This is an open-source DIY subwoofer design intended to spark creativity and provide an easy way to get into building subwoofers. It is not a commercial product; it is the direct result of a lot of time spent on AVS Forum learning about bass. The SumpSub is tall (46") and relatively lightweight (under 40 pounds, depending on the driver), making it easy to reposition. That's a plus if you have multiple subs and are trying to find the optimal placement. The SumpSub is not very aesthetically pleasing, but it can easily fit behind an acoustically transparent screen because it doesn't take up much floor space. The SumpSub is passive, requiring an external amplifier. The best choice is a professional amp with built-in DSP that features EQ as well as a digital crossover. The SumpSub comes in only one size, so it's important to choose the right driver for the task. Many 12-inch subwoofer drivers will work well with the SumpSub. Aside from the driver itself, the SumpSub uses standard off-the-shelf parts that you can find at any Home Depot or Lowes. I based the SumpSub's design on one particular make and model of sump basin, the Flotec 18x22-inch Sump Pump Basin. It is available from Home Depot as well as other retailers and costs about $23. Lowes does not sell a suitable alternative. Each SumpSub requires two sump basins. Perhaps another sump basin would work, but this model is commonly available. Building a SumpSub does not require a workshop. A drop cloth, a drill, a pair of pliers, a wire stripper, and a jigsaw are all the tools you need.

Safety goggles ($10) Jigsaw (with blade for cutting countertop laminates) ($50) Drill (with 1/4" drill bit and a Phillips head screw bit ) ($40) Vice-grip pliers ($10) Wire stripper ($10) Hot-melt glue gun (optional) ($10) Flat head screwdriver (optional) ($5) Drop cloth ($10) Sandpaper ($3) Magic marker ($2) Latex gloves ($2) Compass that can draw a 12-inch circle (if needed) ($10)

One 12-inch subwoofer driver ($75+) Two Flotec Sump Pump Basins ($50) Two pre-cut 24" x 3" PVC pipes ($15) Two 3" PVC couplings ($6) Two 16 oz. cans of spray insulating foam (e.g. Great Stuff) ($10) One package of poly foam caulk saver/gap filler (5/8" diameter x 20 feet) ($4) One package of duct putty ($5) Four heavy-duty doorstops ($12) One pair of speaker binding posts* ($5+) One pair of banana plugs* ($5+) 10-gauge speaker wire ($15+) Glue; either hot-melt, contact cement, or epoxy ($5) Four ¼"-20 x 1½" machine screws ($2) Package of #10 x 1" pan-head sheet-metal screws ($5)

Draw two circles to use as cutting guides on the bottom of one of the sump basins. Use a drill to bore a hole just inside the circle. Using a jigsaw, start cutting at the drilled pilot hole and carefully cut out each hole. You want to be as accurate as possible. Use sandpaper to smooth the cut edges. Make sure the PVC pipes fit snugly in the holes.

Attach one PVC coupling to the end of each piece of PVC pipe. These are the vent tubes. Put the vent tubes into their respective holes in the sump basin. Turn the whole contraption upside down, so the PVC couplings are on the floor, and the sump basin is open. The two vent tubes should stand straight up inside the basin. Wearing gloves, spray the foam so it entirely covers the area where the vent tubes meet the sump basin. Then, spray foam in the gap between each tube and the sidewall of the basin. Deplete an entire can doing this and wait for the foam to cure (about one hour). When the first foam application cures (after about an hour), apply a second can of foam insulation on top of the first. Apply some more foam to the gap between the tubes and the sidewall, but also make sure you cover the entire bottom of the basin with foam. Leave the entire contraption to cure overnight. While you wait, you can prepare the bottom half of the SumpSub.

Draw a circle as a cutting guide on the bottom of the bottom sump basin. Make sure you center the circle! Use a drill to bore a hole just inside the circle. Use a jigsaw with a blade designed to cut countertop laminates or PVC. It's not critical what blade you use; the sump basin's wall is easy to cut with almost any jigsaw blade. Start at the pilot hole and carefully cut out the circle. Be accurate. Use sandpaper to smooth the edge of the newly cut hole. Make sure the driver fits. If the hole is slightly too small, carefully trim it until the driver fits.

About two years ago, I fell into the AVS rabbit hole known as the DIY Speakers and Subs forum. I started building subwoofers based on different designs, and I read up on the various mega-subs that members built. One day, as I was shopping at Home Depot, I saw something that would change my life: a sump basin. I immediately saw its potential as a subwoofer enclosure—sump basins may look like trashcans, but they have much thicker sidewalls, an important attribute for a subwoofer.My first attempt at building a DIY sub with a sump basin used a sealed design. That's still an option, but I eventually built a variation of the SumpSub that had a dual-opposed, force-cancelling alignment. It sounded great, but I wanted even more bang-for-the-buck out of my subs. Thanks to all the time I spent reading about subwoofers here on AVS, I became interested in a category of ported-sub design known as LLT (large, low-tuned) that's a popular choice among DIY enthusiasts. Ultimately, I figured out a way to build what's known as an EBS (extended bass shelf) subwoofer enclosure—inspired by LLT designs—using inexpensive, commonly available parts from Home Depot.To my surprise, the ported SumpSub does not just sound good; it sounds great. The SumpSub also turned out to be very durable and easy to move. In fact, because they are so easy to move, back in December 2012 I brought my original four SumpSubs to an AVS get-together This article is about how to build your own ported, passive SumpSub. But before I get into how to build it, there are a few things I'd like to mention:When I built my first SumpSub, I had no tools aside from a drill and a screwdriver—I had to start from scratch. I expect most people will have at least some of the required items on hand. In terms of power tools, all you need is a drill and a jigsaw. Here's a complete list of the tools (with approximate prices) you'll need to build all the SumpSubs you could ever want:In addition to basic tools, building a SumpSub requires the following parts:*I suggest banana plugs for the binding posts because some binding posts have a hollow shaft that can leak air—as was the case with the ones I used.Those tools and parts are all you need to build a high-performance subwoofer in a kitchen or garage. When I came up with this design, I wanted to make sure that it did not require a workshop. If you do have a workshop and woodworking skills, you'll find this project is truly a cinch. If you don’t have any skills, fear not—this project is about as easy as assembling a grill or an Ikea bookcase.One more note before I get into the build itself: I encourage modification and experimentation. I based the design on the goal of getting the maximum performance out of minimal investment in time, cost, and effort. There are plenty of ways to modify—or deviate from—the original plan. There's plenty of room for larger or longer ports to achieve different tuning. One of the nice things about the 16 Hz tuning is it uses pre-cut PVC pipe, which saves some measuring and cutting. The sump basin itself is lightweight, strong, and easy to work on; plus, its cylindrical shape naturally resists wall flexing, which can make many cube-shaped subwoofers sound boxy.I started my project at Home Depot, where it's possible to buy all the parts needed to build a SumpSub, with the exception of the 12-inch subwoofer driver. However, most of the items are also available from other retailers and via Amazon.Importantly, Home Depot stocks the Flotec 18x22-inch Sump Pump Basin that is the key to the SumpSub's design; that's the main reason I bought all my supplies there. Some items (including speaker cable, binding posts, and banana plugs) are cheaper and offered in more varieties online, but it is possible to buy all the parts in a local brick-and-mortar store, and that was one of my design goals for the SumpSub—all parts are locally available. In my case, Home Depot and Wal-Mart (where I bought my drivers) were right next to each other! I know that a lot of DIY folks on AVS Forum use parts-express.com as a source for their DIY goodies, and of course Amazon has a bit of everything.Selecting a driver is the most important step when building a SumpSub. I used Sony XS-GTX121LW 12-inch automotive subwoofers that I bought at Walmart for $80 each. The Sony is a competent driver, and Walmart still sells them in-store, but they are not the only option that will work. Although the usual DIY approach is "find a driver, build a cabinet to suit," it's necessary to reverse the equation for the SumpSub—the cabinet is already a known quantity, so you need to find a driver that suits it. The Sony driver happens to model particularly well (more in a moment); I can run my subs with no EQ, and they are close to flat in-room. Other 12-inch subwoofers offer greater efficiency and/or power handling, but I found no reason to spend more on my drivers; the Sonys kick butt daily in my home.The best way to find the right driver is through computer modeling. Simulating the SumpSub driver/enclosure interactions using software is relatively easy when you have the Thiele-Small parameters for your chosen subwoofer—I used a free program called WinISD to model mine. Modeling drivers is a completely separate topic that deserves its own article, but basically, you want to confirm that the driver you use exhibits a smooth response curve in this particular cabinet.After choosing a suitable driver, putting a SumpSub together is almost as simple as cutting a few holes, drilling a couple more holes, applying some glue, spraying some insulating foam, attaching some speaker cable, and tightening some screws. Let's go through the process step by step:First things first—wear safety goggles when working with tools.Cutting the holes for the ventsThe vent tubes are a pair of pre-cut 24" x 3" PVC pipes, capped by 3" PVC couplings. If you have a compass, use that to draw cutting guides. Otherwise, you can trace either the inside of the PVC coupling or the outside of the PVC pipe. You want a snug fit between the tubes and the sump basin.Securing the vent tubes and sealing the top half of the SumpSubThis is one of the most critical steps; it's what makes the SumpSub so light yet strong!You should wear protective gloves and clothes you don't care about when working with spray foam; it is very sticky and almost impossible to remove once it gets on something.Once the foam cures, the entire top half of the SumpSub is ready. The cured foam adheres the vent tubes to the basin; you'll find it is incredibly strong. The foam that cured at the bottom of the basin adds structural rigidity to the whole piece while helping to reduce resonances.Cutting the hole for the driver:The Sony driver I used included a cutout stencil that I used to draw a circle as a cutting guide. It's important to cut a hole that's the right size for the driver you use, so it hopefully included a diagram or stencil. If not, you'll need to find out what the diameter of the cutout needs to be and use a compass to draw the cutting guide.Once you've cut out a hole for the driver, it's time to install the binding posts. Drill a pair of holes into the bottom of the sump basin, near the edge. Make sure the binding posts fit snugly into the holes; this connection needs to be airtight.After you secure the binding posts to the sump basin, it's time to install the driver. In order to achieve an airtight seal, I use duct putty between the driver and the sump basin; it provides an airtight seal and makes securing the driver easy. Apply the duct putty around the edge of the hole, so it makes a ring. Press down on the putty, so it adheres to the sump basin. If your subwoofer driver came with a rubber or foam gasket, feel free to try that out. I'm fond of duct putty because you do not have to tighten the driver too much in order to get a good seal.At this point, connect the driver's terminals to the binding posts using a short length of 10-gauge speaker cable (about one foot). Then, insert the driver into the cutout and secure it with #10 x 1" pan-head sheet-metal screws. The screws will self-tap into the sump basin. Don't fully tighten the screws yet, just get them all close to tight. Then, go around and slightly tighten each screw a bit. Repeat. You might see a little bit of duct putty squeeze out; that's what you want to see. The crews don’t need to be crazy tight, although it's surprising how tight you can make them before the threads strip.Once the driver is in place, it's time to screw in the doorstops, which serve as feet. It's important to buy heavy-duty doorstops—the first batch I tried were too weak, and they bent after I moved the sub around. Heavy-duty doorstops cost $3 each instead of $1.50, and it's money well spent. There's not much to this step; you might need pliers to get them tight, I managed to do it by hand.With the driver and feet installed, it's time to flip the bottom half of the SumpSub over onto its feet and prepare to join the two halves. Just make sure the foam in the top half had enough time to cure!Take the poly gap filler (the foam noodle) and make an O-ring out of it that's the precise diameter of the lip on the sump basin. Cut the foam to that exact length and glue it to the rim of the bottom half. Now, take the remaining foam noodle and make a second O-ring inside the first one. Cut and glue. Make sure you glue the ends of each ring together as well. I used hot-melt glue, which works well, but you have to be careful not to melt the poly, which will happen if the glue-gun tip touches it.With the two poly rings in place, it's time to join the two halves. Pick up the top half and place it on the bottom. Turn it until the threaded holes line up between the top and bottom halves. Remove the T-nuts from the top half. Use a ¼"-20 x 1½" machine screw fitted with a washer to make sure you align the holes, and partly tighten it—just a little bit. Do the same thing to the other three holes, then proceed with tightening the whole contraption. You want to make sure lips of the two sump basins make contact, and then tighten it a bit beyond that point. It doesn’t need to be super-tight, just firm.If all went well, you now have a fully functional passive subwoofer on your hands. Connect it to an amp—don't forget to use banana plugs if your binding posts have hollow cores—and run a nice low sine wave; 18 Hz is perfect for the task. Get the driver moving, and you'll hear any air leaks, no matter how small. If you followed my instructions, you won't hear anything, but you'll definitely feel that 18 Hz bass. If you do have to fix a leak, figure out exactly where it is, separate the two halves, and use a bit of duct putty to fill any gaps.The last step is subwoofer placement and EQ. Your choice of driver affects the performance of the sub, but room placement affects it even more. The key to integrating any sub—DIY or not—is to understand room placement and the role of EQ, digital delay, and crossovers. If you have the room and the budget, I recommend building at least two subs; deploying four or more subs is even better. Regardless of how many subs you use, you'll want to take time to find the right position and EQ for each sub in your system. Some AVRs have built-in bass management, in which case all you need is an amp. That's also true if you use an external DSP processor such as a miniDSP or a Behringer Ultracurve Pro. Otherwise, I recommend powering SumpSubs with a professional amp that features DSP such as the Behringer iNuke or Crown Xti series.Whether you buy a subwoofer from a store, put one together from a kit, assemble one from parts, or build one from scratch, the only way you'll get the most out of it is by understanding how bass interacts with the room. There's a ton of information here on AVS about how to EQ your subs and treat your room for better sound. As I said earlier, if it were not for AVS, the SumpSub would not exist. I've heard many subwoofers over the years, and the SumpSub is one of the best-sounding 12-inch ported subs I've heard, even when using inexpensive Sony Xplod drivers from Walmart. I wonder how they would sound if I used the best-quality drivers I could find…but that's a topic for another article!There are lots of other subwoofer designs worth checking out here in the DIY Speakers and Subs forum. The SumpSub is very similar to the Sonosub , a tried-and-true design that typically uses a heavy-duty cardboard cylinder as an enclosure. It's worth having a look at all the different designs that you'll find in the forum. That's what inspired me to build my own!