Bass/Room probelm

I have theil 2.2s that are place four feet out from the back wall (all glass) and 3 feet in from each side wall in an L shaped room that is roughly 24 ft by 22 ft with a 11 ft by 11 ft inset in one corner. Using a radio shack spl and stereophile test cd (vol 1)my bass response measures (and sounds)10db higher than normal at 31 hz and 10 db lower than normal at 64 hz and is otherwise pretty flat from 20 hz to 150 hz. What is going on? Is there anything I can do to address this with speaker placement/ room treatment etc?

Thanks

Greg