Proline X
Proline X P8Q-S | Quad 8" Sealed Subwoofer Enclosure | V3
SKU: P8Q-S III G
- 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
Financing available — choose Shop Pay Installments at checkout.
Proline X P8Q-S | Quad 8" Sealed Subwoofer Enclosure | V3
Proline X P8Q-S
Quad 8" Sealed Subwoofer Enclosure | V3
Four Drivers. One Sealed Enclosure. Maximum Cone Area Without the Depth.
The Proline X P8Q-S is a quad 8" sealed enclosure built for dedicated trunk builds that need maximum cone area without the depth requirement of a large single-driver ported box. At 1.80 ft³ net and sealed alignment, four 8" drivers in a shared air space with heavy internal bracing produce combined cone area that exceeds a single 15" while keeping individual mounting depth at 9.25". That combination does not exist in any single-driver format.
At 38" wide, 11" tall, and 10.75" deep, the P8Q-S is designed to span a full trunk floor. It is not a behind-seat option — 38" requires a dedicated trunk installation in most vehicles. The low 10.75" depth makes it viable in applications where a 15" ported box would require more depth than the trunk allows. Four drivers share a single air space rather than individual separated chambers — the interior is heavily braced throughout to control panel resonance and maintain structural integrity under the combined mechanical load of four motors.
A single terminal cup handles wiring for all four drivers internally — all four must be run at the same impedance. Every panel is CNC-cut from Langboard Elite MDF and assembled by hand in our Tennessee facility. Finish options are Dark Gray Trunkliner or Plush Black. Shipping is included.
Why Four 8" Drivers in a Shared Sealed Air Space
The quad 8" configuration in a shared sealed air space is a purpose-built solution for a specific install problem: maximum cone area in minimum depth. Four 8" drivers collectively move more air than a single 15" while keeping every individual driver's mounting depth requirement at 9.25". The sealed alignment preserves the transient accuracy and flat response that makes the 8" format valuable — applied at a scale that approaches large-format SPL output.
The shared air space rather than individual separated chambers is a deliberate engineering choice. A single 1.80 ft³ shared volume provides each driver with a larger effective acoustic load than four individual 0.45 ft³ chambers would — the drivers interact with a combined air mass that produces a more cohesive low-frequency response across the full 38" baffle width.
Exceeds Single 15" Cone Area
Four 8" drivers produce combined cone area that exceeds a single 15" subwoofer while keeping individual mounting depth at 9.25" and total enclosure depth at 10.75". No single-driver format delivers this combination.
Shared Air Space — Cohesive Response
The shared 1.80 ft³ interior with heavy internal bracing provides a larger effective acoustic load per driver than separated chambers would. Four drivers interact with a combined air mass for a more cohesive low-frequency response across the full 38" baffle.
Maximum Width, Minimum Depth
At 38" wide and 10.75" deep, the P8Q-S spans a full trunk floor while requiring less depth than most single 12" or 15" ported enclosures. The output-to-depth ratio is unmatched in the Performance Series lineup.
Heavy Internal Bracing
Four motors in a shared air space generate significant combined pressure on every panel simultaneously. The P8Q-S uses heavy strategic bracing throughout the interior to control panel resonance and maintain structural integrity under the full mechanical load of four drivers at volume.
Construction: Four Driver Bays, One Shared Air Space, Maximum Bracing
The P8Q-S uses the same Langboard Elite MDF and V-groove and dado joinery construction as every enclosure in the Proline X Performance Series. The distinguishing construction feature is the internal bracing strategy — four motors in a shared air space require more bracing than any other enclosure in the lineup to control panel resonance at the output levels four drivers can generate.
Langboard Elite MDF — Named, Verified, Documented
Every panel is cut from Langboard Elite MDF — 3/4" (18mm), a named, mill-documented panel stock produced in the United States. The specifications below are pulled directly from Langboard's published mill data.
Langboard Elite — Published Mill Data
Density: 48.5 lbs/ft³ — higher density means less porosity, better screw retention, and reduced resonance
Internal Bond: 200 psi — resistance to delamination under sustained bass pressure cycling
Modulus of Elasticity: 410,000 psi — panel stiffness under load; less flex means less resonance
Face Screw Holding: 325 lbs — baffle hardware stays locked under vibration
Edge Screw Holding: 250 lbs — joint integrity at every panel edge connection
V-Groove and Dado Joinery
Every panel joint uses V-groove and dado joinery — CNC-cut interlocking grooves that mechanically lock panels before adhesive is applied. On an enclosure this wide, panel rigidity and joint integrity are critical — the 38" side panels span a distance that creates significant flex potential under bass pressure without proper joinery. Every joint on the P8Q-S is mechanically locked before adhesive is applied.
Single Terminal Cup — All Four Drivers Internal
The P8Q-S uses a single ABS/Carbon Fiber Composite recessed terminal cup built in-house at our Tennessee facility. All four drivers are wired internally to the cup with stainless steel hardware, aluminum landing plates, and copper ring terminals, pre-wired with 12g OFC speaker wire. All four drivers must be run at the same impedance. With four drivers pulling from the same cup, a wiring error affects all four simultaneously — confirm your amplifier output and driver impedances before wiring.
ShopSabre CNC Routers
Every panel is machine-cut on ShopSabre industrial CNC routers. All four driver cutouts are machined to identical diameter and position across the 38" baffle. Consistent geometry across every unit.
Hand-Assembled in Tennessee
Every enclosure is hand-assembled at our Tennessee facility and inspected before it ships. No overseas manufacturing. No batch assembly shortcuts.
Dark Gray Trunkliner or Plush Black
Both finish options are professionally applied. Dark Gray Trunkliner blends with factory trunk materials. Plush Black delivers the traditional aftermarket look. Both are durably bonded for long-term wear.
Shipping Included
No freight charges at checkout. The price you see is the price you pay. The enclosure ships assembled and ready to install.
Fitment Guide
The P8Q-S is designed to span a full trunk floor. At 38" wide, this is a dedicated trunk build — measure your available trunk width carefully before ordering. At 11" tall and 10.75" deep, the profile is low enough to fit in most standard trunk environments without custom fabrication.
Dimensional Specifications
External Dimensions: 38" W x 11" H x 10.75" D
Net Internal Volume: 1.80 ft³ — shared air space, heavily braced
Tuning Frequency: N/A — Sealed
Subwoofer Cutout: 7.25"
Max Mounting Depth: 9.25"
Front Panel Thickness: 0.75" Single Baffle
Driver Compatibility
The P8Q-S accommodates any 8" subwoofer with a cutout diameter at or below 7.25" and a mounting depth at or below 9.25". All four drivers must be the same model and impedance. Verify published specifications before ordering.
Compatible Drivers
The following drivers are available from Audio Intensity and are compatible with the P8Q-S:
Image Dynamics ID8 V4 → Prodigy NB2-8D4 → Image Dynamics IDQ8 V4 → Prodigy NB5-8D4 → Arc Audio Arc Series 8" →Always verify cutout diameter and mounting depth against your specific driver's published specifications before ordering. All four drivers must be run at the same impedance.
Ideal Install Applications
Full Trunk Floor Build
At 38" wide, the P8Q-S is designed to span a full trunk floor in most full-size sedans and trucks. This is a dedicated trunk installation — not a behind-seat or partial trunk option.
Maximum Output, Minimum Depth
Four 8" drivers produce output that exceeds a single 15" while requiring only 10.75" of trunk depth. For vehicles where output is the priority but trunk depth limits large-format enclosures.
Dedicated Competition Builds
Combined cone area exceeding a single 15" in sealed alignment makes the P8Q-S a viable platform for SPL-oriented builds that require maximum cone area in a flat, low-profile format.
Rear Wall Installs
The flat, low-profile form factor makes the P8Q-S well suited for rear wall installations in dedicated build vehicles where the enclosure is mounted vertically against the rear of the cabin.
Quad 8" Output. Full Trunk Floor Footprint. Tennessee-Built.
The Proline X P8Q-S delivers combined quad 8" output that exceeds a single 15" from an enclosure that requires less depth than most 12" ported boxes. Langboard Elite MDF. V-groove and dado joinery. Heavy internal bracing. In-house terminal cup. Hand-assembled in Tennessee and inspected before it ships.
Four drivers. Sealed alignment. More cone area than a 15" — in a 10.75" deep trunk floor enclosure. $249.99 Dark Gray Trunkliner. $259.99 Plush Black. Shipping included.
| 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 |
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 — 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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