Proline X
Performance Optimized Wedge Wide Sealed Dual 15" Enclosure | Stereo Integrity SQL-15
SKU: PO 15DW-S W SQL BB
- Best For: Dual Stereo Integrity SQL-15 Wide Cargo-Floor Builds
- Net Volume: 2.00 cu ft per chamber (4.40 cu ft Gross Total)
- Driver Match: Pair of Stereo Integrity SQL-15 (dual 2 or dual 4 ohm), matched
- Construction: Dual Chamber | 44" Wide Wedge | V-Groove/Dado | Double 1.5" Baffle | 1 Shared Terminal Cup | Insert Kit
Financing available. Choose Shop Pay Installments at checkout.
Performance Optimized Wedge Wide Sealed Dual 15" Enclosure | Stereo Integrity SQL-15
More enclosures cut for Stereo Integrity subwoofers: Stereo Integrity Subwoofer Boxes
Performance Optimized Wedge Wide | Dual Stereo Integrity SQL-15
Dual 15" Sealed Wide Wedge Enclosure | 44" Wide, 18" Tall
A Pair of Stereo Integrity SQL-15 in a Wide Sealed Wedge
This is the wide version of PO 15D-S W SQL: a 44 inch by 18 inch face that spreads two SQL-15 across a cargo floor and keeps the cabinet shallow. The SQL-15 is Stereo Integrity's 15 inch, 1000 watts RMS, 26 mm of one-way excursion on 823 square centimeters of cone, and 7.4 inches of mounting depth. Every figure comes from the parameter table Stereo Integrity publishes for the SQL-15. One set covers both the dual 2 and dual 4 ohm versions, which share the frame, the 14.17 in cutout and the 7.4 in mounting depth.
2.00 cubic feet net per chamber is the same 2.00 cubic feet per chamber as the standard dual wedge, PO 15D-S W SQL, so the wide version sounds the same and only the cabinet shape changes. On Stereo Integrity's figures, Fs 33.0 Hz, Qts 0.57 and Vas 59.4 liters, that is Qtc 0.816 with half power at 41.8 Hz.
Two Fully Separate Chambers
A bonded full-height 3/4 inch MDF divider splits the cabinet into two sealed chambers of 2.00 cubic feet net each, so every driver sees exactly the airspace printed on this page. Two drivers sharing one volume load each other; the divider removes that, and each chamber carries its own polyfill.
The cabinet is 44 inches wide, 18 tall, 10.83 inches deep at the top and 17.38 at the base. One shared side-mounted terminal cup feeds both driver positions.
Wide Wedge Design Explained
The drivers mount on the vertical face and fire rearward; the back panel rakes 20 degrees to sit against the rear seat.
44 Inches Across
Wider than the standard dual, so the cabinet stays shallower and spreads the pair across the floor.
18 Inches Tall
One height for this wide dual, low enough to clear most cargo covers.
Raked Seat-Side Face
Matches the roughly 20 degree lean of a factory rear seat back.
Cargo Space Kept
17.38 inches at the base, so the floor in front stays usable.
Engineered for a Pair of Stereo Integrity SQL-15
Half power lands at 41.8 Hz anechoic, before any cabin gain. Above Qtc 0.707 the response carries a small lift near 47 Hz before the rolloff, and F3 sits below fc. The 0.16 cubic foot driver displacement is taken out of the net figure.
Alignment Numbers (Per Chamber)
| Driver (per chamber) | System Qtc | fc | F3 |
|---|---|---|---|
| SQL-15, dual 2 or dual 4 ohm | Qtc 0.816 | 47.2 Hz | 41.8 Hz |
Mounting Geometry
Both baffle openings are cut to 14.17 in under the 15.55 in frame. The rear panel rakes 20 degrees, so the cavity deepens from 10.83 in at the top to 17.38 in at the base, and the 7.4 in motor clears it with 3.32 in to spare. Stereo Integrity prints no bolt circle for the SQL-15, so the baffle ships 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.
What the Numbers Rest On
Langboard Elite MDF
Premium 3/4 in MDF throughout.
V-Groove and Dado Joinery
CNC cut V-grooves at every panel intersection, sides and divider seated in dados.
Double-Layer 1.5" Front Baffle
Two bonded 3/4 in MDF sheets at the driver face, the outer layer machined as a flush recess.
Published Parameters
Fs 33.0 Hz, Qts 0.57, Qes 0.61, Qms 7.60, Vas 59.4 L, Sd 823 cm2, 87.0 dB 1W/1m.
Wiring a Pair of Stereo Integrity SQL-15 to Your Amplifier
A pair lands on 0.5 ohm with all four coils in parallel, 2 ohms as series pairs in parallel, or 8 ohms all in series with dual 2 ohm drivers; 1, 4 or 16 ohms the same three ways with dual 4 ohm drivers. Anything under 1 ohm, and many amplifiers at 1 ohm, is outside what the amplifier is built for; series wiring is the safe default. Confirm the final load against your amplifier's minimum stable impedance before powering the system.
Power handling is 1000 watts RMS per driver, 2000 across the pair. Aim for roughly 700 to 1000 watts per driver at the impedance you wire.
Built in Tennessee, Backed by Audio Intensity
Cut and assembled in Tullahoma, Tennessee on our own CNC equipment. Finished in plush black carpet with the gloss black acrylic baffle insert, one shared pre-wired terminal cup, 12 gauge OFC to both driver positions. Polyfill wall lining installed in both chambers. Threaded insert kit and stainless machine screws in the box. 1 year limited warranty. Enclosure only, the drivers are purchased separately. Call or text 931-563-5151.
Dual Stereo Integrity SQL-15: 44 Inch Wide Sealed Wedge
2.00 cubic feet net per chamber at Qtc 0.816, F3 41.8 Hz, cut direct fit and built to order in Tennessee.
| Specification | Value |
|---|---|
| Series | Proline X Performance Optimized Wedge Wide |
| Compatible Driver | Stereo Integrity SQL-15, dual 2 or dual 4 ohm, quantity 2. Direct fit |
| Configuration | Dual 15 inch, two separate chambers, sealed wide wedge |
| Mounting Position | Cargo floor or trunk, raked face against the rear seat back |
| Firing Direction | Rearward. Not a down fire design, no feet included |
| External Width | 44 in |
| External Height | 18 in at the seat face |
| External Depth | 17.38 in at the base, tapering to 10.83 in at the top |
| Internal Volume, Gross | 4.40 cu ft total |
| Internal Volume, Net Acoustic | 2.00 cu ft per chamber after the divider and the 0.16 cu ft driver displacement |
| Driver Mounting Depth | 7.4 in required; 3.32 in clearance above the motor against the raked rear panel |
| Alignment Per Chamber | Qtc 0.816, fc 47.2 Hz, F3 41.8 Hz anechoic |
| Standard Dual Version | PO 15D-S W SQL, 2.00 cu ft per chamber |
| Woofer Opening | 14.17 in, two |
| Frame Outer Diameter | 15.55 in |
| Bolt Circle | Not printed by Stereo Integrity; threaded insert kit included |
| Driver Displacement | 0.16 cu ft |
| Fs / Qts / Qes / Qms / Vas | 33.0 Hz / 0.57 / 0.61 / 7.60 / 59.4 L |
| Driver Sd | 823 cm2 |
| Xmax | 26 mm one way |
| Driver Power Handling | 1000 W RMS per driver |
| Wiring Options | A pair lands on 0.5 ohm with all four coils in parallel, 2 ohms as series pairs in parallel, or 8 ohms all in series with dual 2 ohm drivers; 1, 4 or 16 ohms the same three ways with dual 4 ohm drivers. Anything under 1 ohm, and many amplifiers at 1 ohm, is outside what the amplifier is built for; series wiring is the safe default. |
| Parameter Source | stereointegrity.com SQL-15 specifications |
| Material | Langboard Elite MDF |
| Construction | CNC cut, 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 divider |
| Driver Mounting | Threaded insert kit included, NOT pre-installed: no published bolt circle |
| Terminal Cups | One Proline X ABS and carbon fiber composite, side mounted, pre wired 12 gauge OFC to both driver positions |
| Acrylic Insert | Gloss black acrylic baffle insert standard; None variant minus $20 |
| Damping | Light polyfill wall lining in both chambers, does not alter acoustic volume |
| Carpet | Plush black |
| Shipping Weight | 81 lb |
| 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
2.00 cu ft against a 59.4 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 26.0 mm — and a bigger one once a subsonic filter stops it wasting travel below the passband.
| Param | Value | Unit | Note |
|---|---|---|---|
| Fs | 33.00 | Hz | free-air resonance |
| Qts | 0.570 | dual 2 or dual 4 ohm | |
| Vas | 59.40 | L | equivalent compliance |
| Sd | 823.2 | cm² | effective piston area |
| Xmax | 26 | mm | one-way linear travel |
| Pe | 1000 | W | continuous RMS |
| SPL | 87.3 | dB | 1 W / 1 m, derived from T/S |
Driver parameters as published by Stereo Integrity SQL-15 specifications. 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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