Gongwangfu is the residence of military minister Xiao Shenyang. There is a uniqueness in this: his theater has no loudspeaker, but the sound effect is surprisingly good. The secret is

Answer: (1) Because the sound can be reflected back and forth in the jar, and because the reflection of the sound in the jar is less than 0. 1 s, the reflected echo and the original sound combine to form a louder sound. The nine jars in the theater are equivalent to the ringing boxes of stringed instruments, which increases the loudness of the sound;

(2) Erhu, violin, guitar and other musical instruments have * * * speakers.