Ported, Fires Into the Floor

Ported Down Fire Subwoofer Boxes

Down-fire cabinets with an L-wrap slot port folded inside, tuned to the driver and stated on every listing. 8 to 13 inch, CNC-cut in Tullahoma.

Proline X ported down-fire subwoofer enclosure with the slot port exiting the side

Ported, Fires Into the Floor

A ported down-fire enclosure mounts the driver on the bottom baffle so the cone faces the vehicle floor, and folds a slot port inside the cabinet so the box gives more output around its tuning frequency than the same driver sealed. The floor becomes part of the load, the cone sits protected, and the port does the work a bigger amplifier would otherwise do.

Every cabinet here is cut to one driver's published parameters and states its own tuning frequency. CNC-cut in Tullahoma, Tennessee from Langboard Elite MDF on our own ShopSabre routers. We run the machines.

Ported down-fire cabinets in stock today | 8, 10, 12 and 13 inch | single driver, one common chamber | tuning stated per cabinet | cut to the driver you own

Cut, assembled, carpeted and shipped from our own shop in Tullahoma, Tennessee. Stock counts on every card are shelf counts. One year limited warranty on Performance Optimized, from the original date of purchase.

Specified and written by Scott Welch, IASCA National and MECA World Champion, who runs the CNCs these are cut on. Figures come from our own build sheets and the driver manufacturers' published parameters.

Decision Shortcut

Find Your Match

Curated picks matched to common build goals

Best Flat Response

Proline X PO 10-P DF BLACK ported down fire enclosure, front panel on 1.75 inch feet, 31 by 7.75 inches.

Proline X

Performance Optimized Down Fire Ported 10" Enclosure | Arc Audio Black Series 10

Arc Audio Black Series 10. 0.36 dB of passband ripple, the flattest cabinet in the ported down-fire line.

$ 299.99

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Best for Shallow Depth

Proline X PO 12-P DF THINPRO ported down fire enclosure, front panel on 1.75 inch feet, 31 by 7.75 inches.

Proline X

Performance Optimized Down Fire Ported 12" Enclosure | Wavtech thinPRO12

Wavtech thinPRO12. Three inches of mounting depth, 750 W RMS and 20 mm of travel in a ported twelve nothing else here fits where this fits.

$ 329.99

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Best High-Output

Proline X PO 12-P DF T1 ported down fire enclosure, front panel on 1.75 inch feet, 31 by 7.75 inches.

Proline X

Performance Optimized Down Fire Ported 12" Enclosure | Rockford Fosgate T1D412

Rockford Fosgate T1D412. 800 W RMS and 16 mm of one-way travel, the most driver we build a ported cabinet for.

$ 329.99

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Best 8 Inch

Proline X PO 8-P DF IDv4 ported down fire enclosure, front panel on 1.75 inch feet, 31 by 7.75 inches.

Proline X

Performance Optimized Down Fire Ported 8" Enclosure | Image Dynamics ID8 V4

Image Dynamics ID8 V4. A 31 Hz free-air resonance on an eight is what earns the port; 13 inches deep at the lowest price in the line.

$ 269.99

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Ported or Sealed Down-Fire

Same orientation, same feet, same floor loading. The alignment changes the cabinet, the driver count and what you have to do at the amplifier, and this is the comparison that decides between the two pages.

Sealed and ported Performance Optimized down-fire cabinets as built, 4 September 2026.
Sealed down-firePorted down-fire
ChambersOne per driver, volume quoted per chamberOne common chamber, volume quoted for the box
Footprint30 inches wide, 15 deep, fixed31 inches wide, depth set by the driver
Height on feetSet by the driver, feet add 1.75 inches7.75 inches, 9.50 on the feet
PolyfillInstalled on every buildNone. Ships dry so the tuning holds
Tuning statedNo, a sealed box has noneYes, on every listing
Driver countSingle, dual and tripleSingle
Subsonic filterAn improvementA requirement, set just under tuning
Pick it whenHeight or depth is the limit, or you want a dualThe floor has the room and output per watt matters

Shared across both: Langboard Elite MDF at 48.5 lbs per cubic foot, 200 psi internal bond and 410,000 psi MOE, cut on ShopSabre routers in Tullahoma. V-groove and dado joinery, a double 1.5 inch baffle, plush black carpet, ABS feet, and a Proline X ABS and carbon fibre composite terminal cup with stainless hardware, pre-wired in 12-gauge OFC.

The Port Is Folded Into the Box

A down-fire cabinet has no spare face for a port. The baffle points at the floor and the top is where the cargo goes, so the port on these is an L-wrap slot formed by one folded wall: a leg down the long side of the cabinet past the woofer ring, one faceted 90 degree bend, and a leg across the end that exits through the side. One wall and one bend rather than a serpentine's three means less wall area inside the box, fewer joints to leak, and one place for the flow to separate instead of three.

Port area is sized against the driver's excursion and power, and air speed in the channel is held under 17 meters per second at tuning so it does not chuff at full stroke. Change the port and you have a different enclosure, which is why the listing states the tuning and why we do not recommend retuning one.

Tuning is chosen for the car, not for an anechoic chart. A vehicle adds roughly 12 dB per octave below about 45 Hz, so a box tuned very low reinforces a region the cabin already reinforces and leaves 40 to 60 Hz thin. These sit in the low to mid thirties, close to each driver's own resonance, so the cone is barely moving where the port is working hardest.

How to Choose a Ported Down-Fire Enclosure

Start from the driver

Every cabinet is cut to one driver's published parameters. Pick the driver first and the enclosure follows. The brand filter shows every driver line we cut this shape for, and the card says whether we sell the driver too.

Read the tuning, not just the volume

Two cabinets of the same net volume tuned five hertz apart are different products. The tuning frequency tells you how the box will sound in the car; the volume only tells you how big it is.

Ported or sealed

Sealed is the shorter cabinet, takes duals and triples, and forgives a wrong-sized car. Ported gives more output around its tuning for the same power from a deeper single-driver box, and asks for a subsonic filter. If height or depth is the limit, the sealed down-fire build for your driver usually wins. If the cargo floor has the room and output per watt matters, this is the page.

Check the depth the driver needs

The depth on each listing is the number that clears the motor past the port wall. A shallow-mount driver gets a shallower cabinet, which is why the same size can differ by several inches from one card to the next.

Do not add polyfill

Every sealed cabinet we build ships with polyfill. These ship dry on purpose: damping material changes the volume the port is tuned against, so stuffing a ported box moves the tuning without shortening the port.

Floor Space, Clearance and Depth

Four things decide whether a ported down-fire box works in your vehicle.

Width and depth on the floor

Every cabinet is 31 inches wide. Depth is set by the driver, from the shallowest eights to the deepest twelves, and the listing states it. Measure the floor where the box will sit, not at the hatch opening, because wheel wells and seat brackets narrow the space toward the back.

Height on its feet

The cabinet is 7.75 inches tall and 9.50 inches installed, because the feet hold the port wall and the cone 1.75 inches off the carpet. Under a fold-flat seat, measure with the seat at its lowest position, not its highest.

A flat, solid floor

The floor is part of the load. A ribbed plastic cargo tray or a spare-wheel lid flexes under a loaded cabinet and rattles, and gives you none of the boundary loading the orientation was chosen for. Put it on the floor pan or a solid false floor.

A subsonic filter on the amplifier

Below its tuning a ported box stops loading the cone and excursion runs away. Set the amplifier's subsonic filter just under the tuning frequency on the listing. On a sealed build the same filter is an improvement; on a ported one it is a requirement.

One Series, One Chassis, Four Sizes

Every cabinet here is a Performance Optimized build on one chassis: 31 inches wide, 7.75 inches tall and 9.50 on its feet, with the depth solved per driver so the motor clears the port wall. Sizes run 8, 10, 12 and 13 inch, and every one is a single driver in one common chamber. Duals stay sealed, because two drivers sharing one tuned volume is a different design problem.

Each size sits at a fixed price. What changes from card to card is the driver, the depth and the tuning frequency, and those three numbers are the whole decision.

The tight-space build

8 inch, one common chamber

Single, ported·$269.99

The shallowest cabinets in the line, cut for eights whose free-air resonance is low enough to earn a port. A box the depth of a ten that plays lower than an eight has any right to.

1 year limited warranty

The widest driver choice

10 inch, one common chamber

Single, ported·$299.99

Where most of the line sits. Ten inch drivers from every brand we cut for, each with its own tuning and its own depth.

1 year limited warranty

The output end

12 inch, one common chamber

Single, ported·$329.99

The heaviest motors and the highest power ratings in the range. Depth runs to the top of the chassis to clear them.

1 year limited warranty

The odd size

13 inch, one common chamber

Single, ported·$349.99

Cut for the JL Audio 13TW5v2, the one thirteen inch driver we build a ported down-fire cabinet for.

1 year limited warranty

Prices are the fixed tier for each size. Every card is the same series, Performance Optimized, cut to one driver on one chassis; the driver, the depth and the tuning are what change.

Categories

Keep Reading

Supporting guides to help you design, build, and tune your system.

Ported Down-Fire Box Questions

What is a ported down-fire subwoofer box?

An enclosure that mounts the driver on the bottom baffle so the cone fires into the vehicle floor, with a tuned slot port built into the cabinet. The floor loads the cone and protects it from cargo, and the port adds output around its tuning frequency that a sealed box of the same driver cannot reach. Feet hold the cabinet 1.75 inches off the floor.

Where is the port on a down-fire box?

Folded inside the cabinet. It is an L-wrap slot formed by one wall: a leg down the long side past the woofer ring, one faceted 90 degree bend, and a leg across the end that exits through the side of the box. Each port is sized to its driver, and the air speed is held under 17 meters per second at tuning so it does not chuff.

What tuning frequency are these boxes?

Each listing states its own, and they sit in the low to mid thirties. That is deliberate. A vehicle adds roughly 12 dB per octave below about 45 Hz, so tuning very low doubles up on what the cabin already does and leaves 40 to 60 Hz thin. Tuning near the driver's own resonance keeps the cone quiet where the port is doing the work.

Do these ship with polyfill?

No, and do not add any. Every sealed cabinet we build ships with polyfill, but damping material changes the volume a port is tuned against. Stuff a ported box and you move the tuning without shortening the port, which gives you a mistuned enclosure rather than a bigger-sounding one.

Do you make a dual ported down-fire box?

Not in this line. Every ported down-fire cabinet is a single driver in one common chamber. Two drivers sharing one tuned volume is a different design problem, so the duals and the triple in our down-fire range are sealed builds, each with its own chamber per driver.

Do I need a subsonic filter?

Yes. Below its tuning frequency a ported box stops loading the cone and excursion runs away toward the driver's limits. Set the amplifier's subsonic filter just under the tuning stated on the listing. On a sealed build the same filter is an improvement; on a ported one it is a requirement.

Drivers Built to Match

8 Inch Subwoofers Spec'd for These Ported Boxes

The drivers below are matched to the enclosures above by Thiele-Small parameters. Buying together guarantees the alignment, port tuning, and damping work the way the engineering intended.

Image Dynamics ID8 V4 8inch Subwoofer

Image Dynamics

Image Dynamics ID8 V4 8inch Subwoofer

$ 99.99
Prodigy Audio 8 inch Subwoofer NB2 Series - Prodigy Subwoofer for car audio systems

Prodigy Audio

Prodigy Audio 8 inch Subwoofer | NB2 Series

$ 108.99 $ 115.99
Image Dynamics IDQ8 V4 8inch Subwoofer

Image Dynamics

Image Dynamics IDQ8 V4 8 inch Subwoofer

$ 193.99
Arc Audio Arc Series 8 inch Subwoofer

Arc Audio

Arc Audio Arc Series 8 inch Subwoofer

$ 239.00

View all 8 inch subwoofers | Need a custom build? Contact us

Drivers Built to Match

10 Inch Subwoofers Spec'd for These Ported Boxes

The drivers below are matched to the enclosures above by Thiele-Small parameters. Buying together guarantees the alignment, port tuning, and damping work the way the engineering intended.

Prodigy Audio 10 inch Subwoofer NB2 Series - Prodigy Subwoofer for car audio systems

Prodigy Audio

Prodigy Audio 10 inch Subwoofer | NB2 Series

$ 138.99 $ 145.99
Image Dynamics ID10 V4 10-inch Subwoofer

Image Dynamics

Image Dynamics ID10 V4 10-inch Subwoofer

$ 139.99
Prodigy Audio 10 inch Subwoofer NB3 Series - Prodigy Subwoofer for car audio systems

Prodigy Audio

Prodigy Audio 10 inch Subwoofer | NB3 Series

$ 148.99 $ 165.99
Sony XS - W104ES Mobile ES Series 10-inch 4 - ohm component subwoofer

Sony

Sony XS-W104ES Mobile ES Series 10" 4-ohm component subwoofer

$ 198.00 $ 299.99

View all 10 inch subwoofers | Need a custom build? Contact us

Drivers Built to Match

12 Inch Subwoofers Spec'd for These Ported Boxes

The drivers below are matched to the enclosures above by Thiele-Small parameters. Buying together guarantees the alignment, port tuning, and damping work the way the engineering intended.

Prodigy Audio 12 inch Subwoofer NB2 Series - Prodigy Subwoofer for car audio systems

Prodigy Audio

Prodigy Audio 12 inch Subwoofer | NB2 Series

$ 150.99 $ 161.99
Image Dynamics ID12 V4 12 inch Subwoofer

Image Dynamics

Image Dynamics ID12 V4 12 inch Subwoofer

$ 159.99
Arc Audio X2V2 12-inch Subwoofer

Arc Audio

Arc Audio X2V2 12" Subwoofer

$ 229.00
Image Dynamics IDQ12 V4 12 inch Subwoofer

Image Dynamics

Image Dynamics IDQ12 V4 12 inch Subwoofer

$ 280.99

View all 12 inch subwoofers | Need a custom build? Contact us

Amplifiers for the System

Power for Your Subwoofer System

Monoblock amplifiers matched to the power requirements of the drivers these enclosures are built for. Buy the enclosure, match the driver, pick the right amplifier.

Rainbow Audio SL - M2 2 channel micro amplifier

Rainbow

Rainbow Audio SL-M2 2 channel micro amplifier

$ 89.99 $ 549.99
Rainbow Audio Dream 0.5K Mono Class D Amplifier

Rainbow

Rainbow Audio Dream 0.5K Mono Class D Amplifier

$ 89.99 $ 399.99
US Acoustics Lisa 4 Channel Class AB Amplifier 4 x 50w US Acoustics

US Acoustics

US Acoustics Lisa | 4 Channel Class AB Amplifier | 4 x 50w

$ 159.99
US Acoustics Wendy 2 Channel Class AB Amplifier 2 x 75w US Acoustics

US Acoustics

US Acoustics Wendy | 2 Channel Class AB Amplifier | 2 x 75w

$ 159.99

View all car amplifiers | Need a custom build? Contact us

Last updated September 4, 2026