Proline X PO 15D-S W SQL dual sealed wedge, front baffle with two 14.17 inch cutouts and pre-wired leads, 37.5 by 18 inches.
Proline X PO 15D-S W SQL dual sealed wedge, side profile with recessed terminal cup, 19.74 inch base, 13.20 inch top, 18 inches tall.

Performance Optimized · Datasheet

Performance Optimized Wedge Sealed Dual 15" Enclosure Stereo Integrity SQL-15 · Dual 15" Sealed enclosure

Net volume
4.00 cu ft total, 2.00 per driver
Max mounting depth
7.400 in required
Cutout
14.17 in
External dimensions
37.50 in W × 18 in at the seat face H × 19.74 in at the base D
Front baffle
1.5 in, double baffle
Buy at Audio IntensityFactory-direct, ships from Tullahoma
  • 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

Spec of record

Technical specifications

SpecificationValue
SeriesProline X Performance Optimized Wedge
Compatible DriverStereo Integrity SQL-15, quantity 2. Direct fit
ConfigurationDual 15 inch, dual chamber sealed wedge
Mounting PositionTrunk or cargo area, tall face against the rear seat back
Firing DirectionRearward into the trunk. Not a down fire design, no feet included
External Width37.50 in
External Height18 in at the seat face
External Depth19.74 in at the base, tapering to 13.20 in at the top
Internal Volume, Gross4.39 cu ft total, 2.195 per chamber
Internal Volume, Net Acoustic4.00 cu ft total, 2.00 per driver
AlignmentQtc 0.816, fc 47.2 Hz, F3 41.8 Hz anechoic
Driver Cutout14.17 in
Driver Mounting Depth7.400 in required
Power Handling2000 watts RMS total across the set
ImpedanceDual 2 ohm or dual 4 ohm
MaterialLangboard Elite MDF
ConstructionCNC cut, V-groove and dado joinery
Panel Thickness0.75 in
Front Baffle1.5 in, double baffle
Internal BracingFull chamber divider plus a dadoed cross brace behind each woofer
Driver MountingShips undrilled with a threaded insert kit. Inserts, machine screws, screw key and drill bit included
Terminal CupsTwo Proline X ABS and carbon fiber composite, side mounted, one per chamber, pre wired 12 gauge OFC
DampingLight polyfill wall lining, does not alter acoustic volume
CarpetPlush black
Weight76.4 lb
Warranty1 Year Limited
Built InTullahoma, Tennessee

Modelled response

Performance in this enclosure

Net airspace
2.00
cu ft per chamber
System Qtc
0.82
sealed
Half power
41.8
Hz · F3
Xmax at
2744
W RMS · no filter
With 25 Hz subsonic
3208
W RMS · +17%
Amplifier
1000
W RMS per driver
Each chamber of this enclosure holds 2.00 cu ft net. In it the Stereo Integrity SQL-15 runs a system Qtc of 0.82 with half power at 41.8 Hz, and the cone reaches its 26.0 mm travel limit at 2744 W, above the driver’s 1000 W thermal rating, so heat stops you before travel does. Run a subsonic filter at 25 Hz and that becomes 3208 W — +464 W, or 17 percent more power for the same 26.0 mm of travel.

01Is it a sealed driver?

Efficiency bandwidth product places the motor before anything else is decided.

EBP = Fs ÷ Qes = 54.1
SEALED 0–50 TRANSITION 50–100 PORTED 100–150 0 50 100 150 SQL-15 54.1
SQL-15 · EBP 54.1
At 54.1 the SQL-15 sits in the transition band, not the sealed band. That is not a mismatch: a transition motor works in either alignment, and sealed buys a smaller box and a gentler roll-off at the cost of some low-end output. Stage 02 shows what this airspace actually does with it.

02What the box does to it

2.00 cu ft against a 59.4 L Vas.

α = Vas ÷ Vb = 1.05  ·  Fc = Fs√(α+1) = 47 Hz  ·  Qtc = 0.82
20 30 50 70 100 150 200 +6 +0 -6 -12 -18 -24 FREQUENCY · Hz LEVEL · dB −3 dB
SQL-15 · Qtc 0.82, Fc 47 Hz, F3 41.8 Hz
The box lifts resonance from 33.0 Hz free-air to 47 Hz and half power lands at 41.8 Hz, anechoic, before any cabin gain.

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.

PXmax = 2744 W unfiltered  →  3208 W with a 25 Hz subsonic
20 30 50 70 100 150 200 0 8 16 24 32 FREQUENCY · Hz CONE TRAVEL · mm PAST LINEAR TRAVEL · Xmax 26.0 mm 2744 W reaches Xmax here
SQL-15 · 2744 W, no filterSQL-15 · 3208 W with subsonic at 25 Hz, 24 dB/octXmax 26.0 mm one-way
Every trace touches the limit and no further, because each is drawn at the exact power that puts that coil on 26.0 mm. Unfiltered that is 2744 W, reached first at 23 Hz. It sits above the 1000 W the driver can take thermally, so the voice coil gives up before the suspension does. The dashed traces are the same driver behind a subsonic filter at 25 Hz, 24 dB/oct: stopping the cone wasting travel below the passband lets it take 3208 W before hitting the same 26.0 mm. That is 17 percent more amplifier for the price of one filter setting.
ParamValueUnitNote
Fs33.00Hzfree-air resonance
Qts0.570SQL-15
Vas59.40Lequivalent compliance
Sd823.2cm²effective piston area
Xmax26mmone-way linear travel
Pe1000Wcontinuous RMS, per driver
SPL87.3dB1 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.

From the shop floor

Installer's take

Read the alignment first. 2.00 cubic feet net per chamber puts each SQL-15 at Qtc 0.816 with resonance at 47.2 Hz and half power at 41.8 Hz anechoic.

That is a properly damped sealed alignment and it needs no qualification. Going bigger buys almost nothing: 3.90 cu ft per chamber drops Qtc to 0.707 and moves F3 less than one hertz.

On impedance: The SQL-15 comes as a dual 2 ohm or a dual 4 ohm. Across a pair the sensible targets are 1 or 2 ohms on D2 coils and 2 or 4 ohms on D4. Confirm which coil version you have before you buy the amplifier.

Measure the base depth. This cabinet is 19.74 inches deep at the trunk floor, 13.20 at the top, and 37.50 wide. It is a cargo-area box, not a sedan trunk box.

Before you order

Questions

Will this enclosure fit the SQL-15 exactly?

Yes. Both baffle positions are CNC cut to 14.17 in for the SQL-15's cutout, on 17.875 in centers, and the cabinet clears its 7.400 in mounting depth. Stereo Integrity does not publish a bolt circle for the SQL-15, so the baffle ships undrilled with a threaded insert kit.

Why 2.00 cubic feet net per driver?

It puts the SQL-15 at Qtc 0.816 with fc 47.2 Hz and F3 41.8 Hz anechoic. That is a well damped sealed alignment, the target for this driver. A 3.90 cu ft chamber would reach Qtc 0.707 and move F3 less than one hertz, so the larger box buys nothing worth the cabinet.

What amplifier power should I run, and what impedance?

The SQL-15 is rated 1000 watts RMS each, so 2000 across the pair. The SQL-15 comes as a dual 2 ohm or a dual 4 ohm. Across a pair the sensible targets are 1 or 2 ohms on D2 coils and 2 or 4 ohms on D4. Confirm which coil version you have before you buy the amplifier. Aim for roughly 1400 to 2000 watts at the final wired impedance.

How does a wedge enclosure improve the sound in a trunk installation?

The angled seat-side face matches the roughly 20 degree lean of a factory rear seat, so the cabinet sits flat against it instead of leaving a wasted triangle. The vertical trunk-lid-side face carries both drivers, firing rearward into the trunk cavity.

Why is the front baffle double-layered?

The baffle is two bonded 3/4 inch sheets, 1.5 inches through. A subwoofer pushes as hard against its mounting surface as it does against the air, and a single 3/4 inch panel flexes under that load. With two 15s on one baffle that matters twice over.

What is the expected low-frequency extension?

Anechoic F3 is 41.8 Hz at Qtc 0.816. The rolloff is clean rather than peaked. These figures exclude cabin gain, which in most vehicles adds real output below 40 Hz.

Do I need to add polyfill or damping?

No. Polyfill is already installed as a light wall lining in both chambers and the quantity is chosen so it does not change the acoustic volume. Do not add more.

Are the drivers included?

No. This is an enclosure only. You receive the cabinet finished in plush black carpet, two side-mounted pre-wired terminal cups, one per chamber, the polyfill lining already installed, and the threaded insert kit with inserts, machine screws, screw key and drill bit.

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