2013-04-01 12:00 - Messages

How far do you speak in the office?

Should we just accept that it takes 20 metres for the sound level of someone's voice to drop to a comfortable non-distracting level, or should we reduce this to 10 metres so that workgroup-to-workgroup distractions are minimized?

Source : http://www.acousticbulletin.com/EN/2013/04/how_far_do_you_speak_in_the_of.html

Sound Pressure Levels in Rooms: A Study of Steady State Intensity, Total Sound Level, Reverberation Distance, a New Discussion of Steady State Intensity and Other Experimental Formulae

In this publication we include all, or almost all, the valid formulas of sound levels in different types of rooms. We will explain all the theoretical basis of each of them, starting with reflected intensity, both classical and revised theories, the total sound level and its uses in concert venues. We will also deal with empirical formulas mainly for classrooms, churches and religious buildings and industrial use. However, the main significance of this work is not only the wide range of formulas exposed but also that we have found the explanation of why the reverberation radius, or distance radius, cannot exist in the revised theory. This finding can help that the revised theory of M. Barron be slightly modified to apply it to any room for several uses, other than concerts

Source : Higini Arau-Puchades. Sound Pressure Levels in Rooms: A Study of Steady State Intensity, Total Sound Level, Reverberation Distance, a New Discussion of Steady State Intensity and Other Experimental Formulae. Noise notes, Vol.11, No 4 / December 2012, http://dx.doi.org/10.1260/1475-4738.11.4.13

Quantitative neurosensory findings, symptoms and signs in young vibration exposed workers

Background: Long-term exposure to hand-held vibrating tools may cause the hand arm vibration syndrome (HAVS) including vibration induced white fingers and sensorineural symptoms. The aim was to study early neurosensory effects by quantitative vibrotactile and monofilament tests in young workers with hand-held vibration exposure. Methods: This cross-sectional study consisted of 142 young, male machine shop and construction workers with hand-held exposure to vibrating tools. They were compared with 41 non-vibration exposed subjects of the same age-group. All participants passed a structured interview, answered several questionnaires and had a physical examination including the determination of vibrotactile perception thresholds (VPTs) at two frequencies (31.5 and 125 Hz) and Semmes Weinstein's Monofilament test. Results: In the vibration exposed grlogistic multiple regression analysis (result of monofilament oup 8% of the workers reported episodes of tingling sensations and 10% numbness in their fingers. Approximately 5--10% of the exposed population displayed abnormal results on monofilament tests. The vibrotactile testing showed significantly increased VPTs for 125 Hz in dig II bilaterally (right hand, p = 0.01; left hand, p = 0.024) in the vibration exposed group.A multiple regression analysis (VPT - dependent variable; age, height, examiner and five different vibration dose calculations -- predictor variables) in dig II bilaterally showed rather low R2-values. None of the explanatory variables including five separately calculated vibration doses were included in the models, neither for the total vibration exposed group, nor for the highest exposed quartile.A logistic multiple regression analysis (result of monofilament testing - dependent variable; age, height, examiner and five vibration dose calculations -- predictor variables) of the results of monofilament testing in dig II bilaterally gave a similar outcome. None of the independent variables including five calculated vibration doses were included in the models neither for the total exposed group nor for the highest exposed quartile. Conclusion: In spite of the fairly short vibration exposure, a tendency to raised VPTs as well as pathologic monofilament test results was observed. Thus, early neurophysiologic symptoms and signs of vibration exposure may appear after short-term exposure also in young workers.

Source : Lars Gerhardsson, Lage Burstrom, Mats Hagberg, Ronnie Lundstrom, Tohr Nilsson. Quantitative neurosensory findings, symptoms and signs in young vibration exposed workers. Journal of Occupational Medicine and Toxicology 2013, 8:8 doi:10.1186/1745-6673-8-8

Keywords: Vibrotactile thresholds; Monofilament test

Predicting discomfort from whole-body vertical vibration when sitting with an inclined backrest

 

Current methods for evaluating seat vibration to predict vibration discomfort assume the same frequency weightings and axis multiplying factors can be used at the seat surface and the backrest irrespective of the backrest inclination. This experimental study investigated the discomfort arising from whole-body vertical vibration when sitting on a rigid seat with no backrest and with a backrest inclined at 0° (upright), 30°, 60°, and 90° (recumbent). Within each of these five postures, 12 subjects judged the discomfort caused by vertical sinusoidal whole-body vibration (at frequencies from 1 to 20 Hz at magnitudes from 0.2 to 2.0 m s−2 r.m.s.) relative to the discomfort produced by a reference vibration (8 Hz at 0.4 m s−2 r.m.s.). With 8-Hz vertical vibration, the subjects also judged vibration discomfort with each backrest condition relative to the vibration discomfort with no backrest. The locations in the body where discomfort was experienced were determined for each frequency at two vibration magnitudes. Equivalent comfort contours were determined for the five conditions of the backrest and show how discomfort depends on the frequency of vibration, the presence of the backrest, and the backrest inclination. At frequencies greater than about 8 Hz, the backrest increased vibration discomfort, especially when inclined to 30°, 60°, or 90°, and there was greater discomfort at the head or neck. At frequencies around 5 and 6.3 Hz there was less vibration discomfort when sitting with an inclined backrest.

Source :Bazil Basri, Michael J. Griffin. Predicting discomfort from whole-body vertical vibration when sitting with an inclined backrest. Applied Ergonomics, Vol. 44, no 3, May 2013, p.423–434. http://dx.doi.org/10.1016/j.apergo.2012.10.006 Backrest angle; Whole-body vibration; Ride comfort; Prediction model

 

Sound Advice - noise at work in music and entertainment

Sound Advice contains practical guidelines on the control of noise at work in music and entertainment. Representatives of music and entertainment industries together with Environmental Health Officers and the Health and Safety Executive (HSE) prepared the guidance. For more details see About Sound Advice. On this site you will find out what you can do to avoid the harmful effects of prolonged exposure to noise - for yourself and for the people you employ or work with. It is closely related to a printed guide.

Source :

http://www.soundadvice.info/
http://www.hse.gov.uk/noise/musicsound.htm

Noise-Induced Hearing Loss : Scientific Advances

Exposure to loud noise continues to be the largest cause of hearing loss in the adult population. The problem of NIHL impacts a number of disciplines. US standards for permissible noise exposure were originally published in 1968 and remain largely unchanged today. Indeed, permissible noise exposure for US personnel is significantly greater than that allowed in numerous other countries, including for example, Canada, China, Brazil, Mexico, and the European Union. However, there have been a number of discoveries and advances that have increased our understanding of the mechanisms of NIHL. These advances have the potential to impact how NIHL can be prevented and how our noise standards can be made more appropriate.

Source : Editors:Colleen G. Le Prell, Donald Henderson, Richard R. Fay, Arthur N. Popper. Noise-Induced Hearing Loss : Scientific Advances, Springer , 2012. http://link.springer.com/book/10.1007/978-1-4419-9523-0/page/1

(Quelques pages peuvent être consultées à l'intérieur de chaque chapitre)  

Panels Manufactured from Vegetable Fibers: An Alternative Approach for Controlling Noises in Indoor Environments

Noise control devices such as panels and barriers, when of high efficiency, generally are of difficult acquisition due to high costs turning in many cases their use impracticable, mainly for limited budget small-sized companies. There is a huge requirement for new acoustic materials that have satisfactory performance, not only under acoustic aspect but also other relevant ones and are of low cost. Vegetable fibers are an alternative solution when used as panels since they promise satisfactory acoustic absorption, according to previous researches, exist in abundance, and derive from renewable sources. This paper, therefore, reports on the development of panels made from vegetable fibers (coconut, palm, sisal, and açaí), assesses their applicability by various experimental (flammability, odor, fungal growth, and ageing) tests, and characterize them acoustically in terms of their sound absorption coefficients on a scale model reverberant chamber. Acoustic results point out that the aforementioned fiber panels play pretty well the role of a noise control device since they have compatible, and in some cases, higher performance when compared to commercially available conventional materials.

Source : Leopoldo Pacheco Bastos, Gustavo da Silva Vieira de Melo, and Newton Sure Soeiro. Panels Manufactured from Vegetable Fibers: An Alternative Approach for Controlling Noises in Indoor Environments. Advances in Acoustics and VibrationVolume 2012 (2012), Article ID 698737, 9 p.  http://dx.doi.org/10.1155/2012/698737
http://www.hindawi.com/journals/aav/2012/698737/

Reducing of the sound pressure level in industrial areas by screening noise sources

This paper presents several ways in which the propagation of acoustic waves produced by an industrial noise source can be attenuated by identifying the optimal location of an acoustic screen near the noise source. Six types of acoustic screens were used, made of six types of materials (of the category used in the field of construction), with or without sound absorbing qualities. The noise source was placed in four different positions in front of the acoustic screen. The microphone was placed in 16 recording positions, at four distances and four heights. The experimentally obtained values indicate that the efficiency of the acoustic screen is optimal when the screen is placed at a reduced distance from the noise source, in a centered position. To obtain a high degree of sound pressure level attenuation, one can choose among variants with at least two screening walls positioned in a "V" form.

Source : Tomozei, C.; Nedeff,  V.; Lazar, G.; Ciobanu, E. Reducing of the sound pressure level in industrial areas by screening noise sources. Noise & Vibration Worldwide, vol. 43, no 10, p. 28-38. http://dx.doi.org/10.1260/0957-4565.43.10.28

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