For frequencies as low as 20Hz, I would not trust my ears even if you are right at the speaker. If you hear upper harmonics or even the sounds from the attack of the note (which are almost always at higher frequencies) your brain will place the 20Hz at the source of those sounds!\n\n\nThe mains are putting out sound when fed a 20 Hz sine wave tone from REW at low volume with a 250 Hz crossover, that is it. I was surprised they made any sound at all. That's why I made this post. I have not looked into whether the sound they make will cause me any trouble yet, I'm waiting for my family life to give me the opportunity. \n\n\nWhy a 250 hz crossover? That seems really high to start with. Are you using small cube-type speakers or something?\n\n\nTo sweep the subs using a signal to the mains, as I can't get ASIO to work with REW.\n\n\nI trying telling him Audssey's sub EQ HT can do the job nicely, likely better as it will deal with.\n\n\nI'm not going to use Audyssey, I'm going to use a miniDSP, that's why I need to sweep the subs manually.