Proline X

Proline X P8Q-S | Quad 8" Sealed Subwoofer Enclosure | V3

SKU: P8Q-S III G

QUICK SPECS

Best For: Quad 8" sealed installs — maximum cone area, full trunk floor builds
Volume: 1.80 ft³ Net (0.45 ft³ per driver)
Tuning: N/A — Sealed
Sonic Character: Tight, transient-accurate, wide dispersion

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.

$ 249.99

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Proline X P8Q-S | Quad 8" Sealed Subwoofer Enclosure | V3

Enclosure Type Sealed

External Dimensions 38W x 11H x 10.75D

Net Volume 1.8cu ft

Tuning Frequency N/A

Cutout Diameter 7.25

Front Panel Thickness .75

Max Mounting Depth 9.25"

INSTALLER'S TAKE

Four 8" drivers in sealed alignment is a purpose-built configuration. The combined cone area exceeds a single 15" while keeping individual mounting depth at 9.25" — that combination does not exist in any single-driver format. If you are building a dedicated trunk system and want to maximize output without going to a large-format single driver, this enclosure is the better engineering choice for that application.
At 38" wide this enclosure is designed to span a full trunk floor. Measure your available width carefully before ordering — this is not a behind-seat option. The single terminal cup handles all four drivers internally. All four must be run at the same impedance, so confirm your amplifier output and driver impedances before wiring. With four drivers pulling from the same cup, a wiring error affects all four simultaneously — take the time to get it right before the enclosure goes in.

Product Details

Four drivers. One sealed enclosure. The Proline X P8Q-S is a quad 8" sealed box built for installs that need serious cone area without the depth requirement of a single large subwoofer. At 1.80 ft³ net — 0.45 ft³ per driver — and sealed alignment, this enclosure delivers controlled, accurate bass across the full width of a trunk floor or rear deck. Four 8" drivers in sealed alignment produce combined cone area that exceeds a single 15" while keeping individual mounting depth at 9.25" — a configuration that opens up install locations that a single large driver cannot reach.

The enclosure is CNC-cut from 3/4" Langboard Elite MDF and assembled by hand at our facility in Tullahoma, TN. V-groove and dado joinery locks every panel before adhesive is applied. The 0.75" single baffle accommodates a 7.25" cutout with up to 9.25" of mounting depth — covering the majority of standard and high-excursion 8" drivers. The interior is a single shared air space with heavy internal bracing throughout. At 38" wide and 10.75" deep, this enclosure is designed to lay flat across a full trunk floor or mount against a rear wall in a dedicated build.

A single recessed ABS/Carbon Fiber Composite terminal cup handles wiring for all four drivers, with stainless steel hardware, aluminum landing plates, and copper ring terminals — pre-wired internally with 12g OFC speaker wire. All four drivers must be run at the same impedance. Finish options are Dark Gray Trunkliner or Plush Black. Shipping is included.

Specifications

Material	Langboard Elite MDF, 3/4" (18mm)
Enclosure Type	Sealed
Net Internal Volume	1.80 ft³ Net — shared air space, heavily braced
Tuning Frequency	N/A
External Dimensions	38" W x 11" H x 10.75" D
Subwoofer Cutout	7.25"
Max Mounting Depth	9.25"
Front Panel Thickness	0.75" Single Baffle
Finish	Dark Gray Trunkliner / Plush Black (+$10)
Terminal Cup	ABS/Carbon Fiber Composite, recessed mount, stainless hardware, copper ring terminals — single cup, quad driver internal wiring
Wiring	Pre-wired 12g OFC speaker wire
Warranty	1-Year Limited

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 — 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.