Proline X
Performance Optimized Down Fire Wide Sealed Dual 12" Enclosure | Focal SUB 30 KXE
SKU: PO 12D-S DFW KXE
- Alignment: 0.858 cu ft net per chamber, 1.717 total. Qtc 0.804, Fc 50.7 Hz, F3 45.3 Hz
- Down Fire Wide: 41"W x 14"D x 9.5625"H in down fire position, lower than the standard 30 x 15 (11.73 in)
- Height Set By: the airspace, matched to the standard 30 x 15 box
- Drivers: Pair of Focal SUB 30 KXE, 800 W RMS each, 22.5 mm Xmax, 6.77 in mounting depth
- Chambers: Two fully separate sealed chambers, 3/4" MDF full divider, one shared side-mounted terminal cup
- Standoffs: Included, 1.75 in, shipped uninstalled. Installed height near 11.3125 in
Financing available. Choose Shop Pay Installments at checkout.
Performance Optimized Down Fire Wide Sealed Dual 12" Enclosure | Focal SUB 30 KXE
More enclosures cut for Focal subwoofers: Focal Subwoofer Boxes
Proline X Performance Optimized Down Fire Wide Dual 12" Sealed
Cut for a pair of Focal SUB 30 KXE
The Down Fire Wide Format
Down Fire Wide is the same driver in a different shape. The standard Performance Optimized Down Fire cabinet for the Focal SUB 30 KXE is 30 by 15 inches. This one runs 41 inches wide by 14 inches deep: 1 inch shallower front to back and 11 inches longer.
Fourteen inches is not arbitrary. A 12 inch frame needs about 13 inches of baffle to sit on, so 14 is the practical minimum depth for this driver size. The Focal SUB 30 KXE frame measures 12.52 inches across and sits on the 14 inch deep baffle with about 0.74 inches of baffle fore and aft. Both positions are laid out along the 41 inch length.
Spreading the airspace along 41 inches instead of 30 means the cabinet does not have to climb to find it. This box stands 9.5625 inches tall, against 11.73 for the standard 30 x 15 Focal SUB 30 KXE cabinet, both measured in the down fire position without feet. That is 2.1675 inches lower.
Which one to choose. The standard 30 x 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. Plan around the installed height: the 1.75 inch standoffs put the finished stack near 11.3125 inches.
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 airspace, the cutouts and the cabinet height all come from the driver's own numbers. A Performance box fits your subwoofer. A Performance Optimized box was built for it.
Built Around a Pair of Focal SUB 30 KXE
Nothing about this cabinet is generic. The baffles are cut to 11.23 in (285 mm). Loudspeaker Database lists a 284 mm cutout, but Focal's own drawing puts the basket at 284.2 mm just under the flange, which a 284 mm hole would not pass; the 285 mm cut clears it and the 318 mm frame still covers it with margin. The airspace lands on 0.858 cubic feet net per chamber, 1.717 cubic feet net across both.
The SUB 30 KXE is the 12 inch of Focal's K2 Power line: an aramid-fiber K2 sandwich cone on a butyl surround, a 65 mm dual 4 ohm voice coil, rated 800 watts RMS and 1600 watts maximum, with 22.5 mm of one-way excursion. It is 6.77 inches deep on a 12.52 inch frame, which matters on a down fire, where the motor rises into the cabinet. Every figure comes from Focal's own SUB 30 KXE technical sheet, including the published 4 liter displacement.
Net Volume and Alignment
Each chamber holds 0.858 cubic feet net, 1.717 cubic feet net across both, from 2.037 cubic feet gross after the divider, the bracing and each driver's 0.14 cubic feet of displacement.
Height is the free dimension. With the footprint fixed at 41 by 14, the cabinet height was solved to put each chamber on the same airspace as the standard 30 x 15 box, which holds 0.85 cubic feet net per chamber, and the motor clears the top panel with 2.043 inches to spare. Same air, same alignment, lower cabinet.
Computed from Focal's published Fs 29 Hz, Qts 0.46 and Vas 50 liters: Qtc 0.804, Fc 50.7 Hz, F3 45.3 Hz per chamber.
That is a firmer alignment than maximally flat, with a mild rise ahead of the rolloff. The Butterworth volume on Focal's figures is much larger per driver and would make a dual cabinet far taller; this one keeps the pair under 10 inches. Focal's own closed-box response chart is drawn at 25 and 35 liters; at about 24 liters per chamber this cabinet sits on the smaller of the two.
True net, not marketing net. Internal volume is calculated from the machined cavity dimensions and the driver's displacement, not estimated from external dimensions minus wall thickness.
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 removes that. Each Focal SUB 30 KXE gets its own 0.858 cubic feet net and its own polyfill.
On a 41 inch cabinet the divider does structural work as well, tying the front and rear walls together at the centre of the span. One shared side-mounted terminal cup feeds both driver positions.
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 14 inches deep by 9.5625 inches tall, measured in the down fire position. Plan the space around the installed height rather than the cabinet height: the standoffs hold 1.75 inches under the baffle, so the finished stack sits near 11.3125 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. Focal prints no bolt circle, so a threaded insert kit with stainless machine screws ships loose rather than pre-installed.
Separate Chambers
A bonded full-height 3/4 inch divider gives each driver its own 0.858 cubic feet net 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.
Polyfill Installed
Polyfill is installed as a light wall lining in both chambers to control internal reflections. It does not change the acoustic volume, so do not add more.
Motor Clearance and Orientation
The motors rise off the baffle into the cavity, so on a down fire cabinet the clearance that matters runs to the top panel. The 6.77 inch mounting depth leaves 2.043 inches above the motor in a 7.3125 inch internal height, against a 0.75 inch minimum. Height was set by the airspace, above the minimum the clearance alone would have required.
Focal does not publish a position on down firing this driver, and this cabinet makes no claim on their behalf. At the 1.75 inch standoff the floor slot is 0.79 times the cone area, under the 1.0 we aim for: the 12 inch cone is larger than the gap the feet leave under the baffle. Taller feet or a front-firing install both remove that, and the standoffs ship uninstalled so the choice is yours at install time.
Power, Mounting and Warranty
Focal rates the SUB 30 KXE at 800 watts RMS and 1600 watts maximum, 1600 watts RMS combined. Each SUB 30 KXE carries two 4 ohm voice coils (3.2 ohms DC each): series for 8 ohms, parallel for 2. Wire both drivers identically. Each driver in series with the pair in parallel gives 4 ohms, the safe load on any amplifier; each driver in parallel with the pair in series also gives 4; all four coils in parallel is 1 ohm and needs an amplifier rated for it; all in series is 16 ohms. Confirm the load against your amplifier's minimum stable impedance before powering the system.
Focal's drawing shows eight mounting holes but prints no bolt circle, so the baffles ship undrilled with a threaded insert kit and stainless machine screws: set each driver in its recess, mark its holes, drill, press the inserts and bolt it down. The enclosure carries a 1 year limited warranty. Bring your own pair of SUB 30 KXE; the drivers are purchased separately.
Cut for the Driver, Not the Catalog
Down Fire Wide, 41 inches long and 14 deep, cut for one driver model 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 | Focal SUB 30 KXE (K2 Power), quantity 2. Direct fit |
| Enclosure Type | Sealed, dual driver, down fire, floor coupled |
| Chamber Configuration | Two fully separate chambers, full divider, single shared side-mounted terminal cup |
| Intended Fitment | Where height or depth is the limit and 41 in of length is available |
| Firing Direction | Down firing. Feet ship uninstalled, so front or up firing is also possible |
| External Width | 41 in |
| External Depth | 14 in |
| External Height | 9.5625 in, measured in down fire position, excludes standoffs |
| Installed Height | 11.3125 in including the 1.75 in standoff |
| Standard 30 x 15 Equivalent | 30 in W x 15 in D x 11.73 in H, 0.85 cu ft net per chamber |
| Internal Height | 7.3125 in |
| Internal Volume, Gross | 2.037 cu ft total |
| Per-Chamber Net Volume | 0.858 cu ft after displacement |
| Total Net Volume | 1.717 cu ft |
| Height Set By | Airspace; the motor clears the top panel with 2.043 in |
| Alignment per chamber | Qtc 0.804, Fc 50.7 Hz, F3 45.3 Hz, anechoic |
| Focal Closed-Box Chart | Drawn at 25 L and 35 L, Focal technical sheet |
| Fs / Qts / Qes / Qms | 29 Hz / 0.46 / 0.49 / 6.1 |
| Vas / Mms / Cms / Bl | 50 L / 183 g / 0.15 mm/N / 21.3 N/A |
| Driver Sd | 502 cm2, published by Focal |
| Xmax | 22.5 mm one way, Focal spec |
| DC Resistance | 3.2 + 3.2 ohm (6.4 ohm in series) |
| Driver Sensitivity | 86.5 dB at 2.83 V / 1 m, Focal spec |
| Voice Coil | 65 mm dual 4 ohm, CCAW on a glass fiber former, 4 layers |
| Floor Slot | 0.79 times the cone area at the 1.75 in standoff |
| Parameter Source | Focal SUB 30 KXE technical sheet, v1 29/09/2023 |
| Driver Power Handling | 800 W RMS / 1600 W maximum per driver |
| Wiring Options | Dual 4 ohm coils: 2 ohm in parallel, 8 ohm in series; two drivers give 1, 4 or 16 ohm |
| Mounting Depth | 6.77 in |
| Woofer Opening | 11.23 in, both positions |
| Driver Frame Diameter | 12.52 in, sits on the 14 in baffle |
| Driver Displacement | 0.14 cu ft |
| Material | Langboard Elite 3/4 in MDF |
| Joinery | V-groove and dado, CNC cut on ShopSabre routers |
| 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 divider |
| Corner Profile | Square, Down Fire series standard |
| Driver Mounting | Threaded insert kit included, NOT pre-installed: Focal prints no bolt circle |
| Terminal Cup | One Proline X ABS and carbon fiber composite, side mounted, pre-wired 12 gauge OFC to both driver positions |
| Damping | Polyfill installed as a light wall lining in both chambers, does not alter acoustic volume |
| Standoffs | Included, 1.75 in, shipped uninstalled |
| Carpet | Plush black |
| Bundle Options | Enclosure only, bring your own pair of SUB 30 KXE |
| 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
0.858 cu ft against a 50.0 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 22.5 mm — and a bigger one once a subsonic filter stops it wasting travel below the passband.
| Param | Value | Unit | Note |
|---|---|---|---|
| Fs | 29.00 | Hz | free-air resonance |
| Qts | 0.460 | dual 4 ohm, coils in series | |
| Vas | 50.00 | L | equivalent compliance |
| Sd | 502.0 | cm² | effective piston area |
| Xmax | 22.5 | mm | one-way linear travel |
| Pe | 800 | W | continuous RMS |
| SPL | 85.8 | dB | 1 W / 1 m, derived from T/S |
Driver parameters as published by Focal SUB 30 KXE technical sheet. 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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