Don't get too hung up on what the calculations are telling you, low frequency behavior in real rooms is much more complicated than that. Most (many) low frequency problems can be "fixed" by using low frequency absorption, i.e., bass traps. How much absorption will depend upon the frequency range of the problems as well as the intensity. Go to the RealTraps web site (link below) and read all of the articles and watch the videos. There is a ton of useful information on this site to educate yourself on low frequency room problems. Invest the time and effort to fully understand what you are dealing with. Warning: fixing low frequency problems can get very expensive if you are trying to deal with frequencies below 60Hz or so. The products really work (as do products from other makers). Once you experience tight, controlled bass in your room, you will never want to be without it. Personally, I use RealTraps in my room and can fully recommend their products and support.

http://www.realtraps.com

Additional information can be found at

http://gikacoustics.com

The Op didn't say what audible problem he/she had if any, just that the distribution plots were not right. 

Ironically the 5 - 20 Hz region has oft been described as in audible.  Besides, there are precious few systems capable of reproducing frequencies below 30 Hz much less below 20 Hz.  Perhaps even more serious, room aberrations extend through the upper bass, midrange, all the way up through the highest frequencies.  In terms of spoiling the sound, I suggest that the upper bass, midrange and high frequencies are the worst offenders.  An ordinary man has no means of deliverance.

Geoff Kait

Machina Dynamica

Thanks for the correction, now I see what you meant.  My bad.

GK

MD

Yes, your understanding of the theory is correct: too close of a spacing between modes will empasize certain frequency ranges while large gaps between modes will result in a lack of modal support. e.g., nulls, at other frequencies. However, reality is much more complicated than that. There are also tangential and oblique modes and it is very difficult to predict the effects on the room response. There is also constructive and destructive interference due to the build up of sound waves in the room at low frequencies. In a nutshell, trying to predict and manage low frequencies in a listening room can be a nightmare! In my own listening room the axial modes seem to have no effect whatsoever. For example, I should have a mode at 35Hz, yet this frequency seems to be totally absent from the room. If you are truly interested in room mode calculations, try the calculator that I have linked below.

http://www.bobgolds.com/Mode/RoomModes.htm

That % value is actually the spacing percent. It is the percent difference between one mode and the one lower in frequency to it.