We explain what acoustics is, what its branches are and what acoustic phenomena it studies. Also, what is noise pollution.
What is acoustics?
The acoustics It is the branch of physics that studies sound. It is a natural science dedicated to understanding the phenomena of production, transmission, control and reception of sound, infrasound and ultrasound, as well as their effects in the real world.
The acoustics defines sound as a vibration, that is, the mechanical propagation of waves through matter whether in a solid, liquid or gaseous state, and tries to describe this displacement through formulas and mathematical principles.
It is one of the oldest sciences of humanity, whose beginnings can be traced back to Classical Antiquity, between the 6th centuries BC. C and I d. C., especially in Greece and Rome. His first formal studies, carried out by Pythagoras (ca. 569-475 BC), had to do with understanding musical sounds, to try to understand why some sounds are more beautiful than others.
It was Aristotle (384-322 BC), more than a century later, who discovered that sound is composed of contractions and expansions of air, and the first treatise on the subject was written centuries later by the Roman architect Vitruvius (80- 15 BC), around 20 BC. c.
However, it was after the Scientific Revolution of the Renaissance that the laws that govern sound began to be discovered, thanks to the studies of vibrating strings by Galileo Galilei (1564-1642) and Marin Mersenne (1588-1648). They would later be joined by Isaac Newton (1642-1727) and later by the so-called “giants” of acoustics: the German Hermann Helmholtz (1821-1894) and Lord Rayleigh (1842-1919), among other great scientists who studied sound.
The first attempts to measure the speed of sound in air, one of the founding achievements of acoustics, were made in the 17th century and, although they were not very exact, they revealed that the speed of waves does not depend on their frequency. In 1738 the Paris Academy of Sciences achieved a measurement almost equal to the value currently used: 331.29 meters per second.
Nowadays, acoustics is an important discipline that It has numerous technical applications both in the field of architecture and urban planning, as well as in medicine, arts and entertainment, and telecommunications, and even in the military world (such as the radar mechanism).
See also: Physics
Branches of acoustics
Acoustics covers a varied set of subdisciplines or specializations, among which the following stand out:
- Architectural acoustics Branch of acoustics dedicated to the study of the movement of sound in buildings and urban spaces, in order to build them in a way that takes advantage of the nature of sound.
- musical acoustics. Branch of acoustics dedicated to the study of sound in the artistic context, that is, music and sounds considered beautiful. It deals with both musical instruments and scale tuning systems.
- Physiological acoustics. Branch of acoustics dedicated to the study of the functioning of the hearing system, its diseases, disorders and other implications.
- Electroacoustics. Branch of acoustics dedicated to the study of the capture, reproduction, amplification and production of sound using electronic devices such as microphones or speakers.
- Underwater acoustics. Branch of acoustics dedicated to the study of sound when it is produced and transmitted underwater.
- Psychoacoustics. Branch of acoustics dedicated to the study of the relationships between sound and the human mind, that is, the way in which human beings react to sound.
- Bioacoustics. Branch of acoustics dedicated to the study of sound in living beings, especially animals: the function of the sounds they emit, the arrangement of the vocal apparatus, among others.
- Industrial acoustics. Branch of acoustics dedicated to the study of the sound generated by human productive activities, the forms of noise pollution and the impact of sound on the work environment.
Acoustic phenomena
Sound propagates in the physical environment in the form of mechanical waves, whose properties allow them to undergo different alterations and transformations, known as acoustic phenomena. The main phenomena are:
- The reflection. It is a phenomenon that occurs when sound waves encounter a physical object along their path that alters or modifies their original trajectory, which produces a rebound effect that can send them back to their original source. Depending on the conditions under which the reflection occurs, other similar phenomena may occur, such as:
- The echo. It is a type of sound reflection in which the wave returns to its emitter after impacting a reflective surface, in cycles of an interval close to 0.1 seconds. It is similar to the effect that light produces when it hits the mirror, returning part of its own sounds to the emitter, as in the long caves in which we can hear our voice repeated towards us.
- The reverberation. It is a phenomenon associated with sound reflection, in which a sound can be heard some time after it has stopped being emitted, that is, when its sender is silent. This phenomenon is also due to acoustic persistence, and is interpreted as a lengthening of the initial sounds, as in the case of the noise that accompanies an explosion.
- standing waves. It is a phenomenon that occurs when a reflected wave is added to the original wave on the same axis, which modifies the properties of both and increases or decreases their amplitude, so the resulting sound is very different from the one emitted. This is what happens when a microphone records the output on a speaker of its own sound, that is, when the feedback.
- The absorption. It is a phenomenon that can be considered the opposite of reflection, since in this case the sound waves, upon encountering a physical barrier, do not alter their course, but are canceled or neutralized, either partially or totally. This phenomenon is used to soundproof certain spaces, such as places where music is practiced, preventing the waves from propagating further outwards.
- The refraction. It is a phenomenon that occurs when sound waves propagate from one physical medium to a different one (for example, from air to water or vice versa), and in the process their speed and direction are modified, to a degree equivalent to the physical properties. of the environment to which they move. We can experience this phenomenon if we immerse ourselves in a pool and listen to those speaking on the surface.
- diffraction. It is a phenomenon that occurs when sound waves encounter an obstacle in their path, surround it and convert the surface of the obstacle into a source of secondary waves (diffracted waves), which causes the sound to disperse in the environment. It can also occur when sound waves pass through a small opening and propagate into the new environment, such as when we speak through a tube and our voice emerges distorted on the other side.
- The interference. It is a phenomenon that occurs due to the superposition of two harmonic sound waves, which modify their properties in the process. When this superposition causes a gain in amplitude, we speak of constructive interference; When, however, amplitude is lost, we speak of destructive interference. This is what happens when we are in an environment full of people talking and it becomes difficult to hear the person next to us.
- The doppler effect. It is a phenomenon that occurs when the emitter of the waves moves quickly with respect to the receiver, either moving away or approaching, and this movement affects the frequency of the sound waves. This is what happens when an ambulance passes by us and its characteristic sound gains frequency when it approaches and loses it when it moves away.
Noise pollution
Noise pollution is the continuous emission of intrusive sounds in an environment or ecosystem which produce noise and prevent or hinder the propagation of natural sounds typical of said environment. Noise pollution is very noticeable in cities, where the accumulation of sounds can become intolerable and even physically harmful to the body, while in rural and wild areas there is a lower incidence of annoying sound waves.
This type of pollution It has effects on the flora and fauna of the habitats, and especially on the psychological stability of people since it can induce states of agitation, displeasure, anguish or distraction.
References
- “Acoustics” on Wikipedia.
- “The nature of sound” at the National University of Rosario (Argentina).
- “Acoustics: scope of sound science” at the Technological Institute of Buenos Aires (Argentina).
- “Acoustics (physics)” in The Encyclopaedia Britannica.