Shop
Proline X PO 8Q-S W S2 sealed wedge enclosure, product photos pending. Placeholder graphic reading Photos Coming Soon.

Performance Optimized · Datasheet

Performance Optimized Wedge Wide Sealed Quad 8" Enclosure Alpine S2-W8 · Quad 8" Sealed enclosure

Net volume
1.166 cu ft per driver, 4.66 cu ft total, after the divider and Alpine's published 0.030 cu ft displacement per driver
Max mounting depth
3.70 in required; 13.48 in clearance above the motor against the raked rear panel
External dimensions
44 in W × 13 in at the seat face H × 23.00 in at the base D
Front baffle
1.5 in double baffle, outer layer machined as a flush recess
Buy at Audio IntensityFactory-direct, ships from Tullahoma
Alpine S2-W8Buy at Audio Intensity
  • Best For: Quad Alpine S2-W8 SUV Cargo-Floor Builds
  • Net Volume: 1.166 cu ft per Driver (4.66 cu ft Net Total)
  • Driver Match: Four Alpine S2-W8 (Dual 4 Ohm), matched
  • Construction: 2 Chambers | 44" Wide Wedge | V-Groove/Dado | Double 1.5" Baffle | 2 Terminal Cups

Spec of record

Technical specifications

SpecificationValue
SeriesProline X Performance Optimized Wedge Wide
Compatible DriverAlpine S2-W8, quantity 4, matched. Direct fit
ConfigurationQuad 8 inch sealed wedge, 2 chambers, 2 drivers per chamber
Mounting PositionSUV cargo floor, raked face against the rear seat back
Firing DirectionRearward toward the liftgate. Not a down fire design
External Width44 in
External Height13 in at the seat face
External Depth23.00 in at the base, tapering to 18.27 in at the top
Internal Volume, Gross4.87 cu ft total
Internal Volume, Net Acoustic1.166 cu ft per driver, 4.66 cu ft total, after the divider and Alpine's published 0.030 cu ft displacement per driver
Driver Mounting Depth3.70 in required; 13.48 in clearance above the motor against the raked rear panel
Alignment Per DriverS2-W8D4 Qtc 0.709, fc 53.1 Hz, F3 52.9 Hz anechoic
Woofer Openings4 at 7.010 in
Woofer LayoutOne row across the face
Frame Outer Diameter7.72 in
Fs / Qts / Qes / Qms47.9 Hz / 0.640 / 0.740 / 5.900
Vas / Sd / Xmax7.5 L / 194 cm2 / 13 mm
Driver Power Handling300 W RMS per driver, 1200 W RMS for the set of 4 (thermal rating)
Recommended Amplifier180-250 W RMS per driver, 720-1,000 W RMS for the full set, at 2 ohms
Parameter SourceAlpine published specifications
MaterialLangboard Elite MDF
ConstructionCNC cut, V-groove and dado joinery
Panel Thickness0.75 in
Front Baffle1.5 in double baffle, outer layer machined as a flush recess
Internal BracingOne full-height 3/4 in divider
Driver MountingThreaded inserts, stainless machine screws included
Terminal CupsTwo Proline X ABS and carbon fiber composite, side mounted, one per chamber, pre wired 12 gauge OFC
Acrylic InsertGloss black acrylic baffle insert standard
DampingLight polyfill wall lining in every chamber, does not alter acoustic volume
CarpetPlush black
Shipping Weight86 lb
Warranty1 Year Limited
Built InTullahoma, Tennessee

Modelled response

Performance in this enclosure

Net airspace
1.166
cu ft per driver
System Qtc
0.71
sealed
Half power
52.9
Hz · F3
Xmax at
207
W RMS per driver · no filter
With 25 Hz subsonic
257
W RMS per driver · +24%
Amplifier, per driver
180–250
W RMS recommended
This enclosure holds 1.166 cu ft net per driver. In it the Alpine S2-W8D4 runs a system Qtc of 0.71 with half power at 52.9 Hz, and the cone reaches its 13.0 mm travel limit at 207 W per driver, below the driver’s 300 W thermal rating, so travel is what stops you here, not heat. Run a subsonic filter at 25 Hz and that becomes 257 W per driver — +50 W, or 24 percent more power for the same 13.0 mm of travel.

00Sizing the amplifier

Every wattage on this panel is per driver. This cabinet holds four, so the amplifier feeds all four at once.

Per driver 180–250 W RMS  ×  4 drivers  =  full set 720–1,000 W RMS at 2 ohms
Look for a mono amplifier rated 720–1,000 W RMS at 2 ohms, the load the set wires to most easily. Travel sets the top here, not heat: past 257 W per driver the cone runs beyond Xmax even with the subsonic set, under the driver’s 300 W thermal rating. The top of the range needs the 25 Hz subsonic filter set; without it, keep each driver under 207 W, where the cone reaches Xmax unfiltered. Below the bottom of the range it will play, just with less headroom; above the top you are buying power the drivers cannot use.

01Is it a sealed driver?

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

EBP = Fs ÷ Qes = 64.7
SEALED 0–50 TRANSITION 50–100 PORTED 100–150 0 50 100 150 Dual 4 Ohm 64.7
Dual 4 Ohm · EBP 64.7
At 64.7 the S2-W8D4 sits in the transition band, not the sealed band. That is not a mismatch: a transition motor works in either alignment, and sealed buys a smaller box and a gentler roll-off at the cost of some low-end output. Stage 02 shows what this airspace actually does with it.

02What the box does to it

1.166 cu ft against a 7.5 L Vas.

α = Vas ÷ Vb = 0.23  ·  Fc = Fs√(α+1) = 53 Hz  ·  Qtc = 0.71
20 30 50 70 100 150 200 +6 +0 -6 -12 -18 -24 FREQUENCY · Hz LEVEL · dB −3 dB
Dual 4 Ohm · Qtc 0.71, Fc 53 Hz, F3 52.9 Hz
The box lifts resonance from 47.9 Hz free-air to 53 Hz and half power lands at 52.9 Hz, anechoic, before any cabin gain. Figures are Alpine’s published parameters; Qes and Qms reproduce the printed Qts. This cabinet holds four drivers in two sealed chambers of 2.331 cubic feet, two drivers to a chamber, so each driver works into 1.166 cubic feet and that is the volume plotted here.

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

PXmax = 207 W per driver unfiltered  →  257 W per driver with a 25 Hz subsonic
20 30 50 70 100 150 200 0 4 8 12 16 FREQUENCY · Hz CONE TRAVEL · mm PAST LINEAR TRAVEL · Xmax 13.0 mm 207 W reaches Xmax here
Dual 4 Ohm · 207 W, no filterDual 4 Ohm · 257 W with subsonic at 25 Hz, 24 dB/octXmax 13.0 mm one-way
Every trace touches the limit and no further, because each is drawn at the exact power that puts that coil on 13.0 mm. Unfiltered that is 207 W per driver, reached first at 20 Hz. It sits under the 300 W the driver can take thermally, so the enclosure sets the ceiling, not the voice coil. 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 257 W per driver before hitting the same 13.0 mm. That is 24 percent more amplifier for the price of one filter setting.
ParamValueUnitNote
Fs47.90Hzfree-air resonance
Qts0.640Dual 4 Ohm
Vas7.50Lequivalent compliance
Sd194.0cm²effective piston area
Xmax13mmone-way linear travel
Pe300Wcontinuous RMS
SPL82.3dB1 W / 1 m, derived from T/S

Driver parameters as published by Alpine S2-W8D4 published specifications. Curves computed against this enclosure’s actual net airspace.

From the shop floor

Installer's take

Start with the size. 1.166 cubic feet per driver puts the S2-W8 at Qtc 0.709, resonance 53.1 Hz, half power 52.9 Hz anechoic: maximally flat, no peak, the lowest F3 a sealed box reaches without a lift. Alpine publish no sealed recommendation for the S2-W8, so this is the Butterworth box.

Measure the base depth, not the top. This cabinet is 23.00 in deep where it meets the floor, 18.27 at the top, 44 wide and 13 tall. In an SUV the 44 has to clear between the rear wheel wells at floor height, the base depth is measured from the seat back with the seat upright and latched, and the 13 has to clear the cargo cover.

The two terminal cups are on the side panels, one per chamber, so they sit close to the wheel wells. Land the speaker wire on both before the box slides into its final spot, with slack to pull it forward again.

Two drivers share each chamber, so they have to match: same model, same coil, wired in phase. One driver reversed in a shared chamber pushes against its partner and the pair cancels instead of adding. Check polarity at each cup with a battery tap before the box goes in.

Impedance. S2-W8D4: wire for 2 ohms (coils in series, each chamber's pair in parallel, both cups in parallel), the load most monoblocks are built to deliver full power into; 8 ohms is the other clean option (coils in series, each chamber's pair in series, both cups in parallel). Work the load out before you buy the amplifier, not after.

Power. Size the amplifier for the set, not one driver: 180 to 250 W RMS per driver is 720 to 1,000 W RMS across all 4 at 2 ohms. On this driver travel sets the top, not heat: Xmax arrives at 257 W per driver with a 25 Hz subsonic, under the 300 W rating. Set the 25 Hz subsonic to use the top of that range; without it keep each driver under 207 W.

Alpine's Qes and Qms reproduce the printed Qts within 3 percent, so the alignment rests on a self-consistent set.

Polyfill is in as a wall lining in every chamber. Do not add more: it makes the box act larger and walks Qtc off 0.71.

Before you order

Questions

Does this fit the Alpine S2-W8, and its coil versions?

Yes. Each opening is cut to 7.010 in for the 7.72 in frame, and the 3.70 in deep motor clears the raked rear panel with 13.48 in to spare. Coil versions of the Alpine S2-W8 share the frame, cutout and mounting depth, so any of them drops in. The alignment on this page is computed on the S2-W8D4 parameters.

Run four matched drivers, same model and same coil, so every chamber sees the alignment on this page.

Why 1.166 cubic feet per driver, and what alignment does it target?

On Alpine's published Fs 47.9 Hz, Qts 0.640 and Vas 7.5 liters, 1.166 cubic feet per driver gives Qtc 0.709, system resonance 53.1 Hz and half power 52.9 Hz.

Qtc 0.707 is maximally flat: the deepest response a sealed box gives without a lift near resonance.

What amplifier power should I run, and how should I wire it?

Alpine rates the S2-W8 at 300 watts RMS per driver. Recommended amplifier: 180 to 250 W RMS per driver, 720 to 1,000 W RMS for the full set of 4. Travel, not heat, sets the top: the cone reaches Xmax at 257 W per driver with a 25 Hz subsonic set, under the 300 W rating. The top of that range needs the 25 Hz subsonic; without it keep each driver under 207 W.

Each S2-W8D4 has two 4 ohm voice coils, 8 ohms in series or 2 ohms in parallel. Wire every driver's coils in series. With the two drivers in each chamber in parallel and the two cups in parallel, the four present 2 ohms to a mono amplifier. With the two drivers in each chamber in series and the two cups in parallel, they present 8 ohms. Use the lower load only on an amplifier rated stable there.

Will it fit my SUV?

It is 44 inches wide, 13 tall and 23.00 deep at the base, tapering to 18.27 at the top. Measure between the rear wheel wells, the floor depth with the seat upright, and the height under your cargo cover.

The raked face goes against the seat back and the woofers fire toward the liftgate.

Why two drivers per chamber instead of four chambers?

Four chambers would need three dividers, and on a 44 inch face that space is needed for the woofers. Two matched drivers in one sealed chamber move together and see the same pressure, so each behaves as if it had half the chamber to itself: 1.166 cubic feet per driver here.

It also gives two terminal cups, one per pair, which keeps the wiring to the amplifier simple.

What is the expected low-frequency extension?

Anechoic F3 is 52.9 Hz per driver with system resonance at 53.1 Hz.

Those figures exclude cabin gain. An SUV cabin adds real output below about 50 Hz, so in-vehicle response runs deeper than the numbers above.

Do I need to add polyfill or damping?

No. Polyfill is already installed as a light wall lining in every chamber, and the quantity is chosen so it does not change the acoustic volume.

Do not add more. Packing a sealed box makes it behave as though it were larger, which moves the alignment away from 1.166 cubic feet per driver.

Are the drivers included?

No. This is an enclosure only. You receive the cabinet finished in plush black carpet with the gloss black acrylic baffle insert, two side-mounted pre-wired terminal cups, the polyfill lining in place, threaded inserts and stainless machine screws.

Bring four matched Alpine S2-W8 drivers. The cabinet is cut direct fit to them, not a general purpose 8 inch box.

Same series, same size

Other Performance Optimized models