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Noise and light pollution
Published in Abhishek Tiwary, Ian Williams, Air Pollution, 2018
Sound energy travels in waves and is measured in frequency and amplitude. Frequency is the number of sound vibrations in one second. A healthy ear can hear sounds from a very low frequency (20 Hz or 20 cycles per second) to a very high frequency (20,000 Hz); the human sensitivity is highest between 2000 and 5000 Hz (Figure 13.1a). The graph in Figure 13.1a is a frequency-weighting of sound pressure levels that mimics the sensitivity of the auditory system. (To put this in context, the lowest A key on the piano is 27 Hz. The middle C key on a piano creates a 262 Hz tone. The highest key on the piano is 4186 Hz.) Figure 13.1b illustrates the contextual dependence of whether or not a sound is perceived as a noise or not. For example, music at a rock concert is not perceived as a noise by the spectators, whereas residents at home in nearby houses may treat this as noise, even though sound pressure levels are much lower there.
Principles of Noise Control
Published in Junbo Jia, Jeom Kee Paik, Engineering Dynamics and Vibrations, 2018
It is important to note that noise control is not simply reducing noise levels. For employee exposure and environmental noise this is generally true. However, changing the spectrum of the noise moving energy from low to high or high to low frequencies can be helpful. High frequency sound does not propagate as effectively over distance as does low frequency sounds. Thus, if one can move some of the sound energy to a higher frequency it may be less objectionable to the nearby community. On the other hand, human hearing is more quickly damaged by high frequency sounds. Moving sound energy to lower frequencies can help to prevent hearing damage.
Acoustics and acoustic devices
Published in Michael Talbot-Smith, Audio Engineer's Reference Book, 2013
Bob Walker, Talbot-Smith Michael, Chris Woolf, John Borwick, Francis Rumsey, John L. Andrews, Peter Baxandall, Alan Tutton
Sound energy consists of fluctuations of some physical attribute of a compressible medium, for example, the position of an elementary point in a solid or of the local instantaneous pressure in a fluid. It propagates in the form of waves, by virtue of the mass and elasticity of the medium. Such waves falling within a certain range of frequencies produce the sensation of �hearing�. For human beings, the range of frequencies which are audible is usually taken to be about 30-20 000 Hz, although these limits depend significantly on the sound level and the age and otological history of the individual.
Nondestructive Testing by Frequency-Domain Continuous-Wave Ultrasound Reflectometry
Published in Research in Nondestructive Evaluation, 2020
Ultrasound testing is one of the nondestructive inspection techniques used to detect, locate, and size discontinuities [1–3]. In this method, an electrical signal is converted to sound/ultrasound energy, which is further coupled into the tested material. Reflected and/or transmitted sound energy is detected and converted into an electrical signal, which is analyzed. Currently, the primary method employed by ultrasound inspection systems is based on applying pulsed sound/ultrasound energy to the inspected part, and detecting reflected/transmitted pulses. After analysis of the received pulses, different properties of the tested sample and/or the discontinuities present inside the sample can be determined. Usually, the most useful information is the time delay between the transmitted and detected pulses. The pulsed ultrasound inspection method has certain deficiencies, such as: (i) distance measurements and distance resolution are limited by the propagation speed and the duration of the pulse; (ii) pulsed signals typically have a low duty-factor, i.e., there is a limit to the amount of energy used to stimulate the object under test; and (iii) achieving acceptable signal-to-noise ratio (SNR) requires increasing the amplitude of the pulses, which would lead to reduced life-expectancy of the transducers. Trying to overcome these limitations was the main motivation for investigating the applicability of modulated continuous-wave stimulus to the classical nondestructive testing (NDT) techniques.
Textiles in architectural acoustic conditioning: a review
Published in The Journal of The Textile Institute, 2022
M. Pilar Segura Alcaraz, Marilés Bonet-Aracil, Ernesto Julià Sanchís, Jorge G. Segura Alcaraz, Ignacio Montava Seguí
Another way to transform sound energy into mechanical energy is by means of resonators (Fuchs, 2013). Regarding membrane resonators, the sound wave transmits its energy to a non-porous and flexible plate, which vibrates and dissipates energy by the internal friction of its particles.