Yes, quieter is a Scrabble word!

Adjective

1. Characterized by an absence or near absence of agitation or activity

2. Free of noise or uproar; or making little if any sound

3. Not showy or obtrusive

4. In a softened tone

5. (of a body of water) free from disturbance by heavy waves

6. Of the sun characterized by a low level of surface phenomena like sunspots e.g.