For any of you ARC 2 users who have less than ideal (i.e. terrible) rooms -
 
With this year's tax return, I decided that instead of buying some cool gadgets, better monitors, software and all the "fun" stuff, I needed to invest in some acoustic treatment for my room.  I'm in a 10'x10' room with an 8' ceiling, pretty much the worst setting for a mixing desk. :)
 
Knowing that the room's dimensions and layout would never result in a "perfect" studio, I figured that I'd use ARC 2 to help offset any deficiencies that remained after adding treatment.  So I purchased ARC 2 and did an initial measurement with no treatment in place.  As expected, ARC 2 reported some pretty significant cuts/boosts.
 
The first order of business was installing GIK Acoustic Soffit Bass Traps (17"x17"x4') in the front corners.  I did the old "clap loudly" test to see if flutter echo had decreased (not very noticeably), then took another measurement with ARC 2.  There was a slight improvement in the low end frequency response, but not much.
 
Then I built acoustic panels for the side walls.  The panels contain Roxul bats three inches thick and are 2'x4'.  I have two hanging on each side wall at the monitor reflection points, then two more hung from the ceiling above my mixing position.  And holy crap, what a difference those made, at least that's what I thought.  Just talking in that room sounds more like a studio environment, and I finally passed the "clap loudly" test with the side/ceiling panels.  They sucked up that annoying echo and I was no longer worried about ruining vocal takes because of all the reflections.  I was very happy with the way everything sounded.  So I figured I'd substantiate my pride by taking one last ARC 2 measurement.  The frequency response hardly changed at all.
 
Huh???  I can hear a significant difference in the quality of the room.  It's by no means perfect and never will be, but it's unquestionably better than it was.  I couldn't tell an audible difference when I installed the bass traps, but I could hear a significant difference once the remaining panels went up.  Music played through my monitors felt tighter and more balanced, but maybe that was just my brain tricking it into thinking it sounded better because I'd spent around a thousand bucks to improve the sound of my room! 
 
Assuming my brain wasn't playing tricks and the acoustics really have improved, any idea why ARC 2's measurements don't reflect this significant improvement?  I know that adding treatment doesn't change the physical dimensions of the room, but you'd think significantly decreasing reflections would yield a noticeable change in frequency response...

You are simply seeing the fundamental limitations of ARC, which can neither detect nor mitigate the kinds of problems that you've addressed by adding absorption.

Yep, I know that ARC isn't going to turn my project studio with modest hardware and my own limitations into a professionally tuned room, and I do understand that my own skills have as much to do with my mixes as the software/hardware I'm using.  But after seeing how so many people rave about ARC 2 and how it has helped them overcome some limitations in their listening environment, I was really surprised with how little my treatment seemed to effect the measurements.
 
I assumed that an untreated room with tons of reflections would cause phase cancellations and other anomalies that affect a room's sound, and that ARC would identify where in the frequency spectrum those problems are occurring.  It did show significant peaks/dips before I treated the room, so how did it detect those if not from reflections?

streckfus
 
Assuming my brain wasn't playing tricks and the acoustics really have improved, any idea why ARC 2's measurements don't reflect this significant improvement?

 
What are you basing this statement on?  Are you reacting to what the EQ plot in the ARC UI looks like?  If so, be aware that that only tells half the story.  As I understand it, ARC also does things with signal phase across the audible spectrum, and that does not show up on any graphic in the ARC UI.

I THINK you are seeing how little actual room treatment can make, 
especially on the low end side..
 
i mean, i'd have to see your before and after curves,
but i bet the majority of the curving the ARC software is doing, 
is in the low end.
 
and MOST of that curve,
is just for the 'sonic fingerprint' of your particular room.
 
go ahead, add tons of treatment, 
but short of changing the actual dimensions of your room,
and adding 8" deep of rock wool on almost every wall,
your room is, what it is, 
and ARC simply shows it.
 

i use arc 2
 
and recently, 
i simply moved my mix station, from one side of the room (sort of in a corner, and pulled off a false wall) and centered it, perfectly, and pulled it off the wall (1st time) and moved it much closer to the wall (2nd time), and this alone made a large change in my room curve.
 
no additional treatments other than what i already had.
 
 
i basically changed the dimensions of my room from the perspective of what ARC had seen before, and what it is now.
 
i actually reduced how much work ARC had to do, by simply relocating my monitoring location.
 

Here's the crux of the problem...rooms don't really have a "frequency response".
 
If you could see sound, it would be very lumpy with no two locations in the room having the same frequency response. That's largely the result of constructive and destructive interference caused by reflections, and the location at which each type physically occurs and to what degree depends on the wavelength you're talking about and the distance it has traveled before running back into itself.
 
Place a microphone and record white noise and you can easily analyze frequency distribution, but any measurements you make are valid for only the exact place you put the microphone. Move the mike just a little and you get a different frequency response. Move it a foot or two and the difference is huge.
 
This is the fundamental problem when taking such measurements: any measurement is only meaningful for that one spot, and is only going to average the effects of time-based distortion. Any corrections you make at that one spot will not be the right corrections for any other spot, and in fact will make matters worse everywhere else.
 
ARC takes a clever approach to addressing this problem. With ARC, you take multiple measurements at different spots and then use a patented algorithm to come up with an averaged correction that doesn't screw up any one location too badly. And in fact, it does help. But it's a kludge. It's based on a gross over-simplification of room acoustics that doesn't take the time element into account except as a simple aggregate average.
 
In truth there is no way to flatten room response with equalization. It's physically impossible.
 
When you added absorption, you reduced many harmful acoustical effects. Few of them, however, are the types of effects that ARC measures. The perceived frequency response probably does feel flatter now, but ARC won't reflect that because it never saw the reasons for those problems in the first place.
 

Yeah, I'm basing it on the resulting before/after graph in the ARC 2 UI.  I'm assuming that once ARC 2 measures the frequency response of the room, it creates an offset response so that when enabled, what you're hearing is as close to "flat" as possible (assuming the target is a flat response and not a car stereo, TV speaker, etc.).  And since the measured frequency response doesn't seem to have changed, then I get the impression that ARC 2 is applying the same correction it did before I installed the absorption and improved my room.

Sometimes the defeating factor is the need for "symmetry" in things (human nature). Separating direct path from reflections is best at all angles possible being slightly off 45 degrees. Sort of like shooting pool and seeing how many bumper bounces you can get WITHOUT the ball going in the pocket.

ARC 2 is a nice soft but it doesn't replace accoustic treatment and professional accoustic measurements with a good mic (I own Arc2; it's good but...)