typically its referening to a ported box which is achieved with a specific width and length of tubing (ex pvc tubing) to a specific box size to achieve a desired peak frequency the sub can play at which enhances the sound around this area....below the tuning the subwoofer is negatively effected
typically its referening to a ported box which is achieved with a specific width and length of tubing (ex pvc tubing) to a specific box size to achieve a desired peak frequency the sub can play at which enhances the sound around this area....below the tuning the subwoofer is negatively effected