18 months ago, while looking for high efficiency subwoofer designs to augment the vintage Altec and modern full-range speakers I had been experimenting with, I stumbled across Devon Turnbull's IG with pictures of a massive woofer he recently built. After contacting Devon, I received my own Fostex FW800HS 31.5" Superwoofer a week later.
I've struggled with smaller subwoofers and have found them to sound "one note." Because of its overall design, I have found the Fostex Superwoofer to be much more "musical" than other woofers. The Fostex has a significantly different design compared to other common subwoofers on the market. Most woofers overcome the physics of playing low frequencies with high excursion, small boxes, and large amplifiers. In contrast the Fostex has a low excursion, relatively low power handling, and requires a potentially massive enclosure.
To give an example, I compared the specs of the Fostex with another 24" woofer on the market. The Fostex has an RMS power handling of 150 watts. The other 2000 watts. The xmax excursion of the Fostex is 2.3mm vs 78mm! The Fostex isn't just a big woofer, it has a different design philosophy than other woofers on the market. In my experience limiting the excursion solves significant distortion issues that other woofers (such as the Rythmik F12G I also own) address with external servo controls, and gives the Fostex a much more precise sound where individual notes and frequencies are much more distinguishable.
The Fostex is a gentle giant. Because of its efficient design, I have been able to achieve good results with a low powered push/pull tube amp producing about 30watts. If you are looking for chest thumping home theater slam, the Fostex might not be the best option. But if you are looking for more accurate and realistic music reproduction, there are really no equals on the market.
The biggest drawback (outside of cost) of the Fostex FW800HS is the size of the driver and the cabinet required. It is not a trivial undertaking to build the cabinet for the woofer, and my sealed enclosure required in-room assembly. I decided to take cues from old Electro Voice documentation (Electro Voice made a 30" woofer which was likely an influence on the Fostex), and built the sealed cabinet out of 2x4s and framed it like a wall. While the box resonances could be tamed a bit, it works surprisingly well.
The Fostex FW800HS has unparalleled low power performance for bass response in music at the cost of high energy output, size, and cost. With these tradeoffs, I have no regrets, and having chanced good bass reproduction for most of my life, the Fostex woofer is my all-time single favorite component. There really is nothing like it on the market.