About a year and a half ago the wife and I decided to retire our old entertainment center and completely make over our family room. We bought a new TV, a huge couch/sectional, a new area rug, a new leather ottoman (thanks Costco for basically furnishing my house), installed a bunch of ship-lap on the wall (thank you Fixer Upper for putting ideas into my wife’s head) and we bought a new media console (thank you HomeGoods, I really didn’t want to build another entertainment center). Of course after all this I took the opportunity to re-build an old pair pair of 2-way speakers and build a new center channel for the home theater to complement the new family room (thank you Parts Express). And that’s about where everything sat for over a year. It had everything we could have wanted but it lacked one vital thing…a subwoofer. So this past month I decided it was time to break out the power tools and start making some saw dust and built a killer new subwoofer for our family room theater. Now that it’s done I can finally say the room is officially complete! Man I can’t believe I went so long without having crazy bumping bass. Movies, games and music all sound so much better now, the bass is massive, it absolutely rattles the entire house. But before we get into that, let’s get down to the design, the build process, show off some pics, talk about my cool miniDSP enclosure, how I setup the miniDSP as well as how I made a neat little relay box to remote trigger the Crown amp to turn on and off with my receiver. So hunker down and read on below!
So the gist of the setup is this: a single Dayton Audio Ultimax UM15-22 subwoofer in a sealed 2.82 cu.ft. (80 liter) enclosure powered by a Crown XLS 1002 power amp and PEQ’d with a miniDSP 2×4 in a custom aluminum enclosure. Also I built a relay trigger for the Crown amp so that it goes into standby mode anytime the system is not use. This is a great setup for a small family room theater without being too over-the-top. Though it might pale in comparison to what some people have in their theaters, especially when it comes to the Ultimax series of subwoofers, for my modest little setup, it is just right. And quite frankly puts out way more rumble than should be possible for what is basically just a thousand watt 19.5″ cube. I’ll go through each of these parts of this project, explain some of the design choices I made, show a bunch of pics, and hopefully you find some of this useful if you want to build something like this for your home/family room theater.
The start of this project begins with probably one of the most important things – designing the subwoofer and picking out the drivers. I probably tossed around a hundred different ideas over the past year before really starting to commit to something I was going to follow through with. But at one point nothing was off the table, from doing a massive IB in the attic, to just a simple 8″ sub, to multiple sealed subs or just one massive ported sub to a smaller sub with passive radiators. Parts Express has such a great selection that it’s really hard to narrow down what you really want vs. what you really need vs. what you can really afford. Not to mention deciding how much time you want to spend building and integrating this thing into your home theater. All factors which can be very different for everybody, which is why to me there is no one-size-fits-all solution when it comes to subwoofer solutions. Which quite frankly is true for a lot of speakers or just audio gear in general. Here’s ultimately why I landed on the design that you see here today. And it’s based a lot on compromise, trading one design goal for another, putting a bit more emphasis on one factor than another, thus tipping the design in one direction when someone else might go another way. As you read on you will see that for me the major trade off was giving up some low-end SPL for a simple, small, compact enclosure.
I opened up my copy of Unibox 4.08 enclosure modeling software and entered in the T/S parameters for the last few Ultimax and Reference Series drivers that I was missing. Now I was able to compare everything from a single 8″ Ultimax to quad 18″ Reference Series drivers and everything in between. I realize that PE carries other subs and other websites carry other drivers, but truth be told, and let’s be honest, I am a Parts Express fan to the core. So I didn’t do a lot of shopping around on this front. And Dayton Audio make for such a great value proposition, you really can’t go wrong. Anyway, I swear I can spend hours playing around with driver combinations in Unibox, just comparing frequency response graphs of different size enclosures and comparing sealed to ported to PR designs. Seeing which ones have the best low-frequency extension, which designs exceed Xmax too soon, which ones need huge ports to maintain low air speed, which ones aren’t flat or need huge boxes, etc., etc. Everyone has their technique, and I look at a lot of factors when it comes to any notional design at this stage. Cost is always a concern as well, something Unibox can’t predict. I mean sure, I can simulate four 18″ Ultimaxes in 20 cubic foot enclosures all day long and then ooh and ahh at the crazy 14 Hz tune and an SPL approaching 130 dB at 15 Hz. But then I start to look at what that physically might look like in our family room and how much that type of setup might actually cost and I have to ask myself, is it really worth it? Well, duh, of course it would be worth it! But we’re going to choose to go another way with the objective of this build to keeping the cost to something fairly reasonable and that the sub be as inconspicuous as possible, something that fits the room and doesn’t take up a ton of space but can still hit 20-30 Hz with enough energy to shake and rattle the house.
What is a little more nuanced with the Daytons is differentiating between the Reference Series and Ultimax series drivers. They sort of each have their niche and they model completely differently. Ultimax tends to favor larger ported enclosures and needs a lot of power, but ultimately can hit louder and lower than the Reference Series without exceeding Xmax. Reference on the other hand is more efficient, it can do more with the power you do provide, doesn’t require nearly the same volume enclosure to still have great extension, but Xmax can easily be exceeded since they just don’t have quite the same excursion that Ultimax does. It can be a toss-up though and you really have to just look at the frequency response plots, the excursion plots and the box volumes for each and see if it’s something you want to do. Comparing difference designs is pretty easy especially across just two different driver families, if you just stick with one box type, but once you start comparing sealed to ported, to PR designs across different driver series, it can be a little tough to decide. Is it worth making the box just a little bit bigger to gain another 1-2 dB at 20 Hz? The excursion sims are starting to look a little scary, what if I am really easy on the volume knob, hey more power never hurt anyone as long as I am careful it should be fine, right? Whatever you have to tell yourself so that you can get to a design that you’re comfortable and happy with. But most importantly, it should be a design that you’re excited about building. A design so awesome that you can’t sleep the night before you start it because you’re just that excited to work on it. If building a plain-Jane ported 12″ box doesn’t seem like fun, even if the simulations say it will sound great, then don’t build it.
So for me to narrow down the process, I made the executive decision to just go sealed, because everything I modeled ported required a box that was just way bigger than what I wanted to do for this room. And if you really pay attention to port air speed to minimize port chuffing, port area need to be pretty big, which means the ports need to be long for proper tuning, which means the box needs to be that much bigger to account for the added port volume. Passive radiators do fix this problem (at a cost) and I almost bit the bullet on a single 12″ Reference driver with a matching pair of 12″ PRs. It basically checked all the boxes for my design, the box size was reasonable, the low-end extension was good and the cost was right on budget. I had everything in my cart, ready to check out and then at the last minute I backed out. I don’t recall my exact reasons, it would have been a perfectly fine subwoofer, but I think I was just a little bummed that I had settled on just a single 12″ driver. It just didn’t feel big enough. And for the same cost or even less, I realized I could go with a bigger driver in the same size box if I just committed to a sealed design. (Probably spending too much time on AVSForum didn’t help matters). That’s when I turned to Ultimax and realized that these drivers model fantastic in small sealed boxes. Extension rolls off as any 2nd order sealed driver would but you can still hit a decent f3 in enclosures that are not huge. And if you’re willing to compromise a bit on the system Qtc, then you can make the box even smaller, keeping Xmax even more in check without giving up too much on low-end extension. Not to mention the rugged glass fiber woven cone seemed like it would be a bit more durable than the softer aluminum cone of the RS series. Plus, I really think these drivers look awesome. That massively fat high-roll rubber surround, the omission of any sort of dust cap and that sweet-looking woven cone, a cast basket, leads stitched into the spider, plus the dual 2-ohm coils means more flexibility with amplifier options. So this was it, we were going Ultimax. And since I wasn’t too keen on just the 12″ it was really deciding between the 15″ and the 18″.
After modeling the UM15-22 and UM18-22 in various enclosures sizes, I ended up deciding to go with the 15″ as it didn’t require quite as big a box as the 18″ and with the money I saved I put towards a miniDSP. I figured if you had a $300 budget for just the driver, then the 15″ and a miniDSP would be more flexible and could possibly sound better than an 18″ without any DSP. And I realize the volume requirements are not that much different between the two subs, arguably I was splitting hairs a wee bit. The 18″ models fine in only 4 cubes but the 15″ works in a little as 3 cubes (it’s roughly the difference between an 18″ cube and a 20″ cube after bracing with 3/4″ MDF) if you’re willing to put up with a Qtc in the high 0.8’s. I ended up making my box only a 19.5″ cube which is 2.82 cu. ft. after bracing, driver, a double-thick front baffle and 1/4″ MDF finish) for a final Qtc of 0.88 (walls lined). Most people would probably just buy the 18″ and call it day, make the box as big as needed, and then end up buying the miniDSP (or equivalent) anyway. But I was really trying to keep the box under a 20″ cube and the budget wasn’t something I wanted to stretch any more (at least any more than I already had). However that 18″ can do another +2.5 dB over the 15″ at 20 Hz for only an extra 28 liters and at 5 cu. ft it will do +3.5 dB, which isn’t insignificant. But I can say that I am more than happy with just the 15″ so far. It absolutely bumps and shakes my whole house like nobody’s business. I don’t think you can go wrong with either driver. Also the 15″ on paper was a better match for the Crown XLS 1002 that would be driving it. I think the 18″ would have wanted more power. But going back to why I abandoned the 12″ PR design, I figured that the 15″ Ultimax also gave me a better upgrade path to either dual sealed 15’s or just building a 12 cu.ft. ported box down the road for just the cost of a couple sheets of MDF (which by comparison would be +10 dB at 20 Hz compared to the sealed enclosure that is one fourth that size, definitely not insignificant). So into the cart went the UM15-22 along with a miniDSP kit, a pair of terminal cups and some rubber feet. Done, let’s move on…