So I picked up two used Hsu ULS-15's this past weekend to replace my Outlaw LFM-1 Plus. Super exciting! I got them home, hooked them up, and ran some REW sweeps on them. Uh oh. One of them was making some bad noises on the low low end.
Almost like it was bottoming out... I put in Tron: Legacy and it made the same noise at the point where Sam enters The Grid. Crap.
I gain matched them per Hsu's instructions, even swapped the amps, but now BOTH were making bad noises. Double crap! I did some Googling and found that Audyssey MultEQ will look at the frequency response all the way down to 10Hz and below to make its corrections! I re-ran Audyssey, hooked up REW, and did some sweeps. Sure enough, way down in the single digits there was a boost being applied. The graph was still climbing as it went down past 7Hz! God knows what it was doing below that... I didn't run the sweep that low. I guess the ULS-15's had enough output and my room had enough gain that Audyssey figured it could get a flat response way down into the single digits, so it boosted the hell out of those frequencies. I turned off Audyssey and the problem immediately went away.
This sucks, because I liked the Audyssey EQ setting on the Marantz SR5003 in general. I copied the settings from the Audyssey EQ to the "user preset" EQ on the receiver, but I'm sure the resolution of the user preset is far lower than the automatic Audyssey EQ. Of course the sub response is also lumpier without the EQ than with... I do still have output to 10Hz, though. God bless room gain and sub coupling!
I guess one solution would be to get something with a subsonic filter like the Elemental Designs EQ.2 where I could use Audyssey EQ but tell it to cut stuff. That looks like the cheapest and easiest solution... I did try using the ULS-15's "ULF Trim" knob but it didn't make a difference. I guess the Audyssey boost was too much.
Anyway, thought I'd share this to save someone else my frustrations, haha.
Almost like it was bottoming out... I put in Tron: Legacy and it made the same noise at the point where Sam enters The Grid. Crap.I gain matched them per Hsu's instructions, even swapped the amps, but now BOTH were making bad noises. Double crap! I did some Googling and found that Audyssey MultEQ will look at the frequency response all the way down to 10Hz and below to make its corrections! I re-ran Audyssey, hooked up REW, and did some sweeps. Sure enough, way down in the single digits there was a boost being applied. The graph was still climbing as it went down past 7Hz! God knows what it was doing below that... I didn't run the sweep that low. I guess the ULS-15's had enough output and my room had enough gain that Audyssey figured it could get a flat response way down into the single digits, so it boosted the hell out of those frequencies. I turned off Audyssey and the problem immediately went away.
This sucks, because I liked the Audyssey EQ setting on the Marantz SR5003 in general. I copied the settings from the Audyssey EQ to the "user preset" EQ on the receiver, but I'm sure the resolution of the user preset is far lower than the automatic Audyssey EQ. Of course the sub response is also lumpier without the EQ than with... I do still have output to 10Hz, though. God bless room gain and sub coupling!

I guess one solution would be to get something with a subsonic filter like the Elemental Designs EQ.2 where I could use Audyssey EQ but tell it to cut stuff. That looks like the cheapest and easiest solution... I did try using the ULS-15's "ULF Trim" knob but it didn't make a difference. I guess the Audyssey boost was too much.
Anyway, thought I'd share this to save someone else my frustrations, haha.












I will have to confirm it works.
When the low end is not calibrated properly by Audyssey, and yet the ULS-15s still try to produce the signal that is sent to them, the amp on the ULS-15 starts to clip and it makes the driver do some weird stuff. I hope my suggestion works for you.

This is VERY rough on any subwoofer. It will easily cause headroom issues with even normally quite ample systems like the OP's. (This system measured uses sealed subs FWIW.)