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2000 | Buch

Introduction Kapitel lesen Erstes Kapitel lesen

Active Noise Control Primer

verfasst von: Scott D. Snyder

Verlag: Springer New York

Buchreihe : Modern Acoustics and Signal Processing

Enthalten in: Professional Book Archive

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Über dieses Buch

Active noise control - the reduction of noise by generating an acoustic signal that actively interferes with the noise - has become an active area of basic research and engineering applications. The aim of this book is to present all of the basic knowledge one needs for assessing how useful active noise control will be for a given problem and then to provide some guidance for designing, setting up, and tuning an active noise-control system. Written for students who have no prior knowledge of acoustics, signal processing, or noise control but who do have a reasonable grasp of basic physics and mathematics, the book is short and descriptive. It leaves for more advanced texts or research monographs all mathematical details and proofs concerning vibrations, signal processing and the like. The book can thus be used in independent study, in a classroom with laboratories, or in conjunction with a kit for experiment or demonstration. Topics covered include: basic acoustics; human perception and sound; sound intensity and related concepts; fundamentals of passive noise-control strategies; basics of digital systems; basics of adaptive controllers; and active noise control systems.

Inhaltsverzeichnis

Frontmatter
1. Introduction
Abstract
Active noise control is an exciting area of engineering research and development. When applied correctly to problems which are amenable, active noise control technology can provide astonishing results. This is particularly true for low-frequency noise problems, where traditional passive noise control techniques often require a lot of size, mass, and money.
Scott D. Snyder
2. Background: Fundamentals of Sound
Abstract
Sound is the sensation produced at the ear by very small pressure fluctuations present in the surrounding medium (which we will assume to be air). This sensation is produced in response to the pressure fluctuation-induced vibration of the ear drum. The fluctuations in the surrounding air constitute a sound field. The pressure fluctuations themselves are usually referred to as sound pressure or acoustic pressure.
Scott D. Snyder
3. Fundamentals of Noise Control
Abstract
Active and passive noise control are two approaches to a common problem: how to get rid of unwanted noise. Active noise control aims to attenuate unwanted sound by introducing an electronically generated “canceling” sound field. Passive noise control aims to attenuate unwanted sound by modifying (structurally) the characteristics of the environment in which the sound source operates. In many ways, the two approaches are complementary, rather than alternative. To arrive at this conclusion, it is necessary to investigate the conditions under which each noise control technique performs well and the conditions under which they do not.
Scott D. Snyder
4. Free Space Noise Control
Abstract
The first noise control category of interest here is acoustic radiation into free space. What is acoustic radiation, and what is free space? Acoustic radiation is simply the generation of sound waves by a source. Acoustic radiation is a term commonly used amongst noise control practitioners. The term “free space,” or “free field,” refers to the environment in which the sound source is operating. Free space means that there is nothing to reflect the sound back; it can travel away forever. This is as opposed to acoustic radiation into an enclosed space, like a room. The free space environment is also referred to as “anechoic” (literally, no echo). If you are working in the field of noise control, then you may further subdivide free space into spaces where unreflected acoustic radiation is possible in only some directions, like a “half-space” (for example, if the sound source is sitting on the floor, it can only radiate up, not down). This might also be referred to as “semianechoic.” However, for our purposes of qualitative results examination, we will not be particularly fussed. We will simply assume that the sound can travel away without interference.
Scott D. Snyder
5. Enclosed Space Noise Control
Abstract
The second group of noise control problems that we will briefly discuss here concerns the control of sound in enclosed spaces. Examples in this group include noise in rooms, noise in vehicle cabins, and noise inside aircraft. If the concept of control is taken in the most general way, it can also mean preferential modification of the acoustic environment in places like concert halls and video conferencing rooms.
Scott D. Snyder
6. Control of Sound Propagation in Ducts
Abstract
The final group of noise control problems which we will briefly discuss here concerns the control of sound propagation in ducts. Ducts can be viewed as enclosures where one dimension is very long, often terminating into open space. Common examples of a duct include the airways used in central heating and cooling systems, and any piping system (including vehicle exhaust systems). Another example of a duct which may not be so obvious is a long hallway connecting two adjacent rooms or halls. The essential acoustic ingredient for a duct is that sound waves be constrained in two dimensions while being allowed to travel more-or-less freely in the third. For this reason, ducts are often referred to in acoustics literature as waveguides, where the constraining walls guide the travel of sound waves in the third dimension.
Scott D. Snyder
7. Active Noise Controller Overview
Abstract
Active noise control systems provide sound attenuation by introducing a second, electronically generated, sound field into the acoustic environment. If the amplitude of the second sound field is the same as the first, but the phase inverted, then the two will cancel. The end result is quiet. As we have discussed in the preceding chapters, the potential for active control to provide a satisfactory result is largely a function of the physical acoustics of the problem: the characteristics of the unwanted sound field, the response of the acoustic system, the location of the loudspeakers, etc. We can conclude that if the physical acoustics “aren’t right,” then even the biggest, best, and most expensive active noise control system will not be able to provide the desired levels of sound attenuation. Active noise control is not a universal panacea; the problem must be amenable to the recommended solution.
Scott D. Snyder
8. Controller Fundamentals
Abstract
Active noise control is a technique that aims to attenuate unwanted noise by introducing an additional, electronically generated, “canceling “ sound field. This is a simple enough concept to state, and with some basic knowledge of various aspects of acoustics (summarized in the previous chapters of this book) it would seem entirely possible. However, while the basic idea of active noise control can be traced back to original patents over 60 years ago, truly practical implementation has only recently become feasible. The main reason is that precise calculation and output of the appropriate canceling sound field is a complicated task, a task which is now practically possible for reasonable cost and effort as a result of advances in microprocessor and acoustic transducer technology.
Scott D. Snyder
Backmatter
Metadaten
Titel
Active Noise Control Primer
verfasst von
Scott D. Snyder
Copyright-Jahr
2000
Verlag
Springer New York
Electronic ISBN
978-1-4419-8560-6
Print ISBN
978-1-4612-6437-8
DOI
https://doi.org/10.1007/978-1-4419-8560-6