Architectural or building acoustics is the science and engineering of achieving a good sound within a building and is a branch of acoustical engineering. In ancient times, this science applied in the construction of theaters, galleries, ballrooms, and halls for not just entertainment but also security and safety. It analyzes noise transmission from building exterior envelope to the interior and vice-versa and manipulate it according to the function of the building in its construction.
The Ancient Theater of Epidaurus, Greece
The magnificent Epidaurus Theater situated in Greece built in the 4th Century B.C. It can cater to accommodate approximately 15,000 people in one seating. The theater is located amid a sanctuary built on a mountain slope makes it even more aesthetically pleasing. The center stage has a 20 meters wide diameter with the seating spaces going up to a height of 58 meters making it an extremely vast space. For several years, it was covered amongst the trees and was later discovered in the 1800s during an excavation.
The open-air theater serves its purpose successfully with its perfect sound acoustics and aesthetics. Using mathematical and engineering skills in construction to design with perfection has been a remarkable style of Greek architecture. Every spectator can hear the sound of a pin dropping on the stage clearly. Even in the 21st century with all the technological advances, this sort of perfection in acoustic science is rarely achievable.
The functioning of its sound acoustics has remained to be a mystery for a long period until now. The researchers at the Georgia Institute of Technology have discovered that the limestone seats create a filtering effect for sound frequencies. This implies that the corrugations on the natural surface of the seats act as a natural acoustic trap. The low frequencies of crowd murmurs are suppressed and hence the background noise is minimized. Whereas the rows of seating aid in reflecting high frequencies back towards the audience by enhancing the effect. The material used for creating seating plays a vital role in the planning of its acoustic design along on a slope for visual and audio clarity. The perfect acoustics, aesthetics and symmetry with-standing so many centuries is a marvel in itself.
Gol Gumbaz, Bijapur
The Sultan of Bijapur Mohd Adil Shah II built the Gol Gumbaz in the 17th century in the Indo-Islamic style of architecture. It is one of the biggest single chamber structures in the world. It took architect Yakut of Dabul 30 years to build this tomb. Its dome is the second largest dome in the world being 51m high and 38m wide (after the dome of St. Peter’s Basilica in Rome). The material used for construction is grey basalt. It is a seven-story high structure in the form of a cube (each side 156ft) with the four octagonal towers at the four corners. Each tower consists of a staircase leading to the seventh floor (round whispering gallery).
There are two parts of the structure, the whispering gallery at the top floor and the ground floor where resides the cenotaphs. Any sound produced at the ground echoes 7 to 8 times lasting for at least 26 seconds. No visible pillar or column can be seen supporting this structure. A structure of eight arches going up to the height of 90ft called the pendentive caters to the load of the tomb. The dome then rests over the arches as a crown, transferring load from the dome to the arches. The dome and niches made from these arches cause the echoes.
The whispering gallery is a circular pathway spanned over a diameter of 124ft. If two individuals stand opposite to each other in this gallery, they will not be able to see each other clearly but can hear the slightest of whispers easily. This is possible due to the curvilinear propagation of sound as the sound travels in a curved path. This propagates sound to reflect so rapidly that the intensity of sound remains intact.
Everything from the ground floor is audible in the whispering gallery but not vice-a-versa. This happens because the arches are located such that sound travels above it and not below. St. Paul’s Cathedral in London and in Bara Imambara in Lucknow are also among famous places which have a similar whispering gallery.
Golconda is a fortified citadel situated on a granite hill in the Deccan region in Hyderabad enclosed within eight gateways. Granite fortress built about 500 years ago from now became the first fort to have an acoustical alarm system using architectural acoustics. Golconda was a part of a major trade route and vaulted the most precious diamonds from the nearby Kollur mines. For security and safety, an alarm system was installed which can send alert up to a radius of 3 sq.km with the aid of acoustic science in the 7th century A.D. Earthenware was used in the building construction along with building materials to reflect sound. The architects and engineers of that time were well equipped with the knowledge of sound echo and amplification.
The sound alarm system starts from the fort’s entry courtyard. The indentations and geometric patterns created in the ceiling look ordinary but aid acoustics. When a sound is created, vibrations are developed in these indentations. These then reflect through a set of descending arches. The descending arches helped in compressing the sound. The arches refract sound and that is why it can travel back and forth. The sound then travels to the dome which amplifies it in such a way that its heard over the distance of one kilometer. Ultimately, the sound reaches the last and the highest point of the fort where it can be heard clearly.
So, a slight movement in the entrance courtyard or in the judgment hall could be heard in the king’s bedroom. This ensured security by alarming of a possible danger. Different buildings are oriented in such a way that the sound can travel from one point to another and get redirected rapidly without losing its speed.
Inspired from these acoustic wonders many concert halls, theaters, etc have been created by many modern architects. But it’s still fascinating how these opulent structures could acoustically function when there was no wireless telecommunications.