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Noise Pollution
Published in Mary K. Theodore, Louis Theodore, Introduction to Environmental Management, 2021
Mary K. Theodore, Louis Theodore
Sound is a disturbance that propagates through a medium having the properties of inertia (mass) and elasticity. The medium by which audible sound is transmitted is air. The higher the wave, the greater its power; the greater the number of waves a sound has, the larger is its frequency or pitch. The frequency can be described as the rate of vibration that is measured in Hertz (Hz, cycles per second). The human ear does not hear all of the frequencies. The normal hearing range for humans is from 20 to 20,000 Hz. In addition, the human ear cannot define all sounds equally. Very low and very high notes sound fainter to the ear than do 1000 Hz sounds of equal strength; that is how the ear functions. The human voice in conversation covers a median range of 300–4000 Hz; the musical scale ranges from 30 to 4000 Hz. Hearing also varies widely between individuals.
What Is Sound? Seven Important Characteristics
Published in Timothy A. Dittmar, Audio Engineering 101, 2013
The amount of cycles per second (cps) created by a sound wave is commonly referred to as the frequency. If you are a musician, you may have tuned your instrument to A/440. Here, “440” is the frequency of a sound wave. Unlike amplitude, which is measured in decibels, frequency is measured in hertz (Hz), named after the German physicist, Heinrich Hertz. The average human hearing range is from 20 to 20,000 Hz. Typically, once 1000 cycles per second is reached, the frequency is referred in kilohertz (kHz), i.e., 1000 Hz = 1 kHz, 2000 Hz = 2 kHz, and 3000 Hz = 3 kHz. Frequency is related to the pitch of a sound. Here is a handy chart to help identify the frequency ranges of various instruments and how the keys of a piano relate to frequency. The first note on a piano is A, which is 27.5 Hz. Have you ever turned up the bass or treble on your car stereo? If so, you are boosting or cutting the amplitude of a frequency or range of frequencies. This is known as equalization (EQ), a vital aspect of audio production.
Human Hearing and Subjective Response to Sound
Published in Malcolm J. Crocker, A. John Price, Noise and Noise Control, 2018
Malcolm J. Crocker, A. John Price
If very intense noise levels of the order of 135 dB or above at any frequency in the hearing range are experienced, immediate hearing damage is likely to result. However, permanent hearing damage is also produced at much lower sound pressure levels if the noise is experienced over much longer periods (weeks, months, or years). This reminds us of the similar phenomenon of metal fatigue where failure can occur at very much lower stress levels than the breaking stress, provided the stress is produced over a sufficiently long time. The problem is that noise-induced hearing loss, or to give it its technical name – noise-induced permanent threshold shift (NIPTS) is hard to distinguish from presbycusis.
Development of a new nanofibrous composite material from recycled nonwovens to improve sound absorption ability
Published in The Journal of The Textile Institute, 2020
Ayşe Özkal, Funda Cengiz Çallıoğlu, Çiğdem Akduman
The principle of the sound absorption theory is based on the conversion of sound energy into thermal energy (Lee & Joo, 2003). Although there are plenty of factors effecting sound absorption- such as thickness (Liu & Hu, 2010), density, open-cell percentage, velocity of the air particles (Bahrambeygi et al., 2013), porosity, compression, fiber size—it is not easy to find a direct simple relation between the sound absorption coefficient (SAC) and these factors (Qiu, 2016). Two methods are used for measuring the acoustical properties of the textile fabrics; impedance tube method and acoustical chamber method. Hearing range for human ear is 0–20,000 Hz (Tascan & Vaughn, 2008). SACs differ according to the frequency applied. SAC value is rated between 0 and 1. A SAC value of 0.5 is critical in order to evaluate the efficiency of an absorber (Liu & Hu, 2010). Nanofibers have gained great attention as sound absorbing materials (Asmatulu, Khan, & Yıldırım, 2009). They could act as acoustic resonant membranes and dampen the sound (Na et al., 2012). Nanofibers have larger surface area to volume (Cengiz-Çallıoğlu, Jirsak, & Dayık, 2013), very small pore size and high porosity level when compared to conventional fibers (Asmatulu et al., 2009). Electrospinning is the most widely used, efficient and simple nanofiber manufacturing method (Cengiz & Jirsak, 2009; Xiang et al., 2011). Porous structure of nanofibers lead sound waves to have high interactions between the molecules (Asmatulu et al., 2009).
Hearing loss, lead (Pb) exposure, and noise: a sound approach to ototoxicity exploration
Published in Journal of Toxicology and Environmental Health, Part B, 2018
Krystin Carlson, Richard L. Neitzel
Alterations in the amplitude or latency of these waves can be signals of pathology. Hearing thresholds, interpreted as waveforms present, but diminishing in amplitude as the stimulus presented quiets, are another measure of hearing ability. In humans, thresholds from 0 to 19 dB are considered within the normal hearing range. Thresholds of 20 dB or more demonstrate different degrees of HL; thresholds of 20–34 dB show mild HL, 35–49 dB show moderate HL, 50–64 moderately severe, 65–79 dB show severe, 80–94 dB show profound HL, and 95 dB and over show complete HL (Vos et al. 2015). The World Health Organization defines HL as thresholds at or above 25 dB in one or both ears for pure-tone single frequency audiometry (World Health Organization 1991). Mean auditory thresholds vary by species and stimuli (particularly the frequency or pitch), but are similar to humans (Zheng, Johnson, and Erway 1999).