But at the end of the summer 1991, an alarm bell started to ring, discrediting the phenomenon.
但是在1991年夏末，一个打扰警铃开始响起，有了不信怀疑的现象。
2
A theory analysis is made for a phenomenon of "line group" which is bell shaped, and the spectrum interference between direct path sound and reflected sound is revealed.
从理论上分析了钟型的“线谱群”的产生原因，证明了此现象是反射声和直达声之间的谱干涉引起的。
3
Three different entrances, namely bell-mouthed entrance, plane entrance and inclined entrance are used in order to determine the influence of entrance shapes upon the flooding phenomenon.