Proline X
Performance Optimized Down Fire Wide Sealed 10" Enclosure | Hertz Mille Pro MP 250
SKU: PO 10-S DFW MP
- Alignment: 1.063 cu ft net. Qtc 0.731, Fc 40.6 Hz, F3 39.3 Hz (MP 250 D2.3); Qtc 0.712, Fc 38.5 Hz, F3 38.2 Hz (MP 250 D4.3)
- Height: Set by the 5.80 in mounting depth, 0.75 in above the motor; more air than the standard box, lower Qtc
- Driver: Hertz MP 250 D2.3 or D4.3, 600W RMS / 1200W peak, 17mm Xmax, 3.2 L displacement
- Fitment: 236mm cutout, double-layer 1.5" front baffle with flush outer recess
- Cabinet: 41"W x 12"D x 7.3125"H measured in down fire position, square corners
Financing available. Choose Shop Pay Installments at checkout.
Performance Optimized Down Fire Wide Sealed 10" Enclosure | Hertz Mille Pro MP 250
More enclosures cut for Hertz subwoofers: Hertz Subwoofer Boxes
Proline X Performance Optimized Down Fire Wide 10" Sealed
Under rear seat fitment for trucks and SUVs. Cut for the Hertz Mille Pro MP 250
The Down Fire Wide Format
Down Fire Wide is the Performance Optimized answer to a specific problem: the space under the rear seat of a truck or SUV, or a narrow cargo floor, is long and shallow, and the standard 30 by 15 inch Down Fire cabinet will not go in it.
This cabinet takes the same Hertz MP 250 and turns the footprint sideways. It runs 41 inches wide by 12 inches deep by 7.3125 inches tall: 3 inches shallower front to back than the standard 30 x 15 cabinet and 11 inches longer. The airspace given up in depth is recovered along the length.
Which one to choose. If you have 15 inches of depth, the standard 30 x 15 Hertz MP 250 enclosure is the pick. Choose Down Fire Wide when depth is the limit: under a rear bench or on a narrow cargo floor, with at least 12 inches of depth and 41 inches of run.
Performance, Performance Optimized, and Micro
Proline X builds three tiers of Down Fire enclosure. The difference is not finish or materials, it is whether the cabinet was designed for a category or for a driver, and how much of the fitting work is already done for you.
| Performance | Performance Optimized | Micro Series | |
|---|---|---|---|
| Fitment | Universal. Accepts any subwoofer that clears the published cutout and mounting depth. | Woofer specific. Cut for one named subwoofer, with cutout, mounting depth, magnet clearance and displacement drawn in CAD from that driver. | Woofer specific. Cut for one named subwoofer. |
| Footprint | Sized to the driver diameter. 24.5 by 13.5 inches on the 10 inch. | Shared 30 by 15 inch platform on most builds. Down Fire Wide variants like this one run long and shallow for under seat fitment. | Compact per driver footprint. 21.5 by 14.5 inches on the 10 inch. |
| Front baffle | Single, 3/4 inch. | Double layer, outer layer machined as a flush recess. 1.5 inch. | Double, 1.5 inch. |
| Driver mounting | Solid flange. You drill your own mounting holes. | 8/32 threaded inserts, stainless machine screws included. | 8/32 threaded inserts, stainless machine screws included. |
| Joinery | V-groove and dado, CNC cut. | V-groove and dado, CNC cut, perimeter cross brace. | Stack fab, dowel reinforced. |
| Published alignment | Modeled Qtc profiles across a range of drivers. No single response curve. | A real predicted Qtc and F3 for that exact driver, calculated from its own Thiele-Small parameters. | Target alignment described in the listing. |
| Carpet | Gray standard, black optional. | Plush black. | Plush black. |
| Warranty | 1 year limited. | 1 year limited. | 2 years. |
Feet ship with every tier, uninstalled on purpose. Mount them where your floor wants them for a down fire install, or leave them off and run the cabinet front firing or up firing. The orientation is yours to choose.
This page is a Performance Optimized enclosure. The cutout, the cabinet height and the airspace all come from the Hertz Mille Pro MP 250's own published numbers. A Performance box fits your subwoofer. A Performance Optimized box was built for it.
Built Around the Hertz MP 250
The baffle is bored to the MP 250's 236mm cutout, 9.291 inches, and the cabinet height is set by its 5.80 inch mounting depth. The 268mm frame sits on the 12 inch deep baffle, and the driver bolts to 8/32 threaded inserts with stainless machine screws included.
The cone is a V-cone profile pressed from paper pulp with mineral powder injection, the same technique Hertz uses on the Mille Legend line, so the diaphragm resists bending and behaves like a piston instead of flexing at the outer edge. The surround is high-purity IIR butyl rubber. Motor work is a 65mm four-layer CCAW voice coil on a vented TIL-P former in a six-spoke aluminum alloy basket with vents under the spider.
Excursion is 17mm linear with 27mm of mechanical travel before damage. Sensitivity is 83.4 dB at 1W/1m, low for a 10, so plan on giving it power. If you are cross shopping: the Mille Pro MPS 250 is the shallow mount driver and has its own cabinet. This page is cut for the deeper, higher excursion MP 250 only.
Net Volume and Alignment
This cabinet holds 1.063 cubic feet net, from 1.184 gross, after the driver's 0.113 cubic feet of displacement.
Computed from the D2.3 and D4.3 parameter sets separately, per coil version: MP 250 D2.3: Qtc 0.731, Fc 40.6 Hz, F3 39.3 Hz. MP 250 D4.3: Qtc 0.712, Fc 38.5 Hz, F3 38.2 Hz.
Height here is set by the driver, not the airspace. The 5.8 inch mounting depth puts the motor far enough into the cabinet that the height is fixed by motor clearance, 0.75 inch above the motor. At 7.3125 inches tall the wide box holds 1.063 cubic feet net, more than the 1.00 cubic feet the standard 30 x 15 box was built to. More air lowers Qtc, which is the safe direction: a slightly more damped alignment with a gentler rolloff.
Hertz recommends 17 liters sealed for this driver. At 5.80 inches deep, and displacing 3.2 liters on its own, the MP 250 cannot physically fit a cabinet that small on this footprint, and the larger box works in its favor: better damped, tighter on transients.
These are anechoic figures. Firing down into the floor, the sealed rolloff meets rising cabin gain, so in-car response extends below them.
Down Fire Wide Construction
Cut with V-groove and dado joinery on our ShopSabre routers from Langboard Elite 3/4 inch MDF, a dense 48.5 lb/ft³ board with a 200 psi internal bond and 410,000 psi MOE. Every panel joint is a machined interlocking groove that mechanically locks before adhesive is applied, which keeps the cabinet airtight under sustained pressure cycling. Corners are square on Down Fire cabinets, no radii. Polyfill is installed as a light wall lining, finished in plush black carpet.
The cabinet measures 41 inches wide by 12 inches deep by 7.3125 inches tall, measured in the down fire position, excluding feet. The 1.75 inch feet ship with the enclosure but are not installed. Fitted, the installed height is 9.0625 inches, so plan the space around where you intend to mount them.
1.5 Inch Double Baffle
Two 3/4 inch layers laminated to 1.5 inches, the outer layer machined as a flush recess so the driver bolts to the inner layer. 8/32 threaded inserts with stainless machine screws at every mounting location.
Frame on a 12 Inch Baffle
The MP 250's 268mm (10.551 inch) frame sits on the 12 inch deep baffle, bored to the 236mm cutout, with the 5.80 inch motor clearing the top panel by 0.76 inches.
Windowed U-Brace
A windowed U-brace ties the long top and bottom panels together across the 41 inch span without walling off the airspace.
Side-Mounted Terminal Cup
Proline X ABS and carbon fiber composite cup with stainless hardware and copper ring terminals, side mounted and pre-wired in 12 gauge OFC, so it stays accessible with the baffle facing the floor.
Power and Wiring
Hertz rates the MP 250 at 600 watts RMS and 1200 watts peak. Both versions are dual voice coil, so final impedance is set at the driver: the D2.3 gives 1 ohm in parallel or 4 ohms in series, the D4.3 gives 2 ohms in parallel or 8 in series. Confirm your amplifier is stable at your chosen load before powering the system.
Bring your own Hertz Mille Pro MP 250 D2.3 or MP 250 D4.3; the driver is purchased separately. The enclosure carries a 1 year limited warranty. Questions on fitment or amplifier matching, call 931-563-5151.
Cut for the Driver, Not the Catalog
Down Fire Wide, built for the space under a rear bench. We build every one to order in Tullahoma, Tennessee.
| Series | Proline X Performance Optimized Down Fire Wide |
| Compatible Driver | Hertz Mille Pro MP 250 D2.3 or MP 250 D4.3. Direct fit |
| Enclosure Type | Sealed, down fire, floor coupled |
| Intended Fitment | Under the rear seat of trucks and SUVs, or narrow cargo floors, where depth is the limiting dimension |
| Chamber Configuration | Single chamber, windowed U-brace, one side-mounted terminal cup |
| External Width | 41 in |
| External Depth | 12 in |
| External Height | 7.3125 in, measured in down fire position, excludes feet |
| Installed Height | 9.0625 in with the 1.75 in feet fitted |
| Internal Volume, Gross | 1.184 cu ft |
| Internal Volume, Net Acoustic | 1.063 cu ft after displacement |
| Alignment, MP 250 D2.3 | Qtc 0.731, Fc 40.6 Hz, F3 39.3 Hz anechoic |
| Alignment, MP 250 D4.3 | Qtc 0.712, Fc 38.5 Hz, F3 38.2 Hz anechoic |
| Height Set By | Driver clearance: 0.76 in above the motor |
| Comparison, Standard Down Fire | 30 x 15 x 7.4375 in, 1.00 cu ft net |
| Woofer Opening | 236mm / 9.291 in, Hertz spec |
| Mounting Depth Required | 5.80 in, Hertz spec |
| Driver Overall Diameter | 268mm / 10.551 in, Hertz spec |
| Hertz Recommended Sealed Volume | 17 L |
| Driver Fs / Qts / Vas, D2.3 | 30 Hz / 0.54 / 25 L |
| Driver Fs / Qts / Vas, D4.3 | 27 Hz / 0.50 / 31 L |
| Driver Sd | 355 cm² |
| Driver Xmax | 17mm linear, 27mm mechanical |
| Driver Sensitivity | 83.4 dB (1W/1m) |
| Driver Power Handling | 600 W RMS / 1200 W peak |
| Driver Voice Coil | 65mm CCAW, 4-layer, vented TIL-P former |
| Driver Cone | V-cone profile, pressed paper pulp with mineral powder injection |
| Driver Surround | High-purity IIR butyl rubber |
| Voice Coil Configuration | Dual voice coil, impedance set at the driver |
| Driver Displacement | 3.2 L / 0.113 cu ft, published by Hertz |
| Material | Langboard Elite 3/4 in MDF |
| Construction | ShopSabre CNC cut, V-groove and dado joinery, windowed U-brace |
| Front Baffle | 1.5 in double baffle, outer layer machined as a flush recess |
| Corner Profile | Square, Down Fire series standard |
| Driver Mounting | 8/32 threaded inserts, stainless machine screws included |
| Terminal Cup | One Proline X ABS and carbon fiber composite, side mounted |
| Internal Wiring | 12 gauge OFC |
| Damping | Polyfill installed, light wall lining |
| Feet | 1.75 in, included, shipped uninstalled |
| Carpet | Plush black |
| Warranty | 1 Year Limited |
| Built In | Tullahoma, Tennessee |
01Is it a sealed driver?
Efficiency bandwidth product places the motor before anything else is decided.
02What the box does to it
1.063 cu ft against a 25.0 L Vas.
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 17.0 mm — and a bigger one once a subsonic filter stops it wasting travel below the passband.
| Param | Value | Unit | Note |
|---|---|---|---|
| Fs | 30.00 / 27.00 | Hz | free-air resonance |
| Qts | 0.540 / 0.500 | D2 / D4 | |
| Vas | 25.00 / 31.00 | L | equivalent compliance |
| Sd | 354.6 / 348.3 | cm² | effective piston area |
| Xmax | 17 | mm | one-way linear travel |
| Pe | 600 | W | continuous RMS |
| SPL | 82.4 | dB | 1 W / 1 m, derived from T/S |
Driver parameters as published by the Hertz Mille Pro pages at hertz-audio.com. Curves computed against this enclosure’s actual net airspace.
Built From a Spec Sheet, Not a Sales Sheet
Every Proline X Performance Series enclosure is CNC-cut from Langboard Elite MDF, 3/4" (18mm) panels produced to published mill specifications. Most enclosure manufacturers source generic MDF without published data. We can tell you the internal bond rating, the modulus of elasticity, the modulus of rupture, and the face and edge screw holding strength for every panel in this enclosure, because we chose the material based on those numbers, not on price or availability.
Langboard Elite is produced in the United States. The specifications below are pulled directly from Langboard's published mill data and are verifiable. This is the same panel stock used in our full Proline X lineup.
Langboard Elite MDF: Published Mill Data
| Property | Value | Why It Matters |
|---|---|---|
| Panel Stock | Langboard Elite MDF | Named, verifiable panel source, not generic "high-density MDF" |
| Thickness | 3/4" (18mm) | Industry standard for subwoofer enclosures; panels below this flex under pressure |
| Density | 48.5 lbs/ft³ | Higher density = less porosity, better screw retention, reduced resonance |
| Internal Bond | 200 psi | Measures resistance to delamination under sustained internal pressure. The most enclosure-relevant spec on this sheet |
| Modulus of Rupture (MOR) | 4,200 psi | Bending strength before the panel breaks, relevant for larger unsupported baffle spans |
| Modulus of Elasticity (MOE) | 410,000 psi | Stiffness under load; higher MOE means less panel flex under bass pressure, less resonance |
| Face Screw Holding | 325 lbs | How firmly the panel surface holds a screw; critical for baffle joint integrity over time |
| Edge Screw Holding | 250 lbs | Panel edge retention, relevant for every joint that isn't face-to-face |
200 psi: The Number That Actually Matters for Enclosures
The internal bond rating measures how well the MDF panel resists delamination under sustained pressure applied perpendicular to the face. In a subwoofer enclosure, every bass transient generates a pressure pulse that pushes outward on every panel simultaneously. A panel that begins to delaminate internally loses stiffness gradually. The symptoms are slow: a box that starts to sound softer, less defined, less punchy over months of use. 200 psi internal bond is the spec that determines how long this enclosure holds its acoustic integrity under daily use at real power levels.
410,000 psi MOE: Less Flex, Less Resonance
The modulus of elasticity measures panel stiffness, its resistance to bending under load. A stiffer panel flexes less under the pressure generated by a high-excursion driver at volume. Panel flex is a source of acoustic coloration: the panel itself begins to radiate sound at its own resonant frequency, adding distortion to the output. 410,000 psi stiffness combined with V-groove and dado joinery means the panels stay rigid and the bracing controls resonance at the structure level, not the panel level. The bass you hear comes from the driver, not the box.
325 lb Face / 250 lb Edge: Joints That Stay Locked
Screw holding strength determines how firmly the panel grips a fastener at the face and at the edge. This matters most at the baffle joint, where the front panel meets the side panels and where the driver is mounted. A panel with low screw holding strength allows fasteners to loosen over time under vibration, leading to air gaps at the joint and loss of acoustic seal. 325 lb face screw holding strength means the baffle hardware stays put. Combined with dado joinery and adhesive, the front panel on a Proline X Performance Series enclosure is not going anywhere.
Named Panel Stock: Not "Premium MDF"
The phrase "premium MDF" or "high-density MDF" appears on marketing copy for enclosures across every price point, from $40 to $400. It is not a specification. It is a description with no defined standard. Langboard Elite is a named, sourced, mill-documented product with published data. We name it in our copy because naming it holds us accountable to the spec. You can look up Langboard Elite independently, verify the numbers on this page, and confirm you are getting what we say you are getting. That is the point.
Why Proline X?
Most enclosures are built to a price point. Proline X is built to a spec. Every box starts with published-data MDF, gets CNC-cut to exact internal volume, and is assembled by hand in our Tennessee facility. The difference shows up in the measurements, and in how the box holds up two years into daily use.
CNC-Cut to Spec
Panels are machine-cut on ShopSabre CNC routers and joined with V-groove and dado joinery. Consistent geometry, no hand-cut variance, no gaps at the joints.
Handcrafted in USA
Hand-assembled at our facility in Tullahoma, TN. Every enclosure is inspected before it ships.
Tuned to the Build
Internal volume and port geometry are calculated to spec and CNC-cut to exact dimensions. The box performs the same way every time.
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