Proline X
Performance Optimized Down Fire Wide Sealed 10" Shallow Sub Enclosure | JL Audio 10TW3
SKU: PO 10-S DFW TW3
- Alignment: 0.560 cu ft net, just above JL's 0.50 optimum. Qtc 0.930, Fc 48.4 Hz, F3 39.5 Hz
- Down Fire Wide: 41"W x 12"D x 4.75"H, 3" shallower than the standard 30 x 15 TW3 cabinet, for under rear seats. Installed height 6.5" on the 1.75" standoffs
- Driver: JL Audio 10TW3-D4 (DVC 4Ω), 400W RMS / 800W peak, 15.2mm Xmax, 3.25" mounting depth
- Fitment: 9.625" / 244mm cutout, 8/32 threaded inserts, driver mounts to the inner baffle layer
- Build: Proline X V-groove and dado joinery, double-layer 1.5" front baffle with flush outer recess, windowed U-brace, 12g OFC side-mounted terminal cup
Financing available. Choose Shop Pay Installments at checkout.
Performance Optimized Down Fire Wide Sealed 10" Shallow Sub Enclosure | JL Audio 10TW3
More enclosures cut for JL Audio subwoofers: JL Audio Subwoofer Boxes
Proline X Performance Optimized Down Fire Wide 10" Sealed
Under rear seat fitment for trucks and SUVs. Cut for the JL Audio 10TW3-D4
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 30 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 4.75 inches tall. It is the same 10TW3-D4, in a cabinet 3 inches shallower front to back than our standard 30 by 15 inch 10TW3-D4 cabinet and 11 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 30 by 15 inch cabinet is the pick: it is shorter end to end and stands 4.9375 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 JL Audio 10TW3-D4's own published numbers. A Performance box fits your subwoofer. A Performance Optimized box was built for it.
Built Around the 10TW3-D4
Nothing about this cabinet is generic. The baffle is bored to the 10TW3-D4's 9.625 inch cutout, 244mm to JL Audio's own spec, and the cabinet height is set by the driver's 3.25 inch mounting depth. The finished cabinet stands 4.75 inches tall on a 41 by 12 inch footprint, which puts it under rear seats where a 15 inch deep box will not go.
The 10TW3-D4 is a dual 4-ohm subwoofer rated 400 watts RMS and 800 watts peak, with 15.2mm of one-way linear excursion. Polymer and mica composite cone, synthetic rubber surround, cast alloy frame with tab-ear mounting, and a 2 inch aluminum voice coil. JL's patented Thin-Line architecture reworks the motor and suspension geometry so the cone can travel that far in a frame this short.
15.2mm of Xmax on a shallow 10 is a serious figure. Most drivers in this category run 8 to 13mm, and excursion is what produces output at low frequencies. Cone area alone does not do it.
Net Volume, Not Gross
We build this cabinet at 0.560 cubic feet net, just above JL Audio's published 0.50 sealed optimum and inside their 0.50 to 0.75 cubic foot range. Gross internal volume is 0.585 cubic feet; the brace and the driver's 0.019 cubic feet of displacement come out of that.
That volume produces Qtc 0.930, Fc 48.4 Hz, F3 39.5 Hz, computed from JL's published Thiele-Small parameters of Fs 32.3 Hz, Qts 0.620 and Vas 19.82 liters. Qtc 0.707 is the textbook maximally flat sealed alignment, and this enclosure sits above it: a modest rise ahead of the corner that reads as weight and punch, then a 12 dB per octave rolloff that integrates naturally with cabin gain. That is how JL voices the TW3 in its recommended volume, not a shortfall of the cabinet.
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.
Rotated driver layout. The 10TW3's frame carries flange tab ears across an 11.2 inch major axis. The cutout is laid out with the tab ears running along the 41 inch length, so the 10.5 inch minor axis crosses the 12 inch depth with 3/4 inch of baffle outside the flange fore and aft.
Height on this cabinet is set by the driver's mounting depth. The 3.25 inch driver reaches 1.75 inches past the inner baffle into the cabinet, and we hold 0.75 inch of clearance above the motor. That fixes the cabinet at 4.75 inches tall, which on a 41 by 12 footprint holds 0.560 cubic feet net, within a hundredth of the 0.551 cubic feet the standard cabinet holds.
Final impedance is set at the driver: 2 ohms with the two 4-ohm coils in parallel, 8 ohms in series.
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 4.75 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 6.5 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 TW3's 11.2 inch tab-ear 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.
Power and Wiring
JL Audio rates the 10TW3-D4 at 400 watts RMS and 800 watts peak, and recommends 200 to 400 watts of amplifier power. Aim for the top of that range rather than the bottom. Sensitivity is 82.10 dB at 1 watt and 1 meter, which is on the low side; that is the tradeoff for getting 15.2mm of excursion into a 3.25 inch frame.
One side-mounted terminal cup, pre-wired in 12 gauge OFC. Wire the two 4-ohm coils in parallel for 2 ohms or in series for 8 ohms, and confirm the load against your amplifier's minimum stable impedance before powering the system.
Bring your own JL Audio 10TW3-D4; the driver is purchased separately. 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.
| Series | Proline X Performance Optimized Down Fire Wide |
| Compatible Driver | JL Audio 10TW3-D4 (DVC 4Ω) |
| Enclosure Type | Sealed | Down Fire Geometry | Floor-Coupled |
| Intended Fitment | Under The Rear Seat Of Trucks And SUVs, Or Narrow Cargo Floors, Where Depth Is The Limiting Dimension |
| Firing Direction | Down Firing, Driver Fires Toward Floor |
| External Width | 41 Inches |
| External Depth | 12 Inches |
| External Height | 4.75 Inches |
| Dimension Reference | All External Dimensions Measured In Down Fire Position, Excluding Standoffs |
| Installed Height | 6.5 Inches With The 1.75 Inch Standoffs |
| Internal Volume (Gross) | 0.585 Cubic Feet |
| Internal Volume (Net) | 0.560 Cubic Feet, After 0.019 Cubic Feet Driver Displacement |
| JL Audio Sealed Range | 0.50 to 0.75 Cubic Feet (0.50 Optimum) |
| Target System Qtc | 0.930 (Computed from Published T/S) |
| Predicted Fc | 48.4 Hz |
| Predicted F3 | 39.5 Hz |
| Comparison, Standard 30x15 TW3 | 30 x 15 x 4.9375 Inches, 0.551 Cubic Feet Net. Same Airspace Within A Hundredth, Deeper Footprint |
| Driver Fs | 32.3 Hz |
| Driver Qts | 0.620 |
| Driver Qes / Qms | 0.656 / 11.35 |
| Driver Vas | 19.82 Liters / 0.700 Cubic Feet |
| Driver Re (Series) | 9.036 Ohm |
| Driver Sd | 365 cm² / 56.532 sq in |
| Driver Xmax (One-Way Linear) | 15.2mm / 0.60 in |
| Driver Sensitivity | 82.10 dB (1W/1m) |
| Driver Power Handling | 400 Watts RMS / 800 Watts Peak |
| Driver Frequency Response | 24 to 200 Hz |
| Driver Cone | Polymer/Mica Composite | Synthetic Rubber Surround |
| Driver Voice Coil | 2 in / 50.8mm | Aluminum |
| Driver Frame | Cast Alloy | Tab-Ear Mounting |
| Driver Technology | Patented Thin-Line Woofer Technology |
| Driver Overall Diameter | 11.2 Inches Major / 10.5 Inches Minor (JL Audio Spec) |
| Mounting Depth Required | 3.25 Inches / 82.6mm (JL Audio Spec) |
| Woofer Opening | 9.625 Inches / 244mm Cutout Diameter (JL Audio Spec) |
| Material | Langboard Elite 3/4" MDF |
| Construction | ShopSabre CNC / Windowed U-Brace |
| Joinery | V-Groove and Dado (CNC-Cut) |
| Front Baffle Construction | Double-Layer 1.5" MDF | Outer Layer Flush Recess, Driver Mounts To Inner Layer |
| Corner Profile | Square (Down Fire Series Standard) |
| Standoffs | 1.75 Inch, Included, Shipped Uninstalled |
| Voice Coil Configuration | Dual 4-Ohm | 2Ω Parallel or 8Ω Series At The Driver |
| Driver Mounting | 8/32 Threaded Inserts | Stainless Steel Machine Screws Included |
| Terminal Cup | Proline X ABS/Carbon Fiber Composite | Side Mounted | 12g OFC Pre-Wired |
| Damping | Polyfill Pre-Installed As A Light Wall Lining |
| Recommended Power | 200-400 Watts RMS (JL Audio Rated Range) |
| Carpet Finish | Plush Black |
| Bundle Options | Enclosure Only (Bring Your Own JL Audio 10TW3-D4) |
| Warranty | 1-Year Limited (Enclosure) |
| Built In | Tullahoma, Tennessee, USA |
01Is it a sealed driver?
Efficiency bandwidth product places the motor before anything else is decided.
02What the box does to it
0.560 cu ft against a 19.8 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 15.2 mm — and a bigger one once a subsonic filter stops it wasting travel below the passband.
| Param | Value | Unit | Note |
|---|---|---|---|
| Fs | 32.30 | Hz | free-air resonance |
| Qts | 0.620 | D4 | |
| Vas | 19.80 | L | equivalent compliance |
| Sd | 365.0 | cm² | effective piston area |
| Xmax | 15.2 | mm | one-way linear travel |
| Pe | 400 | W | continuous RMS |
| SPL | 81.9 | dB | 1 W / 1 m, derived from T/S |
Driver parameters as published by loudspeakerdatabase.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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