Wow, you know what?  The last time I ran a reference track through ARC 2 was before I put up my side/ceiling panels AND before I replaced the MoPads with Recoil Stabilizers.  I'd listened to some tracks through iTunes after installing those things, and of course it sounded better, but the only music I'd played through ARC 2 were my own mixes in Sonar. 
 
So, I just ran some reference tracks through ARC 2 in Sonar and I must concur that it sounds much better with ARC 2 than without.  Tight bass, clarity across the sound field, better stereo imaging, no more mud or upper-mid honk.  This tells me two things: 1) I'd gotten used to the way my monitors/room used to sound, and 2) my mixes sound like ****. :)
 
Oh well, I knew that already, which is why I installed treatment and bought ARC 2 in the first place!
 
So, I stand corrected.  Thanks for the feedback, everyone, and I'll say this:  ALL of you were right!  ARC 2 is not a replacement for acoustic treatment (nor is it intended to be), but it can certainly help.

codamedia
 Arc adjusts EQ, it cannot absorb reflections.

ARC works both in the frequency and time domain, so it does more than adjust EQ.  It attempts to compensate for reflections, ringing, standing waves etc. but any help you can give it with suitable room treatment makes its job that much easier.
 
I was using my headphones recently (late at night) and had forgotten to turn ARC off.  I was wondering what was causing all the strange echoing I noticed until I realised that ARC was enabled on the master bus.  That's its attempt to correct the room's behaviour in the time domain.

streckfus
...and I'll say this:  ALL of you were right!  ARC 2 is not a replacement for acoustic treatment (nor is it intended to be), but it can certainly help.

No one ever said it was to replace treatment.
 
but the truth is, most rooms cannot be helped with ONLY treatment.
even if you had all the money in the world and threw everything available at it.
 
 
 

streckfus
Wow, you know what?  The last time I ran a reference track through ARC 2 was before I put up my side/ceiling panels AND before I replaced the MoPads with Recoil Stabilizers.  I'd listened to some tracks through iTunes after installing those things, and of course it sounded better, but the only music I'd played through ARC 2 were my own mixes in Sonar. 
 
So, I just ran some reference tracks through ARC 2 in Sonar and I must concur that it sounds much better with ARC 2 than without.  Tight bass, clarity across the sound field, better stereo imaging, no more mud or upper-mid honk.  This tells me two things: 1) I'd gotten used to the way my monitors/room used to sound, and 2) my mixes sound like ****. :)
 
Oh well, I knew that already, which is why I installed treatment and bought ARC 2 in the first place!
 
So, I stand corrected.  Thanks for the feedback, everyone, and I'll say this:  ALL of you were right!  ARC 2 is not a replacement for acoustic treatment (nor is it intended to be), but it can certainly help.

Now that's bitter sweet but definitely a step in the right direction.
 
Rocku

This is a great thread, even with the ups and downs.  We've always been happy to recommend people use treatment along with ARC and had even bundled with some treatment years ago.  I kind of wish we still did that, I should probably kick that conversation up the chain.  I will also recommend that we talk to potential ARC users more specifically about what kind of treatment would help most in conjunction with ARC so you can all get more out of it while planning accordingly.  Basically, what you might do best with first then you can treat your room over time while still having the ability to create mixes that translate much better than they had in the past.
 
Here is the section from http://www.ikmultimedia.com/arc about ARC's use in treated or semi-treated rooms:

Do you need ARC 2 
if your room is already treated?

ARC 2 can improve the acoustics of ANY room. An untreated room will experience a dramatic improvement – but also treated rooms will sound better depending on the quality of the existing treatment. Many of ARC 2 improvements make it more effective in a wide spectrum of applications — from amateur bedroom studios to the most high-end professionally treated studios.

Some technical information, because this stuff is (understandably) poorly understood by people unfamiliar with DSP:
 
1. "Time domain" and "frequency domain" are two different ways of looking at the same thing. Don't think of it as two different things. I use the analogy of decimals vs. fractions: 1.75 and 1 3/4 are different ways of expressing the same thing, but each has different advantages and disadvantages depending on how they are being used. With some caveats you can convert back and forth between the time and frequency (and other) domains. 
 
2. FIR filters, for instance linear phase EQ's, are mathematically the same as a pure convolution reverb. The only difference is the IR. Does a reverb IR contain timing information?

IK_Multimedia
This is a great thread, even with the ups and downs.  We've always been happy to recommend people use treatment along with ARC and had even bundled with some treatment years ago.  I kind of wish we still did that, I should probably kick that conversation up the chain.  I will also recommend that we talk to potential ARC users more specifically about what kind of treatment would help most in conjunction with ARC so you can all get more out of it while planning accordingly.  Basically, what you might do best with first then you can treat your room over time while still having the ability to create mixes that translate much better than they had in the past.
 
Here is the section from http://www.ikmultimedia.com/arc about ARC's use in treated or semi-treated rooms:

Do you need ARC 2 
if your room is already treated?

ARC 2 can improve the acoustics of ANY room. An untreated room will experience a dramatic improvement – but also treated rooms will sound better depending on the quality of the existing treatment. Many of ARC 2 improvements make it more effective in a wide spectrum of applications — from amateur bedroom studios to the most high-end professionally treated studios.

Slightly OT but you know what would be great? If ARC came bundled with a folded piece of card or paper which is marked with the ideal measuring positions around the listening position. You could just tape it to the floor and get measuring straight away. I think one one of the most time consuming and fiddly aspects of doing the measurements is marking out the spots in a symmetrical pattern as illustrated in the manual. I ended up marking them out with tape, but I've since taken the tape up and I'm looking to do another set of measurements quite soon. Not looking forward to marking it all out again....I guess this time I may mark it out on a sheet of construction paper and keep it rolled up in a tube or something.

saw a video once of a guy using a laser to pinpoint the locations needed for Arc..

Elffin
saw a video once of a guy using a laser to pinpoint the locations needed for Arc..

Now that's just showing off.

Elffin
saw a video once of a guy using a laser to pinpoint the locations needed for Arc..

That's a great idea. Laser levels are inexpensive these days. Set it on top of a monitor, line it up and voila first wall reflection spot.
 
Rocky