Performance Optimized Down Fire Sealed Dual 10" Enclosure Focal SUB 25 KXE · Dual 10" Sealed enclosure

The SUB 25 KXE, yes. The baffle is cut to 9.30 in (236 mm). Loudspeaker Database lists a 235 mm cutout, but Focal's own drawing puts the basket at 235.2 mm just under the flange, which a 235 mm hole would not pass; the 236 mm cut clears it and the 268 mm frame still covers it with margin. The 6.77 inch motor clears the cabinet with 3.71 inch to spare, and the KXE ships in one version, dual 4 ohm, so there is no coil variant to choose. Run two so the chambers match.

Any other 10, no. The airspace is engineered around the KXE's 0.52 Qts and 20 liters of Vas, and a different woofer that happened to drop into the hole would not see the alignment printed on this page.

It is the Butterworth volume on Focal's published Fs 38 Hz, Qts 0.52 and Vas 20 liters: system Qtc 0.707, maximally flat, with resonance and half power both at 51.7 Hz. Focal's own closed-box simulations for this driver run at 16 and 30 liters, and this volume sits between them.

One caveat on Focal's sheet: its moving mass and resonance imply a Vas nearer 16 liters than the printed 20. If that is the truer figure, this cabinet reads Qtc 0.67 instead, a touch more damped. Either way it is a well-behaved sealed alignment.

Focal rates the SUB 25 KXE at 600 watts RMS per driver and 1200 watts maximum, so target 420 to 600 watts RMS per driver at the final load.

Each SUB 25 KXE carries two 4 ohm voice coils (3.2 ohms DC each): series for 8 ohms, parallel for 2. Wire both drivers identically. Each driver in series with the pair in parallel gives 4 ohms, the safe load on any amplifier; each driver in parallel with the pair in series also gives 4; all four coils in parallel is 1 ohm and needs an amplifier rated for it; all in series is 16 ohms. Confirm your amplifier's minimum stable impedance first.

The cabinet is 11.23 inches tall measured in the down fire position, and that figure excludes the standoffs. The standoffs hold 1.75 inches under the baffle, so plan your space around a finished stack of roughly 12.98 inches.

The footprint is the standard Performance Optimized down fire platform, 30.00 inches wide by 15.00 deep. Height is the only dimension solved to the driver.

Two drivers sharing one sealed volume load each other: each driver's compression stroke becomes the pressure the other works against, which blurs the alignment either would have alone. A bonded full-height 3/4 inch divider gives each driver its own 0.83 cubic feet and its own polyfill.

It also means a failure in one driver does not unload the other, and the alignment on this page is the alignment in each chamber, not an average across a shared box.

Anechoic F3 is 51.7 Hz per chamber with system resonance at 51.7 Hz. At Qtc 0.71 the response is maximally flat into the rolloff, so F3 and fc coincide.

Those figures exclude cabin gain. In a car the cabin's transfer function adds real output below 50 Hz, so in-vehicle response runs deeper than the numbers above.

No. Polyfill is already installed in both chambers as a light wall lining to control internal reflections, and the quantity 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 walks the alignment away from the 0.83 cubic feet per chamber this cabinet was built to.

No driver. This is an enclosure only. You receive the cabinet finished in plush black carpet, one side-mounted pre-wired terminal cup to both positions, the polyfill lining already in place, the standoffs, and a threaded insert kit with stainless machine screws.

The inserts ship loose on purpose: Focal prints no bolt circle for the SUB 25 KXE, so you set the driver in the recess, mark its holes, drill and press the inserts. The pair of Focal SUB 25 KXE is purchased separately, and the cabinet is cut direct fit to it, not a general purpose 10 inch box.