Literature Reference: The solitary bamboo flute and the hollow mulberry zither. Source from 'Suburban Temple Songs: Zhongzong's Sacrificial Ode to Haotian, Su He'.
空: The heavens, the expanse.
桑: Mulberry and Fusang. They metaphorically represent a person's warm-heartedness, boldness, dignified demeanor, and magnanimous character.
Meaning: Empty Mulberry signifies a pure and tranquil realm, embodying serenity and depth.