Adire says on the site that a Tumult is 2-TIMES the output of a Tempest woofer!!!!!
Tumult is simply the most displacement you can buy, period. Capable of a LINEAR 34mm of one-way excursion, this 15" driver features a low Fs, mid-value Qes, and small Vas. With input from hundreds of dedicated DIYers about their desire for applications for this beast, Tumult excels in IB, sealed box, Linkwitz Transform, and other high-quality installations. With over 5 LITERS of linear displacement, one does not need to turn to vented or PR systems to get high SPL bass (of course, if you choose to use a vented or PR based design, you simply get astounding levels of output).
Best of all, Tumult uses our patent-pending XBL2 motor technology. This new motor design yields the flattest BL curve of any motor design. And a flatter BL curve means lower distortion, and reduced dynamics compression. Truer to the signal - better sound. And contrary to what some claim, it doesn't sacrifice ANY BL or motor strength; in fact, the Tumult has more motor strength than just about any home audio driver available today.