Proline X

Proline X Performance Optimized Wedge Enclosure | Fits Kicker Solo X 18" Subwoofer

Q: Will my Kicker Solo X 18 fit this enclosure?

Yes. The baffle is CNC-cut to Kicker's published cutout spec for the Solo X L7X 18, and the cabinet clears the required 11-3/8 inch mounting depth with margin at every point of the stroke, including breathing room for the vented motor. Both the dual 1-ohm 49L7X181 and dual 2-ohm 49L7X182 fit identically.

Q: How deep does the Solo X 18 actually play in this box?

Deeper than any other box in this line. The system resonance sits at 39.1 Hz for the dual 1-ohm and 40.9 Hz for the dual 2-ohm, with anechoic F3s of 34.7 and 34.0 Hz, and that is before the vehicle helps. Cabin gain in a truck or SUV typically adds output at a rising rate below 60 Hz, which carries usable response well down into the 20s. Pipe-organ and sub-synth content that smaller sealed boxes only hint at is fully present here.

Q: Which coil version should I buy, dual 1-ohm or dual 2-ohm?

Choose by amplifier first. The dual 1-ohm lands at Qtc 0.81 and the dual 2-ohm at 0.90 in this airspace; the D1 is slightly better damped, the D2 slightly warmer, and both reach the same mid-30s F3. Those are shadings, not different characters. What matters more is that your amplifier makes its rated power at the load your wiring produces: dual 1-ohm wires to 0.5 or 2 ohms, dual 2-ohm to 1 or 4.

Q: How much power should I run to the Solo X 18 in this box?

The Solo X 18 handles up to 4000 watts RMS and this cabinet is built to let it use that: the sealed air spring loads the cone progressively through the stroke and the 1.5 inch double baffle takes the mechanical load without flexing. Anything from 2000 watts up wakes it fully. As always, clean power with gains set by scope or DMM beats raw wattage, and the sealed loading is forgiving of the occasional hard transient.

Q: Why is the Qtc higher on the 18 than on your other wedges?

Because the driver is enormous. Qtc is set by the ratio of a driver's Vas to the box volume, and the Solo X 18's Vas is around 126 liters; reaching 0.707 would take a cabinet far too large to stand behind any seat. At 4.01 net cubic feet, already the biggest wedge we build, the alignment lands at 0.81 to 0.90 depending on coils. That range trades a little critical damping for weight and impact, and because Fc sits down near 40 Hz, the mild rise reads as low-end authority rather than midbass boom.

Q: Will this wedge actually fit behind a truck seat?

Only in the biggest cabs, and you should measure before ordering. You need 27 inches of width, 21.25 inches of height, and 22 inches of depth at the floor, tapering to 14.25 at the top. Height is the gatekeeper; most standard and extended cabs will not clear 21.25 inches behind the seat. Full-size crew cabs with the seat bottom flipped, SUV cargo areas, and rear-wall van installs are this box's natural habitat.

Q: Is the subwoofer included with this enclosure?

No, this listing is the enclosure only. It is built specifically for the Kicker Solo X L7X 18 in either coil configuration, and you install your own driver using the pressed 8/32 threaded inserts and included stainless mounting hardware. If you want help pairing a Solo X 18 or an amplifier capable of feeding it, call or text us at 931-563-5151.

SKU: PO 18-S W Solo X

QUICK SPECS

Alignment: 4.01 cu ft net, the biggest sealed wedge we build. Dual 1-ohm 49L7X181 runs Qtc 0.81, Fc 39.1 Hz, F3 34.7 Hz; dual 2-ohm 49L7X182 runs Qtc 0.90, Fc 40.9 Hz, F3 34.0 Hz. Deepest sealed tune in the Solo X line
Geometry: 20° front-firing wedge, vertical rear panel. 27 in W x 21.25 in H x 14.25 in top / 22 in bottom depth
Driver: Kicker Solo X L7X 18 (either coil version). Baffle CNC-cut to Kicker's published cutout spec, 11-3/8 in mounting depth cleared with margin
Wiring: One side-mounted terminal cup, 12 gauge OFC pre-wired. Handles up to 4000 watts RMS; set final impedance at the driver's coils
Cabinet: 3/4 in Langboard Elite MDF, 1.5 in double-layer baffle plus trim, dado-locked brace behind the woofer, plush black carpet with black acrylic insert

Shipping Included No freight charges at checkout. What you see is what you pay.

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

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

$ 649.99

In Stock and Ready to Ship

Financing available. Choose Shop Pay Installments at checkout.

Proline X Performance Optimized Wedge Enclosure | Fits Kicker Solo X 18" Subwoofer

$ 649.99

Enclosure Type Sealed

External Dimensions 27" W x 21.25" H x 14.25" top / 22" bottom D (20° wedge)

Net Volume 4.01cu ft

Tuning Frequency N/A (Sealed)

Cutout Diameter Direct Fit

Front Panel Thickness 1.5"

Max Mounting Depth Direct Fit

INSTALLER'S TAKE

This is the deep-end of the line, in every sense. Four cubic feet net puts the Solo X 18's system resonance down at 39-41 Hz with an anechoic F3 in the mid 30s, before the cab helps. No other box in our sealed wedge family reaches close to that. Add typical truck cabin gain and you have genuine single-digit-teens extension with a cone the size of a manhole cover doing it without strain.

The Qtc runs 0.81 on the dual 1-ohm and 0.90 on the dual 2-ohm, higher than our smaller wedges, and that is physics rather than choice: an 18 with 126 liters of Vas would need a refrigerator to hit 0.707. What the slightly higher Q costs in critical damping it pays back in warmth and impact, and the mild rise near resonance sits low enough that it reads as weight, not boom.

Feed it seriously. The 18 will take up to 4000 watts, and in sealed air the cone stays loaded across the whole stroke, so big clean power translates directly into effortless output. Pick coils for your amplifier as always: dual 1-ohm for 0.5 or 2 ohm finals, dual 2-ohm for 1 or 4.

Respect the tape measure. 27 wide, 21.25 tall, 22 deep at the floor. This is a full-size crew cab or SUV cargo proposition, and the 21.25 inch height is the number that disqualifies most standard cabs. If it fits your space, nothing else we build in a sealed box sounds this big.

Product Details

Performance Optimized Wedge | Kicker Solo X 18

18" Sealed Wedge Enclosure | Behind-Seat Wedge Design for the Kicker Solo X L7X 18

4.30 ft³ Gross4.01 ft³ NetDeepest Fc in the Line27" × 21.25" × 14.25/22"V-Groove / DadoBuilt in Tennessee

The Kicker Solo X 18 in a Purpose-Built Sealed Wedge

The Solo X L7X 18 is the flagship of Kicker's square-sub program: the largest cone, the heaviest motor, and power handling in excess of anything else wearing the L7 badge. Very few production sealed boxes exist for it at all, let alone one solved from the factory Thiele/Small parameters. This wedge runs the deepest profile in our PO line specifically to give the 18 real airspace.

4.30 cu ft gross internal volume produces 4.01 cu ft net after driver displacement. That lands the dual 1-ohm Solo X 18 at a punchy Qtc of 0.81 with a system resonance of 39 Hz and an F3 of 34.7 Hz, the deepest reach in the entire PO Wedge line, with the dual 2-ohm at 0.90 in the same cabinet.

Behind-Seat Wedge Design Explained

This is a front-firing wedge built for behind-seat and rear-wall installs. The rear panel is vertical and sits flat against the cab wall; the woofer mounts on the baffle, raked back 20 degrees to follow the seat lean.

Vertical Rear Panel

Sits flush against the cab back wall or trunk bulkhead, so the full footprint of the box goes to airspace instead of wasted gaps.

20° Raked Baffle

Matches the lean of most factory seat backs and fires the Solo X forward into the cabin instead of into the seat.

Dado-Locked Internal Brace

A 3/4" brace directly behind the woofer halves the largest panel span. Its depth matches the baffle stack, so driver clearance is engineered in, not left to luck.

Carpet-Wrap Ledge

A recessed perimeter ledge terminates the carpet cleanly at the baffle edge for a finished, factory look.

Engineered for the Kicker Solo X 18

Built to 4.01 cubic feet net. The dual 1-ohm 49L7X181 runs a Qtc of 0.81: the impact-forward zone where sealed 18s live at their best, with punch you feel in your chest and a system resonance of just 39 Hz. The dual 2-ohm 49L7X182 runs 0.90 in the same box, trading a touch more mid-bass slam for it. Both variants dig below 35 Hz at the half-power point before cabin gain even enters the math; in a truck cab this alignment plays genuinely full-range subterranean.

Alignment Numbers

Dual 1-Ohm: Qtc 0.81 · Fc 39 Hz · F3 34.7 Hz — Dual 2-Ohm: Qtc 0.90 · Fc 41 Hz · F3 34.0 Hz

Mounting Geometry

The baffle opening is CNC-cut to Kicker's published cutout spec for the Solo X 18. Mounting depth required is 11-3/8", cleared with margin at every point of the stroke, including breathing room for the vented motor. 8/32 threaded inserts pressed into the baffle backside.

Sealed Alignment Response

Predicted anechoic response of the Solo X 18 in this enclosure's 4.01 cu ft net airspace, computed from Kicker factory T/S parameters. This enclosure ships without a driver, so both coil variants are plotted; they do not load the same box identically.

The dashed line marks the half-power point. Roll-off below F3 is the gentle 12 dB/octave slope characteristic of sealed alignments, which cabin gain in a real vehicle substantially fills in. Run the numbers yourself with our sealed box calculator.

Performance Series Construction, Driver-Specific Tuning

Langboard Elite MDF

Premium 3/4" MDF panels milled to documented spec.

V-Groove and Dado Joinery

CNC-cut V-grooves at every panel intersection. Dado joints lock the raked baffle, vertical rear panel, and internal brace into the side walls.

Double-Layer 1.5" Front Baffle

Two bonded 3/4" MDF sheets plus a trim layer at the driver mounting face. A Solo X 18 at full tilt is the hardest mechanical load in car audio; this baffle does not flex.

Pre-Wired Terminal Cup

Proline X ABS/carbon-fiber composite terminal cup, side-mounted, with 12 gauge OFC pre-wired.

Finish and Trim

Plush Black Carpet

Every enclosure ships wrapped in plush black automotive carpet, the standard finish for the PO Wedge line.

Black Acrylic Insert

The signature Proline X acrylic insert comes in black.

Box-Only

This listing is box-only. Bring your own Solo X 18.

Wiring the Kicker Solo X 18 to Your Amplifier

The Solo X 18 is rated to handle up to 4000 watts RMS. In this sealed alignment, clean power at the woofer's wired impedance anywhere up to that ceiling makes a headroom-rich system; the sealed loading keeps cone travel controlled through the passband even at full output.

Built in Tennessee, Backed by Audio Intensity

Manufactured in Tullahoma, Tennessee on our ShopSabre CNC equipment. 1-year limited warranty. Call or text 931-563-5151.

Kicker Solo X 18: The Deepest Wedge We Build

4.01 cubic feet net, solved from factory T/S for a punchy 0.81 alignment with an F3 under 35 Hz. Flagship cone area, flagship reach, in a wedge built for the back wall.

Specifications

Series	Proline X Performance Optimized Wedge
Compatible Driver	Kicker Solo X L7X 18 (49L7X181 Dual 1-Ohm / 49L7X182 Dual 2-Ohm)
Enclosure Type	Sealed \| Single Driver \| Front-Firing Wedge
Wedge Angle	20 Degrees, Vertical Rear Panel
External Width	27 Inches
External Height	21.25 Inches
External Depth (Top)	14.25 Inches
External Depth (Bottom)	22 Inches
Internal Gross Volume	4.30 Cubic Feet
Net Volume (After Driver Displacement)	4.01 Cubic Feet
System Qtc (Dual 1-Ohm)	0.81 (Computed from Kicker Factory T/S)
System Qtc (Dual 2-Ohm)	0.90 (Computed from Kicker Factory T/S)
Predicted Fc	39.1 Hz (D1) / 40.9 Hz (D2)
Predicted F3 (Anechoic)	34.7 Hz (D1) / 34.0 Hz (D2)
Driver Fs (D1 / D2)	26.9 Hz / 28.9 Hz (Kicker Factory)
Driver Qts (D1 / D2)	0.5575 / 0.6345 (Kicker Factory)
Driver Vas (D1 / D2)	125.93 L / 113.95 L (Kicker Factory)
Woofer Cutout	CNC-Cut To Kicker Published Spec
Mounting Depth Required	11-3/8 Inches, Cleared With Margin
Power Handling	Up To 4000 Watts RMS
Material	Langboard Elite 3/4" MDF
Construction	ShopSabre CNC \| V-Groove and Dado Joinery
Panel Thickness	3/4 Inch
Front Baffle	Double-Layer 1.5" MDF Plus Trim Layer
Internal Bracing	3/4" Dado-Locked Brace Behind Woofer
Driver Mounting	8/32 Threaded Inserts \| Stainless Machine Screws Included
Terminal Cup	One Proline X ABS/Carbon Fiber Composite \| Side Mounted
Internal Wiring	12 Gauge OFC, Pre-Wired
Finish	Plush Black Carpet \| Black Acrylic Insert
Bundle Options	Enclosure Only (Bring Your Own Solo X 18)
Warranty	1-Year Limited (Enclosure)
Built In	Tullahoma, Tennessee, USA

Performance Graphs

Net airspace

4.01

cu ft per chamber

System Qtc

0.81–0.90

sealed

Half power

34.0–34.7

Hz · F3

Xmax at

4710

W RMS · no filter

With 25 Hz subsonic

6383

W RMS · +36%

Amplifier

1000–2000

W RMS recommended

This enclosure holds 4.01 cu ft net per chamber. In it the Kicker SoloX L7X 18 (49L7X181) runs a system Qtc of 0.81–0.90 with half power at 34.0–34.7 Hz, and the cone reaches its 31.25 mm travel limit at 4710 W, above the driver’s 2000 W thermal rating, so heat stops you before travel does. Run a subsonic filter at 25 Hz and that becomes 6383 W — +1673 W, or 36 percent more power for the same 31.25 mm of travel.

01Is it a sealed driver?

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

EBP = Fs ÷ Qes = 41.1–44.4

D1 · EBP 44.4D2 · EBP 41.1

EBP under 50 means a motor that wants a sealed load. The SoloX L7X 18 (49L7X181) sits at 41.1–44.4, inside that band, which is why this is a sealed build rather than a ported one.

02What the box does to it

4.01 cu ft against a 125.9 L Vas.

α = Vas ÷ Vb = 1.11 · Fc = Fs√(α+1) = 39–41 Hz · Qtc = 0.81–0.90

D1 · Qtc 0.81, Fc 39 Hz, F3 34.7 HzD2 · Qtc 0.90, Fc 41 Hz, F3 34.0 Hz

The box lifts resonance from 26.9–28.9 Hz free-air to 39–41 Hz and half power lands at 34.0–34.7 Hz, anechoic, before any cabin gain. This enclosure ships without a driver, so both coil variants the maker offers are plotted. They do not load the same box the same way.

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 31.25 mm — and a bigger one once a subsonic filter stops it wasting travel below the passband.

P_Xmax = 4710–5304 W unfiltered → 6383–6428 W with a 25 Hz subsonic

D1 · 4710 W, no filterD2 · 5304 W, no filterD1 · 6428 W with subsonic at 25 Hz, 24 dB/octD2 · 6383 W with subsonic at 25 Hz, 24 dB/octXmax 31.25 mm one-way

Every trace touches the limit and no further, because each is drawn at the exact power that puts that coil on 31.25 mm. Unfiltered that is 4710 W, reached first at 20 Hz. It sits above the 2000 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 6383 W before hitting the same 31.25 mm. That is 36 percent more amplifier for the price of one filter setting.

Param	Value	Unit	Note
Fs	26.90 / 28.90	Hz	free-air resonance
Qts	0.557 / 0.634		D1 / D2
Vas	125.93 / 113.95	L	equivalent compliance
Sd	1406.2	cm²	effective piston area
Xmax	31.25	mm	one-way linear travel
Pe	2000	W	continuous RMS
SPL	87.9	dB	1 W / 1 m, derived from T/S

Driver parameters as published by Kicker published Klippel T/S sheet. Curves computed against this enclosure’s actual net airspace.

Materials

Material

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.

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 Performance 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.