Generally IMD measurements are done on a single driver. Doing IMD on a multi-way speaker, and setting one tone well in the passband of one driver and the other tone well into the passband of a different driver should give you no IMD at all. In the case of a standard two-way tweeter over woofer, a tone of 100Hz and a tone of 4kHz would put the first tone in the woofer range and the second in the tweeter range, so there should be practically no IMD (assuming infinite slope crossovers). But a tone of 100Hz and a tone of 400Hz *would* show some IMD because both tones are played by the same driver. Likewise 4kHz and 10kHz.\n\nI think you're chasing ghosts trying to capture this complex problem with a simple measurement.\n\nI agree, I never thought there was an issue myself, especially when used at typical listening levels with a subwoofer, as I believe all smallish monitors should be used. I was mostly getting some kind of data to show it's not a problem because for some reason there is this myth of IMD distortion whenever coaxials come up. \n\nAnd I understand how IMD distortion works and you're right in a typical 2 way but we're talking about a coaxial driver, where the midwoofer cone acts as a waveguide to the tweeter so driver excursion could affect the tweeter response., That's also why I assumed, maybe falsely, that the crossover frequency wouldn't be a bad place to play the 2nd tone. Maybe if I'm in the mood to measure soon I'll try 100Hz along with 200, 400 as well just out of curiousity but again I don't think even the LS50 have a problem, my driver doesn't move when I'm cranking them pretty loud.