The guitar’s sustaining, playability and profusion of harmonics are characteristics expected in a good acoustic guitar. Its voice must be heard acoustically by the human ear as well as with the use of an external microphone. Its voice should remain, even when played through the amplifier. All of this can be obtained through flawless planning and artful workmanship, as well as taking into account all the wood specifications.
While acoustic guitars are instruments clearly defined by tradition, semi-acoustics are more complex without a sound archetype. It means there's not something like a "semiacoustic guitar's sound", but there is a wide range of sounding possibilities depending on desired comparison of acoustic to electric sound.
Semi-acoustics are designed to eliminate feedback by the use of braces or central block, linking the top and back so they become a hybridization of the resonating chamber, which is conceived to play though the pickup and amplifier. Such hybridization manifests itself in a resonating chamber not totally hollow. In some ways, it “compromises” the exclusively acoustic qualities, but at the same time, is the factor that allows the playability as an electric, without feedback.
The vibrations and rich sounding sustain, as well as harmonics are still maintained by the correct amount of closing and dampening of the resonating chamber. This creates an excellent semi-hollow instrument.