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Proline X PO 12D-S DFW XLT sealed down-fire wide enclosure for two PowerBass XL-1240T, 41 inches wide by 6.125 inches tall, feet add 1.75 inches of height.
Proline X PO 12D-S DFW XLT sealed down-fire wide enclosure, end panel with side-mounted terminal cup, 6.125 inches tall by 14 inches deep.

Performance Optimized · Datasheet

Performance Optimized Down Fire Wide Sealed Dual 12" Enclosure PowerBass XL-1240T · Dual 12" Sealed enclosure

Net volume
0.403 cu ft after displacement
Max mounting depth
3.8 in required, shallow mount
External dimensions
41 in W × 6.125 in in the down fire position H × 14 in D
Front baffle
1.5 in double baffle, outer layer machined as a flush recess
Buy at Audio IntensityFactory-direct, ships from Tullahoma
PowerBass XL-1240TBuy at Audio Intensity
  • Alignment: 0.403 cu ft net per chamber, 0.806 cu ft total. Qtc 1.142, Fc 71.6 Hz, F3 53.5 Hz per driver
  • Down Fire Wide: 41"W x 14"D x 6.125"H in down fire position, excludes standoffs, square corners
  • Versus the standard 30 x 15: 7.28 in tall and 0.40 cu ft net per chamber there, 6.125 in tall and 0.403 cu ft net here
  • Chambers: Two fully separate sealed chambers, 3/4" MDF full divider, one shared side-mounted terminal cup
  • Drivers: Pair of PowerBass XL-1240T, 400 W RMS each, 7.5 mm Xmax, 3.8 in mounting depth, single 4 ohm, rear vented motor
  • Standoffs: Included, 1.75 in, shipped uninstalled. Installed height 7.875 in

Spec of record

Technical specifications

SpecificationValue
SeriesProline X Performance Optimized Down Fire Wide
Compatible DriverPowerBass XL-1240T, pair required. Direct fit
Enclosure TypeSealed, dual driver, down fire, floor coupled
Intended FitmentSpaces where height or depth is the limit and 41 in of run is available
Chamber ConfigurationTwo fully separate chambers, full divider, single shared side-mounted terminal cup
External Width41 in
External Depth14 in
External Height6.125 in in the down fire position, excludes standoffs
Installed Height7.875 in including the 1.75 in standoffs
Internal Volume, Gross1.08 cu ft total
Per-Chamber Net Volume0.403 cu ft after displacement
Total Net Volume0.806 cu ft
Height Set ByAirspace; 1.575 in clearance above the motor
Alignment per chamberQtc 1.142, Fc 71.6 Hz, F3 53.5 Hz anechoic
Comparison, Standard 30 x 157.28 in tall, 0.40 cu ft net per chamber. Wide format is 6.125 in tall with 0.403 cu ft net per chamber
Woofer Opening11.06 in (281 mm, PowerBass template; labelled 11 in), two positions
Driver Mounting Depth3.8 in required, shallow mount
Driver MotorRear vented, pole vent may be fully obstructed
Driver Fs / Qts / Vas33 Hz / 0.526 / 42.37 L
Driver Displacement0.126 cu ft each
PowerBass Published Target0.40 optimum, 0.30 to 0.85 acceptable. Their figures are GROSS and include driver displacement
Driver Power Handling400 W RMS, 800 W peak each
Driver Voice CoilSingle 4 ohm, 2 in
WiringPair presents 2 ohms at the cup, wired in parallel
MaterialLangboard Elite 3/4 in MDF
ConstructionShopSabre CNC, V-groove and dado joinery
Panel Thickness0.75 in
Front Baffle1.5 in double baffle, outer layer machined as a flush recess
Internal BracingFull-height 3/4 in bonded divider
Corner ProfileSquare, Down Fire series standard
Driver MountingThreaded inserts with stainless machine screws
Terminal CupOne Proline X ABS and carbon fiber composite, side mounted, pre-wired 12 gauge OFC to both driver positions in parallel
StandoffsIncluded, 1.75 in, shipped uninstalled
DampingLight polyfill wall lining in both chambers, does not alter acoustic volume
CarpetPlush Black
Bundle OptionsEnclosure only, bring your own pair of PowerBass XL-1240T
Warranty1 Year Limited
Built InTullahoma, Tennessee

Modelled response

Performance in this enclosure

Net airspace
0.403
cu ft per chamber
System Qtc
1.14
sealed
Half power
53.5
Hz · F3
Xmax at
422
W RMS · no filter
With 25 Hz subsonic
422
W RMS · +0%
Amplifier
400
W RMS recommended
This enclosure holds 0.403 cu ft net per chamber. In it the PowerBass XL-1240T runs a system Qtc of 1.14 with half power at 53.5 Hz, and the cone reaches its 7.5 mm travel limit at 422 W, above the driver’s 400 W thermal rating, so heat stops you before travel does. A 25 Hz subsonic filter adds little here: 422 W against 422 W, 0 percent. The box already resonates at 72 Hz, so its own rolloff has removed most of what the filter would have stopped.

01Is it a sealed driver?

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

EBP = Fs ÷ Qes = 55.3
SEALED 0–50 TRANSITION 50–100 PORTED 100–150 0 50 100 150 XL-1240T 55.3
XL-1240T · EBP 55.3
At 55.3 the XL-1240T 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

0.403 cu ft against a 42.4 L Vas.

α = Vas ÷ Vb = 3.71  ·  Fc = Fs√(α+1) = 72 Hz  ·  Qtc = 1.14
20 30 50 70 100 150 200 +6 +0 -6 -12 -18 -24 FREQUENCY · Hz LEVEL · dB −3 dB
XL-1240T · Qtc 1.14, Fc 72 Hz, F3 53.5 Hz
The box lifts resonance from 33.0 Hz free-air to 72 Hz and half power lands at 53.5 Hz, anechoic, before any cabin gain.

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 7.5 mm, and in this alignment a subsonic filter barely moves it.

PXmax = 422 W unfiltered  →  422 W with a 25 Hz subsonic
20 30 50 70 100 150 200 0 4 8 FREQUENCY · Hz CONE TRAVEL · mm PAST LINEAR TRAVEL · Xmax 7.5 mm 422 W reaches Xmax here
XL-1240T · 422 W, no filterXL-1240T · 422 W with subsonic at 25 Hz, 24 dB/octXmax 7.5 mm one-way
Every trace touches the limit and no further, because each is drawn at the exact power that puts that coil on 7.5 mm. Unfiltered that is 422 W, reached first at 56 Hz. It sits above the 400 W the driver can take thermally, so the voice coil gives up before the suspension does. 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: 422 W against 422 W. At 72 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
Fs33.00Hzfree-air resonance
Qts0.526XL-1240T
Vas42.37Lequivalent compliance
Sd510.7cm²effective piston area
Xmax7.5mmone-way linear travel
Pe400Wcontinuous RMS
SPL85.9dB1 W / 1 m, derived from T/S

Driver parameters as published by powerbassusa.com. Curves computed against this enclosure’s actual net airspace.

From the shop floor

Installer's take

Same pair of XL-1240T as the standard 30 by 15 box, laid out 41 by 14. One inch shallower, 11 inches longer, and 6.125 inches tall against 7.28. Measure all three dimensions before choosing between them.

Airspace set the height here, 0.403 cubic feet net per chamber, with 1.575 inches clear above the motor.

Alignment is Qtc 1.142 with F3 at 53.5 Hz per driver.

Rear vented motor, so the pole vent can be blocked. Pair presents 2 ohms at the cup. Tight rather than deep; set that expectation before the sale.

Before you order

Questions

Why is this cabinet 41 inches wide instead of 30?

Because it trades length for depth and height. The standard dual Down Fire platform is 30 wide by 15 deep; this one is 14 deep, 1 inch shallower, and runs 41 inches long to put the airspace along the length instead.

That lets it stand 6.125 inches tall against 7.28 for the standard box. A 12 inch frame needs about 13 inches of baffle, so 14 is as shallow as a 12 can go. If you have 41 inches of run and height or depth is your limit, this is the shape that works.

How does this compare to the standard 30 x 15 dual XL-1240T enclosure?

The standard box is 30 by 15 by 7.28 inches and holds 0.40 cubic feet net per chamber. This one is 41 by 14 by 6.125 inches and holds 0.403 cubic feet net per chamber.

Choose the standard box when length is limited. Choose this one when height or depth is the limit and you have 41 inches of run.

What alignment does this enclosure produce?

At 0.403 cubic feet net per chamber the result is Qtc 1.142, Fc 71.6 Hz and F3 53.5 Hz, calculated from the driver's own published Thiele-Small parameters.

That is above the 0.707 maximally flat reference, so there is real lift near the corner rather than a textbook flat curve. The figures are anechoic; in a car, cabin gain adds real output below 50 Hz, so in-vehicle response runs deeper.

How much power should I run, and how do I wire these subwoofers?

Each XL-1240T is a single 4 ohm voice coil rated 400 watts RMS, 800 watts RMS combined across the pair. The shared cup feeds both positions in parallel, so the pair presents 2 ohms at the cup. Target 400 watts RMS per driver and set gains properly rather than to a number.

How tall is this once the standoffs are on?

The cabinet is 6.125 inches tall measured in the down fire position, excluding standoffs. The standoffs hold 1.75 inches under the baffle, so plan your space around 7.875 inches installed.

The standoffs ship uninstalled, so you can place them to suit your floor, or leave them off and run the cabinet front firing or up firing.

Where is the terminal cup located on a down fire enclosure?

Side mounted, and there is one cup serving both chambers. Every Proline X Performance Optimized enclosure uses a side mounted terminal cup regardless of alignment, whether standard, wedge, or down fire. On this cabinet that keeps the connection accessible with the enclosure installed, since the baffles face the floor. The cup is our Proline X ABS and carbon fiber composite unit with stainless hardware, copper ring terminals, and pre-wired 12 gauge OFC.

How is this enclosure built?

V-groove and dado joinery, CNC cut on ShopSabre routers from Langboard Elite MDF, with square corners as the Down Fire standard. Every panel joint is a machined interlocking groove that locks before adhesive is applied, which keeps the cabinet airtight under sustained pressure cycling.

The 1.5 inch double baffle has its outer layer machined as a flush recess so the driver bolts to the inner layer, and a full-height bonded 3/4 inch divider separates the chambers and ties the walls together across the 41 inch span. Polyfill is installed as a light wall lining; do not add more, since packing a sealed box makes it act larger and moves the alignment. Assembled and inspected in Tullahoma, Tennessee.

Is the pair of PowerBass XL-1240T included with this enclosure?

No. This listing is for the enclosure only. Bring your own pair of PowerBass XL-1240T. The cutout and cabinet height are cut direct fit for both positions. We do not stock PowerBass drivers.

Same series, same size

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