I just got my sub painted, (after sitting in MDF form for a few months) and since it's now in a presentable condition, I thought I'd post a picture and some of the design details. This sub will not be posted on my web site. Sub design is generally simplistic and there's nothing really special here. There are a few cosmetic effects I used, like a combination or roundovers and chamfers. It's primarily black textured paint (Rustoleum) with a clear coat, then metalic aluminum over the texture coat on the front. It lends a futuristic look to it, which goes better in my living room than a wood finish.

Darren's Drake looks like a great design, but this sub takes the other route with a larger enclosure, lower power and the High Fidelity "HF" version of the sub. The larger enclosure offers lower bass distortion due to more linear air pressure and compression. The trade off is of course the size.

The 500 watt plate amp seems to be a good match for the RSS315HF in a 2 cubic foot box. In the graph above, it appears that Xmax is exceeded with 500 watts at about 35 hz, but realize that there is an impedance peak there and the amp's ouput into that impedance is substantially less. Not until you get to around 23 hz is this amp able to drive the woofer past excursion. In summary, above 23 Hz it's power limited, below 23 Hz it's excursion limited. Since it's a smallish sealed enclosure however, output is very well controlled in the low 20's, and damage is unlikely. This is the primary reason I chose sealed over vented - some movies have output in the 15 Hz range, and with the sub unloaded below Fb, there is a higher likelyhood of damage. I consider this sub, amp and enclosure a good balance.

The front baffle is double thick with a countersink for the woofer frame. It's removable, with 1/4" socket head cap screws and Hurricane nuts holding it in place. The woofer is also held in place with similar but smaller hardware. Because of the thickness of the baffle, I put some scallops on the rear for airflow. The baffle mounting bolts double as grill attachments with neo magnets mounted in the grill. This beats the hell out of those plastic pop-in things and it's easier to do than magnets hidden under veneer.

The rest of the sub is designed to be light but rigid as hell. Wall thickness is 3/4" with pine 2x2" diagonal bracing. This may be counterintuitive, but using double thickness walls does not reduce cabinet vibration at all. It just lowers the frequency at which it vibrates. It's all in the bracing, not wall thickness.

Components in a vibrating system have three important properties: mass (weight), elasticity (rigidity) and damping (dissipation). Mass resists acceleration, but the important part that people forget is that mass stores energy in the form of velocity. This is why it's generally misunderstood. Thick walls aren't really solving the problem - once you get them moving, they want to keep moving. Mass is not directly proportional to vibration, it's just a component that along with elasticity determines a resonant frequency. Only rigidity and damping can reduce vibration. Rigidity reduces vibration by reducing the potential of stored energy in the form of deflection, and damping does it by conversion of kinetic energy into heat energy. So think twice before you double up on the wall thickness...

The bracing arrangement I use is only effective in a symmetrical cube enclosure. It's based on the concept that operating pressure is evenly disributed on all 4 side walls. This places the pine gussets in perfect tension and compression with each in and out movement of the driver. The flexing component of the gusset is effectively half it's length, and with 4 per wall, pressure deflection is practically zero. This also has the benefit of not getting in the way of the magnet.

It's not too visible in the PDF drawing, but the amp mounting area is stiffened by a 4.5" thick H-frame arrangement. After some operation, I discovered I needed to cover the inside square of the H-frame with a piece of MDF to keep the plastic sub back from rattling. This whole assembly keeps the back panel rigid.

I used good old yellow glue on all corners and braces.

For stuffing I just grabbed a bunch of dacron fiber and tucked it under the gussets and in the small slots next to the amp bracing. One thing I did do that's probably not required is I glued a 11" square of whispermat WM2 (1"- barrier-1/4") over the sealed plate amp area. This is directly parallel to the baffle, so I thought I would eliminate a peak and dip around 300hz so I could more closely mach the intended sub crossover transfer function, even though it's many db down at that point.

The Quick Summary: I really like sound of this subwoofer design - and I'm someone who generally hates subwoofers.