|The open back of a ’59 Bassman LTD (above), and the closed back of a Hot Rod Deluxe 112 extension enclosure (below). Both enclosure types impart distinctive sonic characteristics.
There are two kinds of speaker cabinet in this world—open back and closed back. Each design has a big effect on tone, so it’s an important consideration when formulating your own preferences and acquiring an amp. Here’s a primer on both types.
An open-back cabinet is one in which the speakers aren’t sealed inside the enclosure. That is, the back is open, or partially open. In this design, sound is less directional because it issues from the front and back of the enclosure, broadening its dispersion (coverage, basically) in the room. The sound seems to be “all around” the amp (your drummer, who is behind you onstage, will appreciate that).
Tonally, the open-back design contributes to less low-end punch and generally looser bass sound than a closed-back design. A great many guitar amps—combo amps in particular—use an open-back design.
In a closed-back cabinet, the speakers are sealed inside the enclosure. The back is closed, meaning that the sound is more directional because it issues only from the front of the enclosure. A closed-back cabinet lets you aim more of the power at the audience. It tightens sound dispersion in the room and imparts tighter and punchier bass to the overall sound.
In the early 1960s, Fender was one of the first amp makers to embrace closed-back design, as seen in pioneering piggyback guitar amps such as the Showman and Bandmaster. Further, because of the greater speaker articulation, the closed-back design dominates the bass amp world.
Prime examples of current Fender closed-back guitar amps include the Super-Sonic 60 Combo, Super-Sonic 100 412 enclosures, and extension cabinets for the (open-back!) Hot Rod Deluxe and Vibro-King Custom.