acoustic

Acoustic means having to do with sound. In concert halls, acoustic panels direct the way sound moves. An audio engineer is trained in acoustic design for music recording.

If you prefer the softer sound of acoustic rock, it means you like rock played on acoustic instruments. These include the guitar, violin, 'cello, viola, or harp––anything really that does not rely on electrical amplification to be heard. If a room has good acoustics, it means sound travels clearly and consistently through the space, and it's good for concerts.