It has a "sustain block", but not as large a chunk as an EB-2, EB-650 or EB-750, where nearly all acoustic characteristics are killed by that feature. That smaller, sustain block (shaped a bit like a staircase IIRC) is in less contact with the top of the bass, hence the more acoustic note. An unplugged LP Sig or JC Sig sounds louder and more open than the aforementioned basses, but still "tighter" than, say, a Gretsch hollow-body.