2 dips in frequency response...

Hello,... we´ve further measured our room especially in the bass range more detailed. There are two dips in the range about 100Hz. One at 87hz and one at 105hz. Both are very strong dips about nearly 10 db. Then there is a room mode and a boost of a few db @ 40hz, with a longer decay time. Would a helmholtz be effective down to such a low frequency? Is there a chance to control the dips? We´ve moved the monitors at different locations and in all possible positions they appear (lightly different). Is a dip a possible pressure whole of a room-mode? So i can control it with some aborber tuned to this frequency in a room corner? Or are these dips direct reflection cancelations from sidewalls or the floor/ceiling? Is than there a chance to control this? I´ve often heard that speaker with a bass reflex port will enhance such room problems, because they send more sonic energy to the front wall of the room. thx so much for an advise...

more details about the room - measurements, construction, existing treatments, etc... to get low you need either some deep bass trapping or membrane (panel) absorbers.