Big Brother Has Arrived – The Sonorous 12S Subwoofer Build

Earlier this year I built the Sonorous 10S subwoofer and have absolutely loved this subwoofer. So when the opportunity presented itself to build a second bigger version of this sub, I knew I had to do it. And so I introduce the Sonorous 12S Subwoofer! This sub is identical to its littler brother with the exception of the use of a Reference Series 12″ Dayton Audio RSS315HF-4 subwoofer driver and an enclosure that is 10 liters bigger. This sub uses the same Dayton Audio SPA300-D subwoofer plate amplifier which pushes a solid 300 watts. If the 10″ version was an awesome little subwoofer, the 12″ version thing takes it to the next level. Even when driven with the same mount of power, the Sonorous 12S has a touch more extension and just about 2 dB more output than the 10S subwoofer. But for the most part these two subs are nearly identical. This post won’t got into nearly as much detail as my previous post since the amplifier is the same, and most of that post was about the amp, but I will talk through some of the differences as compared to the little 10S version.

First let’s get straight to the technical brochure for the Sonorous 12S Subwoofer:

Dayton Audio RSS315HF-4 12″ Reference Series Subwoofer
Dayton Audio SPA300-D 300W Plate Amplifier with Selectable Bass Boost
RCA Inputs, Auto On/Off, 10 mV detect threshold, 30 minute on-time, Adjustable Gain (volume)
Adjustable Low-pass Filter 45 Hz to 150 Hz (24 dB/octave)
0/180 Phase Shift Switch
Switchable +5 dB bass Boost, Q 1.5, at 30 Hz
20 Hz Subsonic Filter (-6 dB at 20 Hz) 12 dB/Octave
Sealed Design, 35L Enclosure (1.48 cuft.)
System Qtc = 0.707 (critically damped, perfectly damped)
f3 = ~44 Hz (Bass Boost OFF)
f3 = ~26 Hz (Bass Boost ON, +5 dB at 30 Hz)
Max SPL = ?????? (measurements to come….) mathematical limit at 300W is 111 dB
15″ x 15″ x 16.25″ (H x W x D)
3/4″ + 1/4″ MDF Construction
Internal Cross Bracing + Corner Cleats
Fiberglass Insulation Damping, Walls Lined, 2″ thick
Semi-gloss Brushed White Finish
1/2″ Radius Cosmetic Roundovers (running front to back)
(4) Large Rubber Feet
5 Year Warranty on amplifier and driver (from Dayton Audio)

If you read the datasheet for the 10S subwoofer, you’ll notice that both subs share a favorable amount of details. Mainly because the amplifier is same across both subs. Honestly this was a decision I struggled with though. I kept tossing around amplifier ideas that pushed more power, I really wanted at least 500W. The Yung SD500-6 was an obvious contender as it had the raw power to push the sub to its limits and the 25 Hz bass boost to keep the response flatter in this tiny 35L box. In fact the 25 Hz boost modeled a bit better than the 30 Hz boost, but in the end I couldn’t justify the $100 price increase for an extra 200W of power at the expense of a solid 5-year warranty, a defeatable bass boost, no turn on/off thump and just good old fashioned Dayton Audio quality. Nothing against Yung, but with plate amps, this thing becomes a part of the sub, and if down the road I did have to replace it, it would mean having to figure out how to cut a new hole or fill this hole to make a new amp fit. I figured this way I’m covered for 5 years no matter what. The only other option that was tempting was the SPA500DSP amp which also offers a solid 500W and offers a complete DSP solution so tailoring the bass response would be right at my fingertips. In the end this option was also ruled out simply due to cost. This option adds significant cost to what otherwise is a pretty affordable subwoofer. Money-no-object scenario though, that would be the amplifier to get with this subwoofer in my opinion. External amplification can also work just fine, especially if you can do some DSP.

Up until now I had been using the 12″ RSS315HF-4 subwoofer for Garage Theater duties in a 95L ported enclosure with a 450W amp and that combo was awesome. I ended up swapping out that sub for an older TC Sounds dB-500 sub that was in my daughter’s car that she is no longer using. So after playing a little bit of musical subs, that landed me this 12″ bad boy to play around with. Since I really liked the way the 10S version sounded in my living room paired with my DM-4 mains, and since that sub was moved to my bedroom, I thought it would be really cool to have a dedicated sub for that system. That way for those times when I really wanted to crank up some tunes with bass, there’d be plenty of bump to go around. Plus I really liked the look of that small, sealed, white enclosure with that single black aluminum cone driver emanating on it its front baffle. I knew I could make a bigger version and have it sound at least as good, while still not taking up a ton of real estate, with the RSS315HF-4 12″ driver.

So with the the driver and amp in mind, I designed up the enclosure. In a similar fashion to the Sonorous 10S, I wanted this sub as small as possible, so naturally a sealed option made sense. And with the +6 dB bass boost of the SPA300-D, I could buy back some extension that’s always lost using a compact sealed design like this. But even without the boost, this sub models/sims great. Being a bit of a perfectionist, I went for a perfectly critically damped Q of dead on 0.707 and was able to design the box to be exactly 34.7 liters. This offers an ideal response that is neither underdamped nor overdamped. Though actually turning on the bass boost does mess with the total system Q overall, this is a great starting point to be at as far as volume goes. F3 is around 44 Hz without the boost and about 27 Hz with the boost enabled. The roll-off below 27 Hz is quite steep, due to the high-pass filter in the SPA300-D. It’s roughly -6 dB down at 20 Hz with a 12 dB/octave filter. Combine that with the natural 12 dB/octave roll-off of the sealed enclosure and the response is rolling off at a combined 24 dB/octave. This is apparent in the excursion plots where you can see that at no time is the subwoofer at fear of over-excursion, no matter the source frequency. So that’s kinda nice as I’m always afraid of blowing my subs from too much power.

The enclosure design is pretty basic but has some unique qualities. It’s made from 3/4″ MDF and finished in 1/4″ MDF for a total panel thickness of 1.0″. Four 3/4″ x 3/4″ corner cleats run front to back to strengthen these joints. Additional panel bracing was added to all four panels in the form of 3/4″ x 1.5″ ribbing pieces. This ribbing is then cross-braced to opposing panels using 3/4″ x 2″ MDF braces that are interlocking in 4 locations. All of this bracing does take up some additional volume but was calculated into the initial design from the start. The overall enclosure sits at 15″x15″x16.25″ (LxWxD). This size looks absolutely sweet with that massive 12.4″ subwoofer on its face. This was absolutely deliberate leaving a mere 1.3″ from the edge of the driver to the edge of the cabinet. The driver is also perfectly centered too to provide a pleasing aesthetic. The top and bottom edges are rounded over at 1/2″ front to back while all other edges are simply sanded down lightly to take off the sharp corner. This is opposite to many of the Dayton Audio cabinets which round-over the front and back edges, top-to-bottom. I just think this way looks better but is up for personal taste. Rounding over the edges is purely cosmetic and provides no other sonic benefits given that the upper frequency of this sub will likely never exceed 100 Hz. Making the box slightly deeper than its width/height is also somewhat cosmetic as I think it looks better, but is also to allow the box volume to increase just to under 35 liters.

So I built the box as shown in the pictures in a single weekend. And then painted it the next. So this took two weekends or so to complete, but could be done in one weekend pretty easily. The cut-sheet is shown here as well if you want to build this sub exactly as-is. All it takes is a 1/3 of a sheet of 4’x8′ MDF (32″x49″) and then two sheets of 1/4″ by 2×4 foot MDF panels. Cuts are made with a table saw and the box was assembled using Gorilla glue and various length 18 gauge brad nails. I screwed some of the panels together also just to make sure they were secured while the glue dried. I don’t have a pile of pipe clamps laying around so I still just use drywall screws, but sparingly. The tic-tac-toe looking cross piece was the most complicated thing to do, as I had to cut and trim each piece so that it fit snuggly into its location but not too tight so it wouldn’t fit, but no so loose that it wasn’t holding the sides together either. These pieces were individually cut one by one to fit into each of their respective locations. I interlocked the 4 pieces as shown and then hammered it into place lined up with the panel braces with a bunch of glue. It went in tight. And I could immediately tell a difference in panel resonance by thwapping the side panels with my knuckles. This box is solid.

I cut the hole for the driver and the amp and of course recessed them perfectly flush to the cabinet baffle. The best thing about any speaker project is getting that driver dead flush to the baffle, no underhang, no protrusion. That’s my favorite part. I nailed it on the nose with both the amp and the driver in this case and it just looks awesome. Also, getting the diameter of the driver recess to be within about 0.01-0.02″ of the diameter of the driver makes for a much cleaner look. You basically want the driver basket to nearly, but not quite, just scrape its way down. Nothing looks more tacky than when the cutout is too oversized for the driver, leaving a visible gap between the cabinet face and the driver basket. This usually takes at least once practice cut with the Jasper Jig on a scrap piece of wood to get just right though. Once you’ve gone too big on your actual box, there’s no going back. If you think a 1/16th of an inch should be “good enough”, you’ll soon realize that it’s far too big. You might need to account for some growth due to painting though. I’ve learned to just make it as small as I can and then try to get as little paint as possible on that inside edge. Cut it small, get it tight, and get it flush, that’s the golden ticket to a truly professional looking sub install.

I still have to measure the FR of this thing, when I do I’ll just update this post. It’s probably going to be few weeks though before I get around to it. For now I’m just listening to it and seeing what she can do. So far I’ve been very impressed. This sub is insanely tight and musical. And it’s dead quiet as far as extraneous mechanical noises even being pushed. It blends great with my DM-4 mains too, so long as the crossover and gain are set right. It’s easy to overpower the mains by maxing out the gains, so I’ve just been playing with balance mostly. I want the sub to be audible, have some presence, but not be noticeable, if that makes any sense. The SPA300-D has no problem driving this sub hard, even if there is some wattage left on the table. And that’s about it. Check out all the build pics and let me know what you think in the comments below. Thanks for stopping by!

About Dan

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