Proline X

Professional Series Ported Dual 15" Enclosure | Stereo Integrity SQL-15

Q: Do I need a subsonic filter?

Yes, at 21 Hz, 24 dB per octave. Below tuning a vented box stops loading the cone and excursion runs away toward DC. With the filter in place this cabinet puts the Stereo Integrity SQL-15 at 50 percent of its usable travel at 2400 W.

Q: Would a sealed box be better for me?

The two alignments converge at the bottom of the band on this driver rather than crossing cleanly, so there is no meaningful subsonic advantage either way. Above 25 Hz the vent is the louder of the two for the same power. The Performance Graphs tab plots this cabinet, 4.20 cubic feet vented at 27.0 Hz, against the 2.00 cu ft sealed wedge we build for this driver (PO 15-S W SQL15) per driver, 4.00 cu ft for the pair, so you can judge it yourself.

Q: How does the front port work?

It is a vertical slot beside the woofer, the full height of the cavity, 4.25 inches wide and 70.1 square inches. It runs 11.00 inches to the back wall and turns once along it for 27.96 inches; the fold costs about 1.5 Hz and the port is cut for it. The channel runs at 17.9 metres per second at 2400 W, 46 percent of its turbulence limit, and the mouth edges carry a 1/2 inch roundover so the air leaves the face at 13.7 metres per second against the 17 metres per second threshold where a slot starts to chuff.

Q: What does the price cover, and how does it ship?

94 lb packed, 46.00" W x 18.00" H x 19.00" D external. This cabinet is 9.10 cubic feet outside. Delivery to the 48 states is inside the price; it ships as a 94 lb parcel and checkout adds nothing. Do not add polyfill; it ships dry on purpose.

Q: Is the SQL-15 included?

No. This is an enclosure only, cut for the Stereo Integrity SQL-15 specifically: the 14.170 inch cutout, the 7.400 inch mounting depth allowance and the 4.20 cubic foot alignment all come from Stereo Integrity's published parameters. It fits both coil versions; the alignment published here is the Dual 2 Ohm. Bring your own driver.

SKU: Pro 15D-P SQL15

QUICK SPECS

Alignment: 4.20 cu ft net vented at 27.0 Hz. F3 33.7 Hz anechoic, 0.79 dB passband ripple
Driver: Stereo Integrity SQL-15 Dual 2 Ohm, 1000 W RMS, 26.0 mm Xmax, 33.00 Hz Fs
Build: Front-firing standard box, 2.25" three-layer baffle with the woofer flush-mounted in the outer layer, Stereo Integrity logo acrylic, dado joinery, 70.1 sq in front slot port beside the woofer with one bend along the back wall, port and excursion gated at 2400 W
Cabinet: 46.00" W x 18.00" H x 19.00" D, 85 lb, threaded inserts pressed into the baffle on the woofer's mounting hole locations

Shipping Included No freight charges at checkout on US orders. International orders are quoted live carrier rates at checkout.

Built in Tennessee CNC cut from 3/4" Langboard Elite MDF. V-groove and dado joinery.

Tools icon: hands-on mobile audio expertise since 1985

Advanced Terminal Cup Built in-house. ABS/Carbon Fiber. Stainless steel hardware. Copper ring terminals.

$ 899.99

In Stock and Ready to Ship

Financing available. Choose Shop Pay Installments at checkout.

Complete Your System

Wavtech Wavtech link1000.1mini 1000w monoblock amplifier $ 399.99

Professional Series Ported Dual 15" Enclosure | Stereo Integrity SQL-15

$ 899.99

More enclosures cut for Stereo Integrity subwoofers: Stereo Integrity Subwoofer Boxes

Enclosure Type Ported

External Dimensions 46.00" W x 18.00" H x 19.00" D

Gross Volume 6.65 cu ft

Net Volume 4.20 cu ft

Tuning Frequency 27.0 Hz

Port Area 70.1 Square Inches

Shipping Weight 94 lbs

INSTALLER'S TAKE

I built this one for a pair of SQL-15 in a single shared chamber, which is how a dual ported box should be built: one volume, one port, both drivers loading the same air.

It gets the full Professional treatment, a 2.25 inch three-layer baffle with both woofers flush mounted in the outer layer, and the port on the left of the face.

Wiring is where a dual bites you. These are two 2 ohm coils each, so you can land on 0.5 ohm with all four coils in parallel, 2 ohms as two series pairs in parallel, or 8 ohms with everything in series. Check what your amplifier is rated for before you wire it, not after.

It ships dry. Do not add polyfill to a ported box. Set your subsonic filter at 21 Hz.

Product Details

Proline X Professional 15" Ported

A ported fifteen inch box for a pair of SQL-15, one shared chamber vented at 27.0 Hz

4.20 cu ft net Tuned 27.0 Hz F3 33.7 Hz 2.25" three-layer baffle Cut for the SQL-15 Built in Tennessee

4.20cu ft net

27.0Hz tuning

33.7Hz F3 anechoic

70.1sq in port area

Why this driver is vented at 27.0 Hz

This cabinet holds two SQL-15 in 4.197 cubic feet net, vented at 27.0 Hz through a 70.1 square inch port. F3 lands at 33.7 Hz with 0.79 dB of passband ripple. It measures 46.00 inches wide, 18.00 tall and 19.00 deep.

Both drivers share one chamber and one port rather than sitting in separate boxes, so the pair works against the whole volume and the port is sized for the pair rather than doubled. The port carries 70.1 square inches of area at 27.0 Hz, and the design power for the velocity and excursion checks is 2400 W for the pair. Passband ripple holds at 0.79 dB across the tuning, with F3 at 33.7 Hz.

What makes it Professional

Three-layer baffle, flush mount

Three layers of 3/4 inch Langboard Elite make a 2.25 inch front. The outer layer is routed to the flange, so the woofer sits flush with the face; the two layers behind it carry the mounting hardware and the load.

Stereo Integrity logo acrylic

A glossy black acrylic insert with the Stereo Integrity mark sits in the outer layer beside the woofer. It is standard on every Professional cabinet.

Mounting

Threaded inserts pressed into the baffle on the woofer's mounting hole locations, stainless machine screws included.

Port gated at 2400 W

The 70.1 square inch slot beside the woofer is sized so the channel runs 17.9 metres per second and the mouth 13.7 metres per second at 1.2 times the driver's rating, under the 17 metres per second where a slot starts to chuff. The channel runs 11.00 inches along its wall and turns once along the back wall for another 27.96 inches, which is why a 27.0 Hz tuning fits a 19.00 inch deep box.

Why this is a Professional build

A single SQL-15 also builds in the Performance Optimized ported wedge, the smaller and cheaper single-driver box. A pair takes this Professional cabinet: one shared chamber on a 2.25 inch three-layer baffle with both woofers flush in the outer layer, and a slot port gated at 2400 W for the pair.

What the price covers

This cabinet is 9.10 cubic feet outside. Delivery to the 48 states is inside the price; it ships as a 94 lb parcel and checkout adds nothing.

What Stereo Integrity recommend

Stereo Integrity publish a vented box for the SQL-15 at 4.25 cubic feet on a basis they do not state, tuned to 22.0 Hz. This cabinet holds 4.20 cubic feet net and tunes to 27.0 Hz.

The cabinet

46.00" W x 18.00" H x 19.00" D external. A windowed brace runs front to back beside the woofer, clearing the cutout by two and a half inches. The box ships dry: polyfill detunes a ported alignment. This is our dual 15 inch Professional envelope, built around the SQL-15's own frame and mounting depth, with both woofers on one face and the port on the left. It ships as a parcel.

Port mouth velocity peaks at 13.7 m/s against the 17 m/s point where a slot begins to chuff, and 17.9 m/s in the channel, both measured at the pair's design power. Both drivers must be the same model and the same coil: mixing them puts unequal loads on one shared chamber, and neither driver sees the airspace it was picked for.

The numbers to respect

Set a 21 Hz subsonic filter, 24 dB per octave. Below tuning the vent stops loading the cone; with the filter in place the cone reaches 11.1 mm of its 22.1 mm at 2400 W.

Enclosure Specifications

Series	Proline X Professional
Driver-Specific Fitment	Stereo Integrity SQL-15 Dual 2 Ohm (Dual 2 Ohm)
Enclosure Type	Ported \| Front-Firing Standard Box
External Width	46.00 Inches
External Height	18.00 Inches
External Depth	19.00 Inches
Internal Volume (Gross)	6.65 Cubic Feet
Internal Volume (Net After Displacement)	4.20 Cubic Feet
Port Type	Vertical Slot Beside The Woofer \| Front Exit \| One 90 Degree Bend Along The Back Wall
Port Geometry	4.25 x 16.50 Inches, 70.1 Square Inches, 46.96 Inches Of Path
Port Area	70.1 Square Inches
Port Tuning (Fb)	27.0 Hz
Port Mouth	1/2 In Roundover On All Four Edges, 91.9 Square Inches At The Face
Port Air Velocity	17.9 m/s In The Channel, 13.7 m/s At The Mouth, At 2400 W (17.0 m/s Chuff Threshold)
Design Power Basis	2400 W RMS (1.2 x The Driver Rating) For Port Velocity And Excursion
Predicted F3	33.7 Hz (Anechoic)
Passband Ripple	0.79 dB (Anechoic)
Subsonic Filter	21 Hz High-Pass, 24 dB/Octave - REQUIRED On A Vented Enclosure
Driver Fs	33.00 Hz
Driver Qts	0.570
Driver Qes / Qms	0.610 / 7.600
Driver Vas	59.400 Liters / 2.098 Cubic Feet
Driver Sd	823.2 Square Centimeters
Driver Mms	374.90 g
Driver BL	20.30
Driver Re	3.2 Ohm
Driver Xmax	26mm (One-Way)
Driver Displacement	0.16 Cubic Feet (Published by Stereo Integrity)
Driver Sensitivity	87.0 dB
Driver Power Handling	1000 Watts RMS
Driver Overall Diameter	15.550 Inches (Stereo Integrity Spec)
Mounting Depth Required	7.400 Inches (Stereo Integrity Spec)
Cutout Diameter	14.170 Inches (Stereo Integrity Spec)
Flush Mount Recess	16.500 Inches In The Outer Layer
Material	Langboard Elite 3/4" MDF
Construction	ShopSabre CNC / Windowed Brace Front To Back Beside The Woofer
Joinery	Dado Joinery (CNC-Cut), Flat Panels
Front Baffle Construction	Three 3/4" MDF layers, 2.25" total \| Woofer Flush-Mounted In The Outer Layer
Baffle Layers	3
Acrylic	Glossy Black Stereo Integrity Logo Insert, Outer Layer, Standard
Mounting Hardware	Threaded Inserts Pre-Installed In The Baffle \| Stainless Machine Screws Included
Voice Coil Configuration	Dual 2 Ohm
Terminal Cup	Proline X ABS/Carbon Fiber Composite \| Back Panel, Terminal-Cup Side \| 12g OFC Pre-Wired
Damping	None - Ships Dry. Polyfill Detunes A Ported Enclosure
Recommended Power	700-1000 Watts RMS (Stereo Integrity Rated: 1000W RMS)
Carpet Finish	Plush Black
Shipping Weight	94 lb
Shipping	UPS Ground Parcel, Included In The 48 States
Bundle Options	Enclosure Only (Bring Your Own Stereo Integrity SQL-15)
Warranty	2-Year Limited (Enclosure)
Manufactured	Tullahoma, Tennessee, USA

Performance Graphs

Net airspace

4.20

cu ft

Tuning

27.0

Hz · Fb

Half power

33.7

Hz · F3, anechoic

Xmax at

13740

W RMS · 21 Hz subsonic

With NO filter

5546

W RMS · unfiltered

Port

13.7

m/s at the mouth · 2400 W

01Is this driver right for a ported box?

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

EBP = Fs ÷ Qes = 54.1

Stereo Integrity SQL-15 · EBP 54.1

Between 50 and 100 a driver takes either load, and the choice becomes one of priorities rather than of physics. The Stereo Integrity SQL-15 reads 54.1. Ported buys output and low-end reach around tuning; sealed buys a shallower rolloff below it. This cabinet takes the first trade.

02What the box does to it

4.20 cu ft net against a 118.8 L Vas, vented at 27.0 Hz.

Fb = 27.0 Hz · F3 = 33.7 Hz · passband ripple 0.79 dB

Stereo Integrity SQL-15 · Fb 27.0 Hz, F3 33.7 Hz

Anechoic, before any cabin gain, with the 21 Hz subsonic filter already applied. The vent takes over below 27 Hz and the cone stops doing the work there, which is what holds travel down at the bottom of the passband.

03Perceived Ported vs Sealed

This cabinet, 4.20 cu ft net vented at 27.0 Hz, against the 2.00 cu ft sealed wedge we build for this driver (PO 15-S W SQL15) per driver, 4.00 cu ft for the pair.

Ported Fb 27.0 Hz · the 4.00 cu ft sealed box runs Qtc 0.82, Fc 47 Hz

Ported · this cabinet, 4.20 cu ft, Fb 27.0 HzSealed wedge we build, 2.00 cu ft x2, 4.00 cu ft, Qtc 0.82

Shaded blue is where the ported alignment is louder for the same power, orange where the sealed one is. The sealed curve is the 2.00 cu ft sealed wedge we build for this driver (PO 15-S W SQL15) per driver, 4.00 cu ft for the pair, not this cabinet with the port blocked: two different boxes, because that is the choice a buyer actually has. Across 25 to 60 Hz the vent is worth 4.1 dB at its widest and 2.7 dB on average. This is the anechoic picture, which is not what you hear in a car.

04Real World Ported vs Sealed

The same two boxes with cabin gain applied, 45 Hz corner, 18 dB ceiling.

Flatness across 25–60 Hz: ported 3.4 dB spread, the 4.00 cu ft sealed box 1.8 dB

Ported, in-car · 3.4 dB spreadSealed wedge we build, 2.00 cu ft x2, 4.00 cu ft, in-car · 1.8 dB spread

Cabin gain lifts both boxes by the same amount, so the gap between them does not change: what changes is the shape each one ends up with. A car pressurises below roughly 45 Hz, which fills in the sealed box's shallower rolloff and over-drives it where the ported box is already flat. Across 25 to 60 Hz, the band kick and bass fundamentals occupy, this alignment holds 3.4 dB of spread against 1.8 dB for the 2.00 cu ft sealed wedge we build for this driver (PO 15-S W SQL15) per driver, 4.00 cu ft for the pair. The sealed curve is flatter on paper; the ported one trades that for output. The two alignments converge at the bottom of the band rather than crossing cleanly, so there is no meaningful subsonic advantage either way here. Cabin gain here is a house assumption, not a measurement of your vehicle.

05The watts that reach Xmax (in this enclosure)

Travel scales with the square root of power, so there is one wattage that puts both cones exactly on Stereo Integrity's published 26.0 mm. The two traces are the same cabinet with the subsonic filter switched on and switched off. Every power figure in this section is for the pair, split evenly.

P_Xmax = 13740 W with a 21 Hz subsonic · 5546 W with none → the filter is worth 2.5×

13740 W · subsonic at 21 Hz, 24 dB/oct5546 W · no subsonic filterXmax 26.0 mm one-way, published

Each trace touches the limit and no further, because each is drawn at the exact power that puts the cone on 26.0 mm. With a 21 Hz subsonic that takes 13740 W, reached first at 20 Hz. Take the filter away and the same cabinet reaches 26.0 mm on 5546 W — the filter is worth 2.5× the safe power. A vent unloads the cone below tuning, so there is nothing holding it once the box stops loading: on a sealed build a subsonic filter is an improvement, here it is required equipment. The unfiltered trace is still rising where this chart stops at 20 Hz, so treat 5546 W as a bound rather than a floor. Every wattage on this page is a MECHANICAL limit, not an electrical one. It is the power at which the cone runs out of linear travel in this cabinet, and nothing more. What the voice coil can dissipate as heat is a separate ceiling set by the driver, not by the box — Stereo Integrity rate this one at 2000 W RMS, and that is the number that binds first here: heat stops you before travel does, so treat 2000 W as the ceiling and the travel figures above as headroom. Final wired impedance, amplifier output and how long you hold the level are all electrical questions this graph does not answer. The dashed line at 22.1 mm is the figure the cabinet was actually designed against: Stereo Integrity publish this Xmax on a 70% BL basis, and we derate it before sizing the port so the alignment carries margin against an optimistic spec rather than sitting right on it.

Woofer Details

Stereo Integrity build the SQL line as a sound quality woofer that still takes real power. The SQL-15 is rated at 1000 watts RMS with 26 mm of one-way travel quoted at 70 percent BL, on a copper voice coil, with the dust cap offered in paper or carbon fiber. Stereo Integrity publish no cone, surround, magnet or coil diameter for this model, so those rows are absent rather than filled in from the SQL-12. They ask for 1.25 inches from the baffle face to the top of the surround. This cabinet takes two of them in one shared chamber, so both drivers see the same air and the same port. Each opening is cut for 7.40 in of mounting depth and a 14.17 in cutout, taken from Stereo Integrity's published figures rather than measured off a sample.

Driver	Stereo Integrity SQL-15
Coil Options	Dual 2 Ohm or Dual 4 Ohm
Coil Wire	Copper
Dust Cap	Paper or Carbon Fiber
Power, RMS	1000 W
Sensitivity	91 dB, SPL at 2.83 V as Stereo Integrity publish it, 87.0 dB at 1 W/1 m
Mounting Depth	7.40 in
Cutout Diameter	14.17 in
Frame Outside Diameter	15.55 in
Driver Displacement	0.16 cu ft
Driver Weight	28 lb
Driver Warranty	3 Year, Original Purchaser, Blown Voice Coils And Competition Use Excluded

Materials

Material

Built From a Spec Sheet, Not a Sales Sheet

Every Proline X Professional 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.

Specifications

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

Internal Bond

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.

Stiffness

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.

Screw Holding

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 Professional Series enclosure is not going anywhere.

Sourcing

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.