I tried to translate this using Google Translate. It is hard to understand what 素弦声断
exactly mean.
does 素弦声断
mean: the sound of the broken guitar strings?
or
does 素弦声断
mean: the guitar breaks its strings?
Literally, It means strings broken so that the sound of 古箏(or 古琴) stopped.
素絃聲斷 comes from a poem. 素絃聲斷 means "It's no longer possible to hear that the beautiful lady plays 古箏(or 古琴) for me again."
倚危亭。恨如芳草,萋萋剗盡還生。念柳外青驄別後,水邊紅袂分時,愴然暗驚。 無端天與娉婷。夜月一簾幽夢,春風十里柔情。怎奈向、歡娛漸隨流水,素弦聲斷,翠綃香減,那堪片片飛花弄晚,蒙蒙殘雨籠晴。正銷凝。黃鸝又啼數聲。
“素弦声断” means the plain Chinese zither broke its strings so the sound stopped. This word is from a poem describing the sadness of farewell with a friend. Thus, the sound from the zither is generalized to the good feeling brought by the friend which was stopped because of the departure.