Avoid setting your speakers, even if they are towers, to the "large" setting in your receiver's setup menus.
Receivers and preamp/processors typically have two settings for your speakers: "small" and "large." You need to get past what these words actually mean in English, as they are a very poor choice for this feature of a processor. This setting actually has nothing to do with the size of the speakers, and everything to do with the range of the speakers. This setting determines when low frequencies are diverted from your front speakers and into your subwoofer (the crossover frequency). In other words, it has a tremendous effect on the bass you'll hear in movie soundtracks.
Very few speakers should actually use the "large" setting. Even most of the big, powered towers should not be used with the "large" setting because they can't produce these low frequencies (or they produce them without power and depth). What you should be thinking is that "large" means you have a truly full-range speaker; use "small" for everything else. If your speaker can't put out more than 100dB at 20 Hz, set it to "small."
There are three main reasons for avoiding the "large" setting. The first is that crossovers aren't brick walls; they have slopes in both directions. The rule of thumb is that with typical bass management crossovers, your speaker should be flat to 1 octave below the crossover point. So, with an 80-Hz crossover point, your speaker ...