I used to think that a semi-acoustic guitar and an electro-acoustic guitar were one and the same thing. After all, they both have a combination of acoustic and electric properties – it’s an easy misconception to make!
A semi-acoustic is basically just an electric guitar with a hollow or semi-hollow body.
The pickups are usually humbuckers and are typical of an electric guitar. They lie under the strings on top of the soundboard. The tone controls are in a similar position to those on a solid-body electric guitar. The hollow body adds to the tone.
The true tonal qualities come out when it’s amplified. These guitars produce a very clean sound which is much favoured by jazz guitarists. They’re also popular with rockabilly and country guitarists. Brian Seltzer of The Stray Cats is a good example.
The f-shaped sound holes on a semi-acoustic are fairly narrow. This means that the sound produced can be rather quiet when unplugged. Great for practising at home without upsetting the neighbours though! Amplification gives a semi-acoustic guitar added warmth. It has a distinctive sound that is very different to an ordinary electric guitar (in my opinion!).
An electro-acoustic, on the other hand, is an acoustic guitar which can be amplified. The microphone, or pick up, is usually found under the saddle within the body of the guitar.
There may also be a control panel for EQ, volume and tone built into the top of the upper bout. The cable plugs into an adapted strap button on the end of the guitar.
Many electro-acoustics have a cutaway design like the one in the picture. This gives greater access to the higher frets.
A pick up and amplifier may colour the tonal qualities a little but an electro-acoustic guitar should sound similar whether it is plugged or unplugged.