Using a CD of test tones and my ears as a measuring tool (I know, I know!) it would seem that there is indeed a room mode in the mid-30Hz but it's not really causing me significant problems. Much more annoying are peaks in the low-to-mid-70s, around 120 and (surprisingly) around 145Hz. The one at 145 is annoying in that it's well in the range of the human voice and can lead to some unpleasant effects (the first vocal notes in Chris Isaak's "Blue Spanish Sky" are the perfect example of that.) The one at 120Hz is not so much of a subjective problem other than adding a bit of "thickening", but the one at 70-something is a doozy. It strikes me that these are all roughly multiples of each other, but with a wavelength in the 15.5' range (for 72Hz) I can't link it to any particular room dimensions.
I don't have corner traps per se, but I have GIK monster traps in the corners and they've helped a lot. However, I've found that putting too much absorption on the front wall leads to a thinness through the mid-range that I find a bit unpleasant. I used to have a lot more absorption there, but I gradually removed it. I'm reluctant to add much more broadband absorption to the area behind the speakers for this reason.
The Cardas method doesn't work so well in my room as the width is too small and it leaves the speakers without any spread between them. I've found the shape of the Sonus Faber Elipsa Reds (my current speakers, crwilli) allows them to go very close to side walls without too much issue, but in any case I don't have a huge amount of room to experiment laterally. It made a much bigger difference with my previous Kharmas than it does with the SFs.
I shouldn't give the impression that this is my first attempt at fixing these problems, nor that I haven't experimented EXTENSIVELY with positioning. I've been in this room for 11 years, been through multiple sets of speakers and ancillaries, speakers have been all over the room, sound treatments have been moved here there and everywhere, and while it's all been a bit haphazard, I feel I have a good sense of how speakers interact with this particular room. These frequencies have always been a problem to a greater or lesser extent and have caused me much mental pain! Hence my question about a more direct approach.
Oh, I should also say that I experimented a little with room correction software a long time ago, and while it improved some areas I felt the system lost a lot of "magic". If I could just get rid of the most obvious booming using some acoustical treatments I'd be able to cope with normal bass lumpiness!
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