Architectural Acoustics

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Architectural Acoustics studies the phenomena related to an adequate, faithful and functional propagation of sound in a venue, be it a concert hall or a recording studio.

Summary

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  • 1 Origin and development
  • 2 Aspects studied
  • 3 Applications
  • 4 Curiosities of Architectural Acoustics
  • 5 Sources

Origin and development

The scientific study of acoustics, particularly theater acoustics, dates back to Greek theaters such as that of Epidaurus. Later, it was the Romans who developed a more complex system for studying acoustics in open-air theatres. The first written reference we owe, as almost always, to the Roman architect Marco Vitrubio Polio, Julius Caesar ‘s military engineer , in his work De Architectura. Various designs to improve the acoustics of ancient Roman theaters are described in these writings. For example, tuned bronze vessels were used that acted as resonators, bass or treble. Architectural acoustics as a modern science began to develop at the end of the19th century thanks to the studies of WC Sabine, who in the period between 1877 and 1905 made the first advances, beginning his work in the Fogg Art Museum of Harvard University in 1895 , and it was at this time that he found his already classic reverb equation.

Later he acted as an acoustic consultant in the design of the Symphony Hall in Boston, still considered one of the best acoustics in the world. Sabine carried out all her studies on reverberation with the only help of his ears and a stopwatch , since at that time, it was when a new technique based on the progress of electricity and electronics was beginning to be developed .

The first to bring the electronic advances brought about by the development of broadcasting (microphones, amplifiers , loudspeakers, etc.) to the field of acoustics (measurement of reverberation time, etc.) was Frederick Vinton Hunt back in the 1930s. After perfecting a device for precisely plotting the decay curves of sound, he undertook the study of the behavior of the sound field in closed rooms. In 1936 Philip M. Morse of the Massachusetts Institute of Technology published “Vibration and Sound” explaining his theory of normal modes of vibration in rectangular enclosures.

From the second quarter of the 20th century, due to the development of the amplifier, vacuum tube, loudspeakers and microphones, is when the specialists began to accumulate the exact data that would make acoustics an effective science of engineering, since before electronic devices were invented, the specialist in acoustics he lacked the necessary means, to produce sounds corresponding to his specifications, as well as to measure the strength of the sounds produced. Before having these instruments, whoever carried out the acoustic design of a room could only do so based on the study of other rooms, considering what characteristics were responsible for the good sound in some points of it, as well as the confusing sounds in other positions. World War II .

At the end of the war, a great cultural boom took place in the United States of America , which brought with it the construction of large concert halls, opera houses, etc., for which a better knowledge of the requirements of the fields was necessary. sound in large rooms. In-depth studies and precise measurements were carried out in rooms recognized for their good acoustic qualities, and the results were compared with the points of view of directors, musicians and music critics, observing that as a general rule:

  • Small rooms “sound” better than large ones.
  • Those built to be used for various purposes are inferior to those built for a specific purpose.
  • Old rooms are better than new ones.

These recommendations went against the needs of the moment. For example, large auditoriums with large capacity were desired, which had to house both a large symphony orchestra and an opera company. In addition, the architects refused to copy the old rooms of recognized fame and good acoustics, since architectural tastes change over the years and the large ornate decorations with many reliefs were left aside, being replaced by a sober and elegant style. functional, with practically smooth walls. All of this produced major echo problems and poor sound distribution throughout the room. In order to avoid these possible defects, sound-absorbing materials were extensively used to control reverberation and avoid echoes, and the diffusers and suspended panels to achieve early reflections and direct the sound where it is desired. The architects were also faced with a problem that at that time was already beginning to be important, it was noise.

In the last century this problem was not such, but in this century, known as the industrial revolution , the great advances in science and technical progress have brought with them serious noise problems.

The old rooms were generally far from the otherwise quiet cities, so the problem was practically non-existent. Today they are usually located in central locations to facilitate public access, so the noise, produced mainly by road traffic, can reach high levels and it is necessary to isolate the enclosure from external noise. Up to this time, architectural acoustics had been developed by general principles and formulas determined on purely experimental bases, and the consequent formation of the appropriate theories. This is the normal process of development within other branches of science as well., but at that time, the tendency began to study theory first and then seek its experimental confirmation. This also happened in architectural acoustics. From purely theoretical bases, a complete series of rules and formulas have been developed to explain the great variety of phenomena that occur in a closed area.

There are, however, many phenomena that, due to their complex nature, require the use of experimental methods for their study. For example, for the optimal reverberation time up to now it has not been possible to develop a theory or suggest rules to fix and it is necessary to resort to experiments and statistics.

Aspects studied

  1. How sounds are emitted by sound sources
  2. What happens from when the sound is heard until it is perceived as music.
  3. What happens from when the sounds are emitted until they reach the audience.
  4. How sounds become sound sensation.

Applications

Architectural acoustics is the science of fighting noise in buildings. The first application of architectural acoustics was seen in the design of opera houses and concert halls. More broadly, noise suppression is critical in the design of multi-unit housing and commercial establishments that generate significant noise, including concert venues such as bars. The more mundane design of workplaces has implications for noise effects.

Architectural acoustics includes room acoustics, the design of recording and broadcast studios, home theaters, and music rooms for media playback . This science analyzes the transmission of construction noise from outside to inside and vice versa. The main noise routes are ceilings, eaves, walls, windows , doors and penetrations.

Sufficient control ensures the functionality of the space and is often required based on building use and local municipal codes. An example would be providing a suitable layout for a home to be built near a high-volume highway , or under the flight path of an airport .main, or the airport itself. Between noise control space: The science of limiting and/or controlling the transmission of noise from the space ensures the construction of one another to guarantee the functionality of the space and privacy of the floor. Typical sound paths are room partitions, acoustical ceiling tiles (wood cut to ceiling tiles), doors, windows, siding, ducts, and other penetrations. An example would be providing appropriate party wall design in an apartment complex to minimize mutual disturbance due to noise from residents in adjacent apartments.

Curiosities of Architectural Acoustics

There are many constructions where it is very important to have good acoustics. For example in theaters, churches , cinemas, auditoriums, recording rooms or anywhere where listening is important.

  • In some places, such as some Mayan pyramids, the reflection of sound is used to achieve things like talking to another person, even at relatively great distances.
  • When sound is reflected off a wall, part of the energy it carried is reflected and another part is “swallowed” by the wall. When we can distinguish the reflected sound we say that there is an echo.
  • In order for us to be able to hear an echo, we must be at least 17m away from the reflecting wall. On other occasions, our ear is unable to detect the reflected sound, however, this modifies the way we perceive the original sound, this is called reverberation.
  • Historically, the Greeks were the first to consider constructions for better acoustics. For example, their theaters used the stands as large reflectors. In this way they managed to add the reflected sound to the direct sound. With this, they managed to quadruple the sound of the venue. Perfect to enjoy the theater.
  • The Romans took up the ideas of the Greeks, but instead of using flat walls for the stands, they used curved walls. Currently, many open spaces continue to use the classic model left by the Greeks and Romans, only sometimes using shell-shaped walls.
  • Modern architectural acoustics arrived in 1895, with the opening of the Fogg Museum of Art (Harvard University’s oldest art museum), which initially had such poor acoustics that the words of the speakers were barely distinguishable. speakers. To solve the problem, they asked the American physicist Wallace Clement Sabine for help, who discovered that the museum had a lot of reverberation. He ended up solving the problem by putting felt on the walls, which turns out to be a good acoustic absorber. Thanks to that, the acoustics of the place improved remarkably and the room could be used without major problems.
  • The best reverberation time depends on what you want to use the room for. For example, a room with a short reverberation time is suitable for speech, because vowels resonate more and can mask subsequent consonants. On the other hand, for music, a longer reverberation time is more convenient, because this way the sounds are better spliced ​​and the small errors that can occur during the execution are hidden.
  • Depending on our needs, it will be good or not to have resonance. For example, resonance favors solo singing, but in music it creates an unpleasant effect, since it distorts what you want to hear.
  • When the room is large or irregular, the resonances tend to be closer to each other, and end up becoming reverb