Which when placed close to the rear wall, have audible port noise. Almost like someone blowing air out. This combined with the resonance caused due to two bass waves, one from the front of the driver, and one from the rear through the port, which are both out of phase. Cause the bass to ring longer than it should. So the bass doesn't stop as soon as it should. This loose bass, along with the rear fart is what I would call forced bass 🙂