Proline X
Helix IK S8 Dual Box: Sealed 8" Shallow Down Fire Enclosure
SKU: PO 8D-S DF IKS8
- Best For: Dual Helix IK S8 Floor-Firing Builds
- Net Volume: 0.35 cu ft per driver (0.39 cu ft Gross per chamber)
- Alignment: Qtc 0.725 to 0.739, fc 62.3 Hz, F3 59.7 to 60.8 Hz anechoic
- Driver Match: Pair of Helix IK S8 (matched), SVC2 or DVC2
- Impedance: 1 or 4 ohm with SVC2; 2 ohm with DVC2
- 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 IK S8 Dual Box: Sealed 8" Shallow Down Fire Enclosure
Performance Optimized Down Fire | Helix IK S8
Dual 8" Sealed Down Fire Enclosure | Floor-Firing Trunk or Cargo Design
Two Helix IK S8 in a Sealed Down Fire
Helix's IK S8, the shallow eight: a 222 square centimeter cone with 6 mm of one-way travel in a 3.13 inch mounting depth, against 3.98 for the IK W8. The alignment below is computed from Helix's published Thiele-Small parameters.
Helix measures the SVC2 and the DVC2 separately rather than publishing one set of parameters for both, but on this model they land on the same recommended volume, 10 litres. That is what this cabinet is cut to, giving Qtc 0.725 with the SVC2 and 0.739 with the DVC2.
Two Fully Separate Chambers
A full bonded 3/4 inch MDF divider gives each IK S8 its own sealed 0.39 cu ft gross chamber and its own polyfill. 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 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 30.00 by 15 inch footprint 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 IK S8
At 0.35 cubic feet net per driver the Helix IK S8 runs a system Qtc of 0.725 to 0.739 with resonance at 62.3 Hz. That is Helix's own recommended sealed volume for this driver, 10 litres, and it is a net figure in their documentation exactly as it is in ours.
Alignment Numbers
Qtc 0.725 to 0.739 · fc 62.3 Hz · F3 59.7 to 60.8 Hz anechoic
On That F3 Figure
Half power lands at 59.7 to 60.8 Hz anechoic, before any cabin gain. Helix's own datasheet prints 46 Hz for this driver, which is a different measurement rather than a disagreement: their figure is quoted with their recommended 46 Hz, Q 1.5 highpass applied, and a filter at that corner lifts the response enough to move the half-power point down to meet it. The number above is the raw sealed response of this cabinet.
Mounting Geometry
Both positions are CNC cut to 7.1000 in. The IK S8 needs 3.13 in of mounting depth and this cabinet 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 IK W series comes in two coil versions and a pair wires differently in each. Two SVC2 drivers, each a single 2 ohm coil, give 1 ohm in parallel or 4 ohms in series. Two DVC2 drivers give more choices; the sensible target is 2 ohms, reached by wiring each driver's coils in series for 4 ohms and then the pair in parallel. Every driver in the cabinet must be wired identically, and 1 ohm needs an amplifier rated for it.
Power handling is 600 watts RMS total across the pair. Aim for roughly 420 to 600 watts at the impedance you wire to.
Built in Tennessee, Backed by Audio Intensity
Cut and assembled in Tullahoma, Tennessee on our own CNC equipment. Finished in plush black carpet. 1 year limited warranty. Enclosure only, the drivers are purchased separately. Call or text 931-563-5151.
Helix IK S8 Dual: Built to Helix's Own Volume
0.35 cubic feet net per driver at Qtc 0.725 to 0.739, F3 59.7 to 60.8 Hz anechoic, cut direct fit and built to order in Tennessee.
| Specification | Value |
|---|---|
| Series | Proline X Performance Optimized Down Fire |
| Compatible Driver | Helix IK S8 SVC2 or DVC2, quantity 2. Direct fit |
| Configuration | Dual 8 inch, dual chamber sealed down fire |
| Mounting Position | Trunk or cargo floor, cone firing downward |
| Firing Direction | Downward into the floor. Feet included, uninstalled |
| External Width | 30.00 in |
| External Height | 5.92 in measured in the down fire position |
| External Depth | 15 in |
| Internal Volume, Gross | 0.79 cu ft total, 0.39 per chamber |
| Internal Volume, Net Acoustic | 0.71 cu ft total, 0.35 per driver |
| Alignment | Qtc 0.725 to 0.739, fc 62.3 Hz, F3 59.7 to 60.8 Hz anechoic |
| Helix Recommended Volume | 10 litres net, which is what this is built to |
| Driver Cutout | 7.1000 in |
| Driver Mounting Depth | 3.13 in required by the driver |
| Power Handling | 600 watts RMS total across the pair |
| Floor Slot Ratio | 1.13 at the standard 1.75 in standoff |
| Feet | Included, uninstalled |
| Impedance | SVC2 is a single 2 ohm coil; DVC2 is dual 2 ohm, 1 ohm parallel or 4 ohm series |
| Xmax | 8 mm one way, both coil versions |
| 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 | 32.7 lb |
| 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
0.35 cu ft against an 11.0 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 6.0 mm — and a bigger one once a subsonic filter stops it wasting travel below the passband.
| Param | Value | Unit | Note |
|---|---|---|---|
| Fs | 43.00 | Hz | free-air resonance |
| Qts | 0.500 / 0.510 | SVC2 / DVC2 | |
| Vas | 11.00 / 11.00 | L | equivalent compliance |
| Sd | 222.0 | cm² | effective piston area |
| Xmax | 6 | mm | one-way linear travel |
| Pe | 300 | W | continuous RMS |
| SPL | 84.0 | dB | 1 W / 1 m, derived from T/S |
Driver parameters as published by audiotec-fischer.de and the HELIX 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.
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