Hi there, I am also a velodyne owner and I do know the reason that they have a slot port. It is so that all of the air displacement is directed at the listener as opposed to tube ported designs that have the port at an opposing angle to the sub therefore directing the sound waves away from the listener. The tube ported designs are tuned to produce a small frequency band really well and the rest only mediocrely and the sloted port design tends to be more frequency friendly than the tube ported.
Both of the designs have their strengths and weak points such as in smaller listening enviroments a downward firing rear ported sub has more of an advantage because driver noise is greatly reduced as opposed to a forward firing woofer that is much more revealing in small listening enviroments. But this can be solved by facing the speaker and port side to a corner which works very well.
Both of the designs have their strengths and weak points such as in smaller listening enviroments a downward firing rear ported sub has more of an advantage because driver noise is greatly reduced as opposed to a forward firing woofer that is much more revealing in small listening enviroments. But this can be solved by facing the speaker and port side to a corner which works very well.