Too much midbass.

I just got a pair of speakers that has 2 ports in the rear of each speaker. My room is fairly small so positioning is very limited. The speakers are not too close to the wall behind them, but do need to be close to the side walls. I get a large hump in the 50-65hz region. Plugging the ports helped but it's not ideal.
What room treatment will specifically tame this hump? The simpler and least expensive the better. I can do homemeade. Any suggestions?
Perhaps a bass eq between the pre and power amp?
Thanks,
Ben.