Proline X
Performance Optimized Wedge Sealed Dual 15" Enclosure | Stereo Integrity SQL-15
SKU: PO 15D-S W SQL B
- Best For: Dual Stereo Integrity SQL-15 Trunk-Fit Builds
- Net Volume: 2.00 cu ft per driver (2.195 cu ft Gross)
- Alignment: Qtc 0.816, fc 47.2 Hz, F3 41.8 Hz
- Driver Match: SQL-15
- Impedance: dual 2 ohm or dual 4 ohm
- Construction: Dual Chamber | Rear-Firing Wedge | V-Groove/Dado | Double 1.5" Baffle | Insert Kit
Financing available. Choose Shop Pay Installments at checkout.
Performance Optimized Wedge Sealed Dual 15" Enclosure | Stereo Integrity SQL-15
Performance Optimized Wedge | Stereo Integrity SQL-15 Dual
Dual 15" Sealed Wedge Enclosure | Rear-Firing Trunk-Load Design
A Pair of Stereo Integrity SQL-15s in a Sealed Wedge
Two 3 inch dual voice coil drivers on 20.3 T-m motors, 26 mm of one-way travel each and 1000 watts RMS apiece, on the largest cone Stereo Integrity puts in the SQL line.
Two isolated chambers at 2.00 cubic feet net each, 2.195 cu ft gross before the driver's 0.160 cu ft displacement. Neither woofer loads against the other.
Trunk-Load Wedge Design Explained
Both SQL-15s mount on the vertical trunk-lid-side face and fire rearward into the trunk cavity.
Seat-Side Face Matches Seat Lean
Angled face matches the roughly 20 degree factory seat lean.
Trunk-Lid-Side Face Fires the Woofers
Vertical baffle, both cones firing rearward into the trunk cavity.
Isolated Dual Chambers
A full 3/4 in center divider. Each driver sees its own sealed 2.00 cu ft.
Trunk Cavity Loading
The trunk acts as an acoustic extension for a smoother presentation.
Engineered for the Stereo Integrity SQL-15
At 2.00 cubic feet net per chamber each SQL-15 runs a system Qtc of 0.816 with resonance at 47.2 Hz. That is a well damped alignment. Half power lands at 41.8 Hz anechoic, before any cabin gain.
Going larger buys almost nothing here. A 3.90 cu ft chamber drops Qtc to 0.707 and moves F3 less than one hertz, so 2.00 is the design point rather than a compromise.
Alignment Numbers
Qtc 0.816 · fc 47.2 Hz · F3 41.8 Hz anechoic · computed from Qts 0.57, Vas 59.4 L, Fs 33.0 Hz
Mounting Geometry
Vertical baffle CNC cut to 14.17 in, two cutouts on 17.875 in centers. Driver mounting depth 7.400 in required. Stereo Integrity does not publish a bolt circle for the SQL-15, so this baffle ships undrilled with a threaded insert kit. The woofer locates its own pattern from the supplied screws, you drill those holes to 13/64 in and press the hurricane nuts in from the baffle backside. Inserts, screws, screw key and drill bit are all included.
External Dimensions
37.50 in wide · 18.00 in tall · 13.20 in deep at the top, 19.74 in at the floor
Performance Series Construction, Driver-Specific Tuning
Langboard Elite MDF
Premium 3/4 in MDF throughout.
V-Groove and Dado Joinery
CNC cut V-grooves at every panel intersection, sides seated in dados.
Double-Layer 1.5" Front Baffle
Two bonded 3/4 in MDF sheets at the driver face, with a dadoed cross brace behind each woofer.
Two Pre-Wired Terminal Cups
Proline X ABS and carbon fiber composite, side mounted, one per chamber, 12 gauge OFC pre-wired to each driver position.
Wiring a Pair of SQL-15s to Your Amplifier
The SQL-15 comes as a dual 2 ohm or a dual 4 ohm. A pair of D2 woofers with each driver in series and the two drivers in parallel lands at 2 ohms. A pair of D4 the same way lands at 4 ohms, or 1 ohm with all four coils in parallel.
Power handling is 1000 watts RMS per driver, 2000 watts for the pair. Aim for roughly 1400 to 2000 watts at the final wired impedance.
Built in Tennessee, Backed by Audio Intensity
Cut and assembled in Tullahoma, Tennessee on our own CNC equipment. Finished in plush black carpet. 1 year limited warranty. Enclosure only, the Stereo Integrity SQL-15 drivers are purchased separately. Call 931-563-5151.
Two Stereo Integrity SQL-15s in a Rear-Firing Wedge
2.00 cubic feet net per chamber at Qtc 0.82, F3 41.8 Hz, cut direct fit and built to order in Tennessee.
| Specification | Value |
|---|---|
| Series | Proline X Performance Optimized Wedge |
| Compatible Driver | Stereo Integrity SQL-15, quantity 2. Direct fit |
| Configuration | Dual 15 inch, dual chamber sealed wedge |
| Mounting Position | Trunk or cargo area, tall face against the rear seat back |
| Firing Direction | Rearward into the trunk. Not a down fire design, no feet included |
| External Width | 37.50 in |
| External Height | 18 in at the seat face |
| External Depth | 19.74 in at the base, tapering to 13.20 in at the top |
| Internal Volume, Gross | 4.39 cu ft total, 2.195 per chamber |
| Internal Volume, Net Acoustic | 4.00 cu ft total, 2.00 per driver |
| Alignment | Qtc 0.816, fc 47.2 Hz, F3 41.8 Hz anechoic |
| Driver Cutout | 14.17 in |
| Driver Mounting Depth | 7.400 in required |
| Power Handling | 2000 watts RMS total across the set |
| Impedance | Dual 2 ohm or dual 4 ohm |
| Material | Langboard Elite MDF |
| Construction | CNC cut, V-groove and dado joinery |
| Panel Thickness | 0.75 in |
| Front Baffle | 1.5 in, double baffle |
| Internal Bracing | Full chamber divider plus a dadoed cross brace behind each woofer |
| Driver Mounting | Ships undrilled with a threaded insert kit. Inserts, machine screws, screw key and drill bit included |
| Terminal Cups | Two Proline X ABS and carbon fiber composite, side mounted, one per chamber, pre wired 12 gauge OFC |
| Damping | Light polyfill wall lining, does not alter acoustic volume |
| Carpet | Plush black |
| Weight | 76.4 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 | SQL-15 | |
| 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, per driver |
| SPL | 87.3 | dB | 1 W / 1 m, derived from T/S |
Driver parameters as published by stereointegrity.com. Curves computed against this enclosure’s actual net airspace, 2.00 cu ft per chamber.
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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