Performance Optimized Down Fire Ported 12" Enclosure Focal SUB 30 KXE · Single 12" Ported enclosure

Focal's parameters put the SUB 30 KXE at an EBP of 59, in the band where a driver takes either load, and it has the travel to use a port well. Sealed at its 1.30 cubic foot Butterworth box it rolls off at 44.6 Hz; vented here it reaches 32.7 Hz with 1.6 dB of passband ripple and a 2.5 dB in-car spread from 25 to 60 Hz. The 21.9 square inch port runs 21.9 m/s, 53 percent of its core limit, and the cone peaks at about 8.6 mm of its 22.5 at rated power, so neither the port nor the suspension is what limits it. Tuning is chosen for in-car response rather than for an anechoic curve: a vehicle adds roughly 12 dB per octave below about 45 Hz, so a box tuned very low reinforces a region the cabin is already reinforcing and leaves 40 to 60 Hz thin. In this cabinet that lands at 2.4 dB of in-car spread across 25 to 60 Hz, which is where kick and bass fundamentals live.

No, and on this build in particular do not add any. Every sealed Proline X enclosure ships with polyfill pre-installed; a ported one must not, because damping material changes the effective volume the port is tuned against. The port on this cabinet is cut to 28.77 inches of centreline path for 34.0 Hz. Stuff it and you move the tuning without shortening the port, which gives you a mistuned box rather than a bigger-sounding one. The 1.59 dB passband you are paying for depends on it staying dry.

Yes, at 27 Hz, 24 dB per octave. Below tuning a vented box stops loading the cone and excursion runs away toward DC. With the filter in place this cabinet puts the Focal SUB 30 KXE at 41 percent of its usable travel at full rated power; without it there is no meaningful number to quote, because the excursion curve does not converge. On a sealed build a subsonic filter is an improvement. Here it is required equipment.

Focal rate the SUB 30 KXE at 800 W RMS and that is the thermal ceiling. The figures on the Performance Graphs tab are a different quantity: they are mechanical limits, the power at which the cone reaches the end of its linear travel in this specific cabinet. Here the cone sits at 41 percent of usable travel at the driver's own rating, so heat is what stops you, not travel. Final wired impedance and amplifier output are separate questions again.

Not one we can show you. We do not build a sealed enclosure for the Focal SUB 30 KXE and Focal publish no sealed volume for it, so the Performance Graphs tab carries no ported-versus-sealed chart: the only sealed box left to plot would be this cabinet stuffed and sealed, which nobody would build, and a comparison against it would tell you nothing you could buy. What a vented box gives up is the region below tuning, where the cone unloads and the 27 Hz subsonic filter takes over; around 34.0 Hz the vent carries the load and cone travel drops to its minimum, which no sealed alignment can do.

It is a slot port formed by one folded wall: a leg down the long side of the cabinet past the woofer ring, one faceted 90 degree bend, and a leg across the end opening through a chamfered corner. On this cabinet that is 28.77 inches of centreline path and 21.9 square inches of channel, exiting a 30.9 square inch mouth. Air leaves at 15.5 metres per second at tuning against a 17.0 threshold, and the channel runs at 53 percent of its turbulence limit. One wall and one bend rather than a serpentine's three means less wall area inside the box, fewer joints to leak, and one place for flow to separate instead of three.

V-groove and dado joinery in 0.75 inch Langboard Elite MDF with a double-layer 1.5 inch baffle. The driver mounts to a 13.500 inch ring bonded under the baffle in a machined recess, carrying eight #8-32 hurricane nuts so it threads into steel rather than MDF. A windowed brace sits 2.73 inches clear of the cutout edge and 1.60 inches clear of the port terminus; the window is not weight saving, a solid panel there would split the cavity and make the box a bandpass. Walls seat into dados in both the lid and the baffle. Square corners, plush black carpet, side-mounted terminal cup.

No. This is an enclosure only, cut and folded for the Focal SUB 30 KXE specifically. The 11.230 inch cutout, the 6.772 inch mounting depth allowance and the 1.40 cubic foot alignment all come from Focal's published parameters for this exact driver, and the port is sized against its Xmax and power rating. It is not a universal box with a 12 inch hole in it. Bring your own driver.