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…
So with the Ultimax 15-incher on order and the basic box volume determined, I set out to finish the details of the enclosure and create my MDF cut-sheet. One thing I did this time around that I had never done in the past, was design the cut-sheet to allow Home Depot to make the first two cuts so that I could easily bring it home in my car. I used to own a Chevy Tahoe so buying 4-foot by 8-foot sheets of MDF was no problem and I could make all the necessary cuts at home from a full sheet. Sadly that car is no more and my Dodge Durango just doesn’t have the width to accommodate a full sheet of MDF. So with a little thought, I was able to layout the panels such that Home Depot would make two cuts at 39″ thus making two 4×3 foot pieces with a third piece only 1-1/2×4 feet. This made handling the MDF much easier over all and of course it also fit into the Durango with no fuss. I am never bringing home a full 95-lb. sheet of MDF again, this was too easy plus it wasn’t that much harder to layout the cut-sheet to allow at least the two cuts by Home Depot. This may not be as easy for other sub designs, for this small box it worked out great.
So a quick note about the bracing technique of this enclosure. I made 4 cross braces, 2 vertical and 2 horizontal, that interlock with each other and each brace contains one more cross brace about midway back into the enclosure. It looks reminiscent of PE’s flat-pack kits but with a bit more cross bracing, ultimately providing 4 locking pieces side-to-side and top-to-bottom and 8 pieces front-to-back. The trick with any bracing structure is to tie opposing panels to each other in as many locations as is reasonable. This design overall braces every panel about every 5-1/2″ to its opposing panel where feasible. The driver hole prevents some cross-bracing towards the front of the enclosure, but you do what you can in this area. I made sure to put the horizontal and vertical cross braces just about 1″ away from the back of the magnet on the driver, which is about 8″ deep into the enclosure. The front of the enclosure is 1.75″ thick and the top and sides are also 1.0″ thick. The bottom and back are the only 2 panels that are only 3/4″ thick. I’d say this is just about the minimum bracing for any sealed box using a driver of this size but at the same time almost feels like it’s overkill. Frankly, you can’t go wrong with more bracing to the extent that you start to sacrifice needed internal volume, for which you can always make the externals of the box a bit bigger to account for it. My total bracing takes up only 0.25 cu. ft. (or 7 liters) but the trade-off is well worth the added stiffness that is achieved. I usually do a more traditional window bracing but that really only catches four of the six panels, where as this does all six. The front to back bracing being one of the strongest areas now especially because this area is usually the weakest due to the driver cutout. Even with the double-thick front baffle, it’s still important to tie what surface are you do have to the back panel and we achieve this about every 6″ around the driver opening. I tapered the braces as well so that they are 2″ at their thinnest point at the front and 3″ at their widest at the back. Even at 3″ wide, if there is no direct tie to an opposing panel, having the brace be 3″ wide provides a much more rigid structure than say if it were only 2″ wide or worse, only 1″ wide. All in all, this box feels extremely rigid, tapping around the different panel locations results in a very nice deep thud sound without any hollowness or knocking sound at all. Plus I really like the fact that each bracing structure is basically cut from one piece of MDF. You could just use scrap pieces to create cross bracing everywhere you think you need it, but having the cross braces be a single homogeneous piece of material just feels like it’s better. I did add 6 little MDF blocks to finish the cross braces on the two internal braces, just because that was the only way to actually build it, but other than that, as you can see from the cut sheet, all the braces are cut from a single panel.
So take a look at the pics for more details. You can pretty much gleam everything you need to from just the pictures. I used my Jasper Jig to flush-mount the driver and set the depth on my router for exactly 0.400 inches. This puts the basket flush to the face of the baffle after adding some 3/8″ foam gasket material and screwing down the driver. I used 1-1/2″ #8 black anodized machine screws from Ace Hardware. I experimented with various screw types and sizes and determined these screws to be more than adequate. I undersized the pilot hole by about 1/64″ just to provide a slightly tighter fit to prevent the screw from stripping out of the MDF. On a test piece of MDF I was able to reach max torque on the the highest clutch setting available on my drill without it stripping out. And that was just a 3/4″ piece of MDF. I’ve used t-nuts and hurricane nuts in the past and their benefit does not outweigh the negatives if that nut strips out in my opinion. Unless you have a removable rear panel or something, it can be almost impossible to get the driver out. Screws work fine, just don’t use drywall screws, pick up a good set of pan-head machine screws and do not drill the pilot hole too big. For double-thick front baffles this provides plenty of material to hold those screw and still give you at least half a dozen install/removals (or more) for playing around with insulation/polyfil. I only wish they made a decent wood screw with a cap head since a phillips head doesn’t look quite as nice. One trick that I absolutely love for finishing ugly MDF boxes is to buy a couple of those pre-cut 1/4″ thick 2×4-foot MDF panels from Home Depot and then basically use it as if it were veneer to “finish” or “wrap” the box. This hides every screw, every rough MDF edge and provides a near perfect finish that is ready to paint. The day I went to Home Depot though they were out of 1/4″ MDF boards, so I ended up buying what was basically the same thing but was labeled as Chalk Board, which was a 3/16″ MDF board that had been pre-painted on one side with what I’m assuming was just chalk paint. I figured hey no problem, board is already primed black, ready to paint. They worked out perfectly and did prove to provide an awesome starting finish for painting this box. Without going into the entire painting process, I basically just spray painted the boxes in a flat black, sanded with some 320-grit sandpaper between coats, did about 4-5 coats overall and then did a final sand with 600-grit before applying a Minwax Polycrylic in semi-gloss with a foam brush for the final finish. I sanded the polycrylic with 320-grit between coats as well and did three coats and then called it good. No mystery here, but I did royally screw this part up a few times, which I won’t go into the details of here since this post is already super long. But I may write about it as a separate blog post because sometimes the easiest way to learn is from other people’s mistakes. Also I had added 48 oz. of polyfil but after listening to it for a while, I pulled out probably 30 or so oz. I think it sounds better with less polyfil, it’s got just a little bit more kick, but it’s really hard to say for sure. I should have taken more measurements in each configuration. I might add back in a half-pound later on for an even 2 lbs. The Qtc is probably still up around 0.8 but seems just fine to me.
So let’s move on and talk about the miniDSP setup. I basically took a 2×4 miniDSP kit and turned it into a 1×1 miniDSP. This wasn’t totally intentional, it just sort of worked out that way. I bought a small aluminum project box on Amazon with the intent of drilling 4 holes in the front for the 4 RCA outputs and then running two short pieces of coax to another pair of RCA panel-mount jacks at the back. But once I started playing around with placement of the miniDSP inside the enclosure, I realized that I didn’t need all 4 outputs and in fact I didn’t even need both RCA inputs. All I really needed was 1 input and 1 output. So I decided to completely enclose the miniDSP, all the RCA connectors, the DC power jack, even the micro USB jack and just leave a clean front panel without anything on it all. Not even a power button. I did debate the power button though and really wanted to do a slick aluminum LED back-lit push-button, but in the end just decided I didn’t need it. On the back of the enclosure is a DC power jack and two gold plated RCA connectors. I cut up an old RCA cable and soldered it to the input and output locations on the circuit board and back to each RCA connector. I used an LM317 voltage regulator board that I had leftover from my DM-4 speaker project and managed to squeeze that thing in there to clean up the voltage from a cheap 12V walwart I had lying around. I set it for 5.5 volts to allow enough headroom over the input voltage so that I would achieve the specified ripple rejection and since the miniDSP can operate down to 4.5 volts, it provided 1V of headroom over the minimum voltage there too. I soldered up the input and output and gave it a quick test. Once plugged in, the miniDSP lit up and the little LED started blinking. Success. The only problem I really ran into was I couldn’t fit a standard micro USB cable into the micro USB jack because it was too close to the back panel. So I had to buy a 5-pin to USB cable so that I could use the 5-pin header instead. This worked out just fine and once the miniDSP is all programmed up, I won’t really need access to the USB port any more anyway because with the cover on, it’s actually not accessible at all. Just a DC power jack and two RCA connectors. Sweet and simple. But it works like a charm. Anyway you can’t even see it in my media console, so realistically I could have made it look worse and nobody would have cared. But you can check out the pictures below.
A few days after I got everything set up and the family started using it, I realized that I didn’t like having to turn the amp on and off all the time. I thought I wouldn’t care, I would just leave it on all the time, or turn it on in the morning and then off again at night, or just turn it on for movies and leave it off for everything else. But I realized I really liked having it on more often than not. Even TV shows sounded better with a little bass. But I didn’t like having to think about turning it on or forgetting to turn it off at night. So I decided to figure out how to utilize the sleep mode on the Crown XLS 1002 amp. This is sort of an unusual configuration for a home setup, and maybe it’s more standard in commercial gear, but normally you would have a 12V trigger to turn things on and off. But the Crown amps use a Phoenix-style connector that requires pins 1 and 2 to be “closed” to put the amp in sleep mode. I’m not sure it actually powers off the amp, but puts it in some kind of low-power mode, then when the contact pins are opened, the amp comes back to life. So basically the only way to make this work with a receiver is to figure out how to get something like 5V or 12V out of your receiver (that powers up and down with the receiver) to turn off and on a relay which can then be connected to the Crown amp to open and close the pins as required. So I was poking around on the back of my Pioneer receiver, hoping to find something that looked like it might turn off and on with the amp, like a switched set of 110V mains, which is common on most receivers, but mine did not have any. Then I found something even better, a USB port labeled “DC Output for Wireless LAN”. Was this switched with the power button? Or was it just on all the time to power some always-on external wireless LAN adapter? A quick check with a voltmeter and wouldn’t you know that sucker was absolutely switched with the receiver power. With a click of the internal relays on the receiver, 5.02V showed up on the meter. And that was that, I had my 5 volts to drive a relay to turn off and on that Crown amp. If you don’t have a convenient 5V USB port on your receiver, but you do happen to have a switched set of mains, you can still use this relay box, but you’ll just need a small 5V USB adapter that you probably have 10 of lying around your house.
So I popped on over to Amazon and picked up a pair of pre-built 5V relay boards for $6. I also bought a small 3x2x1 inch project box to house this contraption for another $5. I used a DC power jack from my miniDSP project (since I bought a pack of 10) just to make the box somewhat modular. I cut off the end of an old USB cable and ran it through a hole in the side of the box and checked for continuity from the +5V and GND and then wired up the relay to turn on when it received 5V. These relays were pretty cool because you could wire them to be active low or active high, so it would have been possible to actually activate the relay with a low on the input (assuming you just had a constant 5V). But in this arrangement we basically power the board and activate the relay all with just the same 5V trigger from the receiver. The relay also allows for NO or NC contacts. For the Crown amp, we want to use the NC position (normally closed), this way when the relay is off, the contacts are closed, thus putting the amp into sleep mode. When the receiver turns on, the 5V kicks in and engages the relay, which opens the contacts and thus the amp comes out of sleep mode and is ready to bump. Also I stole a 4-pin phoenix plug from the Russound amps running my outdoor setup and cut off one of the sockets, but you can buy 3-pin phoenix plugs on Amazon for about $9 for a pack of 20. I highly recommend this setup if you have a Crown amp and want it to turn off and on with your stereo. It’s super easy to build, will only cost you about $20, assuming you have none of these parts just lying around. I took a bunch of pictures of how I wired it so hopefully you can see where to hook stuff up. Hopefully it makes sense and you too can have a remote trigger for your Crown amp.
So I never really explained the Crown XLS 1002 amp that I had picked out for this setup. I’ve read mixed things about these amps, some say they are great, others don’t like them at all, and ultimately decided to give it try myself because I liked a lot of the features the amp had to offer. First and foremost, this thing can drive everything from 8 ohm to 2 ohm loads per channel or 8 to 4 ohm loads when bridged so it’s super flexible for driving either a single sub or multiple subs. While this is typical of most class D amps these days, Crown doesn’t fluff their numbers as much as some other manufacturers might do. Rated at 215 watts into 8 ohms or 1,100 watts bridged into 4 ohms, this amp should be a perfect match for the Ultimax UM15-22 which is rated at 800 watts RMS. I don’t know if Crown’s rating is RMS or not, my guess is it’s not, but might be something close to it, it should still be plenty of power to drive the Utltimax to its limits. I’ve read where people say they’ve pushed way more power to Ultimax and that they can handle it no problem, but I really didn’t want to run the risk of overdriving my brand new sub. Besides, just about the only thing Parts Express doesn’t cover under their 5-year warranty is damage to the voice coil from being overdriven. You could argue about having more headroom and/or room to grow by getting any of the bigger Drivecore II Series amps but for me again it came down to cost and me trying to keep this total project as cheap as possible. Another feature about these Crown amps is the option to run the input sensitivity at 0.775 Vrms. I believe this is a must for any home audio setup, since most receivers probably don’t put out more than 1 Vrms out of their LFE channel. The miniDSP is only rated at 0.9 Vrms in and 0.9 Vrms out (when jumpered properly, otherwise it can do 2.0 Vrms in and 0.9 Vrms out). Without that low sensitivity setting, it would be impossible to drive the amp to full power. I have the amp set at 0.775 Vrms and even still my receiver sub level needs to be set to about +8.0 dB (out of +12 dB max) to feel like it’s really matching the mains. I have seen the clip lights flicker too, during a crazy intense explosion scene, it was just for a second, but the sub was moving. So it is possible to drive this to clipping with this setup, and realistically the Ultimax probably could have taken more, it didn’t feel like it was about to give up one bit. But overall still feels like a safe setup, I won’t have to worry about the kids watching a movie and just blowing up the sub because they’re not paying attention the awful sound of the voice coil clattering against back of the pole piece. Other features of this amp are the ability to turn off all the panel lights, the signal lights, or any combination of lighting you choose. I turned them all off except for the signal lights. Odd thing though, when the amp is in standby, both panel lights blink at about a 1 Hz rate and I can’t figure out how to turn them off. It’s not too annoying though, because when everything is off no one is out there anyway, and it’s kinda nice when everything is off to see that amp blinking, that way I know it is actually “off” too. And lastly the amp does have some nice DSP options, none of which I am utilizing because of the miniDSP. Even still, it only really offers crossover options, which for the LFE output of a receiver isn’t necessary since the receiver takes care of the crossover as well. Overall this is a great amp. Oh and I also forgot to mention, the best feature of all, it is dead silent. I have never had the fan turn on once yet. So that is a huge bonus for a home theater setup where the amp is literally sitting only about 10 feet away from you. The only thing I can hear is my ancient HTPC and the 6 fans in that thing whirling away. But the Crown XLS 1002 is silent as a mouse. Also, it doesn’t look ugly. I mean, it’s sort of ugly, but for a pro amp, it’s less ugly than some others. The all-black front behind the glass in my media console isn’t even noticeable with the door shut.
Okay well with that I think I am going to call it for this blog post and write a new post about setting up the MiniDSP and taking measurements and show you just what this sub combo can do. There is way more to go into regarding driver placement, using REW, measuring the in-room sub response, creating correction filters, exporting the filters from REW and importing them into the miniDSP, so much more to discuss, so for now I will defer to another post. In the meantime, check out all the pics and let me know what you think of this setup in the comments. I’d love to hear your thoughts on my setup. Do you have something similar? Something better? Go ahead and let me know what you like and what you don’t like. And thanks again for stopping by.