Slot ports generally have edges and that is the main reason why they contribute alot of noise relative to round vents. Slot ports with rounded internal joints (no edges) can be very effective in moving air with minimal turbulence, same as a flared cylinder but that is not the case with the DPS-10 and many other slot ported subs. I also suspect that if they didn't round the edges outside then the inside opening will also not be flared. If that slot is similar to many slot design it will be angled at 90 degrees inside the enclosure.
Here is another take on why that is not a good characteristic if you don't mind some of these fluid dynamics principles, so bear with me in the physics below.
There is huge pressure inside that big box during loud passages. Inside the enclosure, air tends to slow down along the four corners of the port causing the air flowing along the middle of it to become more unstable or gusty. The 90degree angle of that edged slot port will also create unlinear air velocity (more artifacts) which in turn adds to internal air turbulence. If that isn't enough as this unstable air exits it must flow over another edge creating eddys and more turbulence as it abruptly contacts the stable air boundary outside the opening. The net result is uneven FR, resonance at higher frequencies which colours the bass, and other noise/distortions. Chuffing may or may not be detected but at high output the effect of these unlinearities will be evident compared to a flared rounded slot or a flared cylindrical port.
The slot port design can be improved by adding flares at both ends but that is more expensive to accomplish with a slot than a round cylinder hence why the cylinder ports are so popular. Flares help by compressing air into the body of the port inside the sub and expanding it upon exit. Because of this compression/expansion of air the length of the port can handle higher inner-port velocities without increasing the mid-section diameter. The angle of the flare is important and it needs to be a minimum of 45Deg along a circular path to achieve this type of airflow. Some people would suggest the flare curve needs to be parabolic but that's another story we don't need to get into right now.
The problem of internal edges also needs to be addressed. It gets expensive but the slot can be made effective if its internal and external edges are rounded and flared. In effect it increase laminar flow causing it to behave much like a cylinder.
Bottom line is avoid slot ports and especially slot ports with edges. Notice how well designed the Axiom sub ports are. Its one of the many underappreciated features of these subs.
