Rockin’ Outdoor Speakers with DIY Sump Pump Basin Subwoofer

At long last, here is the complete write-up on how I installed a killer outdoor speaker setup, complete with 12″ subwoofer, using mostly gear from Craigslist, Amazon, Crutchfield and The Home Depot. I’ll go into how I designed this outdoor speaker setup as well as how I ran the speaker wire, mounted the speakers, built the subwoofer and my preferred method for playing wireless/streaming audio on a budget. If you’re about to tackle a similar project, then read on! Hopefully some of the methods I used here are helpful to you or at the very least will get you thinking about different ways to take on your own outdoor speaker/subwoofer project.

First off, let’s just get right into the specs and the audio gear used in this setup:

Speakers
Polk Audio Atrium5 2-way 5″ Woofer with 3/4″ Dome Tweeter Outdoor Speakers
AudioPulse Epic 12″ Aluminum Cone Subwoofer in a Sealed Sump Pump Basin Enclosure

Audio
Russound R235LS 2-Channel Single Zone Amplifier (2×50 watts into 4 ohms to sub)
Russound DPA1.2 2-Channel Single Zone Amplifier (2×35 watts into 8 ohms to Polks)
Optimus 12-2011 3-way Active Crossover set at 90 Hz

Wireless
Apple Airport Express with iOS or iTunes on PC

Miscellaneous
500 feet 16 gauge 2-conductor speaker wire (direct burial rated) pure copper
100 feet 3/4″ Schedule 40 Conduit and PVC pipe
Various Elbow and T-fittings for conduit and PVC pipe
(4) 1″ Conduit Clamps
SpeakON 4-Pole Connectors for subwoofer
4-speaker Binding Post Wall Plate
(2) Single Gang Low Voltage Retro Boxes (the orange ones)
1/8″ to RCA cable and (2) RCA-RCA Cables
12 Vdc 1A wallwart AC-DC adapter (for the crossover)

The Polk Audio Atrium5 Outdoor Speakers

So let’s talk about the speakers. I don’t buy many commercial speakers, since I enjoy building speakers more (isn’t that obvious?) but I have to make exceptions when it comes to certain types of speakers, like computer speakers, in-ceiling speakers and certainly outdoor speakers. I could have whipped up a 2-way speaker design using some nice poly or aluminum-cone drivers from Parts Express and attempted to build some kind of waterproof enclosure but realistically it seemed faster, easier and simpler just to buy a pair of finished outdoor speakers and save me the time and hassle. Man I’ve gotten lazy in my old age. After I received a gift card from work to Crutchfield for $100 it sort of sealed my fate and ended up buying a pair of Polk Audio Atrium5 outdoor speakers on sale for $169. Why the Polks you might ask? Besides the 5-stars reviews from just about every major retailer who sells these speakers, I’ve been a fan of Polk Audio speakers ever since I was little kid and went to my first real stereo store sometime in the late 80’s. I must have been 12 or 13 years old at the time but I still remember walking into this little store in a strip mall right next to the Miller’s Outpost (tell me you didn’t buy all your clothes from Millers Outpost?) that literally only carried high-end audio gear (this was no Circuit City) and that’s when I saw them, this massive pair of Polk Audio speakers, with a driver array as tall as I was, multiple woofers, of bank of rectangular dome tweeters and a huge 15″ flat subwoofer (that I would later learn was a passive radiator) right there in the middle of the showroom floor. These speakers were like nothing I had ever seen before and I was completely taken back by the shear visual appearance of them towering over every other speaker in the store. I have no idea what they sounded like, we never auditioned them that day, my dad was in the market for a pair of speakers I’m sure, but nothing like what those Polks had to offer. Of course the speakers I saw were none other than the SDA Stereo Dimensional Array line of speakers, what would now be considered Vintage Polk or Classic Polk Audio, the speakers that basically put Polk Audio on the map. I guess I’ve just respected Polk Audio as commercial speaker brand ever since, even if I never owned a pair of those speakers. Even today I don’t actually own any Polk Audio speakers (except for a CS1 center channel that I use in my garage theater and now these Atrium5’s), still whenever I see some Polk Audio speakers on Craigslist I’m always tempted to pick up a pair to play around with. So the Atrium5’s are basically the first pair of Polk Audio speakers I’ve ever really owned. And let’s just say, I am not disappointed. Though 12-year old me would be just a little bit disappointed I didn’t get something flashier. And outdoor speakers? C’mon man!

Anyway, sorry for the diversion, back to the Atrium5’s. After several weeks of very casual listening, I can easily say that these speakers sound awesome, have great treble, clear midrange and decent bass (though they do sound much fuller when supplemented with a subwoofer). You could do without the subwoofer but realize the practical limitation of a 5″ woofer in a small sealed enclosure. I measured the speakers using REW in my house before installing them outside and was pleasantly surprised by the nice flat response from these speakers. Check out the frequency response plots below. There’s a little boost in the treble to keep music sounding bright with a subtle drop in the midrange to prevent overemphasis of vocals. Bass down to about 70 Hz before it starts to roll-off. The enclosure is solid, the 5″ polycone woofer should withstand the elements and you get a legit 3/4″ aluminum dome tweeter. The plethora of 5-star reviews is enough to sell just about anyone on these speakers and after measuring them and listening to them for a few weeks now, I definitely agree with the reviews, these are a great-sounding pair of speakers that will do justice for almost any outdoor setup. A 5-year warranty has you covered for half a decade, so here’s to hoping they withstand the harsh sun of the Arizona desert. I didn’t install them underneath my roof/eaves like they recommend, but I did put them underneath some oleanders which should keep most of the direct sun off of them. They’ll take the full brunt of any rains/monsoons however, so hopefully they can withstand a little water. For now though I give the speakers 5 big stars to add to all the others. I couldn’t have built a better pair of speakers for the price. And certainly not as fast as clicking Complete Order and having them show up on my doorstep 3 days later. I could get used to this whole ‘buying finished/commercial speakers’ thing.

Apple Airport Express and Russound Amplifiers

So let’s move on to how I wired these things up to my whole house audio system. I currently have a 5 zones in my house that use discontinued Apple Airport Express units as the main streaming devices. I think a lot of people forget that these aren’t just wi-fi extenders but actually streaming audio playback devices. This is my go-to setup for whole house audio. They are small, wireless (or wired) and are basically plug and play. Apple Airports work flawlessly with iOS and iTunes. You can pick and choose your zones in iTunes and play music to any single or multiple zones with independent volume control on each. Timing is synced up for all zones so you don’t have the echo/delay effect which can happen when the timing of the music across zones is out of sync. In iOS on your phone you can only select one zone, but that rarely causes too many issues with the wife/kids using their phones as most of the time they only want to play music to one zone at a time anyway. Still you can use iTunes and the Remote App within iOS to control music in your library and play to multiple zones while controlling the music with your phone. You just can’t play music on your phone to more than one zone (or more than one Apple Airport) for some reason. But frankly this setup works great, sounds great, is easy to hook up, is cheap ($20 is the average price for a used Airport Express) and is totally integrated for anyone living within the Apple ecosystem. A similar approach can be done with Amazon’s Echo Dot or Google’s Chromecast, depending on your evil empire of choice. Also, if you pick up Amoeba’s Airfoil software on PC you can stream anything playing on your computer including YouTube, Spotify, Amazon Music, whatever your favorite streaming platform. The Apple Airports just look like an available device and it plays to them like any speaker. Airfoil has worked great for me over the years. The software isn’t free but is definitely worth getting. So we’ll add one Apple Airport Express to create one more zone and we’ll call it “Pool”.

Now that we have a way to get music wirelessly from our phone or computer to something all the way at the other end of the house, the next trick is amplifying that music and then getting it all the way into the backyard and to our speakers. The cheapest way to do this by far is to buy a cheap stereo receiver locally. You can easily find an old Sony or Denon unit for $20-$30 and they have plenty of power for driving a pair of outdoor speakers to levels your neighbors will certainly not appreciate. The only downside, they are big, they are bulky and for the most part you just need to leave it on all the time if you want music anytime. The second best approach is to pick up a small, class-D amp from Amazon brand new. SMSL, Topping and Lepai all make great little amps that can push about 25-50 watts/channel and these things are tiny, they draw very little current and can be placed just about anywhere. Downside again is that they also need to be left powered on all the time. Not as big of a deal as the bulky old receiver because these things are small and don’t draw a lot of current but not exactly an energy-friendly option. The best option, in my opinion, is to pick up an amplifier designed for use in a whole-house audio setup, something from brands like Russound, Niles or Dayton Audio, who specialize in special amplifiers designed for whole house audio distribution. I watched Craigslist and letgo for months before putting together this system and really just got super lucky and managed to find a pair of Russound amps locally from two different sellers. One guy had a brand new, in-box, Russound R235LS single-zone amplifier and he was only asking $20 for it. Another person was selling an older Russound DPA1.2 single-zone amplifier for only $30. I messaged them both and managed to pick them up the next day. So after spending a mere $50 I ended up with a near-matching pair of 2-channel Russound whole-house audio amplifiers to power the Atrium 5’s and the sub. Specs wise these amps can can drive 35 watts/channel into 8 ohms from 20-20,000 Hz at less than 0.05% THD. Both amps are bridgeable, have auto-on/off sensing, and have a 12 Vdc trigger in/out to drive other gear. Plus they are compact and beefy and weigh like 9 pounds a piece. I believe they are class A/B and not not class D although the product manuals do not specify either way. The weight alone makes me think at the very least they are not class D, so class A/B would be the next logical choice. They sound absolutely fantastic and the auto-sensing works perfectly. The amps stay plugged in all the time in standby and kick on as soon as the music starts. I have the trigger out on the one unit feeding the trigger in on the other, so only one unit actually triggers based on audio sensing while the other one just does what it’s told via the trigger. The setup so far works perfectly. So while just about anything can work for powering a pair of outdoor speakers, my recommendation is keep an eye out for anyone looking to get rid of whole-house audio style amplifiers and if nothing shows up in your town then hit up eBay or OfferUp. The auto-sensing and trigger in/outs alone will make it worth your while in the long run.

The Crossover

Now the Optimus crossover purchase was made completely in the moment and honestly you could go any way you like here. The only reason to even need a crossover is if you are going to add a subwoofer to your outdoor setup. If you’re just planning on driving a single pair of outdoor speakers then you won’t need a crossover. But if you’re going to do a subwoofer, and I really think you should, then you are going to want to get a crossover. Of course the first thing I thought of after picking up those amps was – now I gotta buy me another MiniDSP! I could just picture it, that 12″ subwoofer would surely need some bottom-end tailoring to combat a less-than-favorable outdoor environment, plus I could tame a few of those peaks and valleys in those Polk speakers, a MiniDSP would do the job perfectly, and if I bought the kit version it would only set me back another 80 bucks. I envisioned getting REW setup on a laptop outside and moving my ECM8000 microphone all over the yard, taking hundreds of measurements, tuning the sub and dialing in the Polks dB by dB to blend ever so perfectly with the sub until I could achieved a near ideal frequency response over the largest area of the yard, from deep thumping bass all the way to highest highs, my outdoor setup would be the envy of all my friends, and my family would surely appreciate how great all their ripped mp3s sounded. I would just need to figure out how to get the amps connected to the laptop, to the speakers while outside, I’ve got some extension chords, do I have enough XLR cables? What if I…

Then reality hit me.

That sounded like a lot of work, I mean a lot of work. I spent months tuning my DM-4 speakers with those MiniDSPs and while it was fun, it was also such a chore and there was always the thought that just one more tweak, one more change would do the trick and it would be, perfect. I didn’t need the headache. I didn’t want the work. This was an outdoor setup. It needed to be simple. Nobody is going to care what it sounds like, seriously, no one, only I am going to care, and even then, I really don’t care that much. So when I spotted a used Optimus 3-way car audio crossover on Craigslist for only $15 I texted the guy that day and picked it up an hour later. Done and done. The MiniDSP fantasy will have to wait. I looked up the specs on this particular unit just to make sure it would work as a 2-way crossover in my application and sure enough there was an option on the midrange to run the low-pass as flat, effectively acting like a a 2-way. While not the fanciest of active crossovers, it does provide three different crossover frequency options when configured as a two-way, 45 Hz, 90 Hz and 180 Hz with a variable bass boost option fixed at 45 Hz. You’ve got a 0/180 phase button and that’s basically it. Of course once I got this sucker home I couldn’t help but drop it into REW so I could see just what this puppy could do, plus it was an easy way for me to see if it actually worked. After all, this thing is easily 20 years old, the guy said it worked when he pulled it from his car a few months ago, but you never know. Check out some of the REW plots below. I tested out the different crossover settings and the bass boost setting and everything looked to be in working order. 12 dB/octave slopes on both the low and high-pass sections, both the left and right channels were operational, the filter set points seemed to jive as they were 3 dB down at the filter corners. The main thing I was looking for was how flat was this old thing going to be? I know everyone stresses adding unnecessary gear inline with their amps, but fortunately this little crossover from a million years ago was flat from 20-20,000 Hz with only a slight roll-off of -0.25 dB at 20 kHz. There’s no way anyone is going to notice a quarter of a dB at that frequency. I certainly am no going to sweat it. Check out the plots below.

Speaker Wire

Now this is where this project got really fun, running the near-100 feet of speaker wire from a cabinet in my kitchen all the way into the backyard to each of the Atrium5 speakers and the subwoofer location. I had calculated the max speaker run at about 105 feet so I picked up 500 feet of 16 AWG 2-conductor direct burial rated OFC speaker wire from Amazon. The speaker wire was $79 and honestly was a bit of a compromise as most people would recommend a minimum of 14 gauge for this long of a run. I ran some numbers, made a spreadsheet even (image that), and decided the extra cost, like 2x the cost (the cheapest spool of 14 gauge wire I could find was $149) wasn’t worth the extra 0.3 dB I’d gain in overall output when comparing the loss differential in a 100 feet of 14 to 16 gauge speaker wire. And definitely not worth going to 12 gauge (in my case, remember, outdoor speakers, wireless music, mp3s, no one else cares). 18 gauge felt like too much of compromise so 16 gauge is where I landed, sort of the Goldilocks of performance and cost. Plus the 16 gauge 2-conductor wire was just the right diameter to fit 4 sets of wires in regular 3/4 conduit, making the overall cost a bit cheaper again and ever so slightly easier to bury in the ground. I bought about 100 feet of 3/4″ conduit with some nice swept elbows but also towards the end of the run, nearest the speakers, ended up just using regular 90 degree PVC fittings and regular PVC pipe, since again it’s cheaper than buying the nice gray conduit.

Shortly after I received this massive role of 500 feet of 16-gauge speaker wire, I was curious to see how much difference that much wire would actually make to the sound of a pair of speakers when compared against a regular 10-foot run of the same gauge wire. So with REW I measured the Polk Atrium5’s in-room at about 18 inches and then without changing anything, I swapped out the 10-feet of wire for this 500-foot spool of wire and plotted the difference (A/B) and result is what you see here. This is exactly why you don’t want to compromise on speaker wire gauge, even for short runs, look how uneven that response is! You can’t assume that with the added loss you will simply get a flat reduction in output power over frequency, like turning the volume knob on your stereo down just a smidgen. The light-duty gauge wire (given the massive length in this case) completely alters the frequency response throughout the audio spectrum at sporadic levels. It’s not like it’s just one big resistor, it has inductance and capacitance, which reacts with the speaker’s inductance and capacitance differently at different frequencies giving you this jumbled response at the final output (and the round trip resistance was measured at 4.4 ohms) So as always, you want to purchase the lowest gauge speaker wire for your application that is reasonable given overall cost and the length of your run. Lower speaker impedances will exacerbate this issue as well. I wish I did this same experiment with one 125-foot run so I could see what that looks like, but in the moment I was pulling all the cable I didn’t feel like stopping and measuring it. The effect for a run that is 1/4 the length would probably have a similar shape though be far less obvious. The 6 drop would probably drop to only 1.5 dB and the 4 dB drop would come up to 1 dB and that 2 dB drop might sit around 1/2 dB. I plotted a predicted response based on halving the length of speaker wire and therefore also halving the change in response as just a course way to see where we’d sit at 125 feet of wire. While it’s not ideal, it’s not terrible. Though it is down 2 dB at 20 kHz. Realistically 60 ft is about the longest run you probably should do if you want less than 1.0 dB change in response due to the speaker wire. Moving along…

The first trick was getting the speaker wire from this one cabinet in my kitchen (which we never use) which I had dedicated as the ‘home run’ for this setup (Airport, Amps, Crossover, Power Strip, Cables, etc.) down the wall and outside. To do this I cut two holes in the wall the size of a single gang low-voltage box, one in the cabinet and one straight below it almost at ground level. In my case this second hole ended up being behind our stove/range, which was convenient because once I got the speaker wires run, I added a blank wall plate which would have looked fine on its own, but is fortunately out of site behind the stove. I ran a fish tape down the wall and prayed there wasn’t a fire plate blocking my way. I was happy to see the fish tape run the full length of the wall and pop out at the bottom. That was really my first fear, as I was not interested in running an ugly piece of conduit 7-8 feet down the outside of my house. With the fish tape down the wall, I ran 4 poly-strings back up thinking that I was going to have to pull each speaker wire one by one through the conduit and through the wall. After taking a quick measurement of the total runs, I ended up just pre-cutting the 500 foot spool into four 125 foot lengths. I taped them together and just ran all 4 wires at the same time. This worked out great and was a huge time-saver over to trying to do them one by one. Knowing the needed length was the trick. Outside the house I dug a trench with a pick ax starting at the location outside the house opposite where I had ran the speaker wire through the stucco all the way to the locations of each speaker and the sub. This is tedious work, and I barely made the trench deep enough in some spots to really be much deeper that just below the decorative rock, but for what it’s worth, there is no need to run speaker wire conduit 18″ below the surface. This is effectively low-voltage wiring and could be on top of the rocks if you really didn’t care. So having the conduit only an inch below the rocks in some cases wasn’t going to bother me too much. I did have to dig down a little deeper where I had to curve parts just to make sure under the torque of being bent didn’t try and pop it out of the ground.

I won’t go into the details of wiring the wires through the conduit and burying it all, you can look at the pictures below, but I will say that with the 4 wires taped together I didn’t need to use the fish tape as long as I only did 10-foot sections at a time, you could just push the wire all the way through. At 20 feet though it got a little tougher. I used the fish tape for most sections but kept the corners disconnected so my longest pulls were always straight. You cannot just pull 100 feet of wire through twists and turns in 3/4″ conduit, I didn’t even attempt it. Even the swept 90 degree elbows I just pushed the wires through only the elbow then attached it and moved on to the next section. One piece at at time I pulled and/or pushed the wires through either a straight section and elbow or a t-section. I used the two t-sections, right at the end of the run to split the left and right speakers and to create a tap-off point for the subwoofer. I ran the conduit all the way up to each speaker and painted the last 1-foot piece brown to match the poles where the Atrium 5’s were mounted. A few weeks earlier I had installed these 10-foot poles into the ground using 1 inch EMT conduit to hang some lights over the pool and patio area. That’s where I ended up installing the Atrium5’s. I bought a couple of 1″ brackets with some nuts and bolts and bolted the brackets to the Atrium5 bracket which allowed me to basically attach the speakers anywhere on the pole. A foot off the ground seemed like a good place. So that’s where they ended up.

The Sump Pump Basin Subwoofer

Okay so now for the final part of this project, the subwoofer. I couldn’t find a lot of info online for DIY outdoor subwoofers. But I did manage to find one tidbit of information that I basically just ran with. I think it was on an old AVSForum post where a guy said he took a 20 gallon sump pump basin from Home Depot and basically made a sonotube style subwoofer out of it. But he was using it in his basement theater and not outside. He shot some video of the project but didn’t take a lot of pictures. But the key takeaway was that he used a ‘sump pump basin’. I didn’t even know what that was until I Googled it and sure enough, Home Depot sells them, and that’s when this plan started to come together. While my mysterious forum friend built just a regular indoor subwoofer, I knew this enclosure would be perfect for an above-ground outdoor setup. He mentioned that the top of the enclosure flexed a lot under load and in the future he would probably want to glue a 3/4″ MDF panel in there, so I took that information and made sure I designed the enclosure to include a baffle in the bottom (really the top) in addition to the one for the driver.

I sketched up a few designs and in the end came up with what you see here. The overall enclosure is about 18 inches at its widest point and 16 inches at its narrowest, it tapers ever so slightly inward. It’s 22 inches long and has a total spec’d capacity of 20 gallons. Which works out to about 2.67 cubic feet. Assuming you could use the whole enclosure for the woofer, which you could do if you wanted to add some kind of feet to the underside of the basin, but that is not what I did. For starters, my plan was to go sealed, and after modeling up the Audio Pulse Epic 12″ driver, I realized this thing is super happy in a 2.0 cubic foot (57L)enclosure. Any larger and you start to sacrifice f3 and power handling as the enclosure becomes over-damped. But at 2 cubes the Qtc is right at 0.72, so it’s critically damped or maximally flat, right where you want to be for peak performance, perfect transient response and lowest f3. This was convenient because this meant that I could push the 3/4″ MDF driver baffle inwards into the basin just enough to shrink the volume of the enclosure to the perfect amount. Instead of mounting the baffle on the outside edge of the enclosure, it amounts inwards from the edge by about 5″. So you end up with an internal enclosure depth that is only about 15 inches. So with the extra space in the enclosure now in front of the driver, I decided I would use that part of the enclosure as built-in feet, and opened up the entire perimeter with a bunch of large 3 x 3.5 inch holes. This way the subwoofer could sit down-firing and the nice beefy ridge around the sump basin enclosure would basically just sit on the ground and I wouldn’t need to add any additional feet or lifting mechanism to hold the driver up off the ground. The holes in the sides do not attempt to tune the front portion of the enclosure. The total surface area of the holes is greater than the total surface area of the driver, which means the front of the driver is effectively operating into free air. It’s just operating in a downward firing configuration where the lower 5 inches of the enclosure just acts as a means to raise the subwoofer up off the ground. And since it’s outside, it should do a decent job of protecting the driver from sun and rain, though the bugs and critters will probably think this is a nice home. At least they can’t actually get inside the subwoofer-side of the enclosure, as it is completely sealed to the outside world. And by the way, a Dayton Audio RSS315HF-4 models really well in this same size enclosure. Overall Qtc drops to 0.63 since the driver wants to be in a slightly smaller sealed enclosure, but still would work great. You could always make the internal volume a little smaller by pushing the baffle in deeper. A 12″ UM12-22 Ultimax could also work though the Qtc jumps up to 0.87 as this sub really wants to see a larger enclosure when sealed. Either way, there are plenty of other current subwoofer driver options that will work in a sealed ~2.0 cubic foot enclosure, since I know this particular Audio Pulse driver is no longer available. Just run some numbers with your favorite sub and and see what you come up with. Obviously 8″ or 10″ drivers are also possible as well as a single 15″ could be crammed in there if you really wanted.

Here’s a short list of basic items you’ll need to build this sub:

18″ x 22″ Everbuilt Sump Pump Basin
2 x 4 foot x 3/4″ MDF
Titebond II Wood Glue
Loctite or Liquid Nails Construction Adhesive
Rustoleum Painters Touch II Spray Paint
Varathane Spar Urethane
#10 x 1 inch pan head screws
4-pole SpeakON Connectors
16 gauge speaker wire
Small amount of fiberglass insulation and polyfill

With the 2 x 4 foot sheet of 3/4″ MDF I cut out three circles – two baffles and one brace. The bottom baffle needs to have some unique features cut into it so that it will fit all the way down into the basin and sit flush with the bottom. There are these 4 little ridges in the sides of the basin and then these 4 small raised half-circles that prevent the baffle from sitting all the way up against the bottom, so through some trial and error I was able to make about a 15.5″ disc with 4 slots and 4 half-circle cutouts in it so when it drops into the basin would sit flush to the bottom. Note though at this point it no longer really makes contact with the sides because I had cut it down so small to fit all the way into the bottom. There’s probably a better way to do this and my stupid phone died while I was in the middle of this part of the build process so I took zero pictures until I had glued it into basin and it was dry the next day. You can get an idea of what it looks like though from the pics below. This is where I used an entire tube of Loctite PL375 adhesive to secure this baffle to the bottom of the basin. You’ll have to get creative with how you secure it while it drys, since there is no way to really clamp it in place, and you don’t want to use screws because you’ll just put holes in the enclosure (which you don’t want to do) so the best thing to use is weight. I have two 60 pound bags of cured Quikrete concrete (yes, cured, still in their bags, don’t ask) that actually worked great to hold the baffle in place while the glue dried. The next day I pulled out the bags of cement and did a quick tap test on the bottom of this fiberglass tub and it made a nice soft thud. Much better than before.

Next I took a jigsaw and cut out twelve 3 x 3.5″ holes towards the top of the basin. This effectively opens up the front of the driver to the outside world. The total surface area of the openings amounts to about 100 square inches, where as a 12″ driver only has a surface area of about 78 square inches. So once flipped over and sitting upside down on the ground, the ground will enclose this bottom part of the enclosure and the bass will escape through all the holes in all directions without restriction. Note this is not a 4th order bandpass enclosure. Since all of the large-diameter holes provide so much surface area opening to the outside world, the enclosure acts like a standard 2nd order sealed enclosure, but in a down-firing configuration. The driver baffle will end up about 5″ away from the ground, so in effect, this portion of the enclosure just acts like a bunch of ‘feet’ to hold the driver above the ground. But since it’s just all one piece, it makes a super strong and very convenient.

Next I cut out the ring which would make up the center brace. This piece is about 16-5/8″ at it’s widest and tapered to 16-1/2″ to match the taper of the basin. I cut the hole in the middle at 11″ in diameter. At this diameter the brace ends up sitting just on the top of these 4 little ridges that extend about 1/3 of the way up the tub leaving a little ledge. The trickiest part with cutting these MDF inserts is making them just the right size and you have to cut them with your jigsaw set to very subtle ~5° angle. Since the basin tapers towards the bottom (which will actually be the top once we flip it over) if the insert is too big, it won’t drop down in far enough, if it’s too small, then it drops down too much or flops around if it hits these little ridge things. If the angle isn’t just right, then the glue won’t adhere well to the wood and basin sides. I did a lot of cutting and checking and trimming and checking over an over until I was happy with the fit. But this does take some time and can be a little frustrating. Since I was low on scrap MDF I didn’t want to cut the circles too small initially, because I knew at that point I would just have to start over. I sanded the ring a bit too until it fit in nice an snug. I used a liberal amount of glue around the edge and pressed it into place with a few taps of a mallet. This brace sits about midway inside the enclosure and seems to provide a good job of keeping the enclosure really solid.

Last I cut the baffle for the driver. This one started out a little big but after some trimming ended up at 17-1/2″ at the top and 17-3/8″ at the bottom. This ends up sitting just about 1.25″ below each of the 3″ oblong holes but it sits in there really tight. Remember since the tub is tapered, the diameter of the baffle determines how deep it sits into the enclosure. It takes a bit of trial and error, and I trimmed and trimmed until it fit just at the right depth. Once it looked like the right size, I applied glue to the baffle edge and then I hammered the baffle deep into place so that it was firmly and tightly pressed against all sides. Note that the driver is offset about 1″ from center, and that was really just to make sure I had room for the SpeakON connector. I drilled a 1″ hole for the SpeakON connector as well. The speaker hole is 11-1/8″ in diameter. I drilled holes for the screws, did a quick fit check and then let the whole thing dry for a day. During this time I went ahead and spray painted the entire enclosure brown so that once tucked behind one of my big oleander bushes it would blend in nicely and not be noticeable. I did a quick clear coat on the MDF as well to seal it from water and rain. I also added a small amount of fiberglass insulation and polyfill and just stapled it into the bottom (or I guess now the top) of the enclosure with some scrap fabric.

And that’s about it! Check out all the pictures which probably do a much better job on their own telling the story of how I put this whole backyard setup together than I can do writing it. And as far as how it sounds? What can I say, it sounds absolutely fantastic. It quite literally fills my entire backyard, the pool area and patio with great sound. The Polk Audio Atrium5’s hold their own and sound great. And even though they are high-passed at 90 Hz, before getting the sub installed I was listening to them full range and they still sounded pretty decent. But they also don’t quite measure up to what a 12″ dedicated subwoofer can do. Quite frankly the sub is what makes this setup sound really great. While I haven’t measured the bass response outside, yet, I am sure we are getting down into the low 30’s no problem and for most music that is really the sweet spot for low-end bass. My kids listen to pretty much all your typical pop artists of today and man some of those songs lay down some pretty wicked bass lines. This sump pump subwoofer has no problems bumping and even just at low volumes adds a significant amount of presents to almost all music. The Polks make up the top end perfectly providing clear midrange, clean vocals, a nice mid-bass region and crystal clear highs. And this is with zero EQ. Other than the 90 Hz filter, everything is flat, but it definitely doesn’t sound flat, nor does it sound too bright or boomy in any way. I did have to play around with the two Russound amps to get the volume just right between the Polks and the sub. Which would be typical for any 2.1 setup. You want it balanced just right so the bass compliments and blends with mains but doesn’t overpower them or sound weak. Plus you still have to respectful of the neighbors. Despite that fact that this is basically a 170 watt setup, I haven’t cranked it all the way up to see what it can really do. I’ve probably not got above 1 watt. So far we’ve just been enjoying it as good background music for when you’re chillin’ in the pool, laying out and getting tan or just hanging out playing games on the lawn. Overall I’m quite happy with the setup, though it does take some work to complete, and is certainly more complicated than picking up a cheap bluetooth speaker and just throwing it by the pool, this is much more integrated with the rest of my whole house audio setup, is basically permanent, is always on and ready to play, and of course sounds way better than pretty much any other cheaper bluetooth offering you could find.

So I hope this blog gave you some ideas if you’re about to venture into a similar project. And if you are I’d love to hear about it in the comments below! Or if you have a question, feel free to ask in the comments below too. See ya!

About Dan

For a complete biography, stop by www.danmarx.org and click around for a while.
This entry was posted in Audio/Video, General and tagged , , , , , , , , , , , , , , , , , , , , , , , . Bookmark the permalink.

One Response to Rockin’ Outdoor Speakers with DIY Sump Pump Basin Subwoofer

  1. Sean says:

    Thanks for measuring the Atriums – you seem like the only person on the net who has bothered, great set up too!

Leave a Reply

Your email address will not be published. Required fields are marked *