Proline X
Proline X P8D-S | Dual 8" Sealed Subwoofer Enclosure | V3
SKU: P8D-S III G
- Best For: Dual 8" sealed installs — front stage support, rear fill, compact builds
- Volume: 0.80 ft³ Net (0.40 ft³ per driver)
- Tuning: N/A — Sealed
- Sonic Character: Tight, transient-accurate, flat response
Financing available — choose Shop Pay Installments at checkout.
Proline X P8D-S | Dual 8" Sealed Subwoofer Enclosure | V3
Proline X P8D-S
Dual 8" Sealed Subwoofer Enclosure | V3
Two Drivers. One Sealed Enclosure. Built for Installs That Need Width, Not Depth.
The Proline X P8D-S is a dual 8" sealed enclosure built for installs that need the output and soundstage of two drivers without the depth requirement of a larger single-driver ported box. At 0.90 ft³ net — 0.45 ft³ per driver — and sealed alignment, this enclosure delivers controlled, accurate bass across a wider presentation than a single 8" can produce. Two drivers in sealed alignment produce a more even low-frequency field across the vehicle cabin, a wider perceived soundstage, and combined cone area that approaches a single 12" driver.
At 19" wide, 10" tall, and 13" deep, the P8D-S fits behind most rear seats and under most truck bench seats without requiring custom mounting. The 11.5" max mounting depth is the deepest specification in the dual 8" sealed lineup — it covers high-excursion competition motors that exceed the depth limit of shallower dual enclosures and opens up the compatible driver list considerably.
Two independent terminal cups handle wiring — each driver gets its own recessed ABS/Carbon Fiber Composite terminal cup with stainless hardware and copper ring terminals, pre-wired with 12g OFC speaker wire. Finish options are Dark Gray Trunkliner or Plush Black. Shipping is included.
Why Dual 8" Sealed
Two 8" drivers in sealed alignment occupy a specific performance tier that no single-driver format replicates exactly. The combined cone area approaches a single 12", but the individual driver mass remains low — each 8" starts and stops with the speed and accuracy that the format is known for. The sealed alignment preserves that transient precision while the dual configuration adds output, width, and bass presence that a single 8" sealed cannot match.
At 0.40 ft³ per driver, each chamber puts its driver in the center of the recommended sealed range for most 8" subwoofers. No damping material needed. No volume correction required. Both drivers are working the same correctly-sized air load.
Combined Cone Area
Two 8" drivers produce combined cone area approaching a single 12" while maintaining the low moving mass and transient speed that makes the 8" format the preferred choice for SQ-oriented builds.
Wider Bass Presentation
Two drivers spaced across a 19" baffle produce a wider, more even low-frequency field across the vehicle cabin than a single point source. Bass is more evenly distributed from driver seat to passenger seat.
Transient Accuracy Preserved
Sealed alignment on both drivers preserves the start-stop precision that defines the 8" format. The P8D-S produces tight, accurate bass at combined output levels that a single 8" sealed cannot approach.
11.5" Max Mounting Depth
The deepest spec in the dual 8" sealed lineup. High-excursion competition motors that will not fit the P8-S or shallower dual enclosures are candidates here. Check your driver's published mounting depth before ordering.
Construction: Two Independent Terminal Cups, One Consistent Build Standard
The P8D-S uses the same Langboard Elite MDF, V-groove and dado joinery, and in-house terminal cup construction as every enclosure in the Proline X Performance Series. The distinguishing feature on the P8D-S is the dual independent terminal cup configuration — each driver bay gets its own cup, its own wiring, and its own connection point.
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. For a sealed enclosure, joint integrity is non-negotiable — a single air leak degrades output and accuracy across the entire frequency range. Every seam on the P8D-S is mechanically locked before adhesive is applied.
Dual Independent Terminal Cups
The P8D-S uses two independent ABS/Carbon Fiber Composite recessed terminal cups — one per driver bay — built in-house at our Tennessee facility. Each driver is wired independently to its own cup with stainless steel hardware, aluminum landing plates, and copper ring terminals, pre-wired with 12g OFC speaker wire. Independent cups allow you to run separate impedance loads per driver or wire to a bridged amplifier channel per side without dealing with internal splices you did not make.
ShopSabre CNC Routers
Every panel is machine-cut on ShopSabre industrial CNC routers. Both driver cutouts are machined to identical diameter and position. 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 P8D-S is sized to fit behind most rear seats and under most truck bench seats. At 19"W x 10"H x 13"D it occupies a footprint that works in most standard vehicle configurations without custom mounting.
Dimensional Specifications
External Dimensions: 19" W x 10" H x 13" D
Net Internal Volume: 0.90 ft³ (0.45 ft³ per driver)
Tuning Frequency: N/A — Sealed
Subwoofer Cutout: 7.25"
Max Mounting Depth: 11.5"
Front Panel Thickness: 0.75" Single Baffle
Driver Compatibility
The P8D-S accommodates any 8" subwoofer with a cutout diameter at or below 7.25" and a mounting depth at or below 11.5". Both 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 P8D-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.
Ideal Install Applications
Behind Rear Seat
At 10" tall and 13" deep, the P8D-S fits behind most rear seats in full-size sedans and trucks. The 19" width spans most rear floor openings without obstructing access to cargo or the spare tire.
Under Truck Bench Seat
The low profile and 11.5" max mounting depth make the P8D-S a strong candidate for under-seat installs in full-size trucks where high-excursion 8" drivers are the target.
SQ and Competition Builds
Two sealed 8" drivers produce the wide, even bass presentation and combined output that SQ competition builds demand — without the ported alignment that trades accuracy for efficiency.
High-Excursion Driver Builds
The 11.5" max mounting depth is the deepest specification in the dual 8" sealed lineup. Competition-grade 8" motors that will not fit shallower enclosures are viable here.
Dual 8" Accuracy. Tennessee-Built. Shipping Included.
The Proline X P8D-S delivers dual 8" sealed performance from an enclosure that fits where larger boxes cannot. Langboard Elite MDF. V-groove and dado joinery. Dual independent terminal cups. Hand-assembled in Tennessee and inspected before it ships.
Two drivers. Sealed accuracy. Combined output a single 8" cannot match. $169.99 Dark Gray Trunkliner. $179.99 Plush Black. Shipping included.
| Material | Langboard Elite MDF, 3/4" (18mm) |
| Enclosure Type | Sealed |
| Net Internal Volume | 0.80 ft³ (0.40 ft³ per driver) |
| Tuning Frequency | N/A |
| External Dimensions | 19" W x 10" H x 13" D |
| Subwoofer Cutout | 7.25" |
| Max Mounting Depth | 11.5" |
| 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 — dual independent cups |
| 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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