I haven't heard the Def Tech's, but I have been up to my ears in the Ultra's. In absolute terms, they're a pleasant enough speaker unless you're waaaay younger than I am and have acutely sensitive hearing above 15 kHz, where the Ultra's take off like a rocket. They do have a slightly recessed response in the mid-treble due either to a deliberate voicing decision, a consequence of a sub-optimal high pass filter, or both. I have a pair here with a reworked crossover that measures much better and I think qualifies as a truly accurate speaker. I can send you before and after measurements if you email me at
info@philharmonicaudio.com Oh--did I mention they're for sale?