This subwoofer project was 6 months in making but after a couple of weekends of really focusing on it, I’m happy to say that it is finally done! This will be the complete (and exhaustive) detailed design and build review of The Sonorous 10S Subwoofer. This subwoofer has changed my perspective of how much deep bass can be achieved in small packages. And you don’t need to spend a fortune to get good, detailed, deep bass for your home theater or stereo system. So read on to find out more about this sweet little subwoofer project and maybe it will fit the bill for a similar project you’re working on.
Here’s what would be the marketing brochure for The Sonorous 10S Subwoofer:
Dayton Audio RSS265Hf-4 10″ 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, 25L Enclosure (0.88 cuft.)
System Qtc = 0.785 (slightly under-damped)
f3 = ~40 Hz (Bass Boost OFF)
f3 = ~26 Hz (Bass Boost ON, +5 dB at 30 Hz)
Max SPL = ?????? (measurements to come….) mathematical/physical limit is 109 dB
13.5″ x 13.5″ x 14.5″ (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
3/4″ Radius Cosmetic Roundovers
(4) Large Rubber Feet
5 Year Warranty on amplifier and driver (from Dayton Audio)
I don’t normally give my speakers names, but I decided to try something new with this one. Sonorous means “capable of producing a deep or ringing sound.” I thought it fitting for this sub project. Now on to the real fun!
Enclosure Design – My Thought Process
First and foremost, my main reason for selecting a 10″ driver was two parts: size and cost. First a 10″ driver doesn’t require a huge enclosure so a small footprint can be easily be achieved. In most cases this will come at a compromise in terms of total output and low-end extension, but depending on your needs, that may be acceptable trade to make. Although with this sub you’ll see that we hardly give up that much and still are able to deliver a very compelling bass experience. And second, this driver as of this writing costs about $209 with free shipping from Parts Express. Compared to larger comparable drivers, this is definitely cheaper than most options and very reasonably priced for what you get. And since this is only a 10″ driver, the amplifier needs are reasonable as well. You can get away with a simple 300-watt plate amp and you’ll be able to push this driver to its limits. The SPA300-D amp is brand new from Dayton Audio and runs $149 and is the cheapest of the bunch that PE offer in the 300W range. Other options you might consider would be the SPA250, Bash 300S, SPA250DSP, or the Yung SD300 which will run you from $180 – $225. I’ll go ahead and recommend the SPA300-D as it measures well, has the bass boost which can be turned on and off, plus all the other features you’d expect from a basic plate amp. In my opinion it’s the better value of these 5 units, unless you want the DSP options for additional in-room tailoring.
Since we’re going for a cute little sub here, I’m going to rule out a ported design from the start. Not that the RSS265HF-4 doesn’t model great in a port box, because it absolutely does, it just requires more than twice the volume to get there. So I modeled up 6 different sealed enclosure volumes, that were based on going from an 11″ cube and working my way up to a 15″ cube in 1″ increments to see if there was sort of a sweet spot between output, extension, excursion and size. Ultimately what you see in the plots is that all of these enclosure volumes can work. The smallest sub sacrifices some low-end extension, but excursion is best kept in check. The largest box does produce the lowest f3, but excursion limits will be exceeded at max power, so you gotta be careful with the volume knob. Somewhere in the middle you get what I would call the Goldilocks sealed design: acceptable f3, Qtc < 0.8 and driver excursion is no more than 15% above the specified Xmax.
With Xmax being the physical design constraint and all other parameters being design nice-to-haves, if we fix the input power at 300 watts (based on the amplifier selection) and we target 14.1 mm excursion (12.3 + 1.8) we end up with a volume of 23 liters. After playing around with some physical box dimensions, this ends up being an odd 13.25″ inch cube. What I ended up settling on was the dimensions shown above which result in a total enclosure volume of 25 liters, give or take. In this case we are at about +20% of xmax instead of the general rule of +15% but since PE doesn’t spec Xmech, the 15% is only a rule of thumb, so I will allow it. Plus, as you will see, once we model the excursion taking into consideration the high-pass cutoff of the SPA300-D, our peak excursion drops to 14.4mm at 300W which reduced the excursion to only +17% of xmax which is even better. Fundamentally you can play around in this region of about 20 to 30 liters pretty safely with this driver without a high-pass filter, but with the inclusion of a high-pass filter around 20-25Hz, you can get away with a slightly larger volume, which results in a slightly better f3 and lower Qtc.
So with the enclosure size decided upon and the basic dimensions roughed out, I drew up an cut-sheet and hopped on over to Home Depot some 3/4″ MDF. Man oh man has the cost of lumber gone up! I paid over $60 for a 4×8 sheet of 3/4″ MDF. I’ve never paid that much for MDF in my life. I’m hoping costs comes down because with lumber costs this high, it really starts to eat into the savings that make DIY speaker building so appealing. I bought a 2×4 foot piece of 1/4″ MDF as well as some other odds for projects around the house (gotta make the trip worthwhile since gas prices are also insane). I had one of the employees cut the board into three ~32″x49″ pieces so I could fit them into the back of my Durango. I’m hoping to actually get either another subwoofer out of this sheet or a pair of bookshelf speakers. The cut-sheet requires only one ~32″x49″ piece and even with that, there is some scrap for the bracing and corner cleats. You can download the basic plans by clicking on the pics and download the cut-sheet here.
I won’t go into details on building the enclosure as it’s pretty much just a basic box. I made all the cuts on my table saw and with some Gorilla Glue and my nail gun I just popped the thing together. You can use screws or clamps or whatever your joinery method of choice. After getting 5 of 6 sides together, I paused to add the 3/4″ x 3/4″ cleats that run front to back in each of the corners. My intent here was to further secure the butt joints and because I really wanted to create a larger round-over on the edges and if I can get my hands on a larger bit, then one day I am going to cut those corners down in which case most of the butt joint will be cut away. I will need the corner cleats to really secure the enclosure. For now I just did a 3/4″ round-over so the cleats just help to strengthen the fairly week butt joints as they are. I added a center beam brace going front to back on all four sides and added the cross bracing which connects the beams to the sides and the top and bottom. Given how small this enclosure is, the interior panels are only about 1 square foot, this feels like just enough bracing without being too much and taking up precious internal volume. We’ve cut the panels in half and then cross braced them basically about 7″ back (not totally centered). The only other thing to do may have been to run a another set of beam supports around the inside of the box, thus cutting the panels in half again. But this seemed fine to me so I left it at that.