By Abby Gemechu
Over time, humans have developed various types of architectural structures, and each one serves its own purpose. Some structures were built to hold acoustic specialties, like the pyramid of Kukulkan in Mexico, whose clapping echoes sound uncannily similar to the call of the quetzal. The Barossa Reservoir in Southern Australia whispering wall effect is shocking. Others, on the contrary, just happen to be hotspots for acoustical activity. Grand Central Station in New York, for instance, is a location known for its acoustical abilities. If a speaker stands near one wall of the station, and the other person is positioned by the other wall 30 feet away, they are still able to have a normal conversation at normal volume, granted the station is not overcrowded with people. Regardless of the already-designated ones, such architectural structures can be found almost anywhere.
Archaeoacoustics is the study of the relations between sound and archaeological sites. It is a fascinating subject, but might be too fascinating and far-off, according to Nadia Drake of Science News, because of the “glossy sheen of charisma that blankets [it].” Many are unsure whether it is a real science or a convenient coincidence. She and some of the public think it isn’t a real science because, for starters, there is very little proof/science to back up the theory that many historical sites were built to have these specific acoustical abilities. However, the scientists of this study strongly disagree, and devote their career to finding acoustics in ancient structures. For example, Steven Waller, a researcher studying Stonehenge, claims, “We need to stop thinking like scientists as we study these sites. We need to realize what the ancient people would have thought of these things instead of thinking about what we know today. We have to forget those things so that we can, you know, see what it was like for them.”
For a structure to have high-quality acoustics, sound must reflect off the surfaces easily, which is why a very effective characteristic in buildings is the parabola effect. This specific shape is important in architecture because of the way sound reflects off the shape. The focusing rays of a parabola are turned outward and are parallel, which makes it ideal for projecting sound. When aimed from a far away focusing point, it can pick up and amplify sounds from surprising distances. The parabola shape/effect is used for many auditoriums, concert halls, and theaters for its exceptional acoustic abilities.
The rotunda effect is a similar phenomenon. In an arch shaped room, sound will travel along the wall in an arch shape. If both the speaker and the listener are close to the wall, they can be heard very well.
Another characteristic or shape that amplifies sound is the elliptical enclosure. An elliptical enclosure is a parabola that is closed off. Whispering galleries are usually ellipses. Elliptical enclosures always have two focus points, and one sound is always sent to another focus point. No matter what, each sound always has some point it is focused on. However, though it is projected to another point, nothing can be heard in between the two points that the sound travels from and to. For example, if two people were standing on separate sides of an ellipse shaped room 20 feet away from each other, and one person was standing in the middle of both of them, the two opposing people could have a conversation without being overheard by the person in the middle. Consequently, while it has its benefits, the elliptical enclosure is generally not suitable for acoustical purposes.
Anti-focusing surfaces are also useful when building an acoustical-purposed structure. It is desired because, with focusing surfaces, even dispersion is not guaranteed. When one uses anti-focusing surfaces, however, the uneven dispersion that curved walls like parabola bring can be overcome.
There are other factors in having excellent acoustics, and one of them is materials. Sound has been found to reflect off of brick and metal best. As a result, many structures can end up having acoustical properties or the whispering wall effect.
Sources:
http://www.lastwordonnothing.com/2017/11/21/acoustic-architecture/
www.sciencenews.org/blog/scene/archaeoacoustics-tantalizing-fantastical
http://hyperphysics.phy-astr.gsu.edu/hbase/Acoustic/reflc.html#c4
https://www.nde-ed.org/EducationResources/HighSchool/Sound/reflection.htm
HB IN RETROSPECT 