Acoustics
Acoustics is the branch of physics that deals with the study of sound, its production, transmission, and effects. It encompasses the behavior of sound waves in various media, such as air, water, and solids, and explores topics like sound absorption, reflection, and diffraction. Acoustics also investigates the perception and psychological effects of sound on humans and animals.
6 Key excerpts on "Acoustics"
eBook - ePubAuditory Archaeology
Understanding Sound and Hearing in the Past
- Steve Mills(Author)
- 2016(Publication Date)
- Routledge(Publisher)
...Appendix 1 D EFINITIONS AND T ECHNICAL D ETAILS ON THE P HYSICAL P ROPERTIES OF S OUND, THE C HARACTERISTICS OF H UMAN H EARING, A COUSTICS AND T ECHNOLOGIES OF S OUND D EFINITIONS The following are definitions of terms related to sound and hearing as they are intended to be understood in the book. Acoustic: Of or relating to sound and particularly in reference to the physics of sound produced through vibrations in solids, liquids and gases. Acoustics: The scientific study of sound and sound waves or the characteristics of a space that determine how sound can be heard within it. Auditory: Of or relating to hearing or the sense of hearing. Aural: A listener’s experience of sound. Hearing: The detection of sound. Listening: Active attention to sound to discern information or meaning. Noise: Unwanted sound. Oral: Of or relating to spoken or verbal sounds. Sonic: Involving or producing. sound. Sonorous: Producing or capable of producing sound. Sound: A physical concept concerning anything that can be heard resulting from vibrations in solids, liquids and gases. Soundscape: The sonic environment and the auditory equivalent of landscape. T HE P HYSICAL P ROPERTIES OF S OUND This section provides additional detail to complement that provided in Chapter two, with more available in the publications referenced. Frequency, Wavelength and Waveform The rate of oscillation in a medium is known as the frequency and is quoted in cycles per second or, hertz (Hz). Oscillations in air pressure that occur between 20 and 20,000 times per second (20–20,000 Hz) are potentially audible to the human ear (Gales 1979: 8.4). This is known as the audio frequency range. Variations in air pressure below 20 Hz cannot be detected by the ear as sound but they can be felt through the body as vibrations...
eBook - ePubPlumbing, Electricity, Acoustics
Sustainable Design Methods for Architecture
- Norbert M. Lechner(Author)
- 2011(Publication Date)
- Wiley(Publisher)
...At ground level, all around the inside of the walls, he hung bronze vessels. Any that vibrated indicated that there was digging below (Hunt, 1978). Acoustical principles tell us today that the sounds generated by the diggers’ metal tools hitting soil and rock is structure-borne instead of airborne, and structure-borne sounds travel fast and far. Another life and death application of Acoustics can be found in the shogun’s palace in Kyoto, Japan, where the floorboards were built on clever devices that squeaked whenever someone stepped on the floor. In a palace where the indoor partitions and doors were made of paper, this squeaky “nightingale” floor protected the shogun from assassins. In the eighteenth century, the science of general Acoustics was started by the French scientist and mathematician Joseph Sauveur; in the nineteenth century, major advances were made by the German Hermann von Helmholtz, and in the early twentieth century, American W. C. Sabine started the science of architectural Acoustics. 5.3 THE PHYSICS OF SOUNDS Sound is a form of energy that travels as a wave. The energy in the wave moves great distances but the wave medium only oscillates in place. A wave traveling in water demonstrates this phenomenon. When a water wave moves across a body of water, the water itself only bobs up and down. The movement of the water is, therefore, transverse to the direction of the wave. Unlike a water wave, a sound wave moving through air causes the air molecules to move forward and backward in the same direction as the wave, thereby alternately compressing and rarefying the air (Fig. 5.3a). Waves of this kind are called longitudinal rather than transverse waves. Fig. 5.3a A source of sound, such as a vibrating tuning fork, alternately compresses and rarifies the air. These compressions and rarefactions move away from the source as a longitudinal wave. However, the air molecules just oscillate forward and backward and essentially remain in the same place...
eBook - ePub- John Watkinson(Author)
- 2012(Publication Date)
- Routledge(Publisher)
...Chapter 3 Sound and psychoAcoustics In this chapter the characteristics of sound as an airborne vibration and as a human sensation are tied together. The direction-sensing ability of the ear is not considered here as it will be treated in detail in Chapter 7. 3.1 What is sound? There is a well-known philosophical riddle which goes ‘If a tree falls in the forest and no one is there to hear it, does it make a sound?’ This question can have a number of answers depending on the plane one chooses to consider. I believe that to understand what sound really is requires us to interpret this on many planes. Physics can tell us the mechanism by which disturbances propagate through the air and if this is our definition of sound, then the falling tree needs no witness. We do, however, have the problem that accurately reproducing that sound is difficult because in physics there are no limits to the frequencies and levels which must be considered. Biology can tell us that the ear only responds to a certain range of frequencies provided a threshold level is exceeded. If this is our definition of sound, then its reproduction is easier because it is only necessary to reproduce that range of levels and frequencies which the ear can detect. PsychoAcoustics can describe how our hearing has finite resolution in both time and frequency domains such that what we perceive is an inexact impression. Some aspects of the original disturbance are inaudible to us and are said to be masked. If our goal is the highest quality, we can design our imperfect equipment so that the shortcomings are masked. Conversely if our goal is economy we can use compression and hope that masking will disguise the inaccuracies it causes. A study of the finite resolution of the ear shows how some combinations of tones sound pleasurable whereas others are irritating. Music has evolved empirically to emphasize primarily the former...
- E. Reid(Author)
- 2013(Publication Date)
- Routledge(Publisher)
...6 Acoustics THE NATURE OF SOUND The circular ripples from a stone splashed into a pond carry the energy of the disturbance through the water surface to the banks. Sound behaves in an analogous way in air except, of course, that the spread is three-dimensional. When the man shown shouts, the energy from the vibration of his vocal chords is causing sound waves to radiate in the air around him as a series of successive, concentric spheres growing in size (6.1). These waves vibrate the ear drum of the listener, producing the subjective sensation we call sound. WAVE THEORY In truth, wave theory is not all that simple but some grasp is essential to a working understanding of Acoustics. If you have no particular physics background, take courage. 6.1 Sound energy waves can be pictured radiating in air as a series of concentric rings – or, in fact, spheres – growing in size. Imagine a simple tuning fork. Normally, the air particles around it are at rest but, when the prongs are struck and vibrate at their designated frequency (this depends on their stiffness and mass), they impart rapid pushes to the surrounding layer of air, the particles of which are, therefore, compressed together at one instant and decompressed the next. These pushes or pressure fluctuations are then passed on to the next layer of air and so on, so that a wave motion is set up, carrying the prong’s energy outwards. The air particles are momentarily displaced from their normal position as the wave passes, but do not themselves radiate, any more than does the water on the pond’s surface. They merely oscillate within their own area of influence, each ‘layer’ compressing and decompressing like a sponge (6.2a). The classroom analogy to sound waves, where a string is fixed at one end and shaken at the other, causing waves to pass along the length, is actually rather misleading. Waves so produced are transverse, meaning that the up and down oscillations are at right angles to the wave travel...
eBook - ePubOccupational Noise and Workplace Acoustics
Advances in Measurement and Assessment Techniques
- Dariusz Pleban, Dariusz Pleban(Authors)
- 2020(Publication Date)
- CRC Press(Publisher)
...1 Basic Concepts and Quantities Characterizing Sound Dariusz Pleban From the physical point of view, sounds (acoustic vibrations) are mechanical vibrations of an elastic medium (gas, liquid, or solid state matter). Such mechanical vibrations may be considered as an oscillatory motion of particles of the medium relative to their equilibrium positions, resulting in variations of local pressure in the medium relative to the static pressure (atmospheric pressure in the case of airborne sounds). Such changes in pressure (or disturbances of the equilibrium of the medium) propagate in the form of a sequence of local concentrations and expansions of medium particles in the space surrounding the source of the vibrations creating a sound wave. The difference between the instantaneous value of pressure in a medium in the course of the passage of sound waves and the static pressure value is called the sound pressure or the acoustic pressure, denoted p, and expressed in pascals. Assuming that the sound pressure (as well as all the quantities characterizing the sound wave) vary harmonically (sinusoidally) as functions of both time t and the position of an observer x, one deals with the simplest form of wave motion in which particles of the medium perform simple harmonic motion and such disturbances propagate uniformly along a straight line. As a result, the harmonic sound wave that occurs is described with the following formula: p (x, t) = A p sin [ 2 π (t / T + x / λ) + Φ ] (1.1) where: p (x, t) (Pa): instantaneous sound pressure A p (Pa): amplitude of sound pressure variations t (s): time T (s): period of vibration λ (m): length of the wave (called also the wavelength) Φ (rad): the phase, a constant depending on the choice of point x = 0 (or the time t = 0) Among the basic quantities characterizing acoustic phenomena, the following are primary: • The frequency f characterizing oscillatory periodic phenomena (such as the harmonic wave), representing what is popularly called...
eBook - ePub- David M. Green(Author)
- 2021(Publication Date)
- Routledge(Publisher)
...1 The Physical Nature of Sound INTRODUCTION The human senses are all remarkably acute. Under optimal conditions, the eye can detect a few photons. The skin can detect a vibratory stimulus that moves only a few microns. The ear can detect, at about 3,000 Hz (cycles per second), movements of the eardrum about a hundred times smaller than the diameter of a hydrogen molecule. How is such sensitivity possible? How can the ear detect such minute vibrations? Why does the random vibration of the molecules in the air not obscure such faint sounds? These are some questions that arise in studying auditory perception. To understand in detail the answers to such questions, we must have a firm grasp of the physical nature of sound. Indeed, one of our goals is to understand the relation between what we hear and its physical properties. We begin, then, by first considering what a sound wave is, how it is propagated, and what the rules are that govern its behavior. Answering these questions involves defining the units used to describe the intensity or energy of the sound wave. We review here several formulas specifying the intensity of the sound wave. We also discuss sinusoidal wave motion, in part because the absolute sensitivity of the ear depends strongly on the frequency of the signal. Finally, reflection of sound waves and resonance is discussed. This background material will permit us to answer some of our initial questions about absolute sensitivity. We begin by considering the nature of sound. WHAT IS SOUND? In ordinary usage the word “sound” refers to that which is heard. However, we want to understand the relation between what we hear and the physical aspects of sound. We therefore begin with a consideration of sound as a physical entity. From a physical viewpoint, sound is a mechanical disturbance that is propagated through an elastic medium...
