Help With Room Acoustics - Big Peaks

Hello!  I need some help with some poor room-acoustics.  Basically, the more I know, the worse off I am!  So after noticing that mixing tracks has become increasingly difficult, I decided to perform some tests of my room studio.  I am experiencing some BIG peaks and valleys from 1kHz down to about 60Hz.  The lower bass frequency peaks are super-terrible, causing bad mixes altogether.  See below.  Because of this crap, I perfer to mix on--gasp!--headphones (with help from Waves NX)!
 

 
You may need to save each image so it can be zoomed in.  All plots are of a sine sweep 20kHz to 20Hz, Audio Technica AT2020 mic at the "head position," which is at the point of the equilateral triangle.  Note the big boomy peaks around 500-80Hz.  The same plot, but zoomed in, is below.  Between the largest peak and the adjacent valley at 120-100Hz is about 13dB!  In fact, a single-sine-wave test at 120Hz is VERY LOUD!  HORRIBLE!
 

 
I took one of the monitors outside in the yard and performed the same sine-sweep test with the mic about 3 feet away from the speaker.  This test was to eliminate any room-acoustical and standing wave issues.  The recording hardware was changed, however; now a Tascam DR-07mkII field recorder.  Though not the same quality as the studio mic, it did show a flat response.  See below.
 

 
Brought the monitor back inside, and performing the same test now with the Tascam recorder, here is what it looks like.  See below. Compare the plot below to the first plot and note that it is quite similar to the AT2020 mic test.  High frequencies are not as linear, but it did pick up the boomy peaks at the bottom end.
 

 
Monitors are KRK Rokit 6's on 36" monitor stands filled with sand.  The monitors-to-head triangle is very near 48" for all sides.  Monitors are close to the wall, about 1" from the back of the cabinet to the wall.  Desk and speakers are NOT in the center of the room (i.e. the R monitor is 2' from the wall and the L monitor is 6' from the opposite wall).  Room is 14'-3" x 16'-6" but not completely square.  See below.  Room is partially treated for high frequencies with custom-made 2'x4' Auralex 2" foam panels on either side of the desk and behind on the back wall.  No bass traps at this time.  Wall-to-wall carpet on floor.  Furniture and other stuff in the room.
 

Given the side of the desk, and windows on the left side of the desk and along the long wall, with wood shutters on them that open inward, the desk position in the room is limited.
 
Looking for some guidance to what I should do to get a better sounding room, and thereby creating setup and sound I can trust when mixing.  Because of the fairly low frequencies causing the problems, I don't want to invest in bass traps and/or make them myself with Roxul or "703" panels only to find out that it was completely in vain!  After all, the corner traps, if truly needed, will most likely need to be very thick.  Thanks!

couple quick wins - reach out to GIK Acoustics for some help in getting the right amount of absorption into your space. also, center the desk. positioned as you are, the right side will experience additional low freq "compression/boost" in that corner. treat the corners with deep absorption. 

actually, if you place a 4" thick trap diagonally across a corner - leaving air space behind it, or filling it with light insulation, you'll find the absorption can be effective even as low as 70-80hz. you do want the corners treated floor to ceiling though for the most effect. but you can also start off small - say 8 4'x2'x4" absorbers - 1 in each corner, 2 on either side of the desk, 2 overhead as clouds. if you cannot put one in the corner by the door, put one on the door itself. if you can space it off the door by 4" or so, that will help as well.
 

Or you could just see what ARC2 or Sonarworks does for you. 

Thanks for all of the replies and information, fellas.  Sorry it took me this long to reply, but I've been out of town and typing/posting on the phone is a PITA!
 
I've redeveloped my room's and desk's measurements in AutoCAD much better, and I intend to see if I can move things around a bit to see what happens.  From what I've sifted through online, the recommendation is to have the desk face a "long wall."  Given a big window area with opening plantation shutters, the desk is sort of stuck in the corner, as seen in the pic in the first post.  I can rotate the desk and monitors 90 degrees so that it is against the "long wall," but then the back of the left monitor will face directly into a corner; probably highly undesirable!  It will, however, be almost 2' from the wall/corner, so perhaps that will help as well.  The keep the orientation as is and pull everything back from the wall another 2' or so.  This introduces additional problems as my 30" monitor is mounted to the wall via a radial-arm-swivel-mount, which in turn sets it back off the desk's edge so the viewing distance is more appropriate (i.e. 36").  If sweep tests confirm an improvement is made, then I can always put the monitor back on its stand and set it on a small table.  Wait, maybe that old keyboard stand with an added shelf can be used!

Thanks for all of the replies and information, fellas.  Sorry it took me this long to reply, but I've been out of town and typing/posting on the phone is a pain!
 
I've redeveloped my room's and desk's measurements in AutoCAD much better, and I intend to see if I can move things around a bit to see what happens.  From what I've sifted through online, the recommendation is to have the desk face a "long wall."  Given a big window area with opening plantation shutters, the desk is sort of stuck in the corner, as seen in the pic in the first post.  I can rotate the desk and monitors 90 degrees so that it is against the "long wall," but then the back of the left monitor will face directly into a corner; probably highly undesirable!  It will, however, be almost 2 ft. from the wall/corner, so perhaps that will help as well.  The keep the orientation as is and pull everything back from the wall another 2 ft. or so.  This introduces additional problems as my 30 in. monitor is mounted to the wall via a radial-arm-swivel-mount, which in turn sets it back off the desk's edge so the viewing distance is more appropriate (i.e. 36 in.).  If sweep tests confirm an improvement is made, then I can always put the monitor back on its stand and set it on a small table.  Wait, maybe that old keyboard stand with an added shelf can be used!

 

synkrotron
I'm far from being an expert here, but my nearfield speaker instructions have them placed a lot further off the wall than shown in your drawing.
 
Having said that, I ain't got the room anyway so mine are up to the wall too, and to hell with the consequences... What I have done, however, is put a ninety degree pipe elbow into the port at the back of the speaker.
 
(I see that Dave has already mentioned this in his post)

The KRK Rokit 6's are front-ported, but I agree.  I may stuff some socks into the ports to see what happens.
 
In the current arrangement, I did move the speakers forward as far as I could go, with the space being about 11-1/2" from the back wall.  I kept the test microphone in the listening position and ran a sine-sweep.  The lower frequency peaks actually got worse!  The "flattest" response with good stereo imaging, at this point in time, seems to be the equilateral-triangle config with the speakers close to the wall.  Furthermore, spreading the speakers further apart did level out the bottom-end peaks, but it did introduce new peaks in the 400-500Hz range.  Plus this is probably not preferred because of phasing and/or imaging issues.
 
My next test will be to move the entire setup an additional two feet away from the wall.  That's about as far as I can practically go without making the entire room useless.

Oh my! That is a challenging room! I'm not sure what I'd do with that space, but the good news is that you do have a lot of space to work with. I would not get locked into the orientation in your drawing, I'd have to seriously consider facing that big window on the right side of the drawing. Not sure how one keeps things symmetrical at that point, but that's what strikes me.

wst3
Oh my! That is a challenging room! I'm not sure what I'd do with that space, but the good news is that you do have a lot of space to work with. I would not get locked into the orientation in your drawing, I'd have to seriously consider facing that big window on the right side of the drawing. Not sure how one keeps things symmetrical at that point, but that's what strikes me.

It's a big space and it should be considered for sure.  Thanks for your input!