built Around the PowerBass XL-1040T
The baffle is bored to the XL-1040T's 237 mm cutout. This is a shallow mount driver: 3.4 inch mounting depth, 7.5 mm of one-way excursion on a 2 in voice coil, 350 watts RMS and 700 peak, rated 35 Hz to 500 Hz.
PowerBass names 0.30 cubic feet as the optimum sealed volume and lists a 0.25 to 0.75 cubic foot acceptable range. They do not recommend a ported enclosure for this driver at all.
Net Volume, Not Gross
We build this cabinet at 0.546 cubic feet net: true internal airspace after panel thickness, the brace and the driver's own 0.0771 cubic feet of displacement are accounted for. Gross is 0.629 cubic feet.
Worth knowing when you compare figures. PowerBass quotes its 0.30 cubic foot recommendation as internal airspace that includes the driver's displacement, so their number is gross where ours is net.
Height on this cabinet is set by the driver's mounting depth, not by a volume target. The 3.4 inch driver reaches 1.9 inches past the inner baffle into the cabinet, and we hold 0.75 inch of clearance above the motor. That fixes the cabinet at 4.9375 inches tall, and on a 41 by 12 footprint that height holds 0.546 cubic feet net, more than the 0.30 cubic feet the standard cabinet was built to. More air in a sealed box lowers Qtc, which is the safe direction: slightly more damping and a gentler approach to the rolloff.
That is still inside the 0.25 to 0.75 cubic foot range PowerBass lists as acceptable. Calculated from PowerBass's own published Thiele-Small parameters, Fs 35 Hz, Qts 0.487 and Vas 21.02 litres, the cabinet gives Qtc 0.748, Fc 53.8 Hz, F3 51.0 Hz anechoic, a looser and better damped alignment than the tight 0.30 box, with cabin gain adding real output below 50 Hz in a car.
Down Fire Wide Construction
Cut with V-groove and dado joinery on our ShopSabre routers from Langboard Elite 3/4 inch MDF, a dense 48.5 lb/ft³ board with a 200 psi internal bond and 410,000 psi MOE. Every panel joint is a machined interlocking groove that mechanically locks before adhesive is applied, which keeps the cabinet airtight under sustained pressure cycling. Corners are square on Down Fire cabinets.
The cabinet measures 41 inches wide by 12 inches deep by 4.9375 inches tall, measured in the down fire position and excluding standoffs. The 1.75 inch standoffs ship uninstalled so you can place them to suit your floor; installed, the finished stack is 6.6875 inches. Plan the space around that figure, not the cabinet height.
1.5 Inch Double Baffle
Two 3/4 inch layers laminated to 1.5 inches, with the outer layer machined as a flush recess so the driver bolts to the inner layer. The driver lands on 8/32 threaded inserts, with stainless machine screws included. The XL-1040T's 10.709 inch frame sits on the 12 inch deep baffle.
Windowed U-Brace
A windowed U-brace dadoed to the shell ties the front and rear walls together across the 41 inch span, and polyfill is installed as a light wall lining.
Side-Mounted Terminal Cup
Proline X ABS and carbon fiber composite cup with stainless hardware and copper ring terminals, pre-wired in 12 gauge OFC. Side mounted so it stays accessible with the baffle facing the floor.
Standoffs Included
1.75 inch standoffs ship with the enclosure, uninstalled. Mount them for a down fire install, or leave them off and run the cabinet front firing or up firing.
Rear Vented Motor, So the Floor Is Not a Problem
The XL-T uses a vented rear motor, so the pole vent can be obstructed without harming the driver. On a down fire cabinet that matters more than it sounds: the motor sits inside the enclosure firing at the top panel, and a driver that needs its pole vent kept clear forces either a taller box or a compromised one.
This cabinet clears 0.79 inches above the motor at 2.6875 inches of internal height, against our 0.75 inch minimum. The feet ship uninstalled, so front firing or up firing stays available to you at install time without changing anything about the enclosure.
Power and Wiring
The XL-1040T is a single 4 ohm voice coil, so it presents 4 ohms and there is no wiring decision to make. Target 350 watts RMS.
Bring your own XL-1040T; the driver is purchased separately. We do not stock PowerBass drivers. The enclosure carries a 1 year limited warranty.
Cut for the Driver, Not the Catalog
Down Fire Wide, built for the space under a rear bench, one at a time in Tullahoma, Tennessee. Questions on fitment or amplifier matching, call 931-563-5151.
| Specification | Value |
|---|---|
| Series | Proline X Performance Optimized Down Fire Wide |
| Compatible Driver | PowerBass XL-1040T, quantity 1. Direct fit |
| Configuration | Single 10 inch shallow mount, sealed down fire wide |
| Mounting Position | Under a rear seat or on a narrow cargo floor where depth is limited, baffle facing down on standoffs |
| Firing Direction | Downward. Feet ship uninstalled, so front or up firing is also possible |
| External Width | 41 in |
| External Depth | 12 in |
| External Height | 4.9375 in in the down fire position, excludes standoffs |
| Installed Height | 6.6875 in including the 1.75 in standoff |
| Internal Volume, Gross | 0.629 cu ft |
| Internal Volume, Net Acoustic | 0.546 cu ft after the brace and 0.0771 displacement |
| PowerBass Published Target | 0.30 cu ft optimum, 0.25 to 0.75 acceptable. Their figures are GROSS and include driver displacement |
| Height Set By | Driver clearance: 3.4 in mounting depth plus 0.75 in above the motor |
| Alignment | Qtc 0.748, Fc 53.8 Hz, F3 51.0 Hz anechoic |
| Comparison, Standard Down Fire | 21.05 x 15 x 4.90 in, 0.30 cu ft net. The wide cabinet holds more air at its clearance-set height |
| Woofer Opening | 9.3125 in (237 mm) direct fit |
| Driver Mounting Depth | 3.4 in required, shallow mount |
| Driver Motor | Rear vented, pole vent may be fully obstructed. 0.79 in clearance above the motor |
| Driver Power Handling | 350 W RMS, 700 W peak |
| Driver Voice Coil | Single 4 ohm, 2 in |
| Wiring | 4 ohms, no wiring choice |
| Material | Langboard Elite MDF |
| Construction | CNC cut, V-groove and dado joinery, square corners |
| Panel Thickness | 0.75 in |
| Front Baffle | 1.5 in double baffle, outer layer machined as a flush recess |
| Internal Bracing | Windowed U-brace, dadoed to the shell |
| Driver Mounting | Threaded inserts, stainless machine screws included |
| Terminal Cups | One Proline X ABS and carbon fiber composite, side mounted, pre wired 12 gauge OFC |
| Standoffs | Included, 1.75 in, shipped uninstalled |
| Damping | Light polyfill wall lining, does not alter acoustic volume |
| Carpet | Plush black |
| Warranty | 1 Year Limited |
| Built In | Tullahoma, Tennessee |
01Is it a sealed driver?
Efficiency bandwidth product places the motor before anything else is decided.
02What the box does to it
0.546 cu ft against a 21.0 L Vas.
03The watts that reach Xmax (in this enclosure)
Travel scales with the square root of power, so there is one wattage that puts the cone exactly on 7.5 mm — and a bigger one once a subsonic filter stops it wasting travel below the passband.
| Param | Value | Unit | Note |
|---|---|---|---|
| Fs | 35.00 | Hz | free-air resonance |
| Qts | 0.487 | XL-1040T | |
| Vas | 21.02 | L | equivalent compliance |
| Sd | 346.4 | cm² | effective piston area |
| Xmax | 7.5 | mm | one-way linear travel |
| Pe | 350 | W | continuous RMS |
| SPL | 83.8 | dB | 1 W / 1 m, derived from T/S |
Driver parameters as published by powerbassusa.com. Curves computed against this enclosure’s actual net airspace.
Built From a Spec Sheet, Not a Sales Sheet
Every Proline X Performance Series enclosure is CNC-cut from Langboard Elite MDF, 3/4" (18mm) panels produced to published mill specifications. Most enclosure manufacturers source generic MDF without published data. We can tell you the internal bond rating, the modulus of elasticity, the modulus of rupture, and the face and edge screw holding strength for every panel in this enclosure, because we chose the material based on those numbers, not on price or availability.
Langboard Elite is produced in the United States. The specifications below are pulled directly from Langboard's published mill data and are verifiable. This is the same panel stock used in our full Proline X lineup.
Langboard Elite MDF: Published Mill Data
| Property | Value | Why It Matters |
|---|---|---|
| Panel Stock | Langboard Elite MDF | Named, verifiable panel source, not generic "high-density MDF" |
| Thickness | 3/4" (18mm) | Industry standard for subwoofer enclosures; panels below this flex under pressure |
| Density | 48.5 lbs/ft³ | Higher density = less porosity, better screw retention, reduced resonance |
| Internal Bond | 200 psi | Measures resistance to delamination under sustained internal pressure. The most enclosure-relevant spec on this sheet |
| Modulus of Rupture (MOR) | 4,200 psi | Bending strength before the panel breaks, relevant for larger unsupported baffle spans |
| Modulus of Elasticity (MOE) | 410,000 psi | Stiffness under load; higher MOE means less panel flex under bass pressure, less resonance |
| Face Screw Holding | 325 lbs | How firmly the panel surface holds a screw; critical for baffle joint integrity over time |
| Edge Screw Holding | 250 lbs | Panel edge retention, relevant for every joint that isn't face-to-face |
200 psi: The Number That Actually Matters for Enclosures
The internal bond rating measures how well the MDF panel resists delamination under sustained pressure applied perpendicular to the face. In a subwoofer enclosure, every bass transient generates a pressure pulse that pushes outward on every panel simultaneously. A panel that begins to delaminate internally loses stiffness gradually. The symptoms are slow: a box that starts to sound softer, less defined, less punchy over months of use. 200 psi internal bond is the spec that determines how long this enclosure holds its acoustic integrity under daily use at real power levels.
410,000 psi MOE: Less Flex, Less Resonance
The modulus of elasticity measures panel stiffness, its resistance to bending under load. A stiffer panel flexes less under the pressure generated by a high-excursion driver at volume. Panel flex is a source of acoustic coloration: the panel itself begins to radiate sound at its own resonant frequency, adding distortion to the output. 410,000 psi stiffness combined with V-groove and dado joinery means the panels stay rigid and the bracing controls resonance at the structure level, not the panel level. The bass you hear comes from the driver, not the box.
325 lb Face / 250 lb Edge: Joints That Stay Locked
Screw holding strength determines how firmly the panel grips a fastener at the face and at the edge. This matters most at the baffle joint, where the front panel meets the side panels and where the driver is mounted. A panel with low screw holding strength allows fasteners to loosen over time under vibration, leading to air gaps at the joint and loss of acoustic seal. 325 lb face screw holding strength means the baffle hardware stays put. Combined with dado joinery and adhesive, the front panel on a Proline X Performance Series enclosure is not going anywhere.
Named Panel Stock: Not "Premium MDF"
The phrase "premium MDF" or "high-density MDF" appears on marketing copy for enclosures across every price point, from $40 to $400. It is not a specification. It is a description with no defined standard. Langboard Elite is a named, sourced, mill-documented product with published data. We name it in our copy because naming it holds us accountable to the spec. You can look up Langboard Elite independently, verify the numbers on this page, and confirm you are getting what we say you are getting. That is the point.
Why Proline X?
Most enclosures are built to a price point. Proline X is built to a spec. Every box starts with published-data MDF, gets CNC-cut to exact internal volume, and is assembled by hand in our Tennessee facility. The difference shows up in the measurements, and in how the box holds up two years into daily use.
CNC-Cut to Spec
Panels are machine-cut on ShopSabre CNC routers and joined with V-groove and dado joinery. Consistent geometry, no hand-cut variance, no gaps at the joints.
Handcrafted in USA
Hand-assembled at our facility in Tullahoma, TN. Every enclosure is inspected before it ships.
Tuned to the Build
Internal volume and port geometry are calculated to spec and CNC-cut to exact dimensions. The box performs the same way every time.
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