@smaarch1 Your ears can act as a tone control to a certain degree. If the bass is missing the ear will tilt things towards the treble. So if you add a sub (and have it placed properly so its audible at the listening position) you'll find the highs to be a bit calmer.
To get the sub to blend properly the trick is it should not have any output above 80Hz or it will attract attention to itself. In most rooms below that frequency the bass is entirely reverberant owing the wavelength being so long- at 80Hz its already 14 feet long, so within a couple of iterations its bouncing off every wall in the room. The lower the frequency the longer the waveform.