I know I've said this before, but, just when I think that subwoofer technology has pretty much reached its pinnacle, a new sub comes along to shatter my illusions of stability. The new high-powered subwoofer that came to my attention is from a company whose Super Fi electrostatics have made a serious impact in the world of high-end mobile sound--Critical Mass. Critical Mass was formed by sometimes-race kart driver Wayde Alfarone in Orlando, FL, in 1990. Later acquired by Icon-TV, it has been leading the way to max performance hi-fi on the road with their $259,000 CES 5.1 system introduced earlier this year. The subject of this month's review is the subwoofer incorporated into that megabuck system, the Critical Mass UL12 12" subwoofer.
There has always been a strong correlation between subwoofer performance, dollar cost and sheer mass. That truism seems to have come to a grinding halt with the new Critical Mass UL12, as this serious maximum performance 5,000-watt peak subwoofer weighs in like a high-maintenance supermodel at a mere 16.6 pounds. The story of how this is done is a tutorial in state-of-the-art speaker engineering.
Let's start with the frame construction. The Critical Mass UL12's proprietary cast aluminum frame acts as both a giant heatsink and as one of two highly effective faraday shields, or shorting rings, that are incorporated into the motor system of this design. Each of the vertical-orientation frame spokes also does double duty as heatsink fins that protrude through slots in the metal return cup and are aligned in close proximity to the outside diameter of the voice coil. This aids in the critically important tasks of wicking heat away from the voice coil.
If you look at the cutaway drawing of the Critical Mass UL12 (Fig. 1), the first thing you notice is that this woofer not only has two somewhat small separate magnets, but also two gaps. These diminutive magnets are a special high-temperature neodyminum-iron-boron magnetic material (N-35, for you speaker engineers) that is far stronger per square inch than standard ceramic ferrite magnets and is the key to the UL12's light weight. The twin-gap technology is known as Multiple Magnet Air Gap (MMAG). Due to the layout of the MMAG neo motor format, Critical Mass was able to mount their frame in such a way as to surround the motor system and form a shorting ring around the outside perimeter of the voice coil. The second shorting ring is located on the inside perimeter of the voice coil and surrounds the smaller upper magnet.
The UL12 also has three other thermal pathways, two in the spider-mounting area and one at the rear of the motor. Integrated into the spider-mounting shelf are eight large roughly 2" x 1.75" vent areas formed by the mounting shelf and the frame that provide copious amounts of airflow over the area of the frame that couples to the top of the motor return cup. Another not-so-obvious feature is the aerodynamic quality of the small neo motor structure that provides an unobstructed pathway for airflow induced by cone motion. Along with the large vents below the spider-mounting shelf are twelve 1/4" vent holes in the upper part of the voice coil former that are staggered around the perimeter of the former and force airflow though the gap area and over the top plate. The last vent area is a series of eight slot vents located below each frame spoke in the lower outside perimeter of the forged and milled motor return cup that vents air pumped by the motion of the voice coil.