OFFICIAL29 Why does the professor say this:

[00:00.00]NARRATOR: Listen to part of a lecture in an architecture class.[00:04.66]MALE PROFESSOR: Today I'd like to talk a bit about the relationship between the built world and sound. [00:11.97]Uh, the design of buildings like concert halls or theaters. [00:15.78]So, what's the most important aspect in the design of such a building?[00:20.58]MALE STUDENT: Acoustics?[00:21.51]MALE PROFESSOR: Yes. Now, people have been concerned about how sound carries in auditoriums and theaters for at least 2,000 years. [00:30.41]But it was not until the beginning of the twentieth century that architectural acoustics became a scientific field. [00:38.47]That was when the physicist Wallace Sabine started to do extensive studies on reverberation.[00:46.00]Sabine wanted to find out why the audience could not understand speakers at a lecture hall in Boston. [00:54.73]He designed a series of studies on reverberation to figure it out. [00:59.77]So, what is reverberation? [01:02.49]It's the persistence of sound in a room after the source has stopped making sound.[01:09.23]You see, sound made in a room reflects off the walls, floors and ceiling— [01:15.47]that's the reverberant sound. [01:17.86]The time it takes for the reverberant sound to die down is important for the acoustic quality of a room. [01:25.30]Sabine recognized this and he came up with an equation to measure a room's reverberation time. [01:32.50]So, what happens if the reverberation time is very long?[01:37.94]MALE STUDENT: Wouldn't it be difficult to hear new sounds if you can still hear the old sounds?[01:44.23]MALE PROFESSOR: Exactly. A long reverberation time may cause musical notes to drown one another out. [01:51.03]On the other hand, if the reverberation time is very short, meaning, the reverberations are absorbed very quickly, the room is called dead. [02:00.91]Performers would feel they have to struggle to fill the room with sound. [02:06.21]We don't want that. [02:07.91]In a concert hall or theater, we prefer a live room, where the sound has fullness.
[02:14.31]So we need to control the reverberation time. [02:18.25]After all, we don't want the listeners or the performers to have to struggle, right? [02:23.14]So what are some important considerations when we design a theater or a concert hall?[02:30.81]MALE STUDENT: The size of the place?
[02:33.02]MALE PROFESSOR: Absolutely. The larger the room, the longer the reverberation time. [02:37.28]So we'll have to take into account what the room will be mainly used for, since music requires more reverberation than speech. [02:46.77]A room intended for music needs to be designed differently from a room intended for drama.
[02:52.91]For music, we need a very large room, a concert hall, actually I should say for full orchestras. [03:02.16]Because for a single instrument, say something like a piano recital, a room with a short reverberation time is better. [03:10.77]So for a solo piano a smaller room works well. Yes?[03:17.70]MALE STUDENT: I read that concert halls designed for symphony orchestras have too much echo for jazz music.[03:23.15]MALE PROFESSOR: That doesn't surprise me. [03:25.41]Most small jazz groups would need rooms with a shorter reverberation time. [03:30.56]But besides the size of the room, another variable affecting reverberation is the shape of the room.[03:37.87]Let's say you design a rectangular box-like space with bare walls and ceiling, this would allow the sound to act like a ball in a racquetball court, you know, bouncing around and hitting some parts of the walls and ceiling but missing many others. [03:56.12]If that happens in a concert hall, audience members may hear some sounds, but not others. [04:02.36]So what can be done to distribute the sound evenly in every direction? [04:08.00]The answer is: avoid straight, parallel walls. Karen?[04:14.40]MALE STUDENT: But I think I've seen photos of rectangular concert halls.[04:21.15]MALE PROFESSOR: Right. Older concert halls from the 1800s are generally rectangular. [04:26.58]But they all have a lot of decorations on the walls inside, lots of ornamental plasterwork like statues, which distribute sound very efficiently, reflecting it in all different directions. [04:40.32]And that brings me to another variable we need to consider. [04:44.29]The acoustic characteristics of the building materials as well as the wall and floor coverings.
[04:51.99]In fact, most objects you see in a concert hall or theater serve double duty. [04:58.11]The plush chairs absorb sound and soften reverberation.[05:03.00] And the beautiful crystal Chandeliers? [05:06.14]They are very good at diffusing sound. [05:10.08]You see, everything must be planned down to the last detail in order to predict the acoustic performance of a room.
[05:18.97]That being said, there's something that can't be controlled by the architect. [05:24.47]The audience has an effect on acoustics too. [05:28.66]The heads of people are good diffusers of sound. [05:32.93]And Architects try to account for this effect in their design, but they can't guarantee a full auditorium.