Some rough guidelines: Solo – 1 to 50 guests, Duo – 25 to 75 guests, Trio – 50+ guests, Quartet – 75+ guests. A solo is light, ambient. The sound still carries very well on the beach. As your guest lists grows, you should consider a larger group. The sound will be fuller, and will have more of an impact. For 75 to 100 or more guests, a duo or larger is recommended.