I have had the chance to review two Alumapro subwoofers in the last several years and twice have been impressed not only by the excellent build quality of their woofers, but also by the design technology incorporated into them. If you happened to miss the previous two reviews of the Alchemy subwoofers, here's a little background on Alumapro. Unlike most loudspeaker company's whose only business is woofers, midranges and tweeters, Alumapro is actually a division of Syntronic Instruments, Inc, a leading manufacturer of precision magnetic devices and a long-time contractor for the U.S. military.
This 51-year-old company has supplied the government with a number of magnetic type devices including a specialized CRT deflection yoke for computers. In fact, the founder of Syntronic developed a high tech deflection yoke that made the first earth-to-the-moon communication possible. Needless to say, the company's ability to produce high-tech magnetic equipment goes way beyond the engineering expertise that's normally found in the loudspeaker business. However, as the cold war was coming to an end, so did the company's military contracts, which meant that Syntronic would have to look for new ways to apply their experience. Fortunately, one of the company's engineers also happened to be a bass guitar player with a lot of experience with loudspeakers. His knowledge and enthusiasm for music influenced the company's decision to develop an aluminum cone bass guitar speaker. After developing a driver that could take the abuse of an electric bass guitar on stage, the company turned its attention to another type of woofer that typically takes an extreme amount of abuse: car audio subs!
The subject of this review is a very specialized Alchemy 12" subwoofer, one that is intended for "marine" applications. For those of you with boats big enough to include a 12V audio system, just any speaker isn't going to cut it. Speakers installed in boats are subjected to not only high levels of moisture, but also salt-water spray that can cause damaging corrosion. If a woofer is going to survive that environment, it has to have some special "bells and whistles" - and that's exactly what the folks at Alumapro have done. The Alchemy 12-H2O 4-ohm 12" subwoofer uses a specially painted cast frame to resist corrosion along with corrosion-resistant coatings on all metal parts. Since all the Alumapro cones are made from anodized aluminum, it has built resistance to moisture and corrosion.
Alumapro's Alchemy Marine 12-H2O has all the same high performance features that I noted in the two other Alumapro Alchemy subs. First, they have incorporated a very well designed cast frame. Cosmetically good looking, the Alchemy frame has several important features such as 1" of depth between the spider and the front plate to allow long rear excursion strokes. Large air vents beneath the spider-mounting shelf built into the sides of the frame, called "aeroport" venting by Alumapro, were created for more efficient voice coil cooling.
The Alchemy motor system uses a T-yoke (single piece frontplate and polepiece) with a 4mm extended pole to linearize the magnetic circuit in the forward direction. Primary cooling is provided by a 7/8-inch pole vent. Both the T-yoke and frontplate have a black corrosion resistant coating to increase heat dissipation (black body radiation effect). Since the driver also uses magnetic fluid in the gap for cooling, it has four 1/8-inch peripheral gap area vents to provide the appropriate air flow that prevents the magnetic fluid from squirting out of the gap. The nearly 13 Tesla Meters of BL required to power the 12" spun aluminum cone is produced by two stacked 140mm x 15mm magnets, covered by the an injection molded rubber "boot".