Proline X
Helix IQ W12 Dual Box: Sealed 12" Down Fire Enclosure
SKU: PO 12D-S DF IQW12 TM0
- Best For: Dual Helix IQ W12 Floor-Firing Builds
- Net Volume: 1.17 to 1.66 cu ft per driver by Tuning Mass setting
- Alignment: Qtc 0.689 to 0.700, fc 42.3 to 51.7 Hz, F3 42.7 to 53.1 Hz anechoic
- Tuning Mass: 2 settings offered, cut and built to order
- Driver Match: Pair of Helix IQ W12 (matched), DVC2
- Impedance: 2 ohms with each driver in series, pair in parallel
- Construction: Dual Chamber | Down-Firing Sealed | V-Groove/Dado | Double 1.5" Baffle | Threaded Inserts | Feet Included
Financing available. Choose Shop Pay Installments at checkout.
Helix IQ W12 Dual Box: Sealed 12" Down Fire Enclosure
Performance Optimized Down Fire | Helix IQ W12
Dual 12" Sealed Down Fire Enclosure | 2 Tuning Mass Sizes | Cut and Built to Order
Two Helix IQ W12 in a Sealed Down Fire
Helix's IQ W12: a 515 square centimeter cone on a 63 mm dual 2 ohm coil, 750 watts RMS and 12 mm of one-way travel, and the widest Tuning Mass span in the line, 33 litres at the base setting to 115 at plus three. The alignment below is computed from Helix's published Thiele-Small parameters, one set per Tuning Mass setting.
The IQ series carries Helix's Tuning Mass System: bolt-on weights that thread onto the cone assembly and let one driver run several alignments. Each weight raises moving mass, which drops free-air resonance and raises the driver's total Q, and Helix publishes a different recommended sealed volume for every setting to keep the system in hand. This cabinet is offered in no added mass and +1 mass ring, 33 to 47 litres of Helix's own recommended volume, and across those the system Q works out at 0.69 at the base setting and 0.70 at the top of the range offered. What does not change is compliance, and therefore Vas, because mass and spring rate are independent.
Two Cabinets, One Listing
Every one of these is cut and built to order. Nothing is pre-cut and nothing sits on a shelf waiting for a Tuning Mass setting to be chosen, because each setting is a different cabinet rather than a label on one. Pick the setting you intend to run and the panels are cut to it.
| Tuning Mass | Helix volume | Net built | External | Qtc | fc | F3 anechoic | Helix F3 |
|---|---|---|---|---|---|---|---|
| No Added Mass | 33 L | 1.17 cu ft per driver | 30.00" W x 15" D x 14.17" H | 0.689 | 51.7 Hz | 53.1 Hz | 53 Hz |
| +1 Mass Ring | 47 L | 1.66 cu ft per driver | 30.00" W x 15" D x 18.90" H | 0.700 | 42.3 Hz | 42.7 Hz | 44 Hz |
Choose the setting on this page and the cabinet is cut to it. Pricing follows the cabinet, so the settings are not all the same price.
The IQ W12 ships with three weights. The top setting, all three fitted, is not offered as a listed size here; call or text 931-563-5151 if that is the alignment you want and we will quote the cabinet for it.
Two Fully Separate Chambers
A full bonded 3/4 inch MDF divider gives each IQ W12 its own sealed chamber and its own polyfill, 1.28 to 1.79 cu ft gross each depending on the Tuning Mass setting. Two drivers sharing one volume interact acoustically, each cone's compression stroke becoming the pressure the other works against. A divider removes that entirely.
Why One Setting Is Missing
The plus 2 setting is not offered in this chassis, because the air will not fit inside dimensions we are willing to ship. Plus 2 asks for 65 litres, which would need 25.0 inches of down-fire height, or 23.0 on the wide floor, and is available as a single wedge, a single down fire or a dual wedge. The settings in the table above are unaffected.
Why Down Fire
A down fire cabinet sits flat on the trunk or cargo floor with the cones facing down, which keeps the top surface usable and puts the enclosure where a wedge cannot go. It is the answer when there is no rear seat back to lean against, when the load floor has to stay flat, or when the build is a truck rather than a sedan trunk.
Cones Fire Downward
The floor becomes the first reflecting surface, which loads the cabin evenly rather than aiming at one seat.
Feet Ship Uninstalled
Mount them to suit your floor, or leave them off and run the cabinet front firing.
Flat Top, Usable Space
A rectangular footprint, 30.00 inches wide by 15 deep, stacks and straps in a way a wedge cannot.
Flush Recess Baffle
The outer 3/4 inch layer is machined as a recess so the driver bolts to the inner layer, recovering 3/4 inch of internal clearance.
Engineered for the Helix IQ W12
Across the settings offered here the Helix IQ W12 runs a system Qtc of 0.689 to 0.700 with resonance from 42.3 to 51.7 Hz, on 1.17 to 1.66 cubic feet net per driver. Every figure is Helix's own recommended sealed volume for that setting unless the table marks otherwise.
On The F3 Figures
Helix prints a lower limiting frequency for every Tuning Mass setting, and ours agree with theirs to within 1.3 Hz at every setting offered here. That is worth stating because it is not true of every Helix line. The IK datasheets quote their figure with a recommended DSP highpass applied and read several hertz optimistic against the raw sealed response; the IQ sheets carry no filter recommendation and their numbers reconcile with the anechoic math. Both F3 columns in the table above are anechoic and exclude cabin gain.
Mounting Geometry
Both positions are CNC cut to 11.0600 in and identical at every setting, because the Tuning Mass weights change the cone assembly rather than the frame. The IQ W12 needs 5.70 in of mounting depth and every cabinet here clears it. Threaded inserts pressed into the baffle backside at every mounting location.
Performance Series Construction, Driver-Specific Tuning
Langboard Elite MDF
Premium 3/4 in MDF throughout.
V-Groove and Dado Joinery
CNC cut V-grooves at every panel intersection, sides and divider seated in dados.
Double-Layer 1.5" Baffle
Two bonded 3/4 in MDF sheets at the driver face.
Pre-Wired Terminal Cup
Proline X ABS and carbon fiber composite, 12 gauge OFC pre-wired to both driver positions.
Wiring the Pair to Your Amplifier
The IQ series ships in one coil version, the DVC2: two 2 ohm coils per driver. Across a pair the sensible target is 2 ohms, reached by wiring each driver's coils in series for 4 ohms and then the two drivers in parallel. Both drivers must be wired identically, and any route to 1 ohm needs an amplifier rated for it.
Power handling is 1500 watts RMS total across the pair and does not change with the Tuning Mass setting. Aim for roughly 1050 to 1500 watts at the impedance you wire to.
Built in Tennessee, Backed by Audio Intensity
Cut and assembled to order in Tullahoma, Tennessee on our own CNC equipment. Finished in plush black carpet. 1 year limited warranty. Enclosure only: the drivers and the Tuning Mass weights that come with them are purchased separately. Call or text 931-563-5151.
Helix IQ W12 Dual: One Driver, Two Alignments
1.17 to 1.66 cubic feet net per driver at Qtc 0.689 to 0.700, F3 42.7 to 53.1 Hz anechoic, cut to your chosen Tuning Mass setting and built to order in Tennessee.
| Specification | Value |
|---|---|
| Series | Proline X Performance Optimized Down Fire |
| Compatible Driver | Helix IQ W12 DVC2, quantity 2. Direct fit |
| Configuration | Dual 12 inch, dual chamber sealed down fire |
| Tuning Mass Settings Offered | No Added Mass, +1 Mass Ring. Each is a different cabinet, cut to order |
| Build | Cut and built to order. Nothing is pre-cut |
| Mounting Position | Trunk or cargo floor, cone firing downward |
| Firing Direction | Downward into the floor. Feet included, uninstalled |
| External Width | 30.00 in across the settings |
| External Height | 14.17 to 18.90 in measured in the down fire position |
| External Depth | 15 in at every setting |
| Internal Volume, Gross | 1.28 to 1.79 cu ft per chamber, by setting |
| Internal Volume, Net Acoustic | 1.17 to 1.66 cu ft per driver, by setting |
| Alignment | Qtc 0.689 to 0.700, fc 42.3 to 51.7 Hz, F3 42.7 to 53.1 Hz anechoic, by setting |
| Helix Recommended Volume | 33 to 47 litres net across the settings offered |
| Driver Cutout | 11.0600 in, same at every setting |
| Driver Mounting Depth | 5.70 in required by the driver |
| Power Handling | 1500 watts RMS total across the pair |
| Impedance | DVC2, dual 2 ohm: 1 ohm parallel or 4 ohm series per driver |
| Floor Slot Ratio | 0.76 at the standard 1.75 in standoff |
| Feet | Included, uninstalled |
| Xmax | 12 mm one way |
| Material | Langboard Elite MDF |
| Construction | CNC cut, V-groove and dado joinery |
| Panel Thickness | 0.75 in |
| Front Baffle | 1.5 in, double baffle |
| Internal Bracing | Full chamber divider |
| Driver Mounting | Threaded inserts at every mounting location, stainless machine screws included |
| Terminal Cups | One Proline X ABS and carbon fiber composite, side mounted, pre wired 12 gauge OFC |
| Damping | Light polyfill wall lining, does not alter acoustic volume |
| Carpet | Plush black |
| Weight | 51.7 to 61.1 lb depending on setting |
| 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
1.17–1.66 cu ft against a 35.0 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 12.0 mm — and a bigger one once a subsonic filter stops it wasting travel below the passband.
| Param | Value | Unit | Note |
|---|---|---|---|
| Fs | 36.00 / 32.00 | Hz | free-air resonance |
| Qts | 0.480 / 0.530 | 0 TM / +1 TM | |
| Vas | 35.00 / 35.00 | L | equivalent compliance |
| Sd | 515.0 | cm² | effective piston area |
| Xmax | 12 | mm | one-way linear travel |
| Pe | 750 | W | continuous RMS |
| SPL | 86.7 | dB | 1 W / 1 m, derived from T/S |
Driver parameters as published by audiotec-fischer.de and the HELIX IQ datasheet. 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.
Shop By Series
