Proline X
Performance Optimized Down Fire Sealed 12" Enclosure | Hertz Mille Pro MPS 300
SKU: PO 12-S DF MPS
- Alignment: 0.80 cu ft net - Hertz's own spec. Qtc 1.003 / F3 37.1 Hz (S2), Qtc 0.812 / F3 39.5 Hz (S4)
- Driver: Hertz MPS 300 S2 (2Ω) or S4 (4Ω) SVC, 500W RMS / 1000W peak, 16.8mm Xmax, 3.46" mounting depth
- Build: Proline X V-groove and dado joinery, double-layer 1.5" front baffle, perimeter cross-brace, 12g OFC side-mounted terminal cup
- Cabinet: 30"W x 15"D x 6.375"H measured in down fire position, square corners
Financing available — choose Shop Pay Installments at checkout.
Performance Optimized Down Fire Sealed 12" Enclosure | Hertz Mille Pro MPS 300
The Performance Optimized Down Fire Sealed 12" Enclosure for the Hertz Mille Pro MPS 300 puts a full 12 into a cabinet 6.375 inches tall on a 30 by 15 inch footprint, built around a driver that mounts in 3.46 inches.
The Hertz MPS 300 is available as the MPS 300 S2 (2Ω) or MPS 300 S4 (4Ω), both rated 500 watts RMS and 1000 watts peak. Like the 10 inch model it carries 16.8mm of Xmax, an unusually high figure for a shallow driver. Polypropylene cone, 38mm voice coil, high density flux ferrite motor, mesh grille included that can be rotated 90 degrees or removed.
The 0.80 cubic foot net volume matches Hertz's own sealed recommendation of 22.7 liters, producing Qtc 1.003 with F3 at 37.1 Hz on the S2, and Qtc 0.812 with F3 at 39.5 Hz on the S4.
Pay attention to the coil choice, because it reverses from the 10 inch model. On the MPS 300 the S4 is the better damped driver with a Qts of 0.42 against the S2's 0.51. On the MPS 250 it is the opposite, with the S2 tighter. If you have read the specifications on our 10 inch MPS enclosure, do not carry the assumption across.
The practical read: the S4 gives the more controlled alignment at Qtc 0.812, the S2 reaches about 2.4 Hz lower at Qtc 1.003 with a modest lift at the corner. Both are usable. The S2's 37.1 Hz F3 is among the deepest in the Proline X Down Fire line, and it comes from a 24 Hz free-air resonance paired with a 64.9 liter Vas.
Hertz publishes Thiele-Small measured with the coils in parallel and states that Fs, Vas and Qts are identical in series wiring, with only Re, Le and BL changing. One cabinet is correct for either configuration.
Worth saying plainly: Hertz's published enclosure data reconciles with their own T/S parameters. Running their Qts and Vas through standard sealed box math at their recommended volume lands within 0.2 Hz of their stated Fc on both variants. That is not true of every manufacturer in this category.
Firing down into the floor, the sealed rolloff meets rising cabin gain below 60 Hz. Hertz suggests a 15 Hz subsonic filter at 24 dB per octave and a 70 to 80 Hz low pass for sealed applications.
Construction is the full Proline X Performance Optimized platform: ShopSabre CNC-cut Langboard Elite MDF with V-groove and dado joinery, perimeter cross-bracing, and a double-layer 1.5 inch front baffle (two 3/4 inch sheets bonded) for maximum baffle rigidity and driver isolation. Corners are square on Down Fire cabinets. The driver fires down into the floor with the terminal cup side mounted, keeping the connection accessible with the cabinet in place. Terminal cup is our Proline X ABS/carbon fiber composite pre-wired with 12 gauge OFC.
Bring your own MPS 300 S2 or MPS 300 S4. Both are single voice coil, so your final impedance is set by which model you buy.
Manufactured in Tullahoma, Tennessee. 1-year enclosure warranty.
| Enclosure Type | Sealed | Down Fire Geometry | Floor-Coupled |
| Driver-Specific Fitment | Hertz MPS 300 S2 (2Ω SVC) or MPS 300 S4 (4Ω SVC) |
| Internal Volume (Gross) | 0.89 Cubic Feet |
| Internal Volume (Net) | 0.80 Cubic Feet - Matches Hertz Spec of 22.7 Liters |
| Target System Qtc (MPS 300 S2) | 1.003 |
| Target System Qtc (MPS 300 S4) | 0.812 |
| Predicted F3 (MPS 300 S2) | 37.1 Hz |
| Predicted F3 (MPS 300 S4) | 39.5 Hz |
| Driver Fs | 24 Hz (S2) / 23 Hz (S4) |
| Driver Qts | 0.51 (S2) / 0.42 (S4) - S4 Is The Better Damped On This Size |
| Driver Qes / Qms | 0.55 / 7.5 (S2) | 0.45 / 6.3 (S4) |
| Driver Vas | 64.9 Liters (S2) / 62.1 Liters (S4) |
| Driver BL | 12.3 T·m (S2) / 18.7 T·m (S4) |
| Driver Mms | 295 g (S2) / 320 g (S4) |
| Driver Cms | 0.16 mm/N (S2) / 0.15 mm/N (S4) |
| Driver Xmax | 16.8mm |
| Driver Sensitivity | 84.5 dB (S2) / 85 dB (S4) |
| Driver Power Handling | 500 Watts RMS / 1000 Watts Peak |
| Driver Voice Coil | 38mm | Single Voice Coil |
| Driver Motor | High Density Flux Ferrite |
| Mounting Depth Required | 3.46 Inches (Hertz Spec) |
| Cutout Diameter | 283mm / 11.14 Inches (Hertz Spec) |
| Suggested Filters | 15 Hz Subsonic at 24 dB/Oct | 70-80 Hz Low Pass at 24 dB/Oct (Hertz) |
| Baffle Configuration | Down Firing - Driver Fires Toward Floor |
| Material | Langboard Elite 3/4" MDF |
| Front Baffle Construction | Double-Layer 1.5" MDF (Two 3/4" Sheets Bonded) |
| Joinery | V-Groove and Dado (CNC-Cut) |
| Corner Profile | Square (Down Fire Series Standard) |
| Construction | ShopSabre CNC / Perimeter Cross-Brace |
| External Width | 30 Inches |
| External Depth | 15 Inches |
| External Height | 6.375 Inches |
| Dimension Reference | All External Dimensions Measured In Down Fire Position |
| Voice Coil Configuration | Single Voice Coil - Impedance Set By Driver Model |
| Mounting Hardware | 8/32 Threaded Inserts | Stainless Steel Machine Screws Included |
| Terminal Cup | Proline X ABS/Carbon Fiber Composite | Side Mounted | 12g OFC Pre-Wired |
| Damping | Polyfill Pre-Installed |
| Carpet Finish | Dark Gray Trunkliner (Standard) or Plush Black (+$10) |
| Bundle Options | Enclosure Only (Bring Your Own MPS 300 S2 or S4) |
| Warranty | 1-Year Limited (Enclosure) |
| Manufactured | Tullahoma, Tennessee, USA |
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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