low bass response

Try reversing the polarity on 1 speaker, not both.

@jw944ts 

You want to measure from your listening position. Bass response will vary from location to location in your room due to room modes.

If you've tried moving the speakers and/or your listening position and you know your gear's frequency response is flat down to 20 Hz, then you should probably consider adding a sub. 

You don’t need room for bass but you kind of do…, I mean headphones make good low bass with zero distance but you hear the direct wave.  A 20hz wave is 54’ long and will bump into walls, bounce back and cancel itself out. Like two baseballs coming from different directions and hitting each other. 

35hz is 32’ long so the 1/4th wave will be 8’. 1/4th wave matters as because once it bounces off the wall and comes back it is a 1/2 wave and 100% out of phase with the first wave. 
 

That is 8’ from the acoustic center of the 3 woofer and port combined. So your ceiling will be canceling the bass at 9’ but the side and back walls will not be. They all sum together.  Anyway I would just move the speakers around a bit and see what happens. Closer to the walls for more low bass. Same goes for your seat. 
 

In a domestic home I personally think subs with DSP is the only way for flat low bass. 

Listen to RAP music they usually have good bass. 😀

very interesting post @james633