A corrugated plastic sheet with fold lines, as centerlines of V-shaped grooves, that can be folded by hand into a plastic acoustic enclosure, with or without additional corrugated plastic panels. A speaker opening is provided in the sheet, and a speaker support fixture, ring, or panel may assist in supporting the speaker on the enclosure. Foldable flanges and foldable narrow panels with adhesive strips, preferably with release layers, enable assembly of the enclosure without tools, other than for speaker installation. An amplifier attached to a panel of the enclosure, preferably on an external surface, is presented. An enclosure that supports more than one speaker is presented. The plastic acoustic enclosure that can be shipped flat and unassembled and then assembled by a user. The enclosure is lightweight, and so ships economically and does not significantly burden automobiles in which such enclosures may be installed.