My suggestion would be to play with placement (as others have suggested)
In addition, if you can't find the Bungs, I suggest creating one by grouping a bundle of straws held together by rubber band ; you need to cut the straw length once you happy with it ; this will tighten the bass.
Also if you have wooden floors try to use large (thick) pavement Alba under the speakers
Hope that helps.
And if all of this doesn't help, try some non ported speakers