Performance Optimized Down Fire Sealed Dual 12" Enclosure Hertz Mille Pro MPS 300 · Dual 12" Sealed enclosure

10.75 inches, which makes it the tallest enclosure in the Proline X Down Fire line. This is not an under-seat build. It suits a cargo floor, a rear wall, or the space behind a bench seat. The footprint is the standard 30 by 15 inches, so it occupies no more floor area than any other Down Fire cabinet, it simply stands taller to give each of the two MPS 300 drivers its full 0.856 cubic feet.

If vertical clearance is your constraint, the single 12 inch MPS enclosure at 6.375 inches or the dual 10 inch at 7.6875 inches are the alternatives.

Because two drivers in a shared sealed volume interact acoustically. Each driver's compression phase becomes the pressure environment the other driver is working against, which smears transient response and blurs the alignment each would have on its own. A full-height bonded 3/4 inch MDF divider eliminates that completely. Each MPS 300 gets its own 0.856 cubic feet net, plus its own polyfill. Separate chambers are the standing design rule on every Proline X dual sealed enclosure.

On this size the S4 is the better damped driver, with a free-air Qts of 0.42 against the S2's 0.51, landing at Qtc 0.793 per chamber versus 0.978. The S2 reaches deeper, F3 36.6 Hz against 39.2.

Note this is the opposite of the 10 inch MPS 250, where the S2 is the tighter driver. Whichever you choose, use two of the same model - mismatched drivers between chambers will not track each other. Both are single voice coil, so your final load depends on the model and how the pair is wired at the amplifier.

The enclosure uses one side-mounted Proline X terminal cup with a single pair of posts, pre-wired in 12 gauge OFC to both driver positions in parallel. You do not wire the two chambers separately at the amplifier.

Both MPS 300 models are single voice coil, so there is no coil configuration decision at the driver. Your final load is determined by which model you install - 2 ohms each for the S2, 4 ohms each for the S4 - and how that pair resolves through the cup. Confirm the resulting impedance against your amplifier's minimum stable load before powering the system.

Side mounted, and there is one cup serving both chambers rather than one per chamber. 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 fully accessible with the enclosure in its installed position, since both baffles face the floor. The cup is our Proline X ABS and carbon fiber composite unit, recessed, with stainless hardware, copper ring terminals, and pre-wired 12 gauge OFC.

Down Fire cabinets are built with square corners as a series standard. The 3 inch top down corner radius used on other Proline X alignments does not apply here. A down fire box is a low, wide platform that sits flat against a floor or cargo deck, and square corners maximize usable internal volume for a given footprint while keeping the cabinet stable on its mounting surface.

V-groove and dado joinery, CNC-cut on ShopSabre routers from Langboard Elite MDF. Every panel joint is a machined interlocking groove that mechanically locks the panels before adhesive is applied, which is what keeps both chambers airtight under sustained pressure cycling. The chamber divider is a full-height bonded 3/4 inch panel. Front baffles are double-layer at 1.5 inches, two bonded 3/4 inch sheets, at both driver positions, which matters with two 11 inch cutouts in the same cabinet. Perimeter cross-bracing and pre-installed polyfill in each chamber complete the build. Assembled and inspected in Tullahoma, Tennessee.

No. This listing is for the enclosure only. Bring your own pair of Hertz Mille Pro MPS 300 S2 or MPS 300 S4 subwoofers. The cutouts and mounting depth are direct fit at both driver positions for either version. Use two of the same model.