An auditorium is a room built to enable an audience to hear and watch performances at venues such as theatres. For movie theatres, the number of auditoriums is expressed as the number of screens. Auditoriums can be found in entertainment venues, community halls, and theaters, and may be used for rehearsal, presentation, performing arts productions, or as a learning space.
Sound expands away from the loud speaker. Most of what is created is not directly heard but goes past the audience and begins reflecting around the hall. If a reflection is strong and we know where it comes from, it is called an echo. If we hear many reflections at one time from seemingly no special direction, it is called reverberation. Generally, any echo is bad. In addition, and to put it simply, loud reverberation is bad.
But quiet reverberation can be interesting, if it is in limited doses. Both reverberation and echoes degrade the perception of timing in the material being presented. Strong echoes are disorienting to the timing aspect of speech or music, like trying to be coordinated in a disco strobe dance floor. It is not unusual for echoes to bother the performer more than anyone else in the auditorium. Echoes usually bounce off the back wall of the auditorium and because the person on stage is farthest from the back wall, the echo for the performer is the most delayed.
And it is most important that the performer does not suffer disorientation due to echoes. We cannot forget Pavarotti walking off the stage of a large hall filled with people because the echo was so strong that he couldn’t sing –but certainly, as we understand acoustics, we can understand and forgive. Reverberation is the ongoing part of sound in a large hall that gradually decays away, a totally chaotic lingering presence of a previous direct sound, a sonic afterglow, a remembrance. Loud reverberation upsets the timing of sequential sonic events by blurring everything together. It is especially detrimental to speech and music in small hard-surfaced rooms. However, it can also be great personal fun, as in singing in the shower, but, in this case, the singer and the listener are one and there are no concerns for improving the communication.
Quiet reverberation can contribute to the feeling that a larger-than-life experience is taking place. It adds a dramatic flair of importance to speech. It is an essential accompanist to acoustic music sources as orchestra, ensemble, choir and organ. Reverberation generally ruins the presentation of modern electronic bands. There are three aspects of reverberation to be understood. Onset time delay is the time between the direct signal is heard and the reverberation begins to be heard. The second is how loud the reverberation becomes.
The third is how long the reverberation lasts or can be heard; the “reverb time” is officially the number of seconds it takes for sound to die down a full 60 dB. Reverberation in an auditorium that is used for speech, lectures and talks should have one-third second onset time delay, be at least 10 dB-A quieter than the direct signal and have a reverb time die out within 1.25 seconds.
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