Are you using single frequency tones or warbled test tones? Single frequency tones can give some deep spikes/nulls which I would tend to ignore if they are very sharp....30 db swing from peak to trough in your size room is not surprising. Check out what Ethan Winer's or Realtraps website says about typical room response...it is a real eye opener....don't worry you are not alone in having discovered a far from flat room response.
The dip between 100 Hz and 400 Hz is very worrying if it is a continuous and deep trough as is the decline above 6300 Hz - unless you are talking only a few db average drop (say less than 6 db from average). Although you will always have peaks and troughs due to the room modal response, which in your case will be quite obtrusive (small and close to a cube in shape), you should aim for a broadly even response when taking an average....a little bass heavy and a little roll off in the treble seems to be what most people enjoy most.
Room treatments can help and so can a PEQ like the one made by Behringer... but your room may pose a challenge which you can only expect to mitigate.
The dip between 100 Hz and 400 Hz is very worrying if it is a continuous and deep trough as is the decline above 6300 Hz - unless you are talking only a few db average drop (say less than 6 db from average). Although you will always have peaks and troughs due to the room modal response, which in your case will be quite obtrusive (small and close to a cube in shape), you should aim for a broadly even response when taking an average....a little bass heavy and a little roll off in the treble seems to be what most people enjoy most.
Room treatments can help and so can a PEQ like the one made by Behringer... but your room may pose a challenge which you can only expect to mitigate.