阅读理解-理工B、理工C-第一篇：Can you hear This ?
When something creates a sound wave in a room or an auditorium (礼堂)，listeners hear the sound wave directly from the source. They also hear the reflections as the sound bounces off the walls , floor ,and ceiling . These are called the reflected wave or reverberant (反射的) sound , which can be heard even after the sound is no longer com#ing from the source .
The reverberation time of an auditorium is determined by the volume or interior size of the auditorium .It is also determined by how well or how poorly the walls , ceiling, floor , and contents of the room (including the people ) absorb sound. There is no ideal reverberation time .The full-sound performance of music such as Wagner operas or Mahler symphonies should have a long reverberation time . The light ,rapid musical passages of Bach or Mozart need a reverberation time somewhere between .
Acoustic problems often are caused by poor auditorium design .Smooth , curved (弯曲的)reflecting surfaces create large reflections . Parallel (平行的)walls reflect sound back and forth, creating a rapid ,repetitive pulsing(有节奏的跳动)effect. Large pillars (柱)and corners can cause acoustic shadows as the sound waves try to pass around the object . Some of these problems can be solved by using absorbers and relectors to change the reverberation time of a room .For example , hanging large reflectors , called clouds , over the performers will allow some sound frequencies to reflect and others to pass to achieve a pleasing mixture of sound.