Architectural acoustics is a branch of acoustics applied to architecture, which studies acoustic control in premises and buildings, either to achieve adequate acoustic insulation between different rooms, or to improve acoustic conditioning inside premises. Architectural acoustics studies the control of sound in open places (outdoors) or in closed spaces.
Historical evolution
Architectural acoustics in ancient times
The oldest known writings on architectural acoustics date back to the century BC. C., more specifically, the year and are due to Marco Vitruvius Polio, military engineer of Julius Caesar. In these writings they describe various designs for the acoustics of ancient Roman theaters. For example, tuned bronze vessels were used that acted as resonators, bass or treble. Although the vessels served to redirect the sound in a direction different from the initial one, they did not reinforce it.
In Christian churches, with high vaults, with many acoustic problems, a tornavoz, a kind of marquee, was placed above the pulpit, which prevented the sound of the preacher's voice from being lost through the vaults. Very notable results were achieved.
Until the 19th century, acoustic design was purely practical and consisted mainly of imitating layouts of existing rooms in which music sounded good. In addition, there were sometimes almost superstitious practices, such as placing wires (which had no function) in the high places of a church "Church (building)") or auditorium.
More than 1000 years before the creation of modern architectural acoustics, at the mouth of the water witches' well, Chichén Itzá, the creation of one of the most outstanding phenomena of ancient architectural acoustics was beginning. Standing 40 meters from the Kukulkan Temple, on the perpendicular of the staircase and producing an impulsive sound (short duration but loud volume) such as clapping or playing a percussion instrument, an acoustic effect called “The Tail of the Quetzal” is produced.
This effect is a high-pitched sound, similar to the song of a Quetzal, the sacred bird of the Mayans. At first glance, the peculiar acoustic effect at Chichén Itzá seems to be the product of luck and coincidence, however in 2004 Nico Declerq and several Belgian scientists from the University of Ghent demonstrated the way in which sound waves bounced around the staircase produced sounds that had been interpreted in ancient times, such as the song of a Quetzal or the pattering of raindrops.
Sound architecture
Introduction
Architectural acoustics is a branch of acoustics applied to architecture, which studies acoustic control in premises and buildings, either to achieve adequate acoustic insulation between different rooms, or to improve acoustic conditioning inside premises. Architectural acoustics studies the control of sound in open places (outdoors) or in closed spaces.
Historical evolution
Architectural acoustics in ancient times
The oldest known writings on architectural acoustics date back to the century BC. C., more specifically, the year and are due to Marco Vitruvius Polio, military engineer of Julius Caesar. In these writings they describe various designs for the acoustics of ancient Roman theaters. For example, tuned bronze vessels were used that acted as resonators, bass or treble. Although the vessels served to redirect the sound in a direction different from the initial one, they did not reinforce it.
In Christian churches, with high vaults, with many acoustic problems, a tornavoz, a kind of marquee, was placed above the pulpit, which prevented the sound of the preacher's voice from being lost through the vaults. Very notable results were achieved.
Until the 19th century, acoustic design was purely practical and consisted mainly of imitating layouts of existing rooms in which music sounded good. In addition, there were sometimes almost superstitious practices, such as placing wires (which had no function) in the high places of a church "Church (building)") or auditorium.
More than 1000 years before the creation of modern architectural acoustics, at the mouth of the water witches' well, Chichén Itzá, the creation of one of the most outstanding phenomena of ancient architectural acoustics was beginning. Standing 40 meters from the Kukulkan Temple, on the perpendicular of the staircase and producing an impulsive sound (short duration but loud volume) such as clapping or playing a percussion instrument, an acoustic effect called “The Tail of the Quetzal” is produced.
After several acoustic simulations and calculations, they showed that while exact prediction of the resulting sounds was probably impossible, the peculiar construction of the pyramid was carried out intentionally, so that it produced surprising sounds.
The secret of the pyramid's edge is due to the long, strange stairs, in which the steps are much higher than normal and with a base much smaller than the size of a person's entire foot today. This combination of measurements makes the steps a kind of acoustic filter that emphasizes some frequencies while suppressing others. It then follows that when a loud sound is produced, it travels colliding with multiple “walls” separated by a few centimeters of base, creating a multiple echo, which returns with a small gap with respect to the previous sound. The result of this game of acoustic geometry is the succession of almost glued echoes of different tones (the lower tones are given by the rebound of the higher steps and vice versa).
The human ear does not discern the different sound waves that stimulate it and therefore assimilates them as a continuous sound that changes tone, creating the song of the Quetzal. With this, the staircase acts as a giant sound diffractor.
Although it is scientifically impossible to prove whether the construction of the pyramid was really an intentional project of architectural acoustics, and the idea that the main idea behind the construction was the play of light during the equinox is more plausible, the idea that the construction of such uncomfortable steps had a higher purpose cannot be ruled out.
Likewise, the existence of other sites with similar effects in Mesoamerica, such as Teotihuacán, gives rise to the study of the existence of an explicit relationship between the buildings in which this phenomenon occurs, especially because the Quetzal had an important religious-mythological role throughout the region. The study of the specific elements for the production of the acoustic phenomenon could lead to comparison between archaeological sites, and the result could both support or rule out the hypothesis that the effect was intentionally incorporated by the builders.
Another fascinating acoustic phenomenon was discovered by UNAM archaeologist Francisca Zalaquett, who discovered that the temples and plazas of the Mayan city of Palenque in Chiapas had as a secondary function the amplification of sound waves, to project them clearly at a distance of at least one hundred meters. An archaeoacoustic analysis of the public rituals that took place in the plaza area was carried out, which suggested that the buildings functioned as sound amplifiers and that the layer of stucco that covered them was especially used to stimulate said acoustic effect, since it alters the reflection and absorption of sounds.
Likewise, Zalaquett and his team identified rooms that were used exclusively by musicians, priests and orators. These compartments played a key role in the sound structure of the buildings, since any sound that was produced in them was projected with much greater intensity and clarity than if it were emitted from another point of the construction.
Likewise, some of Palenque's multiple plazas seem to be designed in such a way that they function as sound receptors and are somehow destination niches in the journey of sound waves.
Wallace Clement Sabine
Modern architectural acoustics were born at the end of the century thanks to the American physicist Wallace Clement Sabine.
In 1895, when the Fogg Museum of Art opened), the members of the Harvard University board, finding that the acoustics of the premises were terrible and that the speech of the speakers were unintelligible, asked Sabine to solve the problem.
Sabine came to the conclusion that the problem lay in the excessive reverberation of the room. To reduce it, he covered the walls with felt, which is an acoustic absorber. Although it was not an ideal solution, the acoustics improved and the room could be used.
Following this achievement, Sabine was called to advise on the construction of the new Boston Symphony Hall. In the development of this project, during his research, he established a formula for calculating the reverberation time that he applied to the venue.
When the time came for the inauguration in 1900, Sabine was greatly disappointed, as the hall's reverberation time did not match what he had theoretically predicted. It was highly criticized by the media and by other experts in the field.
After this failure, Sabine abandoned her research and returned to the university world, dedicating herself to teaching until her death in 1919.
However, the story put Sabine in the place she deserved. In 1950, fifty years after the theater was built, some tests were carried out and it was confirmed that Sabine's calculations were correct. In fact, today (2005), Boston Symphony Hall is considered, from an acoustic point of view, one of the best halls in the world.
After Sabine
Many authors tried to improve the reverberation time equation for a room and, although there are other formulations that are accepted, such as that of Eyring and Milligton, without better results than those of Sabine; so Sabine's formula is still in use.
At Bell Laboratories, E. N. Gilbert demonstrated that by using an integral equation, a result could be obtained by an iterative procedure. Good results have been obtained for certain applications.
Starting in 1968, computer methods of sound ray tracing have been developed with the idea of following all the reflections "Reflection (sound)") that occur and in this way calculating the reverberation time.
Nor have these recent techniques given much better results than Sabine's. Sabine's formula has only been improved by introducing an air absorption factor (x) for a given temperature and humidity. Factor that is of great importance if they are large venues.
Although Sabine is the father of architectural acoustics, it must be taken into account that Sabine's formula is neither the only one, nor is it absolutely reliable. It is just one of the most used formulas.
Acoustics in open spaces
In open spaces the predominant phenomenon is the diffusion of sound. Sound waves are three-dimensional waves, that is, they propagate in three dimensions and their wave fronts are radial spheres that emerge from the disturbance source in all directions. The acoustics will have to take this into account, to try to improve the conditioning of the stage enclaves to make the most of their possibilities and look at how to redirect the sound, focusing it on the place where the spectators are located.
The Greeks built their theaters, where dramatic works and musical performances were held, in outdoor spaces (open spaces) and took advantage of the stands where the spectators were located (staggered stands with vertical walls) as reflectors, thus achieving that the reflected sound "Reflection (sound)") reinforced the direct sound, so that they quadrupled the sound of the space that was protected by the stands. The size of the Greek theaters, some of which, thanks to their acoustic properties, could hold up to 15,000 spectators, has not been equaled.
The Romans used a similar technique, however, the wall of the stands was not flat, but curved, which allowed less sound to be lost and they focused it better towards the same point (similar approach to the parabolic reflector). However, the largest among the Romans only had capacity for about 5,000 spectators. The loss of conditions was largely due to the fact that the orchestra, which the Greek theater served to reflect sound, in Rome was the place occupied by senators and other positions, which worsened conditions.
Currently (2005), the knowledge that classical culture has bequeathed us is taken advantage of and the open spaces are built with curved, bulging walls in the shape of a shell or shell. The materials used have reflective properties to facilitate the routing of sound to where the spectators are located. The problem is that the frequency response is not uniform and the bass reaches the audience with greater difficulty than the treble.
Acoustics in closed spaces
In closed spaces, the predominant phenomenon that must be taken into account is reflection "Reflection (sound)"). The audience will receive both direct and reflected sound, which if they occur in different phases can produce reinforcements and in extreme cases lack of sound. Echo is a different phenomenon from reverb and tends to be avoided.
When conditioning a premises, it must be taken into account that sound from outside does not enter (acoustic insulation).
Furthermore, the optimal quality of the sound must be achieved inside, controlling the reverberation and reverberation time, through the placement of absorbing materials and acoustic reflectors.
Acoustic characteristics of recording studios
The acoustic characteristics of each room will be specific for the use to which it will be given.
It is important that the sound field of the room is diffuse. To this end, diffusers, absorbers, and insulators will be installed to uniformly redistribute the sound and approximate the ideal diffuse field.
This effect is a high-pitched sound, similar to the song of a Quetzal, the sacred bird of the Mayans. At first glance, the peculiar acoustic effect at Chichén Itzá seems to be the product of luck and coincidence, however in 2004 Nico Declerq and several Belgian scientists from the University of Ghent demonstrated the way in which sound waves bounced around the staircase produced sounds that had been interpreted in ancient times, such as the song of a Quetzal or the pattering of raindrops.
After several acoustic simulations and calculations, they showed that while exact prediction of the resulting sounds was probably impossible, the peculiar construction of the pyramid was carried out intentionally, so that it produced surprising sounds.
The secret of the pyramid's edge is due to the long, strange stairs, in which the steps are much higher than normal and with a base much smaller than the size of a person's entire foot today. This combination of measurements makes the steps a kind of acoustic filter that emphasizes some frequencies while suppressing others. It then follows that when a loud sound is produced, it travels colliding with multiple “walls” separated by a few centimeters of base, creating a multiple echo, which returns with a small gap with respect to the previous sound. The result of this game of acoustic geometry is the succession of almost glued echoes of different tones (the lower tones are given by the rebound of the higher steps and vice versa).
The human ear does not discern the different sound waves that stimulate it and therefore assimilates them as a continuous sound that changes tone, creating the song of the Quetzal. With this, the staircase acts as a giant sound diffractor.
Although it is scientifically impossible to prove whether the construction of the pyramid was really an intentional project of architectural acoustics, and the idea that the main idea behind the construction was the play of light during the equinox is more plausible, the idea that the construction of such uncomfortable steps had a higher purpose cannot be ruled out.
Likewise, the existence of other sites with similar effects in Mesoamerica, such as Teotihuacán, gives rise to the study of the existence of an explicit relationship between the buildings in which this phenomenon occurs, especially because the Quetzal had an important religious-mythological role throughout the region. The study of the specific elements for the production of the acoustic phenomenon could lead to comparison between archaeological sites, and the result could both support or rule out the hypothesis that the effect was intentionally incorporated by the builders.
Another fascinating acoustic phenomenon was discovered by UNAM archaeologist Francisca Zalaquett, who discovered that the temples and plazas of the Mayan city of Palenque in Chiapas had as a secondary function the amplification of sound waves, to project them clearly at a distance of at least one hundred meters. An archaeoacoustic analysis of the public rituals that took place in the plaza area was carried out, which suggested that the buildings functioned as sound amplifiers and that the layer of stucco that covered them was especially used to stimulate said acoustic effect, since it alters the reflection and absorption of sounds.
Likewise, Zalaquett and his team identified rooms that were used exclusively by musicians, priests and orators. These compartments played a key role in the sound structure of the buildings, since any sound that was produced in them was projected with much greater intensity and clarity than if it were emitted from another point of the construction.
Likewise, some of Palenque's multiple plazas seem to be designed in such a way that they function as sound receptors and are somehow destination niches in the journey of sound waves.
Wallace Clement Sabine
Modern architectural acoustics were born at the end of the century thanks to the American physicist Wallace Clement Sabine.
In 1895, when the Fogg Museum of Art opened), the members of the Harvard University board, finding that the acoustics of the premises were terrible and that the speech of the speakers were unintelligible, asked Sabine to solve the problem.
Sabine came to the conclusion that the problem lay in the excessive reverberation of the room. To reduce it, he covered the walls with felt, which is an acoustic absorber. Although it was not an ideal solution, the acoustics improved and the room could be used.
Following this achievement, Sabine was called to advise on the construction of the new Boston Symphony Hall. In the development of this project, during his research, he established a formula for calculating the reverberation time that he applied to the venue.
When the time came for the inauguration in 1900, Sabine was greatly disappointed, as the hall's reverberation time did not match what he had theoretically predicted. It was highly criticized by the media and by other experts in the field.
After this failure, Sabine abandoned her research and returned to the university world, dedicating herself to teaching until her death in 1919.
However, the story put Sabine in the place she deserved. In 1950, fifty years after the theater was built, some tests were carried out and it was confirmed that Sabine's calculations were correct. In fact, today (2005), Boston Symphony Hall is considered, from an acoustic point of view, one of the best halls in the world.
After Sabine
Many authors tried to improve the reverberation time equation for a room and, although there are other formulations that are accepted, such as that of Eyring and Milligton, without better results than those of Sabine; so Sabine's formula is still in use.
At Bell Laboratories, E. N. Gilbert demonstrated that by using an integral equation, a result could be obtained by an iterative procedure. Good results have been obtained for certain applications.
Starting in 1968, computer methods of sound ray tracing have been developed with the idea of following all the reflections "Reflection (sound)") that occur and in this way calculating the reverberation time.
Nor have these recent techniques given much better results than Sabine's. Sabine's formula has only been improved by introducing an air absorption factor (x) for a given temperature and humidity. Factor that is of great importance if they are large venues.
Although Sabine is the father of architectural acoustics, it must be taken into account that Sabine's formula is neither the only one, nor is it absolutely reliable. It is just one of the most used formulas.
Acoustics in open spaces
In open spaces the predominant phenomenon is the diffusion of sound. Sound waves are three-dimensional waves, that is, they propagate in three dimensions and their wave fronts are radial spheres that emerge from the disturbance source in all directions. The acoustics will have to take this into account, to try to improve the conditioning of the stage enclaves to make the most of their possibilities and look at how to redirect the sound, focusing it on the place where the spectators are located.
The Greeks built their theaters, where dramatic works and musical performances were held, in outdoor spaces (open spaces) and took advantage of the stands where the spectators were located (staggered stands with vertical walls) as reflectors, thus achieving that the reflected sound "Reflection (sound)") reinforced the direct sound, so that they quadrupled the sound of the space that was protected by the stands. The size of the Greek theaters, some of which, thanks to their acoustic properties, could hold up to 15,000 spectators, has not been equaled.
The Romans used a similar technique, however, the wall of the stands was not flat, but curved, which allowed less sound to be lost and they focused it better towards the same point (similar approach to the parabolic reflector). However, the largest among the Romans only had capacity for about 5,000 spectators. The loss of conditions was largely due to the fact that the orchestra, which the Greek theater served to reflect sound, in Rome was the place occupied by senators and other positions, which worsened conditions.
Currently (2005), the knowledge that classical culture has bequeathed us is taken advantage of and the open spaces are built with curved, bulging walls in the shape of a shell or shell. The materials used have reflective properties to facilitate the routing of sound to where the spectators are located. The problem is that the frequency response is not uniform and the bass reaches the audience with greater difficulty than the treble.
Acoustics in closed spaces
In closed spaces, the predominant phenomenon that must be taken into account is reflection "Reflection (sound)"). The audience will receive both direct and reflected sound, which if they occur in different phases can produce reinforcements and in extreme cases lack of sound. Echo is a different phenomenon from reverb and tends to be avoided.
When conditioning a premises, it must be taken into account that sound from outside does not enter (acoustic insulation).
Furthermore, the optimal quality of the sound must be achieved inside, controlling the reverberation and reverberation time, through the placement of absorbing materials and acoustic reflectors.
Acoustic characteristics of recording studios
The acoustic characteristics of each room will be specific for the use to which it will be given.
It is important that the sound field of the room is diffuse. To this end, diffusers, absorbers, and insulators will be installed to uniformly redistribute the sound and approximate the ideal diffuse field.