Speaker cabinets mainly come in two flavors: a closed box, sometimes called an infinity baffle, or an open box, meaning that a bass reflex or port is left open within the design. There are variations of both design types, but the vast majority of commercial speakers can be described by one of these two types. 

Ported (or open) speakers take the sound from the rear side of the woofer diaphragm to increase the efficiency of the system to reach either lower frequencies or higher sound pressure levels. This comes at the cost of irregularities in the bass up to midrange frequencies, originating from additional nonlinear sound emanating from the tubes. An ideal impulse response is not possible with open designs, and good approximations of precise low-end reproduction are possible though not always implemented. Ultimately, ported designs are used in a majority of professional and hi-fi speakers because they can sound appealing and impressive. 

Closed boxes, for their part, have the advantage of being able to deliver a theoretically perfect impulse response for low frequencies. The sound output can be well calculated and consequently digital filters can be correctly applied to the output. The price paid is that only 50% of the acoustical output reaches the listener, with the remaining 50% emanating from the backside of the diaphragm disappearing in the damped volume of the cabinet. As a consequence the lower corner of the frequency response (the so-called -3 dB point) is more difficult to reach and the maximum sound pressure level is ~6 dB lower.