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 coming 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 orhow poorly the walls, ceiling, floor, and contents of the room (including thepeople) absorb sound. There is no ideal reverberation time .The full-sound performance of music such as Wagner operas or Mahler symphonies should have along reverberation time. The light, rapid musical passages of Bach or Mozartneed 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 andforth, 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 relectorsto 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 yo achieve a pleasing mixture ofsound.
31. This Passage is mainly about
A sound waves and their acoustic effect . B the types of music orchestras play
C walls of an auditorium D the design of an auditorium
32.Wagner operas and Mahler symphonies sound fuller in an auditorium with
A a short reverberation time B a long reverberation time
C an intermediate reverberation time D no reverberation time
33. This passage suggests that a good auditorium should
A achieve a pleasing mixture of sound B get rid of all reflections
C not have absorbers. D have smooth surfaces
34.Large pillars and corners may
A make sound rich and full B be cures for sound problems
C be sources of sound problems D function as well as clouds
35.The word “acoustic” in the last paragraph has something to do with
A performance B Music C sound D noise
参考答案：31、D 32、B 33、A 34、C 35、C