Bass Reflex Speakers:
A bass reflex or vented speaker enclosure increases or reinforces bass response by using the sound from the back of the speaker cone. A bass reflex speaker has a port or vent on the front of the cabinet that allows the sound waves from the rear of the cone to exit into the room and has the effect of increasing bass. Depending on the size of the cone and the speaker cabinet or enclosure, the effect usually increases bass below 100Hz.
Acoustic Suspension Speakers:
Acoustic suspension or sealed-box speaker enclosures are designed to get more bass out of a smaller enclosure, such as a bookshelf speaker. Acoustic suspension speaker cones are characterized by smaller drivers with longer woofer excursion (the distance that the cone moves in and out). In this type of speaker enclosure, the air trapped in the cabinet acts like a spring and produces bass down to about 50Hz depending on the model.
Horn Speakers:
A horn loudspeaker acts like a megaphone and produces louder sound levels with less effort and a smaller driver. In that sense, horns are the most efficient type of speaker. A horn speaker has a narrow range of operation and are mostly used for midrange speakers and must be carefully designed to avoid sounding shrill or hollow.