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Proline X PO 8TW-S W P3S sealed wedge enclosure, product photos pending. Placeholder graphic reading Photos Coming Soon.

Performance Optimized · Datasheet

Performance Optimized Wedge Wide Sealed Triple 8" Enclosure Rockford Fosgate P3SD2-8 · Triple 8" Sealed enclosure

Net volume
0.418 cu ft per driver, 1.25 cu ft total, after both dividers and Rockford Fosgate's published 0.040 cu ft displacement per driver
Max mounting depth
2.66 in required; 2.62 in clearance above the motor against the raked rear panel
External dimensions
40 in W × 13 in at the seat face H × 11.10 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
Rockford Fosgate P3SD2-8Buy at Audio Intensity
  • Best For: Triple Rockford Fosgate P3SD2-8 SUV Cargo-Floor Builds
  • Net Volume: 0.418 cu ft per Driver (1.25 cu ft Net Total)
  • Driver Match: Three Rockford Fosgate P3SD2-8 (Dual 2 Ohm), matched
  • Construction: 3 Chambers | 40" Wide Wedge | V-Groove/Dado | Double 1.5" Baffle | 3 Terminal Cups

Spec of record

Technical specifications

SpecificationValue
SeriesProline X Performance Optimized Wedge Wide
Compatible DriverRockford Fosgate P3SD2-8, quantity 3, matched. Direct fit
ConfigurationTriple 8 inch sealed wedge, 3 chambers, 1 driver per chamber
Mounting PositionSUV cargo floor, raked face against the rear seat back
Firing DirectionRearward toward the liftgate. Not a down fire design
External Width40 in
External Height13 in at the seat face
External Depth11.10 in at the base, tapering to 6.37 in at the top
Internal Volume, Gross1.43 cu ft total
Internal Volume, Net Acoustic0.418 cu ft per driver, 1.25 cu ft total, after both dividers and Rockford Fosgate's published 0.040 cu ft displacement per driver
Driver Mounting Depth2.66 in required; 2.62 in clearance above the motor against the raked rear panel
Alignment Per DriverP3SD2-8 Qtc 1.100, fc 58.1 Hz, F3 43.9 Hz anechoic
Woofer Openings3 at 7.130 in
Woofer LayoutOne row across the face
Frame Outer Diameter8.72 in
Fs / Qts / Qes / Qms38.0 Hz / 0.720 / 0.837 / 5.000
Vas / Sd / Xmax15.8 L / 220 cm2 / 8 mm
Driver Power Handling150 W RMS per driver, 450 W RMS for the set of 3 (thermal rating)
Recommended Amplifier70-100 W RMS per driver, 210-300 W RMS for the full set, at 3 ohms
Parameter SourceRockford Fosgate 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 BracingTwo full-height 3/4 in dividers
Driver MountingThreaded inserts, stainless machine screws included
Terminal CupsThree Proline X ABS and carbon fiber composite, on the rear panel, 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 Weight54 lb
Warranty1 Year Limited
Built InTullahoma, Tennessee

Modelled response

Performance in this enclosure

Net airspace
0.418
cu ft per driver
System Qtc
1.10
sealed
Half power
43.9
Hz · F3
Xmax at
108
W RMS per driver · no filter
With 25 Hz subsonic
109
W RMS per driver · +1%
Amplifier, per driver
70–100
W RMS recommended
This enclosure holds 0.418 cu ft net per driver. In it the Rockford Fosgate P3SD2-8 runs a system Qtc of 1.10 with half power at 43.9 Hz, and the cone reaches its 8.3 mm travel limit at 108 W per driver, below the driver’s 150 W thermal rating, so travel is what stops you here, not heat. A 25 Hz subsonic filter adds little here: 109 W per driver against 108 W, 1 percent. The box already resonates at 58 Hz, so its own rolloff has removed most of what the filter would have stopped.

00Sizing the amplifier

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

Per driver 70–100 W RMS  ×  3 drivers  =  full set 210–300 W RMS at 3 ohms
Look for a mono amplifier rated 210–300 W RMS at 3 ohms, the load the set wires to most easily. Travel sets the top here, not heat: past 109 W per driver the cone runs beyond Xmax even with the subsonic set, under the driver’s 150 W thermal rating. 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 = 45.4
SEALED 0–50 TRANSITION 50–100 PORTED 100–150 0 50 100 150 Dual 2 Ohm 45.4
Dual 2 Ohm · EBP 45.4
EBP under 50 means a motor that wants a sealed load. The P3SD2-8 sits at 45.4, inside that band, which is why this is a sealed build rather than a ported one.

02What the box does to it

0.418 cu ft against a 15.8 L Vas.

α = Vas ÷ Vb = 1.33  ·  Fc = Fs√(α+1) = 58 Hz  ·  Qtc = 1.10
20 30 50 70 100 150 200 +6 +0 -6 -12 -18 -24 FREQUENCY · Hz LEVEL · dB −3 dB
Dual 2 Ohm · Qtc 1.10, Fc 58 Hz, F3 43.9 Hz
The box lifts resonance from 38.0 Hz free-air to 58 Hz and half power lands at 43.9 Hz, anechoic, before any cabin gain. Figures are Rockford Fosgate’s published parameters; Qes and Qms reproduce the printed Qts. This cabinet holds three drivers in three separate sealed chambers of 0.418 cubic feet each, 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 8.3 mm, and in this alignment a subsonic filter barely moves it.

PXmax = 108 W per driver unfiltered  →  109 W per driver with a 25 Hz subsonic
20 30 50 70 100 150 200 0 4 8 FREQUENCY · Hz CONE TRAVEL · mm PAST LINEAR TRAVEL · Xmax 8.3 mm 108 W reaches Xmax here
Dual 2 Ohm · 108 W, no filterDual 2 Ohm · 109 W with subsonic at 25 Hz, 24 dB/octXmax 8.3 mm one-way
Every trace touches the limit and no further, because each is drawn at the exact power that puts that coil on 8.3 mm. Unfiltered that is 108 W per driver, reached first at 45 Hz. It sits under the 150 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, and they sit almost on top of the solid ones: 109 W per driver against 108 W. At 58 Hz the filter sits well below resonance, where the sealed alignment has already rolled the cone off at 12 dB/oct, so there is little wasted travel left for it to recover. Set it anyway to keep road rumble out of the cone, but do not size the amplifier around it.
ParamValueUnitNote
Fs38.00Hzfree-air resonance
Qts0.720Dual 2 Ohm
Vas15.80Lequivalent compliance
Sd220.0cm²effective piston area
Xmax8.3mmone-way linear travel
Pe150Wcontinuous RMS
SPL82.0dB1 W / 1 m, derived from T/S

Driver parameters as published by Rockford Fosgate P3SD2-8 published specifications. Curves computed against this enclosure’s actual net airspace.

From the shop floor

Installer's take

Start with the size. The maker's recommended sealed size calls for 0.21 per driver; we stop at 0.418, where Qtc reaches 1.1. 0.418 cubic feet per driver puts the P3SD2-8 at Qtc 1.100, resonance 58.1 Hz, half power 43.9 Hz anechoic, a pronounced lift near resonance, 1.8 dB above flat.

Measure the base depth, not the top. This cabinet is 11.10 in deep where it meets the floor, 6.37 at the top, 40 wide and 13 tall. In an SUV the 40 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.

All three terminal cups are on the rear panel, and the rear panel is the face that goes against the seat back. Wire all three before the box goes in, with enough slack to slide it into place; once the raked face is against the seat you cannot reach them.

Impedance. P3SD2-8: wire for 3 ohms (coils in parallel, the three in series), the load most monoblocks are built to deliver full power into; 1.33 ohms is the other clean option (coils in series, the three cups in parallel). Work the load out before you buy the amplifier, not after.

Power. Size the amplifier for the set, not one driver: 70 to 100 W RMS per driver is 210 to 300 W RMS across all 3 at 3 ohms. On this driver travel sets the top, not heat: Xmax arrives at 109 W per driver with a 25 Hz subsonic, under the 150 W rating.

Rockford Fosgate'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 1.10.

Before you order

Questions

Does this fit the Rockford Fosgate P3SD2-8, and its coil versions?

Yes. Each opening is cut to 7.130 in for the 8.72 in frame, and the 2.66 in deep motor clears the raked rear panel with 2.62 in to spare. Coil versions of the Rockford Fosgate P3SD2-8 share the frame, cutout and mounting depth, so any of them drops in. The alignment on this page is computed on the P3SD2-8 parameters.

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

Why 0.418 cubic feet per driver, and what alignment does it target?

On Rockford Fosgate's published Fs 38.0 Hz, Qts 0.720 and Vas 15.8 liters, 0.418 cubic feet per driver gives Qtc 1.100, system resonance 58.1 Hz and half power 43.9 Hz.

The maker's recommended sealed size is 0.21 cubic feet per driver; this cabinet stops at 0.418, where Qtc reaches 1.1, so it stays compact without going past a pronounced lift near resonance, 1.8 dB above flat.

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

Rockford Fosgate rates the P3SD2-8 at 150 watts RMS per driver. Recommended amplifier: 70 to 100 W RMS per driver, 210 to 300 W RMS for the full set of 3. Travel, not heat, sets the top: the cone reaches Xmax at 109 W per driver with a 25 Hz subsonic set, under the 150 W rating.

Each P3SD2-8 has two 2 ohm voice coils, 4 ohms in series or 1 ohm in parallel. With each driver's coils in series and the three cups in parallel, the three present 1.33 ohms to a mono amplifier. With each driver's coils in parallel and the three in series, they present 3 ohms. Three drivers do not reach the round loads a pair does, so check the result against your amplifier's minimum stable impedance before powering up.

Will it fit my SUV?

It is 40 inches wide, 13 tall and 11.10 deep at the base, tapering to 6.37 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 are all three terminal cups on the back?

Each driver has its own sealed chamber, and the center chamber has no side wall to take a cup. Putting all three on the rear panel gives a matching set, one cup per chamber.

Wire them at the amplifier end; there is no cross-chamber wiring inside the cabinet.

What is the expected low-frequency extension?

Anechoic F3 is 43.9 Hz per driver with system resonance at 58.1 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 0.418 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, three pre-wired terminal cups on the rear panel, the polyfill lining in place, threaded inserts and stainless machine screws.

Bring three matched Rockford Fosgate P3SD2-8 drivers. The cabinet is cut direct fit to them, not a general purpose 8 inch box.

Same series, same size

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