Ported vs Sealed Down-Fire Subwoofer Box: What Actually Changes

A ported down-fire subwoofer box and a sealed one share the orientation, the feet and the floor loading, and differ in almost everything a buyer has to decide. The ported cabinet is one common chamber with a slot port folded inside it, a stated tuning frequency, no polyfill and a subsonic filter as a requirement. The sealed one is a chamber per driver, takes duals and triples, and forgives a wrong-sized car.

We build both, on two different chassis, so this is not a sales pitch for either. It is the list of what actually changes when you move from the sealed down-fire page to the ported one, with the numbers from our own listings.

What stays the same?

The orientation and everything that comes with it. Both cabinets mount the driver on the bottom baffle so the cone fires into the floor, both sit on ABS feet that hold the cone 1.75 inches off the carpet, and both use the floor as a boundary that spreads output through the cabin instead of aiming it at one panel. Both keep the cone protected under the box where cargo cannot reach it.

Construction is the same too: V-groove and dado joinery in Langboard Elite MDF, a double 1.5 inch baffle, plush black carpet, a side-mounted terminal cup pre-wired in 12-gauge OFC. If you already know you want down-fire, none of that is in play. The decision is the alignment, and the alignment changes the cabinet.

What changes in the cabinet?

The sealed down-fire line is built on a fixed footprint, 30 inches wide by 15 deep, with the height set by the driver: a shallow twelve like the PowerBass XL-1240T sits at 7.28 inches tall, a deeper motor pushes the cabinet up. The ported line is a different chassis: 31 inches wide, 7.75 inches tall, 9.50 on the feet, with the depth solved per driver from 13 inches on the shallowest eights to 18 on the deepest twelves.

The extra length is where the port lives. A ported alignment needs more net volume than a sealed one for the same driver, and the port channel takes volume of its own, so the ported cabinet is deeper on the floor for the same driver. Height barely moves, which is the whole point of doing this in a down-fire chassis: the box grows along the floor, not toward the seat.

Two twelve inch down-fire builds from the listings, sealed and ported.

Where does the port go on a down-fire 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 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.

Why are the ported boxes tuned where they are?

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 is already reinforcing and leaves 40 to 60 Hz thin. Our ported down-fire cabinets sit in the low to mid thirties, close to each driver's own resonance, so the cone is barely moving where the port is doing the work and the in-car response stays flat across the band people actually listen to.

That also decides the winner in the one region where sealed beats ported. Below about 24 Hz on our twelve inch builds the same cabinet sealed is louder by up to 3.5 dB, because a sealed box rolls off gently into the subsonic region where a vented one falls away steeply once it is under tuning. Above that the ported alignment is the louder of the two for the same power. The Performance Graphs on each ported listing plot both at the same net volume, so the alignment is the only variable and you can see where they cross.

Which one should you buy?

Buy sealed when

Height or depth is the limit under the seat or in the well. You want two drivers, or three. You value forgiveness over output: a sealed box lands well in a car it was not measured for, and it needs no filter to protect the driver. Or the driver's published parameters simply point that way, which the sealed versus ported data explains with numbers.

Buy ported when

The cargo floor has the length, output per watt matters more than the last word in accuracy, and you are running one driver. The ported cabinet gives more from the same amplifier around its tuning, and the tuning is stated so you know what you are buying. Set the subsonic filter and leave the polyfill out, and it will do what the listing says.

Both lines are cut to the driver you own. The down-fire collection carries the sealed builds alongside the ported ones, and the ported down-fire collection is the ported half on its own, with the tuning on every card. Which subwoofers work in a down-fire box lists every driver we cut for, sealed and ported, with the volume and tuning of each build, and the subsonic filter guide shows where to set the filter.

Not sure which way your driver wants to go? Call 931-563-5151 and talk to an SQ-judge tech, or send us the driver and the space through the contact page and we will tell you whether the ported build earns its extra depth.

Frequently asked questions