Do they absorb some excess, harsh, over powering bass? Or do they somehow bounce bass back into the listening area? I was under the impression that unlike the upper frequencies of the sound spectrum, bass was non-directional.
The intent is that they absorb excess, harsh, overpowering bass.
If you were listening in a huge anechoic chamber you would only hear the bass coming from your subwoofer. In a normal room, you get a louder signal at certain frequencies and a quieter signal at other frequencies because of room resonances, which are a function of the room dimensions.
Even in a room with ideal dimensions (there are various recommended ratios for length:width:height) you will still get a bumpier bass response from the resonances than you would in an anechoic chamber. You might think bass peaks aren't so bad, but you end up having to turn the subwoofer down to avoid booming and as a result other frequencies get short-changed. In the very worst case you get Mark's room - there's a reason he is so bitter about anything related to bass.
Bass traps absorb some of the energy. As I understand it, placing them in corners and wall junctions results in absorbing relatively more of the energy from the resonances than from other frequencies (although I'm a bit unclear on how that works), reducing the peaks and giving you a somewhat flatter response. They aren't a magic bullet but they do seem to be a useful tool for dealing with specific room problems, and most rooms seem to benefit from having some.
Mark, I hate having to be the one to point this out, but the dimensions of your trap #2 look to be almost exactly 2:1:1, not unlike a cube in terms of bass response
