A Proline Performance Optimized Series S2 woofer enclosure shown on a dark blue graphic background with dimensions labeled 21.97 inches by 15 inches and text describing the sealed wedge design and Alpine compatibility.A dark gray wedge-shaped car audio woofer enclosure shown on a black background with dimension labels 13 inches tall, 6.32 inches wide at the top, and 11.

Performance Optimized · Datasheet

Performance Optimized Wedge Sealed 12" Enclosure | Alpine S2-W12 Single 12" Sealed enclosure

Net volume
0.85 cu ft after 0.06 displacement
Max mounting depth
4.88 in, driver requires 4.88
External dimensions
21.97 in W × 15 in at the seat face H × 11.78 in at the base D
Front baffle
1.5 in, double baffle
Buy at Audio Intensity
  • Best For: Alpine S2-W12 Trunk-Fit Daily Driver Builds
  • Net Volume: 0.85 cu ft (0.91 cu ft Gross)
  • Driver Match: Alpine S2-W12 (D2 or D4)
  • Construction: Rear-Firing Wedge | V-Groove/Dado | Double 1.5" Baffle | Threaded Inserts

Technical specifications

SpecificationValue
SeriesProline X Performance Optimized Wedge
Compatible DriverAlpine S2-W12, quantity 1. Direct fit, either coil version
ConfigurationSingle 12 inch, single chamber sealed wedge
Mounting PositionTrunk or cargo area, tall face against the rear seat back
Firing DirectionRearward into the trunk. Not a down fire design, no feet included
External Width21.97 in
External Height15 in at the seat face
External Depth11.78 in at the base, tapering to 6.32 in at the top
Internal Volume, Gross0.91 cu ft
Internal Volume, Net Acoustic0.85 cu ft after 0.06 displacement
Alpine Published Target0.85 cu ft ideal, 0.61 to 1.06 cu ft recommended range
Alignment, S2-W12D4Qtc 0.780, fc 51.0 Hz, F3 46.7 Hz anechoic
Alignment, S2-W12D2Qtc 0.780, fc 48.2 Hz, F3 44.2 Hz anechoic
Woofer Opening10.75 in (273 mm) direct fit
Max Mounting Depth4.88 in, driver requires 4.88
Driver Power Handling600 W RMS
MaterialLangboard Elite MDF
ConstructionCNC cut, dado and V groove joinery
Panel Thickness0.75 in
Front Baffle1.5 in, double baffle
Internal BracingWindowed C-brace, dadoed to top, back and bottom
Driver MountingThreaded inserts at every mounting location, stainless machine screws included
Terminal CupsOne Proline X ABS and carbon fiber composite, side mounted, pre wired 12 gauge OFC
DampingLight polyfill wall lining, does not alter acoustic volume
CarpetPlush black
Weight30 lb
Warranty1 Year Limited
Built InTullahoma, Tennessee

Performance in this enclosure

Net airspace
0.85
cu ft per chamber
System Qtc
0.78
sealed
Half power
44.2–46.7
Hz · F3
Xmax at
523
W RMS · no filter
With 25 Hz subsonic
628
W RMS · +20%
Amplifier
600
W RMS recommended
This enclosure holds 0.85 cu ft net per chamber. In it the Alpine S2-W12 runs a system Qtc of 0.78 with half power at 44.2–46.7 Hz, and the cone reaches its 15.0 mm travel limit at 523 W, below the driver’s 600 W thermal rating, so travel is what stops you here, not heat. Run a subsonic filter at 25 Hz and that becomes 628 W — +104 W, or 20 percent more power for the same 15.0 mm of travel.

01Is it a sealed driver?

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

EBP = Fs ÷ Qes = 57.8–61.3
SEALED 0–50 TRANSITION 50–100 PORTED 100–150 0 50 100 150 D2 57.8 D4 61.3
D2 · EBP 57.8D4 · EBP 61.3
At 57.8–61.3 the S2-W12 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

0.85 cu ft against a 55.1 L Vas.

α = Vas ÷ Vb = 2.29  ·  Fc = Fs√(α+1) = 48–51 Hz  ·  Qtc = 0.78
20 30 50 70 100 150 200 +6 +0 -6 -12 -18 -24 FREQUENCY · Hz LEVEL · dB −3 dB
D2 · Qtc 0.78, Fc 48 Hz, F3 44.2 HzD4 · Qtc 0.78, Fc 51 Hz, F3 46.7 Hz
The box lifts resonance from 26.6–28.8 Hz free-air to 48–51 Hz and half power lands at 44.2–46.7 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 15.0 mm — and a bigger one once a subsonic filter stops it wasting travel below the passband.

PXmax = 523–565 W unfiltered  →  628–656 W 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 15.0 mm 523 W reaches Xmax here
D2 · 523 W, no filterD4 · 565 W, no filterD2 · 628 W with subsonic at 25 Hz, 24 dB/octD4 · 656 W with subsonic at 25 Hz, 24 dB/octXmax 15.0 mm one-way
Every trace touches the limit and no further, because each is drawn at the exact power that puts that coil on 15.0 mm. Unfiltered that is 523 W, reached first at 20 Hz. It sits under the 600 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 628 W before hitting the same 15.0 mm. That is 20 percent more amplifier for the price of one filter setting.
ParamValueUnitNote
Fs26.60 / 28.80Hzfree-air resonance
Qts0.430 / 0.440D2 / D4
Vas55.10 / 51.50Lequivalent compliance
Sd472.0cm²effective piston area
Xmax15mmone-way linear travel
Pe600Wcontinuous RMS
SPL85.4dB1 W / 1 m, derived from T/S

Driver parameters as published by Alpine’s S2 owner’s manual, with Sd from loudspeakerdatabase. Curves computed against this enclosure’s actual net airspace.

Installer's take

Measure the base depth, not the top. This cabinet is 11.78 inches deep where it meets the trunk floor and 6.32 at the top, and it is 21.97 wide. The floor dimension is what decides whether it goes in.

Wire the terminal cup before the box goes in. Once the tall face is against the seat back you cannot reach behind it, and a wedge will not tip forward to let you.

0.91 cubic feet gross and the driver displaces 0.06, which lands every driver at 0.85 net. Alpine publishes 0.85 as ideal, so this is their number, not ours. Both coil versions land within 0.005 of each other on Qtc, so you do not need to know which one the customer has before quoting the alignment.

Dual 4 ohm coils. Series for 8 ohms, parallel for 2. If the customer has the dual 2 ohm version instead, parallel gives 1 ohm and that is the one to warn about.

Polyfill is already in as a wall lining. Adding more makes the box act larger and walks the alignment off Alpine's target, so leave it alone.

Questions

Will this enclosure fit both the S2-W12D2 and the S2-W12D4?

Yes. Both coil versions share the same frame, the same 10.75 in mounting hole and the same 4.88 in mounting depth, so the baffle is cut once and fits either.

They also land within a few thousandths of each other acoustically in this cabinet: Qtc 0.780 on the S2-W12D2 and Qtc 0.780 on the S2-W12D4. The choice between them is an impedance decision, not an enclosure one.

Why did you pick 0.85 cubic feet net?

Because Alpine did. They publish 0.85 cubic feet as the ideal sealed volume for this driver, inside a recommended range of 0.61 to 1.06 cubic feet. This cabinet is built to the middle of that range rather than to a number we chose.

Each chamber is 0.91 cubic feet gross. Subtract the driver's 0.06 cubic feet of displacement and you are left with the 0.85 net Alpine asks for.

What amplifier power should I run to this enclosure?

The Alpine S2-W12 is rated 600 watts RMS, so target 600 watts RMS at whatever impedance you wire to.

Watch the load. The dual 2 ohm version in parallel gives 1 ohm, which many amplifiers are not stable into. Set gains by ear or with an oscilloscope rather than to a number, and remember a sealed box of this size will take clean power far better than clipped power.

How does a wedge enclosure improve the sound in a trunk installation?

The angled seat-side face matches the roughly 20 degree lean of a factory rear seat, so the cabinet sits flat against it instead of leaving a wasted triangle. The vertical trunk-lid-side face carries the driver, firing rearward into the trunk cavity.

Firing rearward means the output loads into the trunk volume and reaches the cabin through the rear seat and deck rather than beaming at the back of your head, which makes it easier to keep the stage forward. The taper also gives height back where the lid closes, so you keep usable cargo space.

Why is the front baffle double-layered on this enclosure?

The baffle is two bonded 3/4 inch MDF sheets, 1.5 inches through. A subwoofer pushes as hard against its mounting surface as it does against the air, and a single 3/4 inch panel flexes under that load, which smears output and loosens the driver over time.

1.5 inches also gives the threaded inserts real material to hold in, so the driver bolts down to metal rather than into MDF and can come back out as many times as the install takes.

What is the expected low-frequency extension of this enclosure?

Anechoic F3 lands at 44.2 to 46.7 Hz depending on coil, at Qtc 0.780. That is a musical alignment with a little lift at resonance rather than a maximally flat one.

That figure is anechoic and does not include cabin gain. In a car the transfer function of the cabin adds meaningful output below 50 Hz, so in-vehicle response runs deeper than the number above. Build for the alignment, then let the cabin do the rest.

Do I need to add any additional damping or polyfill to this enclosure?

No. Polyfill is already installed as a light wall lining to control internal reflections, and the amount is chosen so it does not change the acoustic volume.

Do not add more. Packing a sealed box with fill makes it behave as though it were larger, which would move the alignment off the 0.85 cubic feet Alpine specifies and undo the reason this cabinet is the size it is.

Is the Alpine S2-W12 subwoofer included with this enclosure?

No. This is an enclosure only. You receive the cabinet finished in plush black carpet, with threaded inserts installed at the driver position, stainless machine screws, a side-mounted pre-wired terminal cup and the polyfill lining already in place.

The Alpine S2-W12 driver is purchased separately. The cabinet is cut direct fit to that driver, so it is not a general purpose 12 inch box.

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