Proline X
Performance Optimized Down Fire Wide Sealed Dual 12" Enclosure | PowerBass XL-1240T
SKU: PO 12D-S DFW XLT
- Alignment: 0.403 cu ft net per chamber, 0.806 cu ft total. Qtc 1.142, Fc 71.6 Hz, F3 53.5 Hz per driver
- Down Fire Wide: 41"W x 14"D x 6.125"H in down fire position, excludes standoffs, square corners
- Versus the standard 30 x 15: 7.28 in tall and 0.40 cu ft net per chamber there, 6.125 in tall and 0.403 cu ft net here
- Chambers: Two fully separate sealed chambers, 3/4" MDF full divider, one shared side-mounted terminal cup
- Drivers: Pair of PowerBass XL-1240T, 400 W RMS each, 7.5 mm Xmax, 3.8 in mounting depth, single 4 ohm, rear vented motor
- Standoffs: Included, 1.75 in, shipped uninstalled. Installed height 7.875 in
Financing available. Choose Shop Pay Installments at checkout.
Performance Optimized Down Fire Wide Sealed Dual 12" Enclosure | PowerBass XL-1240T
More enclosures cut for PowerBass subwoofers: PowerBass Subwoofer Boxes
Proline X Performance Optimized Down Fire Wide Dual 12" Sealed
41 by 14 inch footprint for spaces where height or depth is the limit. Cut for a pair of PowerBass XL-1240T subwoofers
The Down Fire Wide Format
Down Fire Wide takes the same pair of PowerBass XL-1240T our standard 30 by 15 inch Down Fire enclosure is built for and lays the cabinet out along a different axis. It is 1 inch shallower front to back, 14 inches instead of 15, and 11 inches longer, 41 instead of 30.
Fourteen inches is the practical minimum depth for a 12. The frame needs about 13 inches of baffle, and the cabinet walls need land around it, so the depth cannot come down further. The XL-1240T's 12.244 inch frame sits on the 14 inch deep baffle with about 0.88 inch of baffle fore and aft.
Spreading the airspace along 41 inches means the wide box stands lower. This cabinet is 41 inches wide by 14 inches deep by 6.125 inches tall, against 7.28 inches tall for the standard 30 by 15, both measured in the down fire position and excluding standoffs. With the 1.75 inch standoffs installed it stands 7.875 inches.
Which one to choose. The standard 30 by 15 is the pick when length is limited. This one is the pick when height or depth is the limit and you have 41 inches of run. Measure all three before ordering.
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 41 by 14 for spaces where height or depth is the limit. | 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-1240T's own published numbers. A Performance box fits your subwoofer. A Performance Optimized box was built for it.
Built Around the PowerBass XL-1240T
The baffle positions are bored direct fit to the XL-1240T's published cutout. This is a shallow mount driver: 3.8 inch mounting depth, 7.5 mm of one-way excursion on a 2 in voice coil, 400 watts RMS and 800 peak, rated 33 Hz to 450 Hz.
Published parameters are Fs 33 Hz, Qts 0.526 and Vas 42.37 litres, with 0.126 cubic feet of driver displacement. PowerBass names 0.40 as the optimum sealed volume, quoted as internal airspace that includes the driver's displacement, lists 0.30 to 0.85 as the acceptable range, and does not recommend a ported enclosure for this driver at all.
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: the motor sits inside the enclosure firing at the top panel, and a driver that needs its pole vent kept clear forces a taller box.
Net Volume, Not Gross
Each chamber holds 0.403 cubic feet net, 0.806 cubic feet net total from a 1.08 cubic foot gross cavity, after the divider, the brace work and each driver's 0.126 cubic feet of displacement are subtracted.
That produces Qtc 1.142 with Fc at 71.6 Hz and a predicted F3 of 53.5 Hz per driver. The figure is above the 0.707 maximally flat reference, so there is real lift near the corner rather than a textbook flat curve.
PowerBass quotes its 0.40 recommendation as gross airspace that includes the driver. Each chamber here is 0.403 net, so it sits slightly on the larger side of their optimum and well inside the range they list as acceptable. This is a deliberately small-box alignment with real lift at resonance: tight rather than deep.
True net, not marketing net. Internal volume is calculated from the machined cavity dimensions and the driver's published displacement, not estimated from external dimensions minus wall thickness. All figures are anechoic; firing down into the floor, the sealed rolloff meets rising cabin gain below 60 Hz, so in-car response extends below them.
Two Chambers, Not One
This enclosure follows the Proline X standing design rule for dual sealed builds: two fully separate chambers divided by a bonded full-height 3/4 inch MDF panel.
Two drivers sharing one sealed volume interact acoustically. Each driver's compression phase becomes the pressure environment the other is working against, which smears transient response and blurs the alignment each would have on its own. A full divider eliminates that. Each driver gets its own 0.403 cubic feet net and its own polyfill, and one shared side mounted terminal cup feeds both positions.
On a long cabinet the divider does structural work as well, tying the front and rear walls together at the centre of a 41 inch span.
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 both chambers airtight under sustained pressure cycling. Corners are square on Down Fire cabinets.
The cabinet measures 41 inches wide by 14 inches deep by 6.125 inches tall, measured in the down fire position and excluding standoffs. The 1.75 inch standoffs ship with the enclosure but are not installed, so plan the space around the installed height of 7.875 inches.
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. Mounting is threaded inserts with stainless machine screws.
Frame on a 14 Inch Baffle
The 12.244 inch frame sits on the 14 inch deep baffle with about 0.88 inch of material fore and aft.
Separate Chambers
A bonded full-height 3/4 inch divider gives each driver its own 0.403 cubic feet and its own polyfill, and ties the walls together mid span.
One Shared Terminal Cup
Proline X ABS and carbon fiber composite cup with stainless hardware and copper ring terminals, side mounted and pre-wired in 12 gauge OFC to both driver positions in parallel.
Standoffs and Polyfill
1.75 inch standoffs ship uninstalled, so you can place them to suit your floor or leave them off and run the cabinet front or up firing. Polyfill is installed as a light wall lining in each chamber and does not alter the acoustic volume.
Power and Wiring
Each XL-1240T is a single 4 ohm voice coil rated 400 watts RMS, 800 watts RMS combined across the pair. The shared cup feeds both positions in parallel, so the pair presents 2 ohms at the cup. Target 400 watts RMS per driver and set gains properly rather than to a number.
The enclosure carries a 1 year limited warranty. Bring your own pair of XL-1240T drivers; they are purchased separately. We do not stock PowerBass drivers.
Cut for the Driver, Not the Catalog
Down Fire Wide, 41 by 14, cut on our ShopSabre routers and built one at a time in Tullahoma, Tennessee. Questions on fitment or amplifier matching, call us at 931-563-5151.
| Specification | Value |
|---|---|
| Series | Proline X Performance Optimized Down Fire Wide |
| Compatible Driver | PowerBass XL-1240T, pair required. Direct fit |
| Enclosure Type | Sealed, dual driver, down fire, floor coupled |
| Intended Fitment | Spaces where height or depth is the limit and 41 in of run is available |
| Chamber Configuration | Two fully separate chambers, full divider, single shared side-mounted terminal cup |
| External Width | 41 in |
| External Depth | 14 in |
| External Height | 6.125 in in the down fire position, excludes standoffs |
| Installed Height | 7.875 in including the 1.75 in standoffs |
| Internal Volume, Gross | 1.08 cu ft total |
| Per-Chamber Net Volume | 0.403 cu ft after displacement |
| Total Net Volume | 0.806 cu ft |
| Height Set By | Airspace; 1.575 in clearance above the motor |
| Alignment per chamber | Qtc 1.142, Fc 71.6 Hz, F3 53.5 Hz anechoic |
| Comparison, Standard 30 x 15 | 7.28 in tall, 0.40 cu ft net per chamber. Wide format is 6.125 in tall with 0.403 cu ft net per chamber |
| Woofer Opening | Direct fit to the XL-1240T, two |
| Driver Mounting Depth | 3.8 in required, shallow mount |
| Driver Motor | Rear vented, pole vent may be fully obstructed |
| Driver Fs / Qts / Vas | 33 Hz / 0.526 / 42.37 L |
| Driver Displacement | 0.126 cu ft each |
| PowerBass Published Target | 0.40 optimum, 0.30 to 0.85 acceptable. Their figures are GROSS and include driver displacement |
| Driver Power Handling | 400 W RMS, 800 W peak each |
| Driver Voice Coil | Single 4 ohm, 2 in |
| Wiring | Pair presents 2 ohms at the cup, wired in parallel |
| Material | Langboard Elite 3/4 in MDF |
| Construction | ShopSabre CNC, V-groove and dado joinery |
| Panel Thickness | 0.75 in |
| Front Baffle | 1.5 in double baffle, outer layer machined as a flush recess |
| Internal Bracing | Full-height 3/4 in bonded divider |
| Corner Profile | Square, Down Fire series standard |
| Driver Mounting | Threaded inserts with stainless machine screws |
| Terminal Cup | One Proline X ABS and carbon fiber composite, side mounted, pre-wired 12 gauge OFC to both driver positions in parallel |
| Standoffs | Included, 1.75 in, shipped uninstalled |
| Damping | Light polyfill wall lining in both chambers, does not alter acoustic volume |
| Carpet | Plush Black |
| Bundle Options | Enclosure only, bring your own pair of PowerBass XL-1240T |
| 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
0.403 cu ft against a 42.4 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 in this alignment a subsonic filter barely moves it.
| Param | Value | Unit | Note |
|---|---|---|---|
| Fs | 33.00 | Hz | free-air resonance |
| Qts | 0.526 | XL-1240T | |
| Vas | 42.37 | L | equivalent compliance |
| Sd | 510.7 | cm² | effective piston area |
| Xmax | 7.5 | mm | one-way linear travel |
| Pe | 400 | W | continuous RMS |
| SPL | 85.9 | 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.
Shop By Series
