If, for example, a string of a certain length would sound particularly harmonious with a string of twice the length other factors being equal. In modern parlance, if a string sounds the note C when plucked, a string twice as long will sound a C an octave lower. In one system of musical tuning , the tones in between are then given by for D, for E, for F, for G, for A, and for B, in ascending order. Aristotle — BC understood that sound consisted of compressions and rarefactions of air which "falls upon and strikes the air which is next to it In about 20 BC, the Roman architect and engineer Vitruvius wrote a treatise on the acoustic properties of theaters including discussion of interference, echoes, and reverberation—the beginnings of architectural acoustics.
He described the ascending seats in ancient theaters as designed to prevent this deterioration of sound and also recommended bronze vessels of appropriate sizes be placed in theaters to resonate with the fourth, fifth and so on, up to the double octave, in order to resonate with the more desirable, harmonious notes. The physical understanding of acoustical processes advanced rapidly during and after the Scientific Revolution. Mainly Galileo Galilei — but also Marin Mersenne — , independently, discovered the complete laws of vibrating strings completing what Pythagoras and Pythagoreans had started years earlier.
Galileo wrote "Waves are produced by the vibrations of a sonorous body, which spread through the air, bringing to the tympanum of the ear a stimulus which the mind interprets as sound", a remarkable statement that points to the beginnings of physiological and psychological acoustics. Experimental measurements of the speed of sound in air were carried out successfully between and by a number of investigators, prominently Mersenne.
Meanwhile, Newton — derived the relationship for wave velocity in solids, a cornerstone of physical acoustics Principia , The eighteenth century saw major advances in acoustics as mathematicians applied the new techniques of calculus to elaborate theories of sound wave propagation. In the nineteenth century the major figures of mathematical acoustics were Helmholtz in Germany, who consolidated the field of physiological acoustics, and Lord Rayleigh in England, who combined the previous knowledge with his own copious contributions to the field in his monumental work The Theory of Sound Also in the 19th century, Wheatstone, Ohm, and Henry developed the analogy between electricity and acoustics.
The twentieth century saw a burgeoning of technological applications of the large body of scientific knowledge that was by then in place.
Fundamentals of Acoustics / Edition 4
Underwater acoustics was used for detecting submarines in the first World War. Sound recording and the telephone played important roles in a global transformation of society. Sound measurement and analysis reached new levels of accuracy and sophistication through the use of electronics and computing. The ultrasonic frequency range enabled wholly new kinds of application in medicine and industry. New kinds of transducers generators and receivers of acoustic energy were invented and put to use.
The study of acoustics revolves around the generation, propagation and reception of mechanical waves and vibrations. The steps shown in the above diagram can be found in any acoustical event or process. There are many kinds of cause, both natural and volitional.
There are many kinds of transduction process that convert energy from some other form into sonic energy, producing a sound wave. There is one fundamental equation that describes sound wave propagation, the acoustic wave equation , but the phenomena that emerge from it are varied and often complex. The wave carries energy throughout the propagating medium. The final effect may be purely physical or it may reach far into the biological or volitional domains. The five basic steps are found equally well whether we are talking about an earthquake , a submarine using sonar to locate its foe, or a band playing in a rock concert.
The central stage in the acoustical process is wave propagation. This falls within the domain of physical acoustics. In fluids , sound propagates primarily as a pressure wave. In solids, mechanical waves can take many forms including longitudinal waves , transverse waves and surface waves. Acoustics looks first at the pressure levels and frequencies in the sound wave and how the wave interacts with the environment. This interaction can be described as either a diffraction , interference or a reflection or a mix of the three.
If several media are present, a refraction can also occur.
Transduction processes are also of special importance to acoustics. In fluids such as air and water, sound waves propagate as disturbances in the ambient pressure level. While this disturbance is usually small, it is still noticeable to the human ear. The smallest sound that a person can hear, known as the threshold of hearing , is nine orders of magnitude smaller than the ambient pressure. The loudness of these disturbances is related to the sound pressure level SPL which is measured on a logarithmic scale in decibels.
Physicists and acoustic engineers tend to discuss sound pressure levels in terms of frequencies, partly because this is how our ears interpret sound. What we experience as "higher pitched" or "lower pitched" sounds are pressure vibrations having a higher or lower number of cycles per second. In a common technique of acoustic measurement, acoustic signals are sampled in time, and then presented in more meaningful forms such as octave bands or time frequency plots.
Both of these popular methods are used to analyze sound and better understand the acoustic phenomenon. The entire spectrum can be divided into three sections: audio, ultrasonic, and infrasonic. This range is important because its frequencies can be detected by the human ear. This range has a number of applications, including speech communication and music.
This range has shorter wavelengths which allow better resolution in imaging technologies. Medical applications such as ultrasonography and elastography rely on the ultrasonic frequency range. On the other end of the spectrum, the lowest frequencies are known as the infrasonic range.
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These frequencies can be used to study geological phenomena such as earthquakes. Analytic instruments such as the spectrum analyzer facilitate visualization and measurement of acoustic signals and their properties.
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The spectrogram produced by such an instrument is a graphical display of the time varying pressure level and frequency profiles which give a specific acoustic signal its defining character. A transducer is a device for converting one form of energy into another.
In an electroacoustic context, this means converting sound energy into electrical energy or vice versa. Electroacoustic transducers include loudspeakers , microphones , hydrophones and sonar projectors. These devices convert a sound pressure wave to or from an electric signal.
Acoustics - Wikipedia
The most widely used transduction principles are electromagnetism , electrostatics and piezoelectricity. The transducers in most common loudspeakers e. Electret microphones and condenser microphones employ electrostatics—as the sound wave strikes the microphone's diaphragm, it moves and induces a voltage change. The ultrasonic systems used in medical ultrasonography employ piezoelectric transducers.
These are made from special ceramics in which mechanical vibrations and electrical fields are interlinked through a property of the material itself. An acoustician is an expert in the science of sound.
Looks like you are currently in Finland but have requested a page in the United States site. Would you like to change to the United States site? Lawrence E. Kinsler , Austin R. Frey , Alan B. Coppens , James V. It presents the physical and mathematical concepts related to the generation, transmission and reception of acoustic waves, covering the basic physics foundations as well as the engineering aspects of the discipline. This revision keeps the same strong pedagogical tradition as the previous editions by this well known author team.
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Fundamentals of Acoustics and Noise Control 1. Description This 2-day course will cover the fundamentals of acoustics and noise control. Topics include:. Basic acoustics, terminology, measurement metrics, physiology. Sound sources such as machines, roads, pipelines. Environmental noise, sound propagation outdoors, assessment criteria, noise modeling software. Architectural acoustics, sound absorption, sound transmission, assessment criteria. Noise control methods such as barriers, enclosures, vibration isolation.
HVAC acoustics and noise control methods. Occupational noise issues. Target Audience Engineers, Architects, Technologists, Health and Safety officers, environmental scientists, Oil and Gas practitioners, and anyone else who has encountered noise issues as part of their work.