Round Ports

• Round ports are simply circular holes cut into the front or back of the speaker box. In a "tuned port" design, a plastic or metal tube is inserted into the exterior port to form a channel inside the cabinet. This tube is "tuned" by using mathematical calculations in determining its diameter width and length to accentuate particular bass frequencies. The tube is not limited to a cylindrical shape however, and can form a complex maze to fine-tune sound.
  
  

Square Vent Ports

• Square port vents are similar to round tuned ports but offer deign flexibility by virtue of their shape and ease of construction. Square ports can include internal angles, baffles and additional vents to further shape sound.
  
  

Slotted Vent Ports

• Slotted vent ports are typically located at the bottom of a speaker cabinet and can include internal baffles to direct sound toward the slotted area. Some cabinets employing slotted ports use elaborate internal baffle designs, forming channels and chambers to further tune bass frequencies.
  
  

Combination Designs

• Higher-end speaker cabinets for pro-audio use can include more than one port and vent-type and multiple internal baffle configurations. A common example is the "folded-horn" design, with speakers mounted facing the back, center or side of the box. A series of baffles, ports and vents tunes the bass sound, and directs it toward the front of the cabinet.